A solid-liquid extraction approach to elucidate the chemical availability of metals in soil and sediment assuming Langmuir isotherm behaviour

In an earlier paper (Anal. Chim. Acta 514 (2004) 137) we claimed that the maximal extractability of a metal from soil or sediment for a user-defined extractant, i.e. the chemical availability in that particular extractant, may be biased as a result of inadequate volume to mass (V/m) ratios. Correcting for that artifact using an implementation of the simple linear isotherm model gave good results although we cautioned the general applicability. In this paper we will theoretically derive the limitations of that approach based on the more general assumption that sorption processes are described by a Langmuir isotherm.NIST reference material 8704 was extracted with 1 mol l⁻¹ NaOAc (adjusted to pH 5) to experimentally verify the applicability of the Langmuir isotherm approach and illustrate the deviations obtained for some metals using the linear isotherm approach. Of the seven metals measured (Cr, Co, Ni, Cu, Zn, Cd, and Ba) only for Cr and Cu severe discrepancies between both approaches were found, which could be traced back to non-linear isotherm behaviour. Moreover, the Langmuir isotherm approach showed that the above mentioned extractability artifact is even more serious than earlier assumed applying the linear isotherm approach.     

Selective membrane alternative to the recovery of zinc from hot-dip galvanizing effluents

This work reports the study of the kinetics of zinc recovery from spent pickling solutions by means of emulsion pertraction technology (EPT) in order to reuse the metal in electrolytic processes. Tributyl phosphate (TBP) and service water were used as extraction (EX) and back-extraction (BEX) agents, respectively. Kinetic experiments were carried out in hollow fiber membrane contactors in order to analyse the influence of several operation variables on the rate of zinc recovery. A mathematical model that considers the mass transfer resistance shared between the organic liquid membrane and the organic phase boundary layer was developed; the mass transfer coefficients were estimated by means of the parameter estimation tool ASPEN CUSTOM MODELER (from ASPENTECH) to obtain the values k_m = 2.68 × 10⁻⁷ m/s and A_Vk_o = 0.0125 s⁻¹. Simulated results agreed satisfactorily well with experimental data. Consequently, the kinetic model and parameters were confirmed. Finally, a comparison between EPT and non-dispersive solvent extraction (NDSX) was carried out in order to evaluate the advantages and disadvantages of both membrane configurations.     

Molecularly imprinted polymer microspheres prepared by Pickering emulsion polymerization for selective solid-phase extraction of eight bisphenols from human urine samples

The bisphenol A (BPA) imprinted polymer microspheres were prepared by simple Pickering emulsion polymerization. Compared to traditional bulk polymerization, both high yields of polymer and good control of particle sizes were achieved. The characterization results of scanning electron microscopy and nitrogen adsorption–desorption measurements showed that the obtained molecularly imprinted polymer microsphere (MIPMS) particles possessed regular spherical shape, narrow diameter distribution (30–60 μm), a specific surface area (S_BET) of 281.26 m² g⁻¹ and a total pore volume (V_t) of 0.459 cm³ g⁻¹. Good specific adsorption capacity for BPA was obtained in the sorption experiment and good class selectivity for BPA and its seven structural analogs (bisphenol F, bisphenol B, bisphenol E, bisphenol AF, bisphenol S, bisphenol AP and bisphenol Z) was demonstrated by the chromatographic evaluation experiment. The MIPMS as solid-phase extraction (SPE) packing material was then evaluated for extraction and clean-up of these bisphenols (BPs) from human urine samples. An accurate and sensitive analytical method based on the MIPMS-SPE coupled with HPLC-DAD has been successfully established for simultaneous determination of eight BPs from human urine samples with detection limits of 1.2–2.2 ng mL⁻¹. The recoveries of BPs for urine samples at two spiking levels (100 and 500 ng mL⁻¹ for each BP) were in the range of 81.3–106.7% with RSD values below 8.3%.     

