Quantitative information on a targeted analyte in a complex biological system is the most basic premise for understanding its involved mechanisms, and thus precise diagnosis of a disease if it is a so-called biomarker. Here, we designed and synthesized a neodymium (Nd)-cored tag [1,4,7,10-tetraazacyclododecane-1,4,7-trisacetic acid (DOTA)–Nd complex together with a light-harvesting antenna aminofluorescein (AMF, λex/em = 494/520 nm), AMF–DOTA–Nd] with duplex signals, second near-infrared (NIR) window luminescence (λem = 1065 nm, 2.5 μs), and stable isotopic mass (142Nd). AMF–DOTA–Nd covalently linked with a urea-based peptidomimetic targeting group, 2-[3-(1,3-dicarboxypropyl)-ureido]pentanedioic acid (DUPA)-8-Aoc-Phe-Phe-Cys (DUPAaFFC) (DUPAaFFC–AMF–DOTA–Nd), allowing us to detect and quantify prostate-specific membrane antigen (PSMA) and its splice variants (total PSMA, tPSMA), which was set as an example of targeted biomarkers in this study, using NIR and inductively coupled plasma mass spectrometry (ICPMS) with the limit of detection (LOD) (3σ) of 0.3 ng/mL. When it was applied to the analysis of 80 blood samples from prostate cancer (PCa) and benign prostatic hyperplasia (BPH) patients as well as healthy volunteers, we found that 320 and 600 ng/mL tPSMA could be recommended as the threshold values to differentiate BPH from PCa and for the diagnosis of PCa. Moreover, PSMA-positive circulating tumor cells (CTCs) were counted using ICPMS being from 134 to 773 CTCs in the PCa blood samples of the Gleason score from 6 to 9 when the cell membrane-spanning mPSMA was tagged. Such a methodology developed could be expected to be applicable to other clinic-meaningful biomolecules and their host CTCs in liquid biopsy, when other specific targeting groups are modified to the NIR Nd tag.

In this study, novel alkali-resistant nanocomposite nanofiltration (NF) membranes were prepared via phase inversion by immersion precipitation combined with the addition of two kinds of functionalized graphene nanosheets. The effects of the functional groups and the concentrations of the graphene-based nanosheets on the microstructures and performances of nanocomposite membranes were systematically investigated. Compared with the pure polyethersulfone (PES) membrane, incorporation of a small amount of sulfonated graphene (SG) or graphene oxide (GO) into the PES matrix did not change the membrane morphology. However, the hydrophilicity, permeability and antifouling capabilities were remarkably enhanced without obvious reduction in membrane rejection. Particularly, the water fluxes of optimized PES–SG and PES–GO NF membranes at 0.1 wt% were improved by 119.7% and 71.3%, respectively. Moreover, the PES–SG series membranes exhibited better hydrophilicity and membrane separation performance than the PES–GO series membranes, which was attributed to the different ionisable functional groups from the SG and GO nanosheets. Both the optimized PES–SG and PES–GO NF membranes exhibited long-term stability during a seven-day test in alkaline solution, but PES–SG demonstrated greater promise as a novel alkali-resistant NF membrane due to its superior permeability and antifouling performance.

In this work, novel thin-film nanocomposite (TFN) nanofiltration (NF) membranes were developed through modification with maleic anhydride functionalized graphene oxide (MAH-GO) via interfacial polymerization (IP). First, MAH-GO was synthesized by linking MAH molecules to the electrophilic groups (C–OH) of GO nanosheets. The resulting materials were characterized in depth by FT-IR, TEM, SEM, AFM, XPS and Raman spectroscopy. Subsequently, the MAH-GO and GO nanosheets were individually introduced into the polypiperazine-amide (PPA) active layer of TFN NF membranes via IP between piperazine (PIP) and trimesoyl chloride (TMC). The influence of the MAH-GO or GO concentrations on the morphology and performance of TFN NF membranes was systematically investigated. Compared with TFC-blank, the TFN-MG-60 and TFN-GO-80 membranes demonstrated significantly enhanced separation performance without reduction of the salt rejection. Particularly, the water flux of TFN-MG-60 and TFN-GO-80 was found to be 49.3 L m−2 h−1 and 42.0 L m−2 h−1, respectively, corresponding to 176.7% and 150.5% of TFC-blank. Moreover, TFN-MG-60 demonstrated superior water permeability, antifouling capability and chlorine resistance to TFN-GO-80, which was attributed to the incorporation of MAH-GO nanosheets having more hydrophilic carboxyl groups. Meanwhile, TFN-MG-60 retained a high salt rejection rate of 97.6% to Na2SO4, comparable to that of TFC-blank. The MAH-GO nanosheets show great potential in developing high-performance TFN NF membranes to overcome the trade-off effect of conventional thin-film composite membranes.

Although we believe that the cell surface sialic acids (Sias) are playing an important role in cell–cell interactions and related tumor metastasis processes, acquisition of their quantitative information has yet been a challenge to date. Here, we reported the construction of a new analytical platform for Sias-specific imaging and quantification. We used N-azidoacetyl-mannosamine tetraacylated as a metabolic sugar substrate to bioassemble azido-Sias on the surface of cells via the metabolic pathway of Sias de novo synthesis. These azido-Sias allow us to perform a duplex Sias-specific analysis with various fluorescent and elemental reporters such as DIBO-Alexa Fluor 647, DBCO-DOTA-Eu, and DBCO-PEG4-BODIPY, which can be easily labeled and/or tagged through an effective copper-free bioorthogonal click reaction. Compared to the previous reported strategies, we quantified the cell surface Sias with the LODs (3σ) down to 8.9 fmol and 0.24 pmol using 153Eu- and 10B-species unspecific isotope dilution ICPMS, in addition to their red- and green-CLSM profiling. Such a platform enables us to evaluate Sias regulation under the administration of paclitaxel, finding that 1 μM paclitaxel induced a significant Sias decrease of 67% on the surface of hepatic tumor cell SMMC-7721, while had no obvious adverse effect to that of para-carcinomatous liver cell LO2. Besides Sias, we believe that this metabolism-based click-mediated platform will provide opportunities to study other monosaccharides and their corresponding biological roles when more corresponding chemically modified sugar substrates and specific bioorthogonal reactions are developed.

Low-abundance tyrosine phosphorylation is crucial to not only normal but also aberrant life processes. We designed and synthesized a photocleavable magnetic nanoparticle-based gallium tag for tagging and enrichment as well as UV-release of the phosphate-bearing molecules/ions in cells. HPLC/71Ga species-unspecific isotope dilution (71Ga-SUID) ICPMS was subsequently developed for specific and absolute quantification of phosphotyrosine (pY) under the assistance of a protein tyrosine phosphatase-1B (PTP-1B). pY quantification was thus achieved via determination of Ga in the Ga-phosphate complexes that come exclusively from the Ga-tagged pY. In this way, the method detection limit of pY reached down to 30 amol with the RSD lower than 5.70% (n = 5 at pmol level). Feasibility of this proposed method was validated using VNQIGTLSEpYIK, VNQIGTLpSEpYIK, and extracellular regulated protein kinase 1 peptide (-pTEpY-) standards with the recovery of more than 96% (n = 5). It was applied to the absolute quantification of pY in human breast cancer MCF-7 cells, indicating that pY increased by 1.60 nmol (61.1%) in 3.0 × 106 MCF-7 cells after 100 nM insulin stimulation. We believe that, not limited to pY quantification, this element-tagging and protease-specific reaction mediated ICPMS methodology will pave a simple path for ever more applications of ICPMS to the studies of quantitative protein post-translational modifications (PTMs) when suitable element-tags are designed and specific proteases are available toward targeted PTMs.

