•Supercritical CO2 a competitive alternative reaction medium to organic solvents.•Synthesis of aminopropyl bonded silica (APS) intermediate for LC applications.•Higher %C loading/conversion efficiency for APS using supercritical-CO2 protocol compared to toluene.•Change in surface charge of silica from negative to positive for APS, confirmed by zeta potential measurements.This research reports supercritical carbon dioxide versus toluene as reaction media in silica functionalisation for use in liquid chromatography. Bonded aminopropyl silica (APS) intermediates were prepared when porous silica particles (Exsil-pure, 3 μm) were reacted with 3-aminopropyltriethoxysilane (3-APTES) or N,N-dimethylaminopropyltrimethoxysilane (DMAPTMS) using supercritical carbon dioxide (sc-CO2) and toluene as reaction media. Covalent bonding to silica was confirmed using elemental microanalysis (CHN), thermogravimetric analysis (TGA), zeta potential (ξ), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, scanning electron microscopy (SEM) and solid-state nuclear magnetic resonance (CP/MAS NMR) spectroscopy. The results demonstrate that under sc-CO2 conditions of 100 °C/414 bar in a substantial reduced time of 3 h, the surface coverage of APS (evaluated from%C obtained from elemental analysis) prepared with APTES (%C: 8.03, 5.26 μmol/m−2) or DMAPTES (%C: 5.12, 4.58 μmol/m2) is somewhat higher when compared to organic based reactions under reflux in toluene at a temperature of 110 °C in 24 h with APTES (%C: 7.33, 4.71 μmol/m2) and DMAPTMS (%C: 4.93, 4.38 μmol/m2). Zeta potential measurements revealed a change in electrostatic surface charge from negative values for bare Exsil-pure silica to positive for functionalised APS materials indicating successful immobilization of the aminosilane onto the surface of silica.

•A new non-bonded 1.7 μm thin-shell (TS1.7–100 nm) silica particle for HILIC.•Separation time controllable to sub–1 min on sub 2 μm particle column.•Rapid HILIC method applicable for selective determination of uric acid and creatinine in urine.A rapid chromatographic method for the simultaneous determination of uric acid (UA) and creatinine (Cr) in human urine is described, using a non-bonded 1.7 μm thin-shell (TS1.7-100 nm) silica particle prepared by the seeded-growth approach. The new shell particle was characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS) and BET analysis. TEM reveals 1.5 μm solid core and 100 nm shell thickness. DLS shows polydispersity index <0.2. Expanded pore size of 88 Å and specific surface area of 78 m2/g were determined by BET. Chromatographic results demonstrate that UA, Cr and hypoxanthine (Hyp, as internal standard) can be separated in less than 1 min on the in-house packed TS1.7-100 column (4.6 ID x 100 mm), using chromatographic conditions with mobile phase 70% acetonitrile, 10 mM ammonium acetate buffer, pH 6.78, flow rate 1.25 ml/min and UV detection at 254 nm. A linear relationship between the ratio of the peak area of the standard UA and Cr to that of the internal standard (Hyp) and the concentration of standards was obtained for both UA and Cr with the square of the correlation coefficients, R2 = 0.998 for both renal biomarkers. The calculated detection limits were 0.03 μg/ml and 0.05 μg/ml for UA and Cr respectively. Urine samples tested were found to contain UA and Cr in the concentration range of 782–1206 μg/ml and 535–862 μg/ml respectively. The recovery ranges for spiked urine standards were 85.7–93.2% for UA and 91.9–94.6% for Cr and the relative standard deviations (RSD) for both biomarkers were 3.05% and 0.88% respectively. The developed rapid HILIC method can have application in determining the concentrations of UA and Cr for early prediction in patients with developing disease conditions, including acute kidney injury (AKI).

