A multivariate multianalyte screening method for sulfonamides in milk based on front-face fluorescence spectroscopy

Screening methods are used to detect the presence of a substance or class of substances at the level of interest and are specifically designed to avoid false compliant results. They should allow the running of a high number of samples per day at a low cost under routine conditions. In this work, a rapid and simple method for the screening of six sulfonamides (sulfadiazine, SD; sulfamerazine, SMR; sulfamethazine, SMT; sulfachloropyridazine, SCP; sulfathiazole, STZ and sulfamethoxazole, SMO) in milk samples is proposed and assessed according to the criteria required by the European Regulation, Decision 2002/657/EC. The method is based on modelling front-face fluorescence emission spectra by means of partial least squares class modelling (PLS-CM). The milk samples are pre-treated with a single easy step of derivatization with fluorescamine.After confirming that the method has equal analytical sensitivity for all the six sulfonamides, it is established that the multivariate analytical sensitivity at 100 μg L⁻¹ is 37.5 μg L⁻¹ when analysing a mixture of six sulfonamides added to different brands of milk and measured in different days. In addition, the method is applied to samples from 11 commercial brands of milk. For β = 0.05, threshold value established by the Decision 2002/657/EC for this method, the probability of false non-compliance, α, is equal to 0.17, allowing the suitable screening of these six sulfonamides.     

Feasibility of ultra-high performance liquid and gas chromatography coupled to mass spectrometry for accurate determination of primary and secondary phthalate metabolites in urine samples

Phthalates (PAEs) are ubiquitous toxic chemical compounds. During the last few years, some phthalate metabolites (MPAEs) have been proposed as appropriate biomarkers in human urine samples to determine PAE human intake and exposure. So, it is necessary to have fast, easy, robust and validated analytical methods to determine selected MPAEs in urine human samples. Two different instrumental methods based on gas (GC) and ultra-high performance liquid (UHPLC) chromatography coupled to mass spectrometry (MS) have been optimized, characterized and validated for the simultaneous determination of nine primary and secondary phthalate metabolites in urine samples. Both instrumental methods have similar sensitivity (detection limits ranged from 0.03 to 8.89 pg μL⁻¹ and from 0.06 to 0.49 pg μL⁻¹ in GC–MS and UHPLC–MS², respectively), precision (repeatability, expressed as relative standard deviation, which was lower than 8.4% in both systems, except for 5OH-MEHP in the case of GC–MS) and accuracy. But some advantages of the UHPLC–MS² method, such as more selectivity and lower time in the chromatographic runs (6.8 min vs. 28.5 min), have caused the UHPLC–MS² method to be chosen to analyze the twenty one human urine samples from the general Spanish population. Regarding these samples, MEP showed the highest median concentration (68.6 μg L⁻¹), followed by MiBP (23.3 μg L⁻¹), 5cx-MEPP (22.5 μg L⁻¹) and MBP (19.3 μg L⁻¹). MMP (6.99 μg L⁻¹), 5oxo-MEHP (6.15 μg L⁻¹), 5OH-MEHP (5.30 μg L⁻¹) and MEHP (4.40 μg L⁻¹) showed intermediate levels. Finally, the lowest levels were found for MBzP (2.55 μg L⁻¹). These data are within the same order of magnitude as those found in other similar populations.     

Three-way models and detection capability of a gas chromatography-mass spectrometry method for the determination of clenbuterol in several biological matrices: the 2002/657/EC European Decision

Clenbuterol has been extracted by mixed solid-phase extraction from two biological matrices (bovine hair and urine) and detected by GC/MS (selected ion monitoring (SIM) and full-SCAN modes). The analytical signal has been modelled with univariate and three-way models, namely DTLD, PARAFAC, PARAFAC2, Tucker3 and trilinear PLS. Since clenbuterol is a banned substance a comparative study of the capability of detection (CCβ, X₀=0) has been performed as a function of the sample (hair, 74 μg kg⁻¹ and urine, 0.36 μg l⁻¹), the mode in which the signals are monitored (SCAN, 283 μg kg⁻¹ and SIM, 74 μg kg⁻¹) and the statistical model (univariate, 283 μg kg⁻¹ and trilinear PLS, 20.91 μg kg⁻¹). The capability of detection has been calculated as stated in ISO 11843 and Decision 2002/657/EC setting in all cases the probabilities of false positive and of false negative at 0.05.The identification of the mass spectra must be done to confirm the presence of clenbuterol and has