•Silica-based polypeptide-monolithic stationary phases were designed and prepared via a one-pot process.•Silica-based polypeptide-monolithic stationary phases demonstrated not only typical HILIC but also chiral separation ability.•Nucleotides and peptides could be separated using aqueous mobile phase without any ACN.•Chiral separation of drug enantiomers was realized on the GSH-AuNP-GSH-silica hybrid monolithic column.Glutathione (GSH)-, somatostatin acetate (ST)- and ovomucoid (OV)-functionalized silica-monolithic stationary phases were designed and synthesized for HILIC and chiral separation using capillary electrochromatography (CEC). GSH, ST and OV were covalently incorporated into the silica skeleton via the epoxy ring-opening reaction between their amino groups and the glycidyl moiety in γ-glycidoxypropyltrimethoxysilane (GPTMS) together with polycondensation and copolymerization of tetramethyloxysilane and GPTMS. Not only could the direction and electroosmotic flow magnitude on the prepared GSH-, ST- and OV-silica hybrid monolithic stationary phases be controlled by the pH of the mobile phase, but also a typical HILIC behavior was observed so that the nucleotides and HPLC peptide standard mixture could be baseline separated using an aqueous mobile phase without any acetonitrile during CEC. Moreover, the prepared monolithic columns had a chiral separation ability to separate dl-amino acids. The OV-silica hybrid monolithic column was most effective in chiral separation and could separate dl-glutamic acid (Glu) (the resolution R = 1.07), dl-tyrosine (Tyr) (1.57) and dl-histidine (His) (1.06). Importantly, the chiral separation ability of the GSH-silica hybrid monolithic column could be remarkably enhanced when using gold nanoparticles (AuNPs) to fabricate an AuNP-mediated GSH-AuNP-GSH-silica hybrid monolithic column. The R of dl-Glu, dl-Tyr and dl-His reached 1.19, 1.60 and 2.03. This monolithic column was thus applied to separate drug enantiomers, and quantitative separation of all four R/S drug enantiomers were achieved with R ranging from 4.36 to 5.64. These peptide- and protein-silica monolithic stationary phases with typical HILIC separation behavior and chiral separation ability implied their promise for the analysis of not only the future metabolic studies, but also drug enantiomers recognition.

A novel UV/nano-ZrO2/HCOOH system was developed and fabricated as an atomization unit and as an online interface between HPLC and AFS for Hg determination and speciation for the first time. UV-generated electrons at the conduction band of nano-ZrO2 reduce mercury species into mercury cold vapor, achieving mercury atomization for AFS determination. The LODs (3σ) of inorganic mercury (Hg2+), methylmercury (MeHg) and ethylmercury (EtHg) tested in this study were respectively reduced to 10, 6, and 8 ng L−1 when using AFS under flow injection mode (FI). Moreover, Hg speciation could also be performed when coupled with HPLC, and the LODs (3σ) of Hg2+, MeHg and EtHg were 24, 13, and 16 ng L−1, respectively, using the HPLC-(UV/nano-ZrO2/HCOOH)-AFS system, with the RSDs better than 4.6% (n = 6) at 20 μg L−1 each. FI-(UV/nano-ZrO2/HCOOH)-AFS and HPLC-(UV/nano-ZrO2/HCOOH)-AFS were validated by analyzing a certified reference material (GBW10029, tuna fish) and applied to mercury determination and speciation of the local seafood around Xiamen Island.

An endogenous element-label plus exogenous element-tag strategy was proposed for inductively coupled plasma-mass spectrometry (ICP-MS) to screen and discriminate a family of ultratrace but biologically important biomolecules. The feasibility of this novel idea was demonstrated by setting seleno (SeCys) and Se-containing (SeMet) proteins (peptides) as an example. Se-label naturally occurring in the biomolecules acted as an identifier for picking up them out of a large amount of various coexisting proteins (peptides), and CH3Hg-tag that could bind to SeCys rather than SeMet helped discriminating seleno and Se-containing ones simply based on the Se and Hg signals on ICP-MS. This strategy has been applied to screen and discriminate Seleno and Se-containing proteins (peptides) in water-soluble extracts of Se-enriched yeast, and seven selenoproteins (peptides) were detected with both 202Hg and 82Se signals out of fifteen Se-containing species using RPLC/ICP-MS, providing valuable information for further identification using a high-resolution structure-selective mass spectrometer. This endogenous element-label plus exogenous element-tag dual-element approach implies that ICP-MS is not only able to quantify targeted proteins (peptides) but also helpful to discover unknown ones during a discovery-based proteomic study.A dual-labeling strategy using endogenous Se plus chemically modified exogenous Hg based on the specific and strong interaction between selanyl (−SeH) and Hg towards selenoprotein/peptide was developed. It was effective in selectively recognizing selenoprotein and selenopeptide and “picking up” trace amounts of selenoprotein/peptide in complex biological matrices by ICP-MS.

A novel element-tagged activity-based photo-cleavable biotinylated chemical “Hub” was designed and synthesized to orthogonally integrate ICP-MS and ESI-MS for absolute targeted-protein quantification. This tetrafunctional chemical “hub” allowed us to quantify a targeted protein using species-unspecific isotope dilution ICP-MS and to know which protein is being quantified using ESI-IT-MS at the same time.

P450 3A4 (CYP3A4) is one of the most important isoforms in the human cytochrome P450 superfamily. It was used as an example in this proof-of-concept study in order to demonstrate an activity-based labeling and then click chemistry (CC) mediated element-tagging strategy for simultaneously specific quantification and activity measurement of an enzyme using species-unspecific isotope dilution inductively coupled plasma mass spectrometry (SUID ICPMS). A dual functional hexynylated 17α-ethynylestradiol activity-based probe was synthesized for specifically labeling CYP3A4 and then CC-mediated Eu-tagging with an azido-DOTA-Eu complex for CYP3A4 quantification and activity measurement in human liver microsome and serum samples using 153Eu SUID ICPMS. The LOD (3σ) of CYP3A4 reached 20.3 fmol when monitoring 151/153Eu ICPMS signals, in addition to the merits of specificity and simultaneous activity measurement achieved. We believe that this activity-based CC-mediated element-tagging strategy will liberate more potential advantages of ICPMS in bioanalysis.

