It still remains a great challenge for quantification of trace analytes in complex samples by surface-enhanced Raman scattering (SERS) technique due to potential matrix influence or weak SERS responses of analytes. In this work, a miniaturized thermal-assisted purge-and-trap (MTAPT) device was designed and developed to eliminate matrix influence coupled with derivatization method before SERS analysis. The design of MTAPT chamber was optimized based on quantitative calculation of its dead volume by computational fluid dynamics simulation. The small straight chamber was selected as an optimized design with a recovery of 96.1% for formaldehyde. The practical feasibility of MTAPT was validated based on four real analytical applications including phenthiol in industrial water, formaldehyde in flour, sulfion in wastewater, and methanol in industrial alcohol. The results showed that SERS responses of all analytes dramatically increased by eliminating sample matrices after MTAPT process. Phenthiol, formaldehyde, sulfion, and methanol in real samples could be accurately quantified with recoveries of 80.9–110.0%, and the analytical results were validated by corresponding standard methods. The time consumption of MTAPT-SERS for real sample analysis including sample preparation and determination was within 16 min. It is highly expected that the combination of MTAPT technique with portable SERS instrument can greatly expand the range of SERS analysis. The proposed MTAPT-SERS method has high potential for on-site analysis of complex samples.

Reliable quantification by surface enhanced Raman scattering (SERS) highly depends on the development of a reproducible substrate with excellent anti-interference capability. In this work, an intrinsic internal standard (IS) SERS substrate based on a diblock copolymer, polystyrene-block-poly-4-vinylpyridine (PS-b-P4VP), as a template was developed by a modified block copolymer lithography (BCL) technique of reserving the diblock copolymer template. This substrate generated a stable vibration peak at 1066 cm−1 attributed to poly(4-vinylpyridine) (P4VP) which could be used as an intrinsic IS for precise SERS quantification. A series of characterization results showed that the diblock copolymer template endowed this substrate with homogeneous distribution of Au nanoparticles, excellent stability and reproducibility. A minor relative standard deviation (RSDs) of SERS responses at 1066 cm−1 was measured and calculated to be 4.3% from ten different substrates in the same batch, which suggested good substrate-to-substrate reproducibility of this substrate. Finally, this intrinsic IS substrate was successfully applied for the rapid quantification of a trace banned dye, chrysoidine, in food samples with complicated matrices by SERS. It was proved that chrysoidine could be found and quantified to be 0.50 and 0.41 mg L−1 in a positive dried bean curd stick and chilli powder sample respectively with good recoveries by this substrate coupled with SERS. The development of intrinsic IS substrates would benefit rapid and accurate quantification of trace targets in complex samples coupled with SERS analysis.

•A novel acylhydrazone bond gel based dynamic covalent polymer was prepared.•The adsorption mechanism of AB-gel DCP adsorbent explored in detail.•AB-gel DCP monolith for online coupled with HPLC for food analysis.•Online analysis of trace sulfonamide and fluorescent whitening agent in food samples.A new dynamic covalent polymer (DCP) gel was well designed and constructed based on imine chemistry. Polycondensation of 4,4′-biphenyldicarboxaldehyde and 1,3,5-benzenetricarbohydrazide via Schiff-base reaction resulted in an acylhydrazone bond gel (AB-gel) DCP. AB-gel DCP had three-dimensional network of interconnected nanoparticles with hierarchically porous structure. AB-gel DCP was successfully fabricated as a monolithic column by an in-situ chemical bonding method for online enrichment and separation purpose with excellent permeability. AB-gel DCP based monolithic column showed remarkable adsorption affinity towards target analytes including sulfonamides (SAs) and fluorescent whitening agents (FWAs) due to its strong π-π affinity, hydrophobic effect and hydrogen bonding interaction. Then, AB-gel DCP based monolithic column was applied for online separation and analysis of trace SAs and FWAs in food samples coupled with high-performance liquid chromatography (HPLC). Sulfathiazole (ST) and sulfadimidine (SM2) in one positive weever sample were actually found and determined with concentrations of 273.8 and 286.3 μg/kg, respectively. 2,5-Bis(5-tert-butyl-2-benzoxazolyl) thiophene (FWA184) was actually quantified in one tea infusion sample with the concentration of 268.5 ng/L. The spiked experiments suggested the good recoveries in range of 74.5–110% for SAs in weever and shrimp samples with relative standard deviations (RSDs) less than 9.7% and in range of 74.0-113% for FWAs in milk and tea infusion samples with RSDs less than 9.0%. AB-gel DCP monolithic column was proved to be a promising sample preparation medium for online separation and analysis of trace analytes in food samples with complex matrices.