AbstractRapid detection of pathogenic bacteria present in patient samples is of utmost importance for the clinical management of bacterial-induced diseases. Herein, we describe an efficient and direct electrochemical approach for the detection of 2-heptyl-3-hydroxy-4-quinolone (PQS), 2-heptyl-4-hydroxyquinoline (HHQ), and pyocyanin (PYO) as a molecular signature of Pseudomonas aeruginosa (PA), a frequently infecting pathogen with high antibiotic resistance. The cationic surfactant hexadecyltrimethylammonium bromide (CTAB) enhances the effectiveness of an unmodified thin-film boron-doped diamond (BDD) electrode for the direct detection of PYO, HHQ, and PQS in bacterial cultures of PAO1 and PA14. Differential pulse voltammetry (DPV) is then used to monitor the production of these microbial metabolites in bacterial cultures of PAO1 over 10 h without any sample pretreatment. A proposed mechanism for the interaction of CTAB with bacteria cells is examined by zeta (ζ) potential measurements. Furthermore, the detection method is successfully extended to a clinical fluid matrix and applied to PA spiked cystic fibrosis (CF) sputum samples.

•A critical review of IC-MS and its application to inorganic oxyhalide disinfection by-products.•Comparison of reported method performances at the μg/L level.•Future directions for fast, multi-analyte analysis by IC-MS.This paper is a review of ion chromatographic (IC) separations of inorganic oxyhalide disinfection by-products (DBPs) in water and beverages. The review outlines the chemical mechanisms of formation, regulation of maximum allowable levels, chromatographic column selection and speciation. In addition, this review highlights the application of IC coupled to mass spectrometry (MS) for trace and elemental composition analysis of oxyhalides, along with the analytical considerations associated to enable sensitive analysis. Furthermore, a review of literature concerning IC determination of inorganic oxyhalide DBPs in environmental matrices, including water, published since 2005 is presented, with a focus on MS detection, and a discussion on the relative performance of the methods. Finally some prospective areas for future research, including fast, selective, multi-analyte analysis, for this application are highlighted and discussed.

•l-cysteine self-assembled monolayers on AuNPs/MWCNTs/GCE was successfully fabricated.•The SDS-doped l-Cys/AuNPs/MWCNTs/GCE was demonstrated for the determination of NE.•The modified electrode gave low LOD for the detection of NE at 0.03 μM in the presence of AA and UA.A novel electrochemical sensor consisting of l-cysteine self-assembled monolayers over gold nanoparticles/multi-walled carbon nanotubes modified glassy carbon electrode (l-Cys/AuNPs/MWCNTs/GCE) was fabricated and applied for the determination of norepinephrine (NE) in the presence of sodium dodecyl sulfate (SDS) for the first time. Electroanalytical measurements including cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used. The optimum buffer of pH 5.0 contained 30 μM SDS, the NE oxidation peak current enhanced linearly with concentration ranging from 0.2 to 100 μM (R2 of 0.9998) with a detection limit of 0.03 μM. In the presence of SDS, the modified l-Cys/AuNPs/MWCNTs/GCE electrode showed high selectivity for the detection of NE in the presence of ascorbic acid and uric acid. High recoveries in the range of 80.7–100.2% were obtained in spiked human serum samples. Our modified electrode displayed a high reproducibility, sensitivity and long term stability.