Understanding the metabolic pathways of polybrominated diphenyl ethers (PBDEs) is a key issue in the evaluation of their cytotoxicity after they enter the biota. In order to obtain more information concerning the metabolic pathways of PBDEs, we developed a strong electron-withdrawing pentafluorobenzoyl (PFBoyl) derivatization capillary gas chromatography/electron capture negative ionization quadrupole mass spectrometry (GC/ECNI-qMS). PFBoyl esterification greatly improves separation of the metabolites of PBDEs such as hydroxylated PBDEs (OH-PBDEs) and bromophenols (BPs) metabolites in rat liver microsomes (RLMs). On the other hand, the strong electron-withdrawing property of PFBoyl derivatized on OH-PBDEs and/or BPs makes cleavage of the ester bond on ECNI easier resulting in higher abundance of the structure-informative characteristic fragment ions at a high m/z region, which facilitate the identification of OH-PBDEs metabolites. Subsequent quantification can be performed by monitoring not only 79Br– (or 81Br–) but also their characteristic fragment ions, achieving more accurate isotope dilution quantification using GC/ECNI-qMS. These merits allow us to identify totally 12 metabolites of BDE-47, a typical example of PBDEs, in the RLMs in vitro incubation systems. In addition to the already known metabolites of BDE-47, one dihydroxylated 3,6-di-OH-BDE-47 and one dihydroxylated 3,5-di-OH-tetrabrominated dioxin were found. Moreover, the second hydroxylation took place on the same bromophenyl ring, where the first hydroxyl group was located, and was further confirmed via the identification of the dihydroxylated 2′,6′-di-OH-BDE-28 of an asymmetric 2′-OH-BDE-28. This methodological development and its subsequent findings of the metabolic pathways of BDE-47 provided experimental evidence for understanding its dioxin-like behavior and endocrine disrupting risk.

Highly sensitive and a multiplex assay of viruses and viral DNAs in complex biological samples is extremely important for clinical diagnosis and prognosis of pathogenic diseases as well as virology studies. We present an effective ICP-MS-based multiplex and ultrasensitive assay of viral DNAs with lanthanide-coded oligonucleotide hybridization and rolling circle amplification (RCA) strategies on biofunctional magnetic nanoparticles (MNPs), in which single-stranded capture DNA (ss-Cap-DNA)-functionalized MNPs (up to 1.65 × 104 ss-Cap-DNA per MNP) were used to recognize and enrich target DNAs, and single-stranded report DNA (ss-Rep-DNA-DOTA-Ln) coded by the lanthanide–DOTA complex hybridized with the targeted DNA for highly sensitive readout of HIV (28 amol), HAV (48 amol), and HBV (19 amol). When utilizing the RCA technique in association with the design and synthesis of a “bridge” DNA and a corresponding ss-Rep-DNA-DOTA-Ho, as low as 90 zmol HBV could be detected. Preliminary applications to the determination of the viral DNAs in 4T1 cell lysates and in serum confirmed the feasibility of this ICP-MS-based multiplex DNA assay for clinical use. One can expect that this element-coded ICP-MS-based multiplex and ultrasensitive DNA assay will play an ever more important role in the fields of bioanalysis and virology and in medical studies after further sophisticated modifications.

The chemical affinities of three submetallomes (“Mn, Co, Ni, Cu, Cd”; “Pd, Pt, Au”; and “Hg, CH3Hg, C2H5Hg-THI”) towards metallothionein-2 (Zn7MT-2) in a physiological solution environment were evaluated using SEC/ICP-MS together with RP-HPLC/ESI-IT-MS and MALDI-TOF-MS, and followed the order: “Zn2+ < Cu2+, Cd2+ > Ni2+ > Mn2+, Co2+”; “Pd2+ > Au3+ > Pt2+”; and “Hg2+ > CH3Hg+ > C2H5Hg-THI”. Besides these, the structural change and composition of the CH3Hg–MT-2 complexes formed during the CH3Hg+ titration process were further investigated using CD spectroscopy, RP-HPLC/ESI-MS and MALDI-TOF-MS, indicating that linear and more hydrophobic (CH3Hg)xMT-2 (x = 12, 13, 14, 15, 16, 17, 18, 19 and 20) were formed. This information is important in understanding the interactions of the metals with Zn7MT-2 and their corresponding biological functions and toxicities.

Mercury (Hg) is a toxic heavy metal with its biogeochemical cycling in the ocean depending on the type and behavior of the oceanic microalgae. The present work aimed to evaluate bioaccumulation and transformation of Hg by Phaeodactylum tricornutum, a typical unicellular diatom, when exposed to the extremely high level of Hg in order to understand the possible mechanisms of acute stress response. P. tricornutum can accumulate Hg (its bioaccumulation factor is at 104 level), and the 96 h EC50 was estimated to be 145 μg L−1. The amounts of surface-bound Hg being about 1.2 to 4.8 times higher than those of intracellular Hg under exposure to HgCl2 (from 20 to 120 μg L−1 concentrations) suggested that the cell wall of P. tricornutum is an important “fence” towards Hg. After entering the P. tricornutum cell, Hg underwent transformation in its chemical form via interactions with high molecular weight sulfur-containing proteins (accounting for 68% of the intracellular Hg), and glutathione as well as the induced phytochelatins (PCs) (24% Hg) which alleviated the toxicity of HgCl2. In addition, the existence of organic ligands greatly influenced the uptake and transformation behavior of P. tricornutum towards HgCl2, especially in the case of cysteine (Cys), which increased the uptake of Hg, but alleviated the toxicity of Hg towards P. tricornutum due to the fact that Cys is an important precursor for the synthesis of PCs inside the cell. The uptake process of Hg by P. tricornutum was in agreement with the Freundlich isotherm, suggesting a typical heterogeneous sorption process. More importantly, we observed the conversion of HgCl2 into methylmercury inside the P. tricornutum cells and its release into the culture solution using HPLC/CVG-AFS and GC-MS, although the mechanism needs to be further investigated.

Much progress has been made in identification of the proteins in proteomes, and quantification of these proteins has attracted much interest. In addition to popular tandem mass spectrometric methods based on soft ionization, inductively coupled plasma mass spectrometry (ICPMS), a typical example of mass spectrometry based on hard ionization, usually used for analysis of elements, has unique advantages in absolute quantification of proteins by determination of an element with a definite stoichiometry in a protein or attached to the protein. In this Trends article, we briefly describe state-of-the-art ICPMS-based methods for quantification of proteins, emphasizing protein-labeling and element-tagging strategies developed on the basis of chemically selective reactions and/or biospecific interactions. Recent progress from protein to cell quantification by use of ICPMS is also discussed, and the possibilities and challenges of ICPMS-based protein quantification for universal, selective, or targeted quantification of proteins and cells in a biological sample are also discussed critically. We believe ICPMS-based protein quantification will become ever more important in targeted quantitative proteomics and bioanalysis in the near future.

We reported novel Ag–TiO2- and ZrO2-based photocatalytic vapor generation (PCVG) systems as effective sample introduction techniques for further improving the sensitivity of the atomic spectrometric determination of selenium for the first time, in which the conduction band electron served as a “reductant” to reduce selenium species including SeVI and convert them directly into volatile H2Se, which was easily separated from the sample matrix and underwent more effectively subsequent atomization and/or ionization. These two PCVG systems helped us to overcome the problem encountered in the most conventional KBH4/OH––H+ system, in that SeVI was hardly converted into volatile selenium species without the aid of prereduction procedures. The limits of detection (LODs) (3σ) of the four most typical SeIV, SeVI, selenocystine ((SeCys)2), and selenomethionine (SeMet) species were, respectively, down to 1.2, 1.8, 7.4, and 0.9 ng mL–1 in UV/Ag–TiO2–HCOOH, and 0.7, 1.0, 4.2, and 0.5 ng mL–1 in UV/ZrO2–HCOOH with the relative standard deviations (RSDs) lower than 5.1% (n = 9 at 1 μg mL–1) when using atomic fluorescence spectrometry (AFS) under flow injection mode. They reached 10, 14, 18, and 8 pg mL–1 in UV/Ag–TiO2–HCOOH, and 6, 7, 10, and 5 pg mL–1 in UV/ZrO2–HCOOH with the RSDs lower than 4.4% (n = 9 at 10 ng mL–1) when using inductively coupled plasma mass spectrometry (ICPMS). After the two PCVG systems were validated using certified reference materials GBW(E)080395 and SELM-1, they were applied to determine the total Se in the selenium-enriched yeast sample and used as interfaces between high-performance liquid chromatography (HPLC) and AFS or ICPMS for selenium speciation in the water- and/or enzyme-extractable fractions of the selenium-enriched yeast.