Enzyme-assisted extraction and liquid chromatography mass spectrometry for the determination of arsenic species in chicken meat

Chicken is the most consumed meat in North America. Concentrations of arsenic in chicken range from μg kg⁻¹ to mg kg⁻¹. However, little is known about the speciation of arsenic in chicken meat. The objective of this research was to develop a method enabling determination of arsenic species in chicken breast muscle. We report here enzyme-enhanced extraction of arsenic species from chicken meat, separation using anion exchange chromatography (HPLC), and simultaneous detection with both inductively coupled plasma mass spectrometry (ICPMS) and electrospray ionization tandem mass spectrometry (ESIMS). We compared the extraction of arsenic species using several proteolytic enzymes: bromelain, papain, pepsin, proteinase K, and trypsin. With the use of papain-assisted extraction, 10 arsenic species were extracted and detected, as compared to 8 detectable arsenic species in the water/methanol extract. The overall extraction efficiency was also improved using a combination of ultrasonication and papain digestion, as compared to the conventional water/methanol extraction. Detection limits were in the range of 1.0–1.8 μg arsenic per kg chicken breast meat (dry weight) for seven arsenic species: arsenobetaine (AsB), inorganic arsenite (As^III), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), inorganic arsenate (As^V), 3-nitro-4-hydroxyphenylarsonic acid (Roxarsone), and N-acetyl-4-hydroxy-m-arsanilic acid (NAHAA). Analysis of breast meat samples from six chickens receiving feed containing Roxarsone showed the presence of (mean ± standard deviation μg kg⁻¹) AsB (107 ± 4), As^III (113 ± 7), As^V (7 ± 2), MMA (51 ± 5), DMA (64 ± 6), Roxarsone (18 ± 1), and four unidentified arsenic species (approximate concentration 1–10 μg kg⁻¹).     

On-line monitoring of Soxhlet extraction by chromatography and mass spectrometry to reveal temporal extract profiles

Soxhlet extraction is a popular sample preparation technique used in chemical analysis. It enables liberation of molecules embedded in complex matrices (for example, plant tissues, foodstuffs). In most protocols, samples are analyzed after the extraction process is complete. However, in order to optimize extraction conditions and enable comparisons between different types of extraction, it would be desirable to monitor it in real time. The main development of this work is the design and construction of the interface between Soxhlet extractor and GC–MS as well as ESI-MS system. The temporal extract profiles, obtained in the course of real-time GC–MS monitoring, have been fitted with mathematical functions to analyze extraction kinetics of different analytes. For example, the mass transfer coefficients of pinene, limonene and terpinene in lemon sample, estimated using the first-order kinetic model, are 0.540 h⁻¹, 0.507 h⁻¹ and 0.722 h⁻¹, respectively. On the other hand, the Peleg model provides the following extraction rates of pinene, limonene and terpinene: 0.370 nM h⁻¹, 0.216 nM h⁻¹ and 0.596 nM h⁻¹, respectively. The results suggest that both first-order kinetic and Peleg equations can be used to describe the progress of Soxhlet extraction. On-line monitoring of Soxhlet extraction reveals extractability of various analytes present in natural samples (plant tissue), and can potentially facilitate optimization of the extraction process.     

On-line continuous flow ultrasonic extraction coupled with high performance liquid chromatographic separation for determination of the flavonoids from root of Scutellaria baicalensis Georgi

An on-line method, based on coupling dynamic ultrasonic extraction (DUE), continuously sampling the suspension of sample and solvent, high performance liquid chromatographic separation with diode array detection, has been developed for the determination of the flavonoids, including baicalin, baicalein and wogonin, from the root of Scutellaria baicalensis Georgi. Variables influencing the DUE were evaluated by orthogonal test. The extraction yields of baicalin, baicalein and wogonin in the roots of S. baicalensis Georgi obtained from five different cultivated areas are 73.8–131.5 μg mg⁻¹ (RSD ≤ 6.24%), 6.8–15.9 μg mg⁻¹ (RSD ≤ 5.36%) and 4.4–14.3 μg mg⁻¹ (RSD ≤ 5.30%), respectively. The limits of detection for baicalin, baicalein and wogonin are 0.30, 0.37 and 0.41 μg mL⁻¹, respectively. Linearity is from 0.55 to 109 μg mL⁻¹ for baicalin, from 0.51 to 105 μg mL⁻¹ for baicalein and from 0.53 to 102 μg mL⁻¹ for wogonin. Compared with off-line continuous flow-DUE, the proposed method would be more convenient for the determination of the analytes and the rapid optimization of the extraction process. The extraction yields of flavonoids obtained by the proposed method are comparable with those obtained by dynamic microwave assisted extraction, static ultrasonic extraction and reflux extraction. The result indicated that the proposed method is suitable to determine the active components in Chinese herbal medicine.     

