Optimized determination of polybrominated diphenyl ethers and polychlorinated biphenyls in sheep serum by solid-phase extraction-gas chromatography-mass spectrometry

We describe a solid-phase extraction (SPE) method, followed by gas chromatography-mass spectrometry (GC-MS), for the simultaneous determination of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in sheep serum samples. The denaturation of serum proteins by formic acid, water-1-propanol and water-2-propanol were compared and optimized. Seven different solid-phase sorbents were tested and it was found that Strata-X cartridge (200 mg, 6 mL) gave the best recoveries (92-106%, SD < 6%, n = 3) for all the target analytes. The different extraction solvents (iso-hexane and dichloromethane), either alone or in combination, were used to extract these persistent organic compounds from spiked serum samples by SPE. Removal of co-extracted biogenic materials was achieved using adsorption chromatography with acid modified silica and activated silica. Iso-hexane was found to be the most appropriate solvent for clean-up providing good recoveries and clear chromatographic separation; its use is preferable to that of DCM because it is less environmentally toxic. The limits of detection (LOD) of the proposed method were 47-105 pg g⁻¹ and 16-24 pg g⁻¹ for the different PBDEs and PCBs studied, respectively. The developed method was linear over the range from 0.05 to 30 ng g⁻¹, for all PBDEs except PBDE 183 (0.10-30 ng g⁻¹), and from 0.02 to 30 ng g⁻¹ for all tested PCB congeners. The established method was successfully applied to sheep serum samples from Scotland, UK, for the determination of the target PBDEs and PCBs.     

Simultaneous determination of two anti-inflammatory drugs in serum using isopotential fluorimetry

The simultaneous determination of 6-methoxy-2-naphthylacetic acid (6MNA) and diflunisal in serum samples using the combination of matrix isopotential synchronous fluorescence (MISF) and first derivative technique is proposed. 6MNA and diflunisal exhibit overlapped spectra and serum produces background fluorescence that precludes the direct determination of these anti-inflammatory drugs by conventional fluorimetry. This method provides good analytical results for determination of compounds in samples with unknown background fluorescence. The method was applied for the simultaneous determination of 6MNA and diflunisal in serum samples at concentrations between 20-200 and 100-1000 ng mL⁻¹, respectively, by means of absolute values of first derivative of synchronous scan at 247.9/364.0 and 262.6/392.4 nm for 6MNA and diflunisal, respectively. In order to obtain maximum sensitivity and adequate selectivity, factors affecting fluorescence intensity were studied. As a result, the analyses were performed in water at a pH of 7.2, adjusted by using sodium dihydrogen phosphate/hydrogen phosphate (0.1 M) as a buffer solution. Serum samples were diluted 200 times. Analytical parameters of the proposed method were calculated according to the error propagation theory. The limit of detection calculated according to Clayton was 15.8 and 63.0 ng mL⁻¹ for 6MNA and diflunisal, respectively. The sensitivity, repeatability and reproducibility achieved with the proposed method were adequate for the determination of these anti-inflammatory agents in serum samples.     

Development of a sensitive detection method of cancer biomarkers in human serum (75%) using a quartz crystal microbalance sensor and nanoparticles amplification system

A simple and sensitive sensor method for cancer biomarkers [prostate specific antigen (PSA) and PSA-alpha 1-antichymotrypsin (ACT) complex] analysis was developed, to be applied directly with human serum (75%) by using antibody modified quartz crystal microbalance sensor and nanoparticles amplification system. A QCM sensor chip consisting of two sensing array enabling the measurement of an active and control binding events simultaneously on the sensor surface was used in this work. The performance of the assay and the sensor was first optimised and characterised in pure buffer conditions before applying to serum samples. Extensive interference to the QCM signal was observed upon the analysis of serum. Different buffer systems were then formulated and tested for the reduction of the non-specific binding of sera proteins on the sensor surface. A PBS buffer containing 200 μg mL⁻¹ BSA, 0.5 M NaCl, 500 μg mL⁻¹ dextran and 0.5% Tween 20, was then selected which eliminated the interfering signal by 98% and enabled the biomarker detection assay to be performed in 75% human serum. By using Au nanoparticles to enhance the QCM sensor signal, a limit of detection of 0.29 ng mL⁻¹ PSA and PSA-ACT complex (in 75% serum) with a linear dynamic detection range up to 150 ng mL⁻¹ was obtained. With the achieved detection limit in serum samples, the developed QCM assay shows a promising technology for cancer biomarker analysis in patient samples.     