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen, capable of surviving in a broad range of natural environments and quickly acquiring resistance. It is associated with hospital-acquired infections, particularly in patients with compromised immunity, and is the primary cause of morbidity and mortality in cystic fibrosis (CF) patients. P. aeruginosa is also of nosocomial importance on dairy farms and veterinary hospitals, where it is a key morbidity factor in bovine mastitis. P. aeruginosa uses a cell-cell communication system consisting of signalling molecules to coordinate bacterial secondary metabolites, biofilm formation, and virulence. Simple and sensitive methods for the detection of biomolecules as indicators of P. aeruginosa infection would be of great clinical importance. Here, we report the synthesis of the P. aeruginosa natural product, barakacin, which was recently isolated from the bovine ruminal strain ZIO. A simple and sensitive electrochemical method was used for barakacin detection using a boron-doped diamond (BDD) and glassy carbon (GC) electrodes, based on cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The influence of electrolyte pH on the peak potential and peak currents was also investigated. At pH 2.0, the peak current was linearly dependent on barakacin concentration (in the range used, 1–10 μM), with correlation coefficients greater than 0.98 on both electrodes. The detection limit (S/N = 3) on the BDD electrode was 100-fold lower than that obtained on the GC electrode. The optimized method using the BDD electrode was extended to bovine (cow feces) and human (sputum of a CF patient) samples. Spiked barakacin was easily detected in these matrices at a limit of 0.5 and 0.05 μM, respectively.

•Mild sc-CO2 endcapping conditions (100 °C/414 bar/1 h) compared to conventional solvents.•Increase carbon loading after endcapping.•Improved chromatographic performance of PFPP phase attributed to endcapping.•Amitriptyline selectively retained with good peak shape on both phases.•Stability of PFPP phase confirmed by TGA 3½ post-synthesis.This research uses solid-state nuclear magnetic resonance (NMR) spectroscopy to characterise the nature and amount of different surface species, and chromatography to evaluate phase properties of a pentafluorophenylpropyl (PFPP) bonded silica phase prepared and end-capped using supercritical carbon dioxide (sc-CO2) as a reaction solvent. Under sc-CO2 reaction conditions (at temperature of 100 °C and pressure of 414 bar), a PFPP silica phase was prepared using 3-[(pentafluorophenyl)propyldimethylchlorosilane] within 1 h. The bonded PFPP phase was subsequently end-capped with bis-N,O-trimethylsilylacetamide (BSA), hexamethyldisilazane (HMDS) and trimethylchlorosilane (TMCS) within 1 h under the same sc-CO2 reaction conditions (100 °C/4141 bar). Elemental microanalysis, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were used to provide support data to solid-state NMR and chromatographic evaluation. Results revealed a surface coverage of 2.2 μmol/m2 for the non-end-capped PFPP silica phase while the PFPP phase end-capped with BSA gave a higher surface coverage (3.9 μmol/m2) compared to HMDS (2.9 μmol/m2) and TMCS (2.8 μmol/m2). 29Si CP/MAS NMR analysis of the PFPP end-capped with BSA shows a significant decrease in the amount of Q3 (free silanols) and Q4 (siloxane groups) species, coupled with the absence of the most reactive Q2 (geminal silanols) in addition to increased amount of a single resonance peak centred at +13 ppm (MH) corresponding to SiO*SiCH3 bond. 13C CP/MAS NMR shows the resonance corresponding to the propyl linkage (CH3CH2CH2) and methyl groups (Si(CH3)n) confirming successful silanisation and endcapping reactions in sc-CO2. Chromatographic evaluation of the BSA end-capped PFPP phase with Neue text mixture revealed improved chromatographic separation as evidenced in the enhanced retention of hydrophobic markers and decreased retention for basic solutes. Moreover, chromatography revealed a change in column selectivity for the BSA end-capped PFPP phase with dipropylphthalate eluting before naphthalene, indicating decreased silanol groups and increased hydrophobicity. The extend of BSA end-capping as measured by the increase in column efficiency (67,260 N/m vs. 60,480 N/m) on a 2.1 i.d. × 50 mm column, methylene group selectivity (αCH2=2.27 vs. 2.14) and decreased silanophilic interactions (S = 3.7 vs. 4.10) indicate that the increase in carbon loading (3.9 μmol/m2 vs. 2.2 μmol/m2) and improvement in chromatography in good peak shape and symmetry is attributed to end-capping with trimethylsilyl groups.