We report the design and synthesis of a trifunctional probe for seeing and counting cancer cells using both fluorescence imaging (FI) and inductively coupled plasma mass spectrometry (ICPMS) for the first time. It consisted of a guiding cyclic RGD peptide unit to catch cancer cells via targeting the αvβ3 integrin overexpressed on their surface, a 5-amino-fluorescein moiety for FI using confocal laser scanning microscopy (CLSM) as well as a 2-aminoethyl-monoamide-DOTA group for loading stable europium ion and subsequent ICPMS quantification of the cancer cells without the use of radioactive isotopes. In addition to FI, the LOD (3σ) of the αvβ3 integrin was down to 69.2–309.4 amol per cell depending on the type of the αvβ3-positive cancer cells when using ICPMS and those of the cancer cell number reached 17–75. This probe developed enables us not only to see but also to count the αvβ3-positive cancer cells ultrasensitively, paving a new way for early diagnosis of cancer.

We reported an alternative strategy to reduce disulphide bonds in peptides with Ag-nanoparticle loaded nano-TiO2 (Ag/TiO2) under UV irradiation. The feasibility of this strategy was adequately demonstrated using the model peptides oxidized glutathione, vasopressin and insulin, which contain various disulphide bonds, as well as by its application to the determination of Cd-induced phytochelatins in Phaeodactylum tricornutum.

In this proof-of-concept study, a novel dual-labelling strategy for conjugating –SH and –NH2 of a peptide was developed, in which an element tag (1,4,7,10-tetraazacyclododecane-1,4,7-trisacetic acid-10-maleimidoethylacetamide loaded with europium) and a fluorescent tag (fluorescein isothiocycanate) were employed. Its feasibility was demonstrated using HPLC-UV/ESI-MS for evaluating labelling-efficiency and HPLC-ICPMS with 153Eu isotope dilution as well as CE-LIF for the determination of peptides.

Inductively coupled plasma mass spectrometry (ICP-MS) coupled on-line with an ion-pair reversed phase HPLC (IP-RP HPLC) was developed for determining the lability of Cd species. The IP-RP HPLC–ICP-MS system measures chromatographic behaviors of Cd species in the presence of different model complexing agents (L) with stability constants (log KCdL) from 3.8 to 19.0. Cd species with log KCdL higher than 16, between 8 and 16, and smaller than 8 was then classified into inert, moderately labile, and labile species, respectively. The conditional stability constants and dissociation rate constants were also estimated from their corresponding chromatographic behavior. This method was applied to evaluating the lability-dependent biouptake of different Cd species in Phaeodactylum tricornutum, a typical unicellular marine diatom. IP-RP HPLC–ICP-MS is a useful and promising technique for determining the lability of noncovalent-bonded metal species (such as Cd species) in the environment and for forecasting their corresponding bioavailability especially when their speciation cannot be rigorously controlled and measured.

Quantitative proteomics requires novel analytical methodology to fill the gap related to absolute protein abundance in different physiological conditions. In this paper, we demonstrate a proof-of-concept study for absolute protein quantification. 1,4,7,10-Tetraazacyclododecane-1,4,7-trisacetic acid−10-maleimidoethylacetamide (MMA−DOTA) loaded with Eu was used to label lysozyme, insulin, and ribonuclease A, and they were subsequently quantified using HPLC coupled with 153Eu species-unspecific isotope dilution inductively coupled plasma mass spectrometry (ICPMS). Labeling procedures were optimized using electrospray ionization mass spectrometry (ESI-MS) based on the labeling efficiency and specificity of the three intact proteins, which suggested that 10-fold or higher MMA−DOTA to cysteine sulphydryl rates at pH from 6.8 to 7.6 and 47 °C for 40 min were optimal conditions for the conjugation of the reduced-form proteins and that a 5-fold excess of Eu with respect to the DOTA present in the MMA−DOTA−conjugated proteins and pH 5.8 are optimal for Eu labeling. Subsequently, these three MMA−DOTA−Eu-labeled proteins were digested with trypsin, and the tryptic peptides were quantified via HPLC coupled with 153Eu species-unspecific isotope dilution ICPMS. The results for the protein studied indicated that not only could 100% digestion efficiency not be achieved but also the resulting peptides needed a chromatographic separation at higher resolution. On the other hand, the labeled intact proteins were quantified without tryptic digestion. The average recovery was found to be 97.9% in six independent experiments, and the precision was evaluated to be 5.8% at the 10 pmol L−1 level. The detection limits (3σ) were determined to be 0.819, 1.638, and 0.819 fmol for lysozyme, the A chain of insulin, and ribonuclease A, respectively, using ICPMS with a normal concentric pneumatic nebulizer. These results demonstrated that high-quality absolute protein quantification could be achieved through labeling the intact proteins but not the tryptic peptides, implying that intact proteins may be more feasible and practical targets than tryptic peptides for ICPMS-based absolute protein quantification.

The methylmercury ion (CH3Hg+) demonstrated a high efficiency for directly labeling peptide/protein based on its specific and strong interaction with the sulfhydryl(s) in the peptide/protein and because of its smallest size among monofunctional organic mercurials studied, including methylmercury, ethylmercury, 4-(hydroxymercuric)benzoic acid, and 2,7-dibromo-4-hydroxymercurifluoresceine disodium. A simple 1:1 stoichiometry between CH3Hg+ and sulfhydryl, confirmed with electrospray ionization-mass spectrometry (ESI-MS) and matrix-assisted laser desorption ionization-time-of-flight-mass spectrometry (MALDI-TOF-MS) studies, made it easy to calibrate the stoichiometry of Hg in the peptide/protein. In order to avoid the direct use of the harmful CH3Hg+, in this study a CH3Hg+-equivalent tag, methylmercurithiosalicylate (CH3Hg-THI), and its 204Hg-enriched homologue (CH3204Hg-THI) were synthesized, and then CH3Hg+ and/or CH3204Hg+ released from CH3Hg-THI and/or CH3204Hg-THI in solution were utilized to demonstrate the dynamic labeling of glutathione (GSH) and two model proteins, β-lactoglobulin (BLG) and ovalbumin (OVA), for the first time. Furthermore, the CH3204Hg-THI isotopical labeled GSH, BLG, and OVA standards (CH3204Hg-GSH, CH3204Hg-BLG, and CH3204Hg-OVA) were used to demonstrate the feasibility of absolute peptide/protein quantification using label-specific isotope dilution inductively coupled plasma mass spectrometry (ICPMS). On the basis of the accurate and sensitive determination of Hg using ICPMS, the detection limits of GSH, BLG, and OVA could reach 45.4, 45.4, and 15.1 pmol L−1, respectively, suggesting the possibility for low-abundance peptide/protein quantification alongside the surefire quantification of moderate and highly abundant peptide/protein.