Solid-phase microextraction (SPME) for the determination of pyrethroids in cucumber and watermelon using liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection

A sensitive and efficient solid-phase microextraction (SPME) method for the determination of seven pyrethroid insecticides including fenpropathrin, λ-cyhalothrin, deltamethrin, fenvalerate, permethrin, τ-fluvalinate and bifenthrin in cucumber and watermelon samples using high performance liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection (SPME-HPLC-PIF-FD) was developed and validated. The optimum SPME conditions were used for the extraction of samples of both matrices (extraction time 30 min, stirring rate 1100 rpm, extraction temperature 65 °C, sample pH 3, soaking time 7 min, desorption time 5 min, ACN content 25%, desorption and soaking solvent was the mobile phase and in static mode). The method was validated in terms of limits of detection (LODs) and the limits of quantification (LOQs) in both IUPAC and EURACHEM criteria. LODs and LOQs were achieved in values lower than the maximum residue levels (MRLs) established in the Spanish regulations for all pesticides in this study (MRLs range between 0.01 and 0.1 mg kg⁻¹ for all pyrethroid insecticides in both matrices). LOQs according to the second criterion were between 1.5 and 5 μg kg⁻¹ for cucumber; and between 1.3 and 5 μg kg⁻¹ for watermelon samples. Precision and recovery studies were evaluated at two concentration levels for each matrix. Good precision was obtained and relative standard deviation values were less than 10% in all cases. Recovery values were calculated at 0.05 and 0.5 mg kg⁻¹ levels (n = 6) and they ranged between 93% and 108% for cucumber and between 91% and 110% for watermelon samples. Applicability of the method to pyrethroids in cucumber and watermelon of commercial samples was demonstrated.     

Preliminary evaluation of monolithic column high-performance liquid chromatography with tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection for the determination of quetiapine in human body fluids

High-performance liquid chromatography (HPLC) with tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection methodology is reported for the determination of the atypical antipsychotic drug quetiapine and the observation of its major active and inactive metabolites in human urine and serum. The method uses a monolithic chromatographic column allowing high flow rates of 3 mL min⁻¹ enabling rapid quantification. Flow injection analysis (FIA) with tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection and HPLC time of flight mass spectrometry (TOF-MS) were used for the determination of quetiapine in a pharmaceutical preparation to establish its suitability as a calibration standard. The limit of detection achieved with FIA was 2 × 10⁻¹¹ mol L⁻¹ in simple aqueous solution. The limits of detection achieved with HPLC were 7 × 10⁻⁸ and 2 × 10⁻¹⁰ mol L⁻¹ in urine and serum, respectively. The calibration range for FIA was between 5 × 10⁻⁹ and 1 × 10⁻⁶ mol L⁻¹. The calibration ranges for HPLC were between 1 × 10⁻⁷-1 × 10⁻⁴ and 1 × 10⁻⁸-1 × 10⁻⁴ mol L⁻¹ in urine and serum, respectively. The quetiapine concentrations in patient samples were found to be 3 × 10⁻⁶ mol L⁻¹ in urine and 7 × 10⁻⁷ mol L⁻¹ in serum. Without the need for preconcentration, the HPLC detection limits compared favourably with those in previously published methodologies. The metabolites were identified using HPLC-TOF-MS.     