Pentafluorophenyl and phenyl silica stationary phases offer alternative selectivity compared to alkyl bonded C18 and C8 stationary phases, through other interactions such as π–π interactions, dipole–dipole and hydrogen bond interactions. Pentafluorophenyl and phenyl silica bonded stationary phases were efficiently prepared in sc-CO2 specifically pentafluorophenyl propyl (PFPP), pentafluorophenyl (PFP), phenyl propyl (PP) and phenyl (P) silica stationary phases. The bonded phases were characterised by elemental analysis, thermogravimetric analysis (TGA), BET, and by solid-state NMR spectroscopy. Chromatographic performance of the supercritical fluid generated phases was also investigated using the Neue test. The authors present results which demonstrate that pentafluorophenyl and phenyl stationary phases can be prepared successfully under supercritical conditions of 100 °C, 414 bar in a reaction time of 1 h with surface coverage comparable to traditional organic solvent based methods. Chromatographic results reveal that the pentafluorophenyl propyl (PFPP) phase provides superior separation performance for Neue test solutes despite having a lower ligand density (C: 5.67%, 2.2 μmol/m2) compared to the phenyl propyl (PP) analogue having the highest ligand density (C: 6.67%, 2.5 μmol/m2). The difference chromatographic performance is attributed to the polarity of the CF bond in PFPP phase. Moreover, as the alkyl chain length decreases, the hydrophobic interaction also decreases, and the PFPP phase (with a propyl linkage) provides better separation compared to the PFP phase.Highlights► Functionalisation of silica to pentafluorophenyl (PFPP, PFP) and phenyl phases (PP, P) in sc-CO2 within 1 h. ► Chromatographic tests more informative than spectroscopic and CHN evaluation. ► Chromatographic results reveal PFPP phase superior to PP and PFP. ► Residual silanol activity confirmed as a contributing property of fluorinated phases.

Coated capillary electrophoresis equipped with a boron doped diamond (BDD) electrode was developed for analysis of chemically synthesised 2-heptyl-3-hydroxy-4-quinolone (HHQ), 2-heptyl-3-hydroxy-4-quinolone (PQS), and 2-methyl analogues. Detection was then extended to biological samples. PQS and its biological precursor, HHQ, are two key regulators of bacterial cooperative behaviour known as quorum sensing in the nosocomial pathogen Pseudomonas aeruginosa. The fused silica capillary was coated with a thin layer of poly (diallyldimethylammonium) chloride to reverse the electroosmosis, allowing fast migration of PQS and HHQ with improved selectivity. The four model compounds were baseline resolved using a 50 mM H3PO4–Tris, pH 2.0 buffer with 20% (v/v) acetonitrile as buffer additive. With an injection time of 3 s, the detection limits of four analytes ranging from 60 to 100 nM (S/N = 3) were observed when the BDD electrode was poised at +1.5 V vs. 3 M Ag/AgCl. As expected, no PQS or HHQ was detected from the supernatant of the P. aeruginosa (pqsA) mutant. A concentration of HHQ of 247 μM was detected from the supernatant of the pqsH mutant, which catalyses the conversion of HHQ to PQS in the presence of molecular oxygen by monooxygenase. The separation and detection scheme was applicable to follow the conversion of HHQ to PQS in P. aeruginosa when entering the stationary phase of growth. The results obtained by coated capillary electrophoresis with BDD detection were validated and compared well with LC–MS data.Highlights► Convenient, early stage detection of potential biomarkers is of clinical significance. ► CE with electrochemical detection is used to separate and quantify key signalling molecules. ► New approach using a PDDA coated capillary coupled to a BDD electrode. ► Technique is capable of separating a number of potential P. aeruginosa biomarkers. ► Detection limit was below normal physiological levels in sputum samples of CF patients.