The risk of nanoparticles (NPs) to organisms and the environment has become more noticeable alongside their rapid applications in many fields. The release of Cd2+ from CdTe-based NPs (CdTe-NPs), an important class of engineered nanomaterials, is one of the possible factors responsible for the cytotoxicity of these NPs. Based on the same CdTe core, CdTe/CdS, CdTe/ZnS and CdTe/SiO2 NPs were synthesized and their Cd2+ release rates were carefully studied based on dialysis using inductively coupled plasma mass spectrometry (ICPMS). Results obtained indicated that the Cd2+ release rates of the CdTe-NPs decreased in the order CdTe (8.78 ng mL−1 mg−1 h−1) > CdTe/CdS (2.63) > CdTe/SiO2 (0.89) > CdTe/ZnS (0.72). Phaeodactylum tricornutum was used as a model diatom for evaluating the cytotoxicity of the CdTe-NPs. Results obtained from the CdTe-NPs exposure experiments together with ICPMS and fluorescence microscopy studies suggested that the cytotoxicity of the CdTe-NPs increased along with the increase in their Cd2+ release rates. Effective coating materials such as ZnS and SiO2 for the CdTe core significantly reduced the cytotoxicity of CdTe.

In vivo phytochelatins (PCs) and their corresponding Hg–PC complexes were characterized using RPLC-ESI-MS/MS in the roots of Brassica chinensis L. under the stress of a mercury cysteine complex (HgCys2) and/or a mercury humic acid complex (Hg–HA). Results indicated that the presence of Cys and/or HA decreased the Hg uptake in both the roots and shoots of B. chinensis but increased the generation of PCs in the roots compared with those where only HgCl2 was in the culture solutions. A series of Hg–PC complexes were synthesized in vitro for predicting the possible Hg–PC formed in vivo in the HgCys2 and/or Hg–HA stressed roots of B. chinensis. The discovery of in vivo oxidized PC2, PC3 and PC4 and their corresponding HgPC2, HgPC3, HgPC4 and Hg2PC4, which were confirmed by their specific isotope distribution, provided definite evidence for understanding the defense and accumulation mechanism of B. chinensis to Hg, in which the induced PCs play an important role not only in Hg detoxification through forming Hg–PC complexes but also for reducing the oxidative stress induced by Hg2+.

Monoliths were prepared in 530 μm I.D. fused silica capillaries via in situ copolymerization of stearyl methacrylate (SMA) with a dimethacrylate cross-linker in the presence of a binary porogenic solvent containing tert  .-butanol and 1,4-butanediol. Alkyl dimethacrylate cross-linkers other than the monomer were used to tune the monolith properties, and, as a result, an increase in the hydrophobicity of the final monoliths (the methylene selectivity αCH2αCH2 increased from 1.396 to 1.475) was observed through an increase in the molecular chain length between two methacrylate units from the 0.360 nm of ethylene glycol dimethacrylate to the 1.241 nm of 1.9-nonanediol dimethacrylate. Moreover, the hydrophobicity of the final monoliths was also greatly affected by the methyl group branch in the cross-linkers, among which the 2-methyl-1,8-octanediol dimethacrylate (2-Me-1,8-ODDMA) mediated monolith exhibited the highest hydrophobicity (αCH2αCH2 was 1.482) and fastest mass transfer kinetics (C-term was 9.14 ms). Besides the effective separation of six model proteins, the poly(SMA-co-2-Me-1,8-ODDMA) monolith also showed an improved performance in the separation of alkylbenzenes. The theoretical plate numbers reached 83 000 plates/m and 52 000 plates/m for thiourea (nonretained compound) and butylbenzene (retained compound), respectively, when using acetonitrile–water (70:30, v/v) as the mobile phase at a typical linear velocity of 1 mm/s. This improved performance towards small molecules was attributed to an increased mesopore proportion in the monolith and the faster dynamic process of mass transfer arising from novel tailoring of the monolith by choosing a suitable monomer/cross-linker pair.

Currently, molecular mass spectrometry is preferred by many for relative quantification but is not appropriate for “absolute” quantification of proteins. In this article we demonstrate a proof of concept for the absolute quantitative analysis of proteinsvia CH3Hg+labeling and integrated application of molecular and elemental mass spectrometry. The smallest size of CH3Hg+ among monoalkyl mercurials and the specific and covalent interaction with sulfhydryl (–SH) in proteins results in forming a simple complex of CH3Hg+:–SH = 1:1 when all –SH are exposed, as confirmed by ESI-MS. Based on the known number of –SH per protein, the absolute protein concentration can be obtained viaHg determination using ICP-MS, in which CH3HgCl could be simply used as an external standard. When bovine pancreatic ribonuclease A, lysozyme and insulin, which have an increasing number of various disulfide linkages in their molecules, were taken as model proteins, their corresponding absolute detection limits (3σ) reached 0.6, 1.2 and 0.4 pmol, respectively. These characteristics may be expected to provide an alternative approach for absolute protein quantification, especially specific biomarker determination, in the near future.

An alternative analytical method was established for simultaneous determination of main urinary low-molecular-mass (LMM) thiols including cysteine (Cys), cysteinylglycine (Cys–Gly), homocysteine (HCys), γ-glutamyl cysteine (γ-Glu–Cys) and glutathione (GSH) as well as N-acetylcysteine (NAC) using RPLC coupled on line with UV/HCOOH-induced cold vapor generation atomic fluorescence spectrometry (UV/HCOOH–CVG–AFS) with 4-(hydroxymercuric)benzoic acid (PHMB) as a tag. The LMM thiols were stabilized and labeled by PHMB allowing the determination of reduced form thiols (R-thiols) and total thiols (T-thiols) without and with Tris-(2-carboxyethyl)-phosphine reduction. UV/HCOOH-induced Hg cold vapor generation was used instead of K2SO8–KBH4/NaOH–HCl and/or KBrO3/KBr–KBH4/NaOH–HCl systems as an effective interface between RPLC and CVG–AFS. The limits of detection (3σ) of RPLC–(UV/HCOOH)–CVG–AFS with PHMB labeling for Cys, HCys, Cys–Gly, γ-Glu–Cys and GSH as well as NAC were 4.6, 5.9, 5.9, 8.1, 7.3 and 5.9 nM with the RSD of 4.4, 5.1, 3.6, 7.5 4.2 and 3.7% (n = 6 at 2 μM), respectively, satisfying the simultaneous determination of the main urinary LMM thiols. This developed method was applied successfully to determine the LMM R-thiols and T-thiols in 10 urine samples contributed by 10 healthy volunteers.