•A nanoarrayed Au@PS-OH SERS substrate was successfully prepared.•The substrate had excellent anti-agglomeration capability, mechanic and chemical stability.•A new method was developed for the sequential quantification of trace 4-aminoazobenzene.•The method was successfully applied to 4-aminoazobenzene analysis in textile samples.Achieving reproducible signals is a key point to improve the analytical precision and accuracy of surface enhanced Raman scattering (SERS) technique and further expand the application scope of SERS for on-site and rapid analysis of real sample with complex matrice. In this work, a novel Au@hydroxyl-functionalized polystyrene (Au@PS-OH) substrate was prepared by atom transfer radical polymerization and chemical assembly method, which possessed promised potential for the rapid and sequential analysis of multisamples coupling with SERS technique. Au@PS-OH substrate with regular nanoarrayed morphology possessed excellent anti-agglomeration capability even for testing solutions with strong basicity or acidity, mechanic and chemical stability due to the large amount of Au nanoparticles homogeneously and stably fixed on substrate surface. Moreover, excellent hydrophobicity of Au@PS-OH substrate could keep testing droplets of multiple samples stable and uniform spherical shape with similar contact angles to substrate, which guaranteed the reproducible SERS light paths and SERS signals during real sequential analysis. Then, an Au@PS-OH based SERS analytical method was developed and practically applied for the sequential determination of trace 4-aminoazobenzene in various textiles. It was satisfactory that the contents of trace 4-aminoazobenzene in black woolen, green woolen and yellow fiber cloth could be actually found and calculated to be 106.4, 120.9 and 140.8 mg/kg with good recoveries of 76.0-118.9% and relative standard deviations of 1.6-5.1%. It is expected that this SERS method is suitable for on-site and rapid analysis of multiple samples in a short period.

•Preparation of new hydrazone linked covalent organic polymer by Schiff-base reaction.•The adsorption mechanism of the HL-COP adsorbent was explored in detail.•An online HL-COP μ-SPE method coupled with HPLC for analysis of Sudan dyes.•Practical application for online analysis of trace Sudan dyes in food samples.Covalent organic polymers (COPs) connected by covalent bonds are a new class of porous network materials with large surface area and potential superiority in sample pretreatment. In this study, a new hydrazone linked covalent organic polymer (HL-COP) adsorbent was well-designed and synthesized based on a simple Schiff-base reaction. The condensation of 1,4-phthalaldehyde and 1,3,5-benzenetricarbohydrazide as organic building blocks led to the synthesis of HL-COP with uniform particle size and good adsorption performance. This HL-COP adsorbent with high hydrophobic property and rich stacking π electrons contained abundant phenyl rings and imine (CN) groups throughout the entire molecular framework. The adsorption mechanism was explored and discussed based on π–π affinity, hydrophobic effect, hydrogen bonding and electron–donor–acceptor (EDA) interaction, which contributed to its strong recognition affinity to target compounds. Enrichment factors were 305–757 for six Sudan dyes by HL-COP micro-solid phase extraction (μ-SPE), indicating its remarkable preconcentration ability. Furthermore, the adsorption amounts by HL-COP μ-SPE were 1.0–11.0 folds as those by three commonly used commercial adsorbents. Then, HL-COP was applied as adsorbent of online μ-SPE coupled with high performance liquid chromatography (HPLC) for enrichment and analysis of trace Sudan dyes in food samples with detection limit of 0.03–0.15 μg/L. The method was successfully applied for online analysis of chilli powder and sausage samples. Sudan II and Sudan III in one positive chilli powder sample were actually found and determined with concentrations of 8.3 and 6.8 μg/kg, respectively. The recoveries of chilli powder and sausage samples were in range of 75.8–108.2% and 73.8–112.6% with relative standard deviations of 1.2–8.5% and 1.9–9.4% (n = 5), respectively. The proposed method was accurate, reliable and convenient for the online simultaneous analysis of trace Sudan dyes in food samples.