Bulk derivatization and cation exchange restricted access media-based trap-and-elute liquid chromatography–mass spectrometry method for determination of trace estrogens in serum

Estrone (E1), estradiols (α/β-E2), and estriol (E3) are four major metabolically active estrogens exerting strong biological activities at very low circulating concentrations. This paper reports a sensitive and efficient method with automated, on-line clean-up and detection to determine trace estrogens in a small volume of serum samples using liquid chromatography–electrospray ionization–tandem mass spectrometry directly, without off-line liquid–liquid or solid-phase extraction pretreatments. Serum aliquots (charcoal stripped fetal bovine serum, 100 μL) were spiked with four estrogen standards and their corresponding isotope-labeled internal standards, then bulk derivatized with 2-fluoro-1-methyl-pyridium p-toluenesulfonate (2-FMP) to establish the calibration curves and perform method validation. Calibration was established in the concentration ranges of 5–1000 pg mL⁻¹, and demonstrated good linearity of R² from 0.9944 to 0.9997 for the four derivatized estrogens. The lower detection limits obtained were 3–7 pg mL⁻¹. Good accuracy and precision in the range of 86–112% and 2.3–11.9%, respectively, were observed for the quality control (QC) samples at low, medium, and high concentration levels. The stability tests showed that the derivatized serum samples were stable 8 h after derivatization at room temperature and at least to 48 h if stored at −20 °C. The method was applied to measure trace estrogens in real human and bovine serum samples, and three of four estrogen compounds studied were observed and quantified.     

Novel flow injection spectrophotometric determination of fosinopril using UV-assisted digestion and an orthophosphates calibration graph

This work describes the first flow injection (FI) method for the spectrophotometric determination of the anti-hypertension drug fosinopril (FSP), a phosphorus-containing compound. The method is based on the UV-assisted digestion of the analyte using ammonium peroxodisulfate as the oxidizing reagent. The yielded orthophosphate ions are determined by a rapid and robust FI method employing the molybdenum blue approach. The time needed for complete conversion of a maximum FSP amount concentration of 2.0×10⁻⁴ mol l⁻¹ was 30 min. Based on the capability of the home-made UV digester used in this work to process eight samples simultaneously, an acceptable samples analysis frequency of 16 h⁻¹ was achieved. Additionally, a very important advantage of the proposed method is that an orthophosphate ions calibration graph can be used instead of FSP, as 100% conversion of FSP was achieved. Quantitative measurements of FSP were made in the range 1.0×10⁻⁶ to 2.0×10⁻⁴ mol l⁻¹. The application of the developed FI method to the analysis of two commercially available pharmaceutical formulations produced accurate results, as the relative errors were <1.5% in both cases, compared to the labeled values.     

High-performance liquid chromatographic/ion-trap mass spectrometric speciation of aquatic mercury as its pyrrolidinedithiocarbamate complexes

Mercury-pyrrolidinedithiocarbamate complexes are first time used for speciation of aquatic mercury with high-performance liquid chromatographic/ion trap-mass spectrometric method utilizing atmospheric pressure chemical ionization (APCI). The separation of the four mercury species was achieved in less than 5 min with a linear gradient profile of aqueous methanol from 70 up to 100% (v/v) in 4th min, isocratic elution at 100% up to 5th min and followed by a negative gradient to 70% in 6th min. The best separation was achieved on a reverse phase Zorbax Eclipse XDB C18 column (50 mm × 2.1 mm i.d., 1.8 μm particle size). The on-column limits of detection (injection volume 1 μL) were 370 pg for methylmercury (MeHg⁺), 280 pg for ethylmercury (EtHg⁺), 250 pg for phenylmercury (PhHg⁺) and 90 pg for inorganic mercury (Hg²⁺) when the data were collected in selective ion monitoring (SIM) mode. A method of isolation and preconcentration of the mercury species using a “home-made” C18 solid phase extraction (SPE) microcolumns was developed to enhance sensitivity of the method. The preconcentration factor as much as 2500 was achieved with on-column complex formation of mercury-pyrrolidinedithiocarbamate. Methanol (100%) was chosen for elution of preconcentrated mercury species. The method was applied for the determination of mercury species in river water samples.     