An alternative thermodiffusion interface (TDI) was designed and constructed for the effective online coupling of capillary gas chromatography (cGC) and inductively coupled plasma mass spectrometry (ICPMS). Pb2+, (CH3)3Pb+, (C2H5)3Pb+, Hg2+, CH3Hg+ and C2H5Hg+ were derived as Pb(C4H9)4, (CH3)3PbC4H9, (C2H5)3PbC4H9, (C4H9)2Hg, CH3HgC4H9, and C2H5HgC4H9 when butyl magnesium bromide was employed as a derivatization reagent for a proof-of-concept study, avoiding the loss of their species specific information. All these derivatives together with the neutral fully saturated (CH3)4Pb and (C2H5)4Pb could be quantitatively separated within 7 min using a 15 m long capillary column, allowing the determination and speciation of organic and inorganic Pb and Hg species in a single run. The method detection limits (3σ) for Me4Pb, Et4Pb, Me3Pb3+, Pb2+, MeHg+, EtHg+, and Hg2+ are 0.07, 0.06, 0.04, 7.0, 0.09, 0.1, and 0.2 pg g−1, respectively. Moreover, tri-n-propyl-lead chloride was synthesized and used as an alternative internal standard for the accurate and simultaneous speciation analysis of Pb and Hg in complicated environmental and biological samples for the first time. This cGC-TDI-ICPMS method was validated by analyzing Pb and Hg species in certified reference materials and then was applied to simultaneous speciation analysis of Pb and Hg in real-life samples. It is expected that these approaches can be extended to the speciation of other organometallic compounds after suitable modifications and so will aid in monitoring the occurrence, pathways, toxicity, and/or biological effects of these compounds in the environment and in organisms.

A mathematical model describing the bark/air partitioning of persistent organic pollutants (POPs) was established taking into consideration the accumulation processes of POPs from air into bark and compound-, species-, and site-specific air-to-bark accumulation factors. It allows the assessment of the concentrations of atmospheric POPs based on those recorded in tree bark. The spatial distribution of atmospheric POPs including 18 polycyclic aromatic hydrocarbons (Σ18PAHs), 5 organic chlorinated pesticides (Σ5OCPs), 10 polychlorinated biphenyls (Σ10PCBs), and 17 brominated flame retardants (Σ17BFRs) were investigated by analyzing 163 bark samples from 68 sites across mainland China. The atmospheric POPs were estimated to be 4.1−399 ng/m3 air, and 11.3−553, 4.5−130, and 0.9−624 pg/m3 air with geometric means of 71 ng/m3 air, and 99, 26, and 25 pg/m3 air for Σ18PAHs, Σ5OCPs, Σ10PCBs, and Σ17BFRs, respectively, based on those recorded in the tree barks of 5.1−1770, 0.05−12.9, 0.21−21.6, and 0.02−48.3 ng/g bark on dry weight basis, with geometric means of 295, 1.47, 3.12, and 2.79 ng/g bark. These results generally indicated that contamination by atmospheric POPs is more serious in eastern and mid China than that in western China.

Inductively coupled plasma dynamic reaction cell-quadrupole mass spectrometry (ICP-DRC-qMS) coupled on-line with anion exchange chromatography (AEC) has been developed for the quantification of selenium-tagged proteins in human plasma. Methane was employed as a reaction gas in the dynamic reaction cell to achieve the determination of 80Se free of spectroscopic interference from 40Ar2+ and 79BrH+. Five selenium species including selenoprotein P (SelP), glutathione peroxidase (GPx), selenoalbumin (SeAlb), and two unknown selenospecies (U1 and U2) in a pooled plasma sample from five healthy people were separated using AEC, and the distribution of selenium in SelP, GPx, SeAlb, U1 and U2 (about 45.5%, 19.1%, 15.1%, 2.9% and 8.1%) was determined by ICP-DRC-qMS using species-unspecific isotope dilution (80Se/77Se). Based on the detection limit (DL) of selenium (0.54 ng mL−1), we estimated that the DLs for SelP and GPx were 0.59 pmol mL−1 and 1.7 pmol mL−1, respectively. Through the stoichiometry of the selenium atom in the selenium-tagged proteins, SelP (2.7 ± 0.1 μg mL−1) and GPx (5.4 ± 0.2 μg mL−1) were successfully quantified.

Brassica chinensis L. was chosen and exposed to different concentrations of Cd exposure to evaluate its Cd-accumulating capacity and its potential cellular defensive mechanisms. Cd accumulation in the shoots and roots of B. chinensis was up to 1348.3±461.8 and 3761.0±795.0 mg per killogram of dry weight, respectively, under 200 μmol/L of Cd exposure. Increasing Cd accumulation in the plant was accompanied by rapid accumulation of phytochelatins (PCs), and the sequestration of Cd by PCs provided a primary cellular mechanism for Cd detoxification and tolerance of B. chinensis. Furthermore, malondialdehyde formation, hydrogen peroxide content and antioxidative enzyme activities such as superoxide dismutase, catalase, guaiacol peroxidase and ascorbate peroxidase were observed in the shoots of Cd-stressed B. chinensis. Increasing enzyme activities in response to concentrations of 5 to 50 μmol/L Cd showed an efficient defense against oxidative stress, suggesting that the antioxidative system was a secondary defensive mechanism. These resulted in reduced free Cd damage and enhanced Cd accumulation and tolerance. Glutathione plays a pivotal role in these two detoxification pathways. In general, these results suggested that PCs and the antioxidative system are synergistic in combatting Cd-induced oxidative stress and that they play important roles in Cd detoxification of B. chinensis, and also give a deep understanding of the natural defensive mechanisms in plants under heavy metal stress.

Organic mercurial compounds are the most specific and sensitive reagents for reaction with the sulfhydryl groups (—SHs) in peptides and proteins because of the strong mercury—sulfur affinity. Using the monofunctional organic mercury ion RHg+ as a mass spectrometry (MS)-tag has the advantages of reacting with one sulfhydryl group, offering definite mass shift, and especially stable and characteristic nonradioactive isotopic distribution. Mass spectrometric analysis of derivatized sulfhydryls in peptides/proteins is thus an alternative for precisely counting the number of sulfhydryl groups and disulfide bonds (—S—S—). Here the tags used include monomethylmercury chloride, monoethylmercury chloride, and 4-(hydroxymercuri) benzoic acid. The feasibility of this strategy is demonstrated using HPLC/ESI-MS to count —SHs and —S—S— in model peptides/proteins, i.e., glutathione, phytochelatins, lysozyme and β-lactoglobulin, which contain increasing —SHs and various —S—S— linkages.

In this study, in vitro synthesized Cd-phytochelatin (PC) complexes and in vivo Cd–PC complexes in Cd-stressed Brassica chinensis, which has been identified as a Cd hyperaccumulator, were characterized using SEC-ICP-MS and ESI-MS/MS. The PCs (n = 1–5) obtained from Cd-stressed B. chinensis together with CdCl2 were used to synthesize the in vitro Cd–PC complexes, and the formation of CdGS1–2, (CdGS)2, Cd1–2PC2, Cd1–3PC3, Cd1–3PC4 and Cd1–3PC5 was observed. In addition, for the first time, in vivo CdPC3 and CdPC4 complexes, as well as Cd-free PCs (n = 2–5) and desGlu-PC3 were detected in the extracts of Cd-stressed B. chinensis and confirmed by means of their corresponding isotopic peak distribution and MS/MS spectra. Nitrogen saturated ammonium bicarbonate buffer (pH 7.8), instead of Tris-HCl and phosphate buffer, was used as a suitable mobile phase in order to stabilize the Cd–PC complexes and effectively avoid possible oxidation of PC analogues during SEC fractionation. Results obtained in this study give definite evidence elucidating the important roles which PCs play in plant defensive mechanisms to Cd stress. SEC-ICP-MS and ESI-MS/MS were demonstrated as powerful and promising techniques for screening and identifying the in vivo metallopeptides, with accurate isotopic distribution assignment, in metal toxicological studies.