Ethylene, an important plant hormone, is of utmost importance during many developmental processes of plants. However, the efficient enrichment and analysis of trace ethylene still remains a challenge. A simple and mild multilayer interparticle linking strategy was proposed to fabricate a novel hybrid MOF-199 enrichment coating. Strong chemical interparticle linkages throughout the coating improved the durability and reproducibility of hybrid MOF-199 coating dramatically. This coating performed a significant extraction superiority of ethylene over commonly used commercial coatings, attributed to the multiple interactions including “molecular sieving effect”, hydrogen bonding, open metal site interaction, and π–π affinity. The hybridization of multiwalled carbon nanotubes (MWCNTs) with MOF-199 further improved the enrichment capability and also acted as a hydrophobic “shield” to prevent the open metal sites of MOF-199 from being occupied by water molecules, which effectively improved the moisture-resistant property of MOF-199/CNTs coating. Finally, this novel enrichment method was successfully applied for the noninvasive analysis of trace ethylene, methanol, and ethanol from fruit samples with relatively high humidity. The low detection limit was 0.016 μg/L for ethylene. It was satisfactory that trace ethylene could be actually detected from fruit samples by this noninvasive method. Good recoveries of spiked grape, wampee, blueberry, and durian husk samples were obtained in the range of 90.0–114%, 79.4–88.6%, 78.5–86.8%, and 85.2–105% with the corresponding relative standard deviations of 4.8–9.8%, 6.9–8.9%, 3.8–8.1%, and 9.3–10.5% (n = 3), respectively.

•An overview of online sample preparation techniques coupled with LC is presented.•The coupling approaches and corresponding interfaces are discussed.•The problems and expected trends in this field are attempted to be discussed.Sample preparation is still considered as the bottleneck of the whole analytical procedure, and efforts has been conducted towards the automation, improvement of sensitivity and accuracy, and low comsuption of organic solvents. Development of online sample preparation techniques (SP) coupled with liquid chromatography (LC) is a promising way to achieve these goals, which has attracted great attention. This article reviews the recent advances on the online SP-LC techniques. Various online SP techniques have been described and summarized, including solid-phase-based extraction, liquid-phase-based extraction assisted with membrane, microwave assisted extraction, ultrasonic assisted extraction, accelerated solvent extraction and supercritical fluids extraction. Specially, the coupling approaches of online SP-LC systems and the corresponding interfaces have been discussed and reviewed in detail, such as online injector, autosampler combined with transport unit, desorption chamber and column switching. Typical applications of the online SP-LC techniques have been summarized. Then the problems and expected trends in this field are attempted to be discussed and proposed in order to encourage the further development of online SP-LC techniques.

•Preparation of sulfonated graphene/polypyrrole coating by in situ electropolymerization.•High extraction selectivity and capacity to volatile terpenes.•Practical application for analysis of trace terpenes from spice samples.In this study, a novel sulfonated graphene/polypyrrole (SG/PPy) solid-phase microextraction (SPME) coating was prepared and fabricated on a stainless-steel wire by a one-step in situ electrochemical polymerization method. Crucial preparation conditions were optimized as polymerization time of 15 min and SG doping amount of 1.5 mg/mL. SG/PPy coating showed excellent thermal stability and mechanical durability with a long lifespan of more than 200 stable replicate extractions. SG/PPy coating demonstrated higher extraction selectivity and capacity to volatile terpenes than commonly-used commercial coatings. Finally, SG/PPy coating was practically applied for the analysis of volatile components from star anise and fennel samples. The majority of volatile components identified were terpenes, which suggested the ultra-high extraction selectivity of SG/PPy coating to terpenes during real analytical projects. Four typical volatile terpenes were further quantified to be 0.2–27.4 μg/g from star anise samples with good recoveries of 76.4–97.8% and 0.1–1.6 μg/g from fennel samples with good recoveries of 80.0–93.1%, respectively.