This research employed 29Si and 13C Cross-Polarisation/Magic Angle Spinning (CP/MAS) NMR spectroscopy to characterise the nature and amount of surface species of di-and trifunctional mercaptopropylsilane (MPS) bonded silica using supercritical carbon dioxide (sc-CO2) as a reaction solvent without additives (co-solvent) or catalysts. The MPS stationary phases were prepared within 1 h at a temperature and pressure of 70 °C and 414 bar, respectively. Complementary analysis including elemental analysis, thermogravimetric analysis (TGA), DRIFT spectroscopy and BET surface area measurements were employed to characterise the bonded MPS intermediate stationary phases in support of data obtained from solid-state NMR analysis. The results revealed that modification of silica with a trimethoxymercaptopropylsilane (MPTMS) results in ligand surface coverage that is larger than when dimethoxymethylmercaptopropysilane (MPDMMS) is employed as a silanisation reagent. This observation is attributed to greater reactivity and cross-linkage of trifunctional silane. Reaction in sc-CO2 in comparison to reflux in organic solvents, is rapid, reducing product recovery procedures.Highlights► Rapid synthesis and extensive purification task avoided. ► Reaction performed at temperature not exceeding ambient conditions (70 °C/414 bar/1 h). ► MPS carbon surface coverage from MPTMS was greater than for MPDMS. ► Q3 species on silica surface dominate as the primary reaction and adsorption site.

This research examines bonding methodology, surface coverage and silanol conversion efficiencies on the preparation of silica hydride (SiH) intermediate from triethoxysilane (TES) and dimethylmethoxysilane (DMMS) using sc-CO2 and dioxane as reaction solvent. Under sc-CO2 reaction conditions (at temperature and pressure of 100 °C, 414 bar, respectively and 3 h reaction time), the surface coverages of SiH (evaluated from %C obtained from elemental analysis) prepared with DMMS (3.39 μmol/m2) and TES (4.46 μmol/m2) increased by 2- and 4-folds respectively, when compared to reaction performed in dioxane (2.66 μmol/m2, SiH, DMMS and 0.69 μmol/m2, SiH, TES). The relatively higher surface coverage of SiH from TES over DMMS generated in sc-CO2 is due to the inherent trialkoxy moiety of the TES that favours siloxane crosslinkage, forming polymeric surface attachments to yield a higher ligand density than the monomeric DMMS ligand. A conversion efficiency of ∼84.4% of SiH prepared from TES in sc-CO2 estimated from 29Si CP/MAS NMR analysis is comparable to TES silanization in dioxane or toluene. Moreover, silica hydride (SiH) conversion efficiency of ca. 42.4% achieved for the hydride intermediate prepared from DMMS in sc-CO2 is more superior to 33.3% efficiency obtained in dioxane. The differences in conversion efficiencies is attributed to the ability of sc-CO2 being able to access silica pores that are inaccessible in organic solvents. Bonded silica hydride from TES, DMMS prepared in sc-CO2 were characterized using elemental analysis, thermogravimetric analysis (TGA), BET surface area, Fourier transform infrared (FI-IR) and solid state NMR spectroscopy. Silica hydride technology/chemical functionalization of silica in sc-CO2 avoid extended purification steps (i.e. filtration and washing), generation of waste organic solvent and the need of costly or energy consuming drying processing with improved modification efficiency.Highlights► Silica hydrides were prepared in sc-CO2 and dioxane as reaction solvents. ► Efficient modification of SiH with sc-CO2 compared to organic solvents. ► 4.46 μmol/m2 (TES), 3.39 μmol/m2 (DMMS) in sc-CO2, 0.69 μmol/m2, 2.66 μmol/m2 in dioxane. ► 84.4% efficiency of SiH (TES), 42.4% (DMMS) in sc-CO2 and 33.3% (DMMS) dioxane. ► sc-CO2 generated SiH (TES) revealed two IR, υSiH bands at 2283 cm−1 and 2250 cm−1.