In this study we report a method for direct vapor generation of mercury species on nano TiO2 under UV irradiation in the presence of a formic acid and sodium formate mixture as a hole scavenger. A novelly designed UV/TiO2 photocatalysis reaction device (UV/TiO2 PCRD) was used as an effective sample introduction unit and an interface for mercury species determination by atomic fluorescence spectrometry (AFS) and speciation by HPLC-AFS for the first time. The detection limits of 10, 20, 30 and 70 pg mL−1 of mercury chloride, methylmercury chloride, ethylmercury chloride and phenylmercury chloride, respectively, were achieved by AFS using flow injection mode. Compared with the traditional KBH4/NaOH-HCl system, UV/TiO2 PCRD is a superior alternative for online vapor generation of Hg species.

A pulsed large-volume injection gas chromatography coupled with electron-capture negative ionization quadrupole mass spectrometry (pLVI-GC/ECNI-qMS) was developed for the simultaneous determination of typical halogenated persistent organic pollutants (H-POPs). By monitoring the characteristic ions of large mass-to-charge ratio (m/z) for each of the H-POPs rather than the chlorine and/or bromine ions, this method avoided the possible interferences arising from the H-POPs themselves and from complex matrices encountered frequently in current GC/qMS methods; and allowed, on the other hand, the use of 13C-labeled and perdeuterated analogues as internal standards for reliable quantification. pLVI up to 120 µL improved the instrumental detection limits down to pg-fg mL−1, comparable to or lower than those obtained by the recognized GC/high-resolution MS methods reported so far. The H-POPs including 12 polybrominated diphenyl ethers, 1 polybrominated biphenyl, 10 polychlorinated biphenyls (PCBs), 4 hexachlorocyclohexane isomers, and hexachlorobenzene were involved in this study. The method developed demonstrated good linearity (r2=0.9904−0.9999) within 0.5 to 50,000 pg mL−1 for PCBs and 0.05 to 5000 pg mL−1 for other H-POPs, and was satisfactory in terms of both repeatability (0.07%–2.2%) and reproducibility (2.1%–8.4%). It was validated by analyzing a NIST standard reference material SRM-1946 of Lake Superior fish tissue with low 0.01 to 63 pg g−1 method detection limits, and successfully applied to the determination of the H-POPs in five reference materials of different matrices.

A newly synthesized alkyl phosphinic acid resin (APAR) was used for on-line preconcentration of trace rare earth elements (REES, lanthanides including yttrium) and then determined by inductively coupled plasma mass spectrometry. REEs in seawater could be on-line concentrated on the APAR packed column (4.6 mm i.d. × 50 mm in length), and eluted from the column with 0.5 mL 0.1 mol L−1 nitric acid within 30 s. An enrichment factor of nearly 400 was achieved for all REEs when the seawater sample volume was 200 mL, while the matrix and coexisting spectrally interfering ions such as barium, tin and antimony could be simultaneously separated. The detection limits of this proposed method for REEs were in the range from 1.43 pg L−1 of holmium to 12.7 pg L−1 of lanthanum. The recoveries of REEs were higher than 97.9%, and the precision of the relative standard deviation (R.S.D., n = 6) was less than 5%. The method has been applied to the determination of soluble REEs in seawater.

A new vapor generation system for mercury (Hg) species based on the irradiation of mercaptoethanol (ME) with UV was developed to provide an effective sample introduction unit for atomic fluorescence spectrometry (AFS). Preliminary investigations of the mechanism of this novel vapor generation system were based on GC–MS and FT–IR studies. Under optimum conditions, the limits of determination for inorganic divalence mercury and methyl mercury were 60 and 50 pg mL−1, respectively. Certified reference materials (BCR 463 tuna fish and BCR 580 estuarine sediment) were used to validate this new method, and the results agreed well with certified values. This new system provides an attractive alternative method of chemical vapor generation (CVG) of mercury species compared to other developed CVG systems (for example, the traditional KBH4/NaOH–acid system). To our knowledge, this is the first systematic report on UV/ME-based Hg species vapor generation and the determination of total and methyl Hg in environmental and biological samples using UV/ME–AFS.

Concentrations of rare earth elements (REEs) were determined in the laminae of 10 species of ferns and their acetone-extractable pigments, as well as their host soil and soil extract, by ICP-MS. A new REE hyperaccumulator, Pronephrium simplex, was discovered which could accumulate REEs up to 1.2 mg g−1 dry mass under natural growth conditions. Three typical species of ferns chosen were divided into lamina, petiole, stem and root for the study of REE translocation and fractionation. A hyphenated technique, size exclusion HPLC coupled with online UV/ICP-MS, was developed to provide reliable evidence of the existence of REE-binding proteins in the fern’s lamina. A new REE-binding protein was discovered and separated from the lamina of natural grown P. simplex. Further characterization of the protein showed that its molecular mass is 5068.4 Da by MALDI-TOF-MS and ESI-MS. Amino acid composition analysis by RP-HPLC indicated that the protein has relatively high contents of proline and glycin.

Organic mercurial compounds are the most specific and sensitive reagents for reaction with the sulfhydryl groups (SHs) in peptides and proteins because of the strong mercury–sulfur affinity. Using the monofunctional organic mercury ion RHg+ as a mass spectrometry (MS)-tag has the advantages of reacting with one sulfhydryl group, offering definite mass shift, and especially stable and characteristic nonradioactive isotopic distribution. Mass spectrometric analysis of derivatized sulfhydryls in peptides/proteins is thus an alternative for precisely counting the number of sulfhydryl groups and disulfide bonds (SS). Here the tags used include monomethylmercury chloride, monoethylmercury chloride, and 4-(hydroxymercuri) benzoic acid. The feasibility of this strategy is demonstrated using HPLC/ESI-MS to count SHs and SS in model peptides/proteins, i.e., glutathione, phytochelatins, lysozyme and β-lactoglobulin, which contain increasing SHs and various SS linkages.

A pulsed large-volume injection gas chromatography coupled with electron-capture negative ionization quadrupole mass spectrometry (pLVI-GC/ECNI-qMS) was developed for the simultaneous determination of typical halogenated persistent organic pollutants (H-POPs). By monitoring the characteristic ions of large mass-to-charge ratio (m/z) for each of the H-POPs rather than the chlorine and/or bromine ions, this method avoided the possible interferences arising from the H-POPs themselves and from complex matrices encountered frequently in current GC/qMS methods; and allowed, on the other hand, the use of 13C-labeled and perdeuterated analogues as internal standards for reliable quantification. pLVI up to 120 μL improved the instrumental detection limits down to pg–fg mL−1, comparable to or lower than those obtained by the recognized GC/high-resolution MS methods reported so far. The H-POPs including 12 polybrominated diphenyl ethers, 1 polybrominated biphenyl, 10 polychlorinated biphenyls (PCBs), 4 hexachlorocyclohexane isomers, and hexachlorobenzene were involved in this study. The method developed demonstrated good linearity (r2 = 0.9904–0.9999) within 0.5 to 50,000 pg mL−1 for PCBs and 0.05 to 5000 pg mL−1 for other H-POPs, and was satisfactory in terms of both repeatability (0.07%–2.2%) and reproducibility (2.1%–8.4%). It was validated by analyzing a NIST standard reference material SRM-1946 of Lake Superior fish tissue with low 0.01 to 63 pg g−1 method detection limits, and successfully applied to the determination of the H-POPs in five reference materials of different matrices.