Toxic formaldehyde is sometimes used illegally as a food preservative, however, on-site rapid analysis of trace formaldehyde in aquatic products remains a challenge. In this work, a simple on-site rapid quantification method for trace volatile formaldehyde in aquatic products was developed by a derivative reaction-based surface enhanced Raman spectroscopy (SERS) technique coupled with a homemade portable purge-sampling device. Trace formaldehyde separated from complicated aquatic matrices via a purge-sampling procedure was reacted with a derivative reagent to produce a Raman-active analyte for consequent SERS analysis. Au/SiO2 nanoparticles (NPs) were employed as the enhancement substrate to achieve significant enhancement of Raman signal intensity. Conditions of derivative reaction and SERS detection were optimized in detail, and the selectivity of this analytical method was also evaluated based on related analogs. Under optimal conditions, an extremely low detection limit of 0.17 μg L−1 was achieved. Trace volatile formaldehyde can be found in fresh squid and shrimp samples without obvious matrix interference, and this was quantified to be 0.13–0.21 mg kg−1 using the described method. The recoveries of spiked aquatic product samples were found to be 70.0–89.1% with RSDs of 2.3–7.2% (n = 3). The results suggest that the proposed method is reliable and suitable for on-site rapid analysis of trace formaldehyde in aquatic products.

•Magnetic separation techniques for biological sample preparation were reviewed.•The preparation of magnetic nanoparticles was reviewed.•The trends of magnetic separation techniques in biological analysis were proposed.Sample preparation is a fundamental and essential step in almost all the analytical procedures, especially for the analysis of complex samples like biological and environmental samples. In past decades, with advantages of superparamagnetic property, good biocompatibility and high binding capacity, functionalized magnetic materials have been widely applied in various processes of sample preparation for biological analysis. In this paper, the recent advancements of magnetic separation techniques based on magnetic materials in the field of sample preparation for biological analysis were reviewed. The strategy of magnetic separation techniques was summarized. The synthesis, stabilization and bio-functionalization of magnetic nanoparticles were reviewed in detail. Characterization of magnetic materials was also summarized. Moreover, the applications of magnetic separation techniques for the enrichment of protein, nucleic acid, cell, bioactive compound and immobilization of enzyme were described. Finally, the existed problems and possible trends of magnetic separation techniques for biological analysis in the future were proposed.

Two novel polypyrrole (PPy) composite solid-phase microextraction (SPME) fiber coatings involving polypyrrole β-naphthalenesulfonic acid (PPy/β-NSA) and polypyrrole graphene (PPy/GR) composite SPME fiber coatings were prepared by a simple sol–gel technique for selectively sampling relatively polar biological volatile organic compounds (VOCs). Crucial preparation conditions of the PPy composite SPME fiber coatings were optimized and are discussed in detail. Physical tests suggested that the PPy composite SPME fiber coatings possessed a porous surface morphology, stable chemical and thermal properties. Due to the inducing polar functional groups in the PPy molecule, the PPy composite SPME fiber coatings achieved a higher extraction capacity and special selectivity for the polar biological VOCs with conjugate structures, compared with commercial SPME fiber coatings. Enrichment factors of most of the VOCs by the PPy/β-NSA and PPy/GR SPME fibers were much higher than those achieved by common commercially available SPME fiber coatings. Finally, the PPy/β-NSA and PPy/GR SPME fiber coatings were applied for the trace analysis of typical polar VOCs from ant and coriander samples coupled with gas chromatography/mass spectrometry (GC/MS) detection, respectively. It was satisfactory that the average contents of 4-heptanone, 4-heptanol, 4-nonanone and methyl 5-methylsalicylate from ant samples were actually found to be 28.0, 58.7, 3.0 and 0.6 μg g−1, and the average contents of nonane, decanal, undecanal and dodecanal from coriander samples were actually found to be 0.79, 0.13, 0.06 and 0.21 μg g−1. The results suggested that PPy composite SPME coatings will be a potentially excellent sampling technique for the trace analysis of polar biological VOCs.