Ligandless-dispersive liquid-liquid microextraction of trace amount of copper ions

In the present work, a new ligandless-dispersive liquid-liquid microextraction (LL-DLLME) method has been developed for preconcentration trace amounts of copper as a prior step to its determination by flame atomic absorption spectrometry. In the proposed approach 1,2-dicholorobenzene and ethanol were used as extraction and dispersive solvents, respectively. Some factors influencing on the extraction efficiency of copper and its subsequent determination were studied and optimized, such as the extraction and dispersive solvent type and volume, pH of sample solution, extraction time and salting out effect. Under the optimal conditions, the calibration curve was linear in the range of 1.0 ng mL⁻¹-0.6 μg mL⁻¹ of copper with R² = 0.9985. Detection limit was 0.5 ng mL⁻¹ in original solution (3S_b/m) and the relative standard deviation for seven replicate determination of 0.2 μg mL⁻¹ copper was ±1.4%. The proposed method has been applied for determination of copper in standard and water samples with satisfactory results.     

Thermodynamics of complexation of aqueous 18-crown-6 with potassium ion: apparent molar volumes and apparent molar heat capacities of aqueous 18-crown-6 and of the (18-crown-6 + potassium chloride) complex at temperatures (278.15 to 393.15) K, at molalities (0.02 to 0.3) mol · kg, and at the pressure 0.35 MPa

We have measured the densities at temperatures T = (278.15 to 363.15) K and heat capacities at T = (278.15 to 393.15) K of aqueous solutions of 18-crown-6 and of (18-crown-6 + KCl) at molalities m = (0.02 to 0.3) mol · kg⁻¹ and at the pressure 0.35 MPa. We have calculated apparent molar volumes V_? and apparent molar heat capacities C_p,? for 18-crown-6(aq), and we have applied Young’s Rule and have accounted for chemical speciation and relaxation effects to resolve V_? and C_p,? for the (18-crown-6: K⁺,Cl⁻)(aq) complex in the mixture. We have also calculated estimates of the change in volume Δ_rV_m, the change in heat capacity Δ_rC_p,m, the change in enthalpy Δ_rH_m, and the equilibrium quotient log Q for formation of the complex at T = (278.15 to 393.15) K and m = (0 to 0.3) mol · kg⁻¹.     

Multivariate optimization of molecularly imprinted polymer solid-phase extraction applied to parathion determination in different water samples

In this work a parathion selective molecularly imprinted polymer was synthesized and applied as a high selective adsorber material for parathion extraction and determination in aqueous samples. The method was based on the sorption of parathion in the MIP according to simple batch procedure, followed by desorption by using methanol and measurement with square wave voltammetry. Plackett-Burman and Box-Behnken designs were used for optimizing the solid-phase extraction, in order to enhance the recovery percent and improve the pre-concentration factor. By using the screening design, the effect of six various factors on the extraction recovery was investigated. These factors were: pH, stirring rate (rpm), sample volume (V₁), eluent volume (V₂), organic solvent content of the sample (org%) and extraction time (t). The response surface design was carried out considering three main factors of (V₂), (V₁) and (org%) which were found to be main effects. The mathematical model for the recovery percent was obtained as a function of the mentioned main effects. Finally the main effects were adjusted according to the defined desirability function. It was found that the recovery percents more than 95% could be easily obtained by using the optimized method. By using the experimental conditions, obtained in the optimization step, the method allowed parathion selective determination in the linear dynamic range of 0.20-467.4 μg L⁻¹, with detection limit of 49.0 ng L⁻¹ and R.S.D. of 5.7% (n = 5). Parathion content of water samples were successfully analyzed when evaluating potentialities of the developed procedure.     