In this study, in vitro synthesized Cd-phytochelatin (PC) complexes and in vivo Cd–PC complexes in Cd-stressed Brassica chinensis, which has been identified as a Cd hyperaccumulator, were characterized using SEC-ICP-MS and ESI-MS/MS. The PCs (n = 1–5) obtained from Cd-stressed B. chinensis together with CdCl2 were used to synthesize the in vitro Cd–PC complexes, and the formation of CdGS1–2, (CdGS)2, Cd1–2PC2, Cd1–3PC3, Cd1–3PC4 and Cd1–3PC5 was observed. In addition, for the first time, in vivo CdPC3 and CdPC4 complexes, as well as Cd-free PCs (n = 2–5) and desGlu-PC3 were detected in the extracts of Cd-stressed B. chinensis and confirmed by means of their corresponding isotopic peak distribution and MS/MS spectra. Nitrogen saturated ammonium bicarbonate buffer (pH 7.8), instead of Tris-HCl and phosphate buffer, was used as a suitable mobile phase in order to stabilize the Cd–PC complexes and effectively avoid possible oxidation of PC analogues during SEC fractionation. Results obtained in this study give definite evidence elucidating the important roles which PCs play in plant defensive mechanisms to Cd stress. SEC-ICP-MS and ESI-MS/MS were demonstrated as powerful and promising techniques for screening and identifying the in vivo metallopeptides, with accurate isotopic distribution assignment, in metal toxicological studies.

In this study we report a method for direct vapor generation of mercury species on nano TiO2 under UV irradiation in the presence of a formic acid and sodium formate mixture as a hole scavenger. A novelly designed UV/TiO2 photocatalysis reaction device (UV/TiO2 PCRD) was used as an effective sample introduction unit and an interface for mercury species determination by atomic fluorescence spectrometry (AFS) and speciation by HPLC-AFS for the first time. The detection limits of 10, 20, 30 and 70 pg mL−1 of mercury chloride, methylmercury chloride, ethylmercury chloride and phenylmercury chloride, respectively, were achieved by AFS using flow injection mode. Compared with the traditional KBH4/NaOH-HCl system, UV/TiO2 PCRD is a superior alternative for online vapor generation of Hg species.

Inductively coupled plasma dynamic reaction cell-quadrupole mass spectrometry (ICP-DRC-qMS) coupled on-line with anion exchange chromatography (AEC) has been developed for the quantification of selenium-tagged proteins in human plasma. Methane was employed as a reaction gas in the dynamic reaction cell to achieve the determination of 80Se free of spectroscopic interference from 40Ar2+ and 79BrH+. Five selenium species including selenoprotein P (SelP), glutathione peroxidase (GPx), selenoalbumin (SeAlb), and two unknown selenospecies (U1 and U2) in a pooled plasma sample from five healthy people were separated using AEC, and the distribution of selenium in SelP, GPx, SeAlb, U1 and U2 (about 45.5%, 19.1%, 15.1%, 2.9% and 8.1%) was determined by ICP-DRC-qMS using species-unspecific isotope dilution (80Se/77Se). Based on the detection limit (DL) of selenium (0.54 ng mL−1), we estimated that the DLs for SelP and GPx were 0.59 pmol mL−1 and 1.7 pmol mL−1, respectively. Through the stoichiometry of the selenium atom in the selenium-tagged proteins, SelP (2.7 ± 0.1 μg mL−1) and GPx (5.4 ± 0.2 μg mL−1) were successfully quantified.

Currently, molecular mass spectrometry is preferred by many for relative quantification but is not appropriate for “absolute” quantification of proteins. In this article we demonstrate a proof of concept for the absolute quantitative analysis of proteinsvia CH3Hg+labeling and integrated application of molecular and elemental mass spectrometry. The smallest size of CH3Hg+ among monoalkyl mercurials and the specific and covalent interaction with sulfhydryl (–SH) in proteins results in forming a simple complex of CH3Hg+:–SH = 1:1 when all –SH are exposed, as confirmed by ESI-MS. Based on the known number of –SH per protein, the absolute protein concentration can be obtained viaHg determination using ICP-MS, in which CH3HgCl could be simply used as an external standard. When bovine pancreatic ribonuclease A, lysozyme and insulin, which have an increasing number of various disulfide linkages in their molecules, were taken as model proteins, their corresponding absolute detection limits (3σ) reached 0.6, 1.2 and 0.4 pmol, respectively. These characteristics may be expected to provide an alternative approach for absolute protein quantification, especially specific biomarker determination, in the near future.

A novel element-tagged activity-based photo-cleavable biotinylated chemical “Hub” was designed and synthesized to orthogonally integrate ICP-MS and ESI-MS for absolute targeted-protein quantification. This tetrafunctional chemical “hub” allowed us to quantify a targeted protein using species-unspecific isotope dilution ICP-MS and to know which protein is being quantified using ESI-IT-MS at the same time.

A novel UV/nano-ZrO2/HCOOH system was developed and fabricated as an atomization unit and as an online interface between HPLC and AFS for Hg determination and speciation for the first time. UV-generated electrons at the conduction band of nano-ZrO2 reduce mercury species into mercury cold vapor, achieving mercury atomization for AFS determination. The LODs (3σ) of inorganic mercury (Hg2+), methylmercury (MeHg) and ethylmercury (EtHg) tested in this study were respectively reduced to 10, 6, and 8 ng L−1 when using AFS under flow injection mode (FI). Moreover, Hg speciation could also be performed when coupled with HPLC, and the LODs (3σ) of Hg2+, MeHg and EtHg were 24, 13, and 16 ng L−1, respectively, using the HPLC-(UV/nano-ZrO2/HCOOH)-AFS system, with the RSDs better than 4.6% (n = 6) at 20 μg L−1 each. FI-(UV/nano-ZrO2/HCOOH)-AFS and HPLC-(UV/nano-ZrO2/HCOOH)-AFS were validated by analyzing a certified reference material (GBW10029, tuna fish) and applied to mercury determination and speciation of the local seafood around Xiamen Island.

In this proof-of-concept study, a novel dual-labelling strategy for conjugating –SH and –NH2 of a peptide was developed, in which an element tag (1,4,7,10-tetraazacyclododecane-1,4,7-trisacetic acid-10-maleimidoethylacetamide loaded with europium) and a fluorescent tag (fluorescein isothiocycanate) were employed. Its feasibility was demonstrated using HPLC-UV/ESI-MS for evaluating labelling-efficiency and HPLC-ICPMS with 153Eu isotope dilution as well as CE-LIF for the determination of peptides.