The chromatographic performance of two types of core−shell particles and two fully porous particles packed in 2.1 ID × 50 mm columns was investigated. Comparisons of the performances of the EiS-150-C18 to that of the Kinetex-1.7 μm-C18, Acquity-BEH-1.7 μm-C18, and Zorbax-XDB-1.8 μm-C18 are made and discussed. The physical factors that govern the performance of these columns, such as particle size distribution and column external, total, and particle porosity of the C18 packing materials were among the prime foci of investigation. The differences in the mass transfer behavior measured using naphtho[2,3-a]pyrene between these columns provides an indication of improved performance of the new EiS-150-C18 column. The minimum reduced height equivalent to a theoretical plate (HETP) value for the EiS-150-C18, hmin = 1.95, was achieved and was comparable to that obtained from the C18 phases of the Kinetex (hmin = 2.53), the Acquity (hmin = 2.26), and the Zorbax (hmin = 2.57) columns. This study reveals the importance of the dimension of the shell thickness in controlling the performance of columns packed with shell particles in narrow bore columns.

Chromatographic and mass transfer kinetic properties of three narrow bore columns (2.1 × 50 mm) packed with new core–shell 1.7 μm EIROSHELL™-C18 (EiS-C18) particles have been studied. The particles in each column varied in the solid-core to shell particle size ratio (ρ), of 0.59, 0.71 and 0.82, with a porous silica shell thickness of 350, 250 and 150 nm respectively. Scanning and transmission electron microscopy (SEM and TEM), Coulter counter analysis, gas pycnometry, nitrogen sorption analysis and inverse size exclusion chromatography (ISEC) elucidated the physical properties of these materials. The porosity measurement of the packed HILIC and C18 modified phases provided the means to estimate the phase ratios of the three different shell columns (EiS-150-C18, EiS-250-C18 and EiS-350-C18). The dependence of the chromatographic performance to the volume fraction of the porous shell was observed for all three columns. The naphtho[2,3-a]pyrene retention factor of k′ ∼ 10 on the three EiS-C18s employed to obtain the height equivalents to theoretical plates (HETPs) data were achieved by varying the mobile phase compositions and applying the Wilke and Chang relationship to obtain a parallel reduced linear velocity. The Knox fit model gave the coefficient of the reduce HETPs for the three EiS-C18s. The reduced plate height minimum hmin = 1.9 was achieved for the EiS-150-C18 column, and generated an efficiency of over 350,000 N/m and hmin = 2.5 equivalent to an efficiency of 200,000 N/m for the EiS-350-C18 column. The efficiency loss of the EiS-C18 column emanating from the system extra-column volume was discussed with respect to the porous shell thickness.

Investigations into the preparation of silica hydride intermediate in supercritical carbon dioxide (sc-CO2) that avoids the use of organic solvents such as toluene or dioxane are described. The effects of reaction temperature, pressure and time on the surface coverage of the supercritical fluid generated silica hydride intermediate were studied. Under optimised supercritical conditions of 120 °C, 483 bar and 3 h reaction time, silica hydride (Si–H) conversion efficiencies of ca. 40% were achieved for the hydride intermediate prepared from a monofunctional silane reagent (dimethylmethoxysilane). Si–H conversion efficiencies (as determined from 29Si CP-MAS NMR spectral analysis) for the hydride intermediate prepared from triethoxysilane (TES) in sc-CO2 were found to be comparable to those obtained using a TES silanisation approach in an organic solvent. 13C and 29Si CP-MAS-NMR spectroscopy was employed to provide a complete structural assignment of the silica hydride intermediates. Furthermore, supercritical CO2 was subsequently employed as a reaction medium for the heterogenous hydrosilation of silica hydride with octadecene and with styrene, in the presence of a free radical initiator. These supercritical fluid generated reversed-phase materials were prepared in a substantially reduced reaction time (3 h) compared to organic solvent based methods (100 h reaction time). Silica functionalisation in sc-CO2 presents an efficient and clean alternative to organic solvent based methods for the preparation of important silica hydride intermediate and silica bonded stationary phases via a hydrosilation approach.