XPS evidence for structure-performance relationship in selective hydrogenation of crotonaldehyde to crotyl alcohol on platinum systems supported on natural phosphates

The design of the oppositely charged ink particles based on titanium dioxide and carbon black for the monochrome electrophoretic display (EPD) was reported. The white ink particles with acidic surface and black ink particles with basic surface were synthesized and sterically stabilized by long alkyl chains, which were charged oppositely by mixing with basic surfactant (OLOA 1200) and acidic surfactant (Span 80), respectively. The electrophoretic mobility and the Zeta potential were −3.87 × 10⁻¹⁰ m² V⁻¹ s⁻¹ and −25.1 mV for the white ink particles, 3.79 × 10⁻¹⁰ m² V⁻¹ s⁻¹ and 24.6 mV for the black ink particles. In addition, the block copolymer, poly(lauryl methacrylate)-b-poly(2-(dimethylamino)ethyl methacrylate) (PLMA-b-PDMAEMA) synthesized by atom transfer radical polymerization (ATRP), was first incorporated in the modification of the pigments for the fine encapsulation. Then, a stable dual-particle electronic ink with contrast ratio of 120:1 was prepared and encapsulated with the gelatin (GE)/sodium carboxymethylcellulose (NaCMC)/sodium dodecyl sulfate (SDS) microcapsules by complex coacervation method. Finally, the matrix character display prototype driven at a low voltage exhibited excellent performance, the contrast ratio of which was 8:1 at 9 V DC.     

Separation of casein micelles from whey proteins by high shear microfiltration of skim milk using rotating ceramic membranes and organic membranes in a rotating disk module

This paper investigates the microfiltration of skim milk in order to separate caseins micelles from two whey proteins, α-lactalbumin (α-La) and β-lactoglobulin (β-Lg), using a modified dynamic filtration pilot (MSD) consisting in 6 ceramic 9-cm diameter membrane disks of 0.2 μm pores, rotating around a shaft inside cylindrical housing. A comparison was made with another dynamic filtration module consisting in a disk rotating near a fixed PVDF 15.5 cm diameter membrane with 0.15 μm pores. Maximum permeate fluxes were 120 L h⁻¹ m⁻² with the MSD module at 1930 rpm and at 40 °C, and 210 L h⁻¹ m⁻² at 2500 rpm and 45 °C, with the rotating disk module. Casein rejection was around 99% at high speed for both membranes. α-La transmission decreased with increasing transmembrane pressure (TMP) from 75% to 60% for ceramic membranes and from 25% to 10% for the PVDF one. β-Lg transmissions were lower, ranging from 23% to 15% for ceramic membranes and from 20% to 5% for the PVDF one. In a concentration test with the PVDF membrane at 2000 rpm, the flux decayed from 200 L h⁻¹ m⁻² at initial concentration to 80 L h⁻¹ m⁻² at VRR = 3.2 and 22.1% of the initial α-La mass was recovered in the permeate, against 8.1% for β-Lg. Permeate fluxes in the mass transfer limited regime (J_lim) of the MSD and rotating disk module operated at various speeds were well correlated by the equation J_lim = 17.13 V_av where V_av denoted the disk azimuthal velocity averaged over the membrane area. Measurements of J_lim, taken from Ref. [G. Samuelsson, P. Dejlmek, G. Tragardh, M. Paulsson, Minimizing whey protein retention in crossflow microfiltration of skim milk. Int. Dairy J. 7 (1997) 237–242] during MF of skim milk using tubular ceramic membranes at velocities from 1.5 to 8 m s⁻¹ with permeate co-current recirculation were found to obey the same correlation.     