Biological terminal metabolites are volatile organic compounds (VOCs) with strong volatility, containing important bio-information related with biological metabolism. As a crucial research precondition, analytical methodology for biological VOCs has attracted much attention to achieve the adequate composition information of biological VOCs at different physiological status and metabolism phases. In this article, the analytical methodology for biological VOCs is summarized, focusing on the latest advances on sampling and analytical techniques followed by the preliminary application of distilling potential, but crucial, bio-information. Systematic study of the relationship among biological VOCs, biological VOC characteristics and corresponding biomarkers would result in a potential but promising research field, bioodoromics. The concept of bioodoromics is described, and the developing trend of bioodoromics in the future is proposed in this paper. It is believed that bioodoromics possesses the power to describe potential but crucial bio-information related with metabolism pathway. The study of biological VOCs and potential bioodoromics would facilitate relevant fields such as insect prevention, disease diagnosis, criminal track-down, agricultural product quality control and food safety, etc..

Compositional study of different soybean varieties was performed by use of 1H nuclear magnetic resonance (NMR) spectroscopy, chromatographic and spectrometric technique. Compositions of amino acids, fatty acids, sugars, elements, and isoflavones in two glyphosate-tolerant soybean varieties and three Chinese conventional soybean varieties were studied by 1H NMR spectroscopy, gas chromatography-mass spectrometry, high performance liquid chromatography and inductively coupled plasma-atomic emission spectrometry, respectively. Principal component analysis suggested that glyphosate-tolerant and conventional soybeans had different compositional profile characteristics of amino acids and fatty acids. Then, the contents of some typical soybean components involving main nutrients and antinutrients were compared. As key nutrients of glyphosate-tolerant soybeans, the content of crude protein increased at 8.9–40%, while the contents of α-tocopherol and γ-tocopherol decreased at 12–64%. As antinutrients of glyphosate-tolerant soybeans, the content of tannin decreased at 32–51%, while the content of raffinose increased at 63–197%, compared with conventional soybeans. Systematical study of compositional profile characteristics provided an effective method for discriminating different soybean varieties and useful reference values for soybean consumption.Highlights► Compositional study of soybean varieties was conducted by a combination analysis. ► Combination analysis of NMR, chromatographic and spectrometric technique was used. ► Compositional profile characteristic is useful for discriminating soybean varieties. ► Reference values for soybean consumption are achieved in the study.

Biological terminal metabolites are volatile organic compounds (VOCs) with strong volatility, containing important bio-information related with biological metabolism. As a crucial research precondition, analytical methodology for biological VOCs has attracted much attention to achieve the adequate composition information of biological VOCs at different physiological status and metabolism phases. In this article, the analytical methodology for biological VOCs is summarized, focusing on the latest advances on sampling and analytical techniques followed by the preliminary application of distilling potential, but crucial, bio-information. Systematic study of the relationship among biological VOCs, biological VOC characteristics and corresponding biomarkers would result in a potential but promising research field, bioodoromics. The concept of bioodoromics is described, and the developing trend of bioodoromics in the future is proposed in this paper. It is believed that bioodoromics possesses the power to describe potential but crucial bio-information related with metabolism pathway. The study of biological VOCs and potential bioodoromics would facilitate relevant fields such as insect prevention, disease diagnosis, criminal track-down, agricultural product quality control and food safety, etc..