Six selected primary carbamate insecticides, methomyl, carbaryl, carbofuran, propoxur, isoprocarb, and promecarb, were hydrolyzed in alkaline solution, resulting in electroactive derivatives detectable at a platinum (Pt) electrode poised at +0.8 V vs Ag/AgCl (3 M NaCl). The Pt electrode was inserted into a small electrochemical cell and positioned close to the capillary outlet as an end-column detector to detect the carbamate derivatives after electrophoretic separation. Based on their predicted pKa values and aqueous solubilities, micellar electrokinetic chromatography (MEKC) was optimized for baseline separation of the derivatives using 20 mM borate, pH 10.2 containing 20 mM sodium dodecyl sulfate as a running buffer. When combined with solid-phase extraction (SPE) on octadecyl silica, a preconcentration factor of 100-fold achieved detection to 0.5 μM methomyl and to 0.01 μM for the remaining five pesticides, significantly below the level regulated by government agencies of most countries. The SPE-MEKC method when applied to the separation and analysis of spiked river water and soil samples, yielded results with excellent reproducibility, recovery and selectivity.

Vertically aligned nanowire array electrodes (NAEs) were prepared by electrodeposition of gold into an anodic aluminium oxide membrane (AAM), providing an ordered three-dimensional (3D) matrix for immobilization of redox proteins. Third-generation H2O2 biosensors were prepared by covalent immobilization of horseradish peroxidase (HRP) on the self-assembled monolayer modified NAEs. Direct electron transfer and electrocatalytic performances of the HRP/NAEs with different nanowire lengths (deposition time of 2, 4 and 5 h) were investigated. Results showed that with longer nanowires, better performances were achieved. The HRP/NAE5 h (5 h deposition time) exhibited remarkable sensitivity (45.86 μA mM−1 cm−2) towards H2O2 with a detection limit of 0.42 μM (S/N = 3), linearity up to 15 mM and a response time of 4 s. The ordered 3D gold nanowire array with high conductivity, excellent electron transfer capability and good biocompatibility proved promising for fabricating sensitive, selective, stable and mediator-free enzymatic biosensors.

Supercritical carbon dioxide has attracted attention as a potential replacement for traditional organic solvents due to its simplified workup procedures and reduced environmental impact—providing a green chemistry approach for organic solvent-free functionalisation. In addition to the environmental benefits, the enhanced diffusivity observed in supercritical solvents can often enhance reaction rates. We have applied these valuable features to the preparation of silica-bonded stationary phases and examined their potential in liquid chromatography. We report the successful preparation and characterisation of polyether silica based on Frechet dendrimers—this significantly enhances the range of stationary-phase chemistries that can be prepared in supercritical fluids. First- and second-generation polyether silicas were prepared, characterised, end-capped and evaluated for use as stationary phases for liquid chromatography.

This research examines the effect of silane reagent functionality for the preparation of fluorinated alkyl silica-bonded stationary phases prepared using supercritical carbon dioxide (sc-CO2) as a bonding medium. We present results that demonstrate that alkyl (C8 and C10) and phenyl (pentafluorophenylpropyl, PFPP) silica bonded stationary phases can be prepared under sc-CO2 conditions of 100 °C, 414 bar and 3 h, with surface coverages comparable to those obtained using organic solvent based methods. Fluorinated alkyl silica bonded phase preparation with a trichloro silane generates high ligand densities and more chemically uniform silica surface species compared to phases prepared using a monochloro or alkoxy silanes, as evidenced by thermogravimetric analysis (TGA) and 29Si cross polarisation magic angle spinning (CP-MAS) NMR spectroscopy. In addition, the sc-trichloro prepared fluorinated C8 bonded phases have demonstrated the ability to separate solutes on the basis of their molecular shape with the separation of the LC column shape selectivity test mixture, SRM 869a in the elution order of PhPh < BaP = TBN with a selectivity value of αTBN/BaP = 1.0. These chromatographic findings are indicative of a fluorinated C8 silica bonded stationary phase that is capable of some shape recognition.