Apparent molar volumes and apparent molar heat capacities of aqueous N-acetyl-d-glucosamine at temperatures from 278.15 K to 368.15 K and of aqueous N-methylacetamide at temperatures from 278.15 K to 393.15 K at the pressure 0.35 MPa

We determined apparent molar volumes V_? from densities measured with a vibrating-tube densimeter at 278.15 ? (T/K) ? 368.15 and apparent molar heat capacities C_p,? with a twin fixed-cell, differential, temperature-scanning calorimeter at 278.15 ? (T/K) ? 363.15 for aqueous solutions of N-acetyl-d-glucosamine at m from (0.01 to 1.0) mol · kg⁻¹ and at p = 0.35 MPa. We also determined V_? at 278.15 ? (T/K) ? 368.15 and C_p,? at 278.15 ? (T/K) ? 393.15 for aqueous solutions of N-methylacetamide at m from (0.015 to 1.0) mol · kg⁻¹ and at p = 0.35 MPa. Empirical functions of m and T for each compound were fitted to our results, which are then compared to those for N,N-dimethylacetamide. Estimated values of Δ_rV_m(m, T) and Δ_rC_p,m(m, T) for formation of aqueous N-acetyl-d-glucosamine from aqueous d-glucose and aqueous acetamide are calculated and discussed.     

Optimization and validation of a low temperature microwave-assisted extraction method for analysis of polycyclic aromatic hydrocarbons in airborne particulate matter

A low temperature microwave-assisted extraction method (MAE) is reported for the analysis of polycyclic aromatic hydrocarbons (PAHs) in airborne particulate matter (PM). The main parameters affecting the extraction efficiency (choice of extractants, microwave power, and extraction time) were investigated and optimized. The optimized procedure requires a 20 ml mixture of acetone:n-hexane (1:1) for extraction of PAHs in PM at 150 W of microwave energy (20 min extraction time). Clean-up of MAE extracts was not found to be necessary. The optimized method was validated using two different SRM (1648-urban particulate matter and 1649a, urban dust). The results obtained are in good agreement with certified values. PAHs recoveries for both reference materials were between 79 and 122% with relative standard deviation ranging from 3 to 21%. Detection limits were determined based on blank determination using two kinds of quartz filter substrates (n = 10), which ranged from 0.001 (0.03) ng m⁻³ (pg/μg) for B(k)Ft to 1.119 (37.3) for Naph in ng m⁻³ (pg/μg), respectively. The repeatability and day-to-day reproducibility obtained in this study were in the range of 4-16 and 3-25% for spiked standards and SRM 1649, respectively. The optimized and validated MAE technique was applied to the extraction of PAHs from a set of real world PM samples collected in Singapore. The sum of particulate-bound PAHs in outdoor PM ranged from 1.05 to 3.45 ng m⁻³ while that in indoor PM (cooking emissions) ranged from 27.6 to 75.7 ng m⁻³, respectively.     

Determination of polycyclic aromatic hydrocarbons by gas chromatography — ion trap tandem mass spectrometry and source identifications by methods of diagnostic ratio in the ambient air of Campo Grande, Brazil

Polycyclic aromatic hydrocarbons (PAHs) were measured in samples collected from July to December of 2003, in Campo Grande — MS (Brazil), on three different sites: Ary Coelho Square (AC), Indigenous Nations' Park (NI) and Indubrasil (IB). Particle-bound PAHs were collected on quartz filters and gas-phase PAHs on glass cartridges using a polyurethane foam sampler, respectively. The substances of interest were extracted with a dichloromethane/methanol mixture (9:1 v/v) and subjected to gas chromatography — ion trap tandem mass spectrometry (GC-MS/MS). The concentration values of PAHs in AC varied from 0.03 to 26.28 μg m^− 3 and the average value for the sum of 16 PAHs was 51.35 μg m^− 3 (range: 2.98-79.91 μg m^− 3). On the NI site were obtained values of PAHs with concentrations of between 0.02 and 13.84 μg m^− 3 and an average value for the total of 16 PAHs was equal to 46.76 μg m^− 3 (range: 21.20-85.32 μg m^− 3). The PAH concentrations obtained in the IB sampling site varied from 0.02 to 16.74 μg m^− 3, with the obtained medium value, for the total of 16 PAHs, equal to 42.79 μg m^− 3 (range: 26.53-58.49 μg m^− 3). Strong positive correlations were found among samples (r: 0.70 to 0.97, p < 0.005) in 39% of the associations and non-significant correlations were observed among PAHs, except for Flu-Acy, BaA-Phe, Chry-BaA, BkF-Naph, BaP-Phe and BghiP-Naph that were poorly correlated. The statistical analysis of the data showed high similarity among samples on the three sites. The diagnostic ratios indicated the vehicular traffic (diesel and gasoline engines) and the biomass combustion, as major PAH sources in the three sampling sites.     