Liquid chromatography with diode array detection and multivariate curve resolution for the selective and sensitive quantification of estrogens in natural waters

Following the green analytical chemistry principles, an efficient strategy involving second-order data provided by liquid chromatography (LC) with diode array detection (DAD) was applied for the simultaneous determination of estriol, 17β-estradiol, 17α-ethinylestradiol and estrone in natural water samples. After a simple pre-concentration step, LC–DAD matrix data were rapidly obtained (in less than 5 min) with a chromatographic system operating isocratically. Applying a second-order calibration algorithm based on multivariate curve resolution with alternating least-squares (MCR-ALS), successful resolution was achieved in the presence of sample constituents that strongly coelute with the analytes. The flexibility of this multivariate model allowed the quantification of the four estrogens in tap, mineral, underground and river water samples. Limits of detection in the range between 3 and 13 ng L⁻¹, and relative prediction errors from 2 to 11% were achieved.     

Significant fluorescence enhancement by supramolecular complex formation between berberine chloride and cucurbit(n=7)uril and its analytical application

The supramolecular interaction of cucurbit(n = 7)uril (Q[7]) with berberine chloride (BER) has been studied in aqueous solution at pH 2.0 and room temperature by spectro-fluorimetry. The association constant of the complex was 2.07 × 10⁶ L mol⁻¹ calculated by using a nonlinear least squares method. ¹H NMR spectra confirmed that a 1:1 stable complex is formed between Q[7] and BER. This work proposes a possible interaction mode, in which the guest BER is incorporated inside the hydrophobic cavity of the host Q[7] via the isoquinoline ring part of the guest molecule. Based on a significant enhancement of the fluorescence intensity of this supramolecular complex, a spectrofluorimetric method with high sensitivity and selectivity has been developed for the determination of BER in aqueous solution in the presence of Q[7]. The linear range of the method was from 7.43 to 11.2 × 10³ ng mL⁻¹with the detection limit 4.2 ng mL⁻¹. There was no interference from the compounds normally used in tablets, serum or urine constituents. The proposed method was applied to the determination of BER in tablets, serum and urine samples with satisfactory results and good consistency with those obtained by the pharmacopoeia method. This shows that it has promising potential for therapeutic drug monitoring and pharmokinetics and for clinical application.     

Analysis of perfluorinated compounds in biota by microextraction with tetrahydrofuran and liquid chromatography/ion isolation-based ion-trap mass spectrometry

An analytical method combining both a simple, fast and efficient solvent microextraction and a sensitive and selective monitoring mode, based on ion isolation ion-trap mass spectrometry (MS), was developed for analysis of perfluorinated compounds (PFCs) in biota. The method involved the vortex-shaking of 0.2 g of tissue sample and 800 μL of tetrahydrofuran (THF):water (75:25, v/v) for 7 min, subsequent centrifugation for 13 min and direct quantitation of PFCs in the extract against solvent-based calibration curves. Selection of solvent composition was based on Hildebrand solubility parameters and their components (i.e. dispersion, dipole–dipole and hydrogen bonding forces). Recoveries in samples for PFCs with hydrocarbon chain lengths between C₄ and C₁₄ ranged from 85 to 111%, with relative standard deviations between 1 and 11%. The ion isolation monitoring mode, proposed for the first time for ion-trap-MS quantitation, proved to be effective in avoiding space-charge effects caused by co-eluting matrix components while keeping the sensitivity of full scan MS operation. Detection limits of the method were in the range 0.8−6 ng g⁻¹ for perfluoroalkyl carboxylates (PFACs) and 0.4–0.8 ng g⁻¹ for perfluoroalkyl sulfonates (PFASs) in wet weight samples. The method was validated using a reference material made up of flounder muscle and by comparison with triple quadrupole MS measurements and it was applied to the determination of PFCs in liver and muscle samples from sea birds and fishes. Only PFASs were found in samples at quantifiable levels (2.9 and 13.1 ng g⁻¹) while PFACs were below the respective quantitation limits. This method allows quick and simple microextraction of PFCs with minimal solvent consumption, while delivering accurate and precise data.     