This research examines the preparation of a mercaptopropyl bonded silica intermediate in supercritical carbon dioxide (sc-CO2) and the subsequent conversion in sc-CO2 to a quinine derived chiral stationary phase (CSP). The effects of reaction temperature, pressure and time on the surface coverage of the silica intermediate were investigated when porous silica particles (Exsil-Avanti, 3 μm) were reacted with 3-trimethoxymercaptopropylsilane in sc-CO2. We present results which demonstrate that a stable mercaptopropyl bonded silica intermediate can be successfully prepared under supercritical conditions of 40 °C, 483 bar, in a substantially reduced reaction time of 1 h with superior surface coverages compared to organic solvent based methods. The further utility of this supercritical fluid technology was demonstrated by the free radical addition of a quinine derived chiral selector onto a mercaptopropyl bonded silica intermediate in sc-CO2. This supercritical fluid generated chiral stationary phase (CSP) was utilised for the direct LC enantioseparation of a series of 3,5-dinitrobenzoyl (DNB) amino acids. Bonded silica samples were characterised using elemental analysis, diffuse reflectance infrared fourier transform (DRIFT) spectroscopy, solid state 13C and 29Si CP-MAS NMR spectroscopy, and thermogravimetric analysis (TGA). This supercritical fluid functionalisation approach offers an efficient and cleaner alternative to existing organic solvent based approaches for the preparation of bonded silica phases.

This is the first reported metal complex speciation of a single metal–ligand system by microchip electrophoresis. The nickel(II)–bathophenanthroline disulfonic acid system consists of three complexes with different stoichiometries, i.e., Ni(BPS)1, Ni(BPS)2 and Ni(BPS)3. These nickel complexes are readily separated by capillary electrophoresis at 30 kV, in 20 mM sodium tetraborate at pH 9.3, 214 nm UV detection. The identity of each Ni(II) complex species was confirmed by CE-ESI-MS. The three metal–complex species, in addition to the free ligand can be successfully separated on a 25 mm quartz microchip with associated UV detection. Optimal electrophoretic parameters for efficient speciation of the nickel bathophenanthroline disulphonic acid complexes were: injection 1.0 kV for 10 s, separation 1.4 kV for 13 s in 10 mM sodium tetraborate at pH 8.0, 214 nm linear imaging UV detection. The influence of electrokinetic injection on the efficiency of metal speciation was also investigated.

A very simple and fast method for the fabrication of poly(dimethylsiloxane) (PDMS) microfluidic devices is introduced. By using a photocopying machine to make a master on transparency instead of using lithographic equipment and photoresist, the fabrication process is greatly simplified and speeded up, requiring less than 1.5 h from design to device. Through SEM characterization, any µ-channel network with a width greater than 50 µm and a depth in the range of 8–14 µm can be made by this method. After sealing to a Pyrex glass plate with micromachined platinum electrodes, a microfluidic device was made and the device was tested in FIA mode with on-chip conductometric detection without using either high voltage or other pumping methods.

On-chip separation of inorganic anions by ion-exchange chromatography was realized. Micro separation channels were fabricated on a silicon wafer and sealed with a Pyrex cover plate using standard photolithography, wet and dry chemical etching, and anodic bonding techniques. Quaternary ammonium latex particles were employed for the first time to coat the separation channels on-chip. Owing to the narrow depths of the channels on the chip, 0.5–10 μm, there were more interactions of the analytes with the stationary phase on the chip than in a 50-μm I.D. capillary. With off-chip injection (20 nl) and UV detection, NO2−, NO3−, I−, and thiourea were separated using 1 mM KCl as the eluent. The linear ranges for NO2− and NO3− are from 5 to 1000 μM with the detection limits of 0.5 μM.