Characteristics of the hydrogen ion-sensitive field effect transistors with sol-gel-derived lead titanate gate

The sol-gel-derived lead titanate (PbTiO₃) membrane has been successfully applied as a pH sensitive layer to form the PbTiO₃ gate ion-sensitive field-effect transistor (ISFET). There exhibit the excellent quasi-Nernstian response of 56-59 mV pH⁻¹, good surface adsorption and anticorrosion characteristics via the C-V measurement of the EIS structure. At a specific pH concentration, the output and transfer characteristics are very similar to the behaviours of MOSFETs, and the ISFET model can be derived by the modified MOSFET model. As it operated in the nonsaturation region, there exhibits a linear pH response of about 56-59 mV pH⁻¹. On the other hand, as it operated in the saturation region, the pH response and linearity can be controlled by adjusting the V_GS values, e.g. the pH responses of −4.2, −24.8 and −31.3 μA pH⁻¹ and the correlation coefficients of 0.9491, 0.9995 and 0.9996 at V_GS=1, 3 and 5 V can be obtained, respectively. Besides, in order to get the best pH response and the minimized leakage current, the heat treatment temperature of the PbTiO₃ membrane must be limited between 350 and 450 °C.     

An automated system for liquid-liquid extraction based on a new micro-batch extraction chamber with on-line detection: Preconcentration and determination of copper(II)

An automated system to perform liquid-liquid extraction is proposed, in which the effective mixture (the intimate contact) between the aqueous phase and the organic phase, as well as the separation of the phases, are carried out in a micro-batch glass extraction chamber. Sample, reagents and organic solvent are introduced into the glass extraction chamber by a peristaltic pump using air as carrier. The detection of the extracted species from the aqueous phase is made in a small volume (120-150 μl) of isobutyl methyl ketone (MIBK). The system allows enrichment factors of 2-10-fold. The proposed automatic system was evaluated for Cu(II) extraction based on complex formation between copper(II) and 1-(2′-pyridylazo)naphthol (PAN) in MIBK. When a volumetric ration of 2:1 (aqueous:organic) was implemented, copper was detected in the concentration range of 100-1600 μg l⁻¹ (r = 0.9995) with a relative standard deviation of 2% (200 μg l⁻¹, n = 5) and a detection limit of 20 μg l⁻¹. The analytical curve was linear over the concentration range 25-500 μg l⁻¹ (r = 0.9994) when a volumetric ratio of 10:1 was employed. With this ratio, the detection limit was 5.0 μg l⁻¹ and the relative standard deviation was 6% (50 μg l⁻¹, n = 5).     

Analysis of potassium formate in airport storm water runoff by headspace solid-phase microextraction and gas chromatography–mass spectrometry

Potassium formate was extracted from airport storm water runoff by headspace solid-phase microextraction (HS-SPME) and analyzed by GC–MS. Formate was transformed to formic acid by adding phosphoric acid. Subsequently, formic acid was derivatized to methyl formate by adding methanol. Using sodium [²H]formate (formate-d) as an internal standard, the relative standard deviation of the peak area ratio of formate (m/z 60) and formate-d (m/z 61) was 0.6% at a concentration of 208.5 mg L⁻¹. Calibration was linear in the range of 0.5–208.5 mg L⁻¹. The detection limit calculated considering the blank value was 0.176 mg L⁻¹. The mean concentration of potassium formate in airport storm water runoff collected after surface de-icing operations was 86.9 mg L⁻¹ (n = 11) with concentrations ranging from 15.1 mg L⁻¹ to 228.6 mg L⁻¹.     