Mixed hemimicelles SPE based on CTAB-coated Fe3O4/SiO2 NPs for the determination of herbal bioactive constituents from biological samples

In this paper, a solid-phase extraction (SPE) method based on mixed hemimicelles of cetyltrimethyl ammonium bromide (CTAB) on silica-coated magnetic nanoparticles (MNPs) is developed for extraction and preconcentration of compounds from the biological samples. We selected rhein and emodin which are the major active anthraquinones of rhubarb as model analytes. A high performance liquid chromatography-fluorescence detection (HPLC/FLD) method was developed for the determination of rhein and emodin in urine and serum samples. The main factors influencing the extraction efficiency including the amount of surfactant, the concentration of MNPs, the shaking time and the desorption ability of organic solvents were investigated and optimized. No interferences were caused by proteins or endogenous compounds in urine and serum samples. Good linearities (r² > 0.9995) for all calibration curves were obtained, and the limits of detection (LODs) for rhein and emodin were 0.2 and 0.5 ng/mL in urine samples and 7 and 10 ng/mL in serum samples, respectively. Satisfactory recoveries (92.76-109.90% and 97.53-107.72% for rhein and emodin) in the biological matrices were achieved.     

Sequential injection immunoassay for human bone morphogenic protein-7 using an immunoreactor immobilized with anti-human bone morphogenic protein-7 antibody–CdSe/ZnS quantum dot conjugates

The detection of human bone morphogenic protein-7 (BMP-7) was achieved using a sequential injection immunoassay (SIIA) system. The SIIA system is based on the binding between BMP-7 and anti-human BMP-7 (AbBMP7)–CdSe/ZnS quantum dot (QD) conjugates immobilized onto a glass disk or an optical fiber, using fluorescence detection at excitation and emission wavelengths of 470 nm and 580 nm, respectively. The AbBMP7–QD conjugates were prepared by conjugating anti-human BMP-7 antibody (AbBMP7) to hydrophilic CdSe/ZnS core/shell quantum dots (QDs). The SIIA system was fully automated using software written in the LabVIEW™ development environment. The analytical performance of the SIIA system was characterized with a number of variables such as carrier flow rate and elution buffer. Under partially optimized operating conditions, the SIIA system had a linear calibration graph at up to 10.0 ng mL⁻¹ BMP-7 (R² ≥ 0.975) and a sample frequency of two samples per hour. The SIIA system with an optical fiber immunosensor was used to detect and quantify BMP-7 in spiked real samples obtained from a biological process with recoveries in the range of 95–102%.     

A microfluidic chip based liquid-liquid extraction system with microporous membrane

A robust and simple approach for microfabricated chip based liquid-liquid extraction was developed for on-chip sample pretreatment. The chip based extraction system was composed of two microfabricated glass plates with a microporous membrane sandwiched in between. A simple bonding approach using epoxy was used to achieve bonding and sealing of the L-L extraction chip. Gravity was employed to drive the aqueous and organic flows through separate channels in the extraction system, separated by the membrane. During extraction, the analyte in an aqueous sample stream was transferred through the membrane into the organic stream. The fluorescence intensity of the analyte extracted into the organic stream was monitored in situ by a laser induced fluorescence detection system. The performance of the system was demonstrated using an aqueous solution of butyl rhodamine B (BRB) and isobutanol as sample and extractant, respectively. The system proved to be an efficient means for achieving chip based microporous membrane liquid-liquid extraction. The precision of fluorescence measurements was 1.5% R.S.D. (n = 4). A linear response range of 1 × 10⁻⁷ to 1 × 10⁻⁴ M BRB was obtained with a regression equation: I = 8.00 × 10⁶ C + 4.91. An enrichment factor of ca. 3 was obtained with an extraction efficiency of 69%.     