Analysis of sesquiterpene emissions by plants using solid phase microextraction

Solid phase microextraction (SPME) was characterized for the sampling and analysis of sesquiterpenes (SQTs) emitted by plants. Constant mixing ratio SQT standards were produced using a capillary diffusion system. Polydimethylsiloxane SPME fibers were characterized with respect to relative absorption of SQTs, and the effects of sample linear velocity and sample relative humidity on SQT absorption. SPME was then utilized to measure SQT emissions from gray pine (Pinus sabiniana) and ponderosa pine (Pinus ponderosa). Total SQT emission rates at a photosynthetic photon flux density of 1200 μmol m⁻² s⁻¹ and 28 °C ranged 0.025–0.050 μgC m⁻² h⁻¹ (α-farnesene) and 0.450–3.325 μgC m⁻² h⁻¹ (α-farnesene, β-farnesene, and α-bergamotene) for gray pine and ponderosa pine, respectively.     

Influence of hole mobility on the response characteristics of p-type nickel oxide thin film based glucose biosensor

RF sputtered p-type nickel oxide (NiO) thin film exhibiting tunable semiconductor character which in turns enhanced its functional properties. NiO thin film with high hole mobility is developed as a potential matrix for the realization of glucose biosensor. NiO thin film prepared under the optimized deposition conditions offer good electrical conductivity (1.5 × 10⁻³ Ω⁻¹-cm⁻¹) with high hole mobility (2.8 cm² V⁻¹ s⁻¹). The bioelectrode (GO_x/NiO/ITO/glass) exhibits a low value of Michaelis–Menten constant (K_m = 1.05 mM), indicating high affinity of the immobilized GO_x toward the analyte (glucose). Due to the high surface coverage (2.32 × 10⁻⁷ mol cm⁻²) of the immobilized enzyme on to the NiO matrix and its high electrocatalytic activity, the prepared biosensor exhibits a high sensitivity of 0.1 mA (mM⁻¹-cm⁻²) and a good linearity from 25 to 300 mg dL⁻¹ of glucose concentration with fast response time of 5 s. Various functional properties of the material (mobility, crystallinity and stress) are found to influence the charge communication feature of NiO thin film matrix to a great extent, resulting in enhanced sensing response characteristics.     

Determination of the carboxylic acid metabolite of clopidogrel in human plasma by liquid chromatography-electrospray ionization mass spectrometry

A rapid and specific liquid chromatographic-mass spectrometric method has been developed and validated for the determination of the carboxylic acid metabolite of clopidogrel in human plasma. Sulphafurazole was used as internal standard. The samples were subjected to a solid phase extraction procedure using Hypercarb cartridges. The chromatographic separation was performed on a reversed phase porous graphitized carbon column using a mobile phase consisting of 70% methanol in water containing 0.1% (v/v) trifluoroacetic acid, pumped at a flow rate of 0.25 ml min⁻¹. The analytes were detected after positive electrospray ionization using the selected ion monitoring mode of the species at m/z 308 for the carboxylic acid metabolite of clopidogrel, m/z 322 for clopidogrel and m/z 268 for sulphafurazole. Calibration graphs were linear (r>0.9994, n=6), in the range 100-1000 ng ml⁻¹ for the carboxylic acid metabolite of clopidogrel. The intra- and inter-day R.S.D. values were <3.1%, while the relative error E_r was less than −9.6% (n=6). The limits of detection (3.3σ) and quantitation (10σ) for the carboxylic acid metabolite of clopidogrel were found to be 28 and 93 ng ml⁻¹, respectively. The efficiency of the solid phase extraction procedure for the carboxylic acid metabolite of clopidogrel averaged 74.6%.