Development of a screening method for cocaine and cocaine metabolites in saliva using hollow fiber membrane solvent microextraction

Hollow fiber membrane solvent microextraction (HFMSME) has been applied as a simple and efficient means of sample preparation for the screening of drugs of abuse in saliva. Extraction of cocaine and its metabolites from a 2 ml saliva solution was achieved in 10 min. This was followed by fast GC separation allowing complete analysis to be achieved in 15 min. Using HFMSME, detection limits ranged between 6 and 28 ng ml⁻¹ with average relative standard deviations of 9.0%. The effect of the presence of various foodstuffs was also investigated.     

The use of anion-exchange disks in an optrode coupled to a multi-syringe flow-injection system for the determination and speciation analysis of iron in natural water samples

A combination of multi-syringe flow-injection analysis (MSFIA) technique with an optical fibre reflectance sensor for the determination of iron in water samples has been developed in this work. Anion-exchange solid phase extraction (SPE) disks have been used as solid phase. Ammonium thiocyanate has been chosen as chromogenic reagent for Fe(III). The complex Fe[SCN]₆³⁻ is retained onto the SPE disk and spectrophotometrically detected at 480 nm. The complex is eluted with 0.25 mol l⁻¹ hydrochloric acid in 75% ethanol. Total iron can be determined by oxidising Fe(II) to Fe(III) with hydrogen peroxide.A mass calibration was run within the range of 0.4-37.5 ng. The detection limit (3s_b/S) was 0.4 ng. The repeatability (RSD), calculated from 9 replicates using 0.5 ml injections of a 25 μg l⁻¹ concentration, was 3.6%. The repeatability between five anion-exchange disks was 5.4%. An injection throughput of 7 injections per hour for a sampling volume of 1 ml has been achieved.The applicability of the proposed methodology in natural water samples has been proved.The properties of anion-exchange and chelating SPE disks have been studied and compared.     

Development of an indirect competitive ELISA for the determination of papaverine

Papaverine (1-(3,4-dimethoxybenzyl)-6,7-dimethoxyisoquinoline, PAP) is a member of the benzylisoquinoline sub-group of the opium alkaloids. It has been widely used for treating diseases like pulmonary arterial embolism and renal or biliary colic. In this paper, a specific conjugate of mono-demethylated papaverine-O-carboxylmethyl ether (MDMPAP-O-CME) and bovine serum albumin (BSA) was synthesized and used as the complete antigen (PAP-BSA), with which we successfully obtained a high-titer anti-PAP polyclonal antibody (pAb) by immunization of rabbits. The anti-PAP pAb showed high affinity to papaverine with an affinity constant (K_aff) of 7.3 × 10⁷ L/mol. With this antibody, we established a sensitive immunochemical method for the determination of papaverine based on indirect competitive enzyme-linked immunosorbent assay (ELISA). The optimal concentrations of the coated antigen (PAP-OVA) and purified pAb used in the ELISA were 5 and 1.2 μg/mL, respectively. The cross reactivity of other benzylisoquinoline derived substances, including 1-(3,4-dihydroxybenzyl)-7-hydroxy-6-methoxy-isoquinoline (6-methoxy-papaveroline, MPAPO), morphine (MP) and codeine (CD) were all lower than 1%. The linear range of the calibration curve was 0.1-1000 ng/mL. Normal human serum samples were spiked with known amount of papaverine and measured by the ELISA. Recoveries were between 102% and 105%. Papaverine content in a commercial papaverine hydrochloride injection sample was also determined using the established ELISA. Compared with the results given by the control experiment of HPLC, the recoveries of ELISA to detect injection samples were 102-110%. The limits of detection for synthetic serum samples and injection samples of papaverine hydrochloride were 0.25 and 0.06 ng/mL, respectively.     

Automatic flow system for the sequential determination of copper in serum and urine by flame atomic absorption spectrometry

In this work, a fully automated flow system exploiting the advantages of the association of multi-pumping, multicommutation, binary sampling and merging zones, to accomplish the sequential determination of copper in serum and urine by flame atomic absorption spectrometry, is described. The developed flow system allowed multiple tasks, such as serum samples preparation (samples and standard solutions viscosity adjustment), serum copper (SCu) measurement, urine copper (UCu) pre-concentration and its subsequent elution and measurement, to be carried out sequentially. The implemented flow manifold presented a modular configuration consisting on two quasi-independent modules, each one accountable for a specific sample manipulation and whose combined operation under computer control enabled the determination of copper in a wide concentrations range.Once optimised and with a sample consumption of about 0.250 mL of serum and 7 mL of urine, the developed flow system allowed linear calibration plots up to 5 mg L⁻¹ with a detection limit of 0.035 mg L⁻¹ for SCu and linear calibration plots up to 300 μg L⁻¹ with a detection limit of 0.67 μg L⁻¹ for UCu. The sampling rate varied according to the module employed and was about 360 determinations h⁻¹ (SCu module), 12 determinations h⁻¹ (UCu module) or 24 determinations h⁻¹ (12 urine and 12 serum samples; UCu and SCu modules simultaneously). Repeatability studies (R.S.D.%, n = 10) showed good precision for UCu at concentrations of 25 μg L⁻¹ (2.54%), 50 μg L⁻¹ (0.90%) and 100 μg L⁻¹ (1.62%) as well as for SCu at concentrations of 0.25 mg L⁻¹ (8.11%), 1 mg L⁻¹ (3.11%) and 5 mg L⁻¹ (0.90%). A comparative evaluation showed a good agreement between the results obtained in the analysis of UCu and SCu (n = 18) by both the developed methodology and the reference procedures. Accuracy was further evaluated by means of the analysis of reference samples (Seronorm™ Trace Elements Urine and Seronorm™ Trace Elements Serum) and the obtained results complied with the certified values.     

Disposable potentiometric sensors for monitoring cholinesterase activity

A highly sensitive disposable screen-printed butyrylcholine (BuCh) potentiometric sensor, based on heptakis (2,3,6-tri-o-methyl)-β-cyclodextrin (β-CD) as ionophore, was developed for butyrylcholinesterase (BuChE) activity monitoring. The proposed sensors have been characterized and optimized according to the constituents of homemade printing carbon ink including β-CD, anionic sites, and plasticizer. The fabricated sensor showed Nernstian responses from 10⁻⁶ to 10⁻² mol L⁻¹ with detection limit of 8 × 10⁻⁷ mol L⁻¹, fast response time (1.6 s) and adequate shelf-life (6 months). Improved selectivity towards BuCh with minimal interference from choline (Ch) was achieved and the sensor was used for determination of 0.06-1.25 U mL⁻¹ BuChE. The developed disposable sensors have been successfully applied for real-time intoxication monitoring through assaying cholinesterases (ChEs) activity in human serum. Determination of organophosphate pesticide was conducted by measuring their inhibition of BuChE with successful assaying of malathion in insecticide samples with high accuracy and precision.     

Determination of Prometryne in water and soil by HPLC-UV using cloud-point extraction

A CPE-HPLC (UV) method has been developed for the determination of Prometryne. In this method, non-ionic surfactant Triton X-114 was first used to extract and pre-concentrate Prometryne from water and soil samples. The separation and determination of Prometryne were then carried out in an HPLC-UV system with isocratic elution using a detector set at 254 nm wavelength. The parameters and variables that affected the extraction were also investigated and the optimal conditions were found to be 0.5% of Triton X-114 (w/v), 3% of NaCl (w/v) and heat-assisted at 50 °C for 30 min. Using these conditions, the recovery rates of Prometryne ranged from 92.84% to 99.23% in water and 85.48% to 93.67% in soil, respectively, with all the relative standard deviations less than 3.05%. Limit of detection (LOD) and limit of quantification (LOQ) were 3.5 μg L⁻¹ and 11.0 μg L⁻¹ in water and 4.0 μg kg⁻¹ and 13.0 μg kg⁻¹ in soil, respectively. Thus, we developed a method that has proven to be an efficient, green, rapid and inexpensive approach for extraction and determination of Prometryne from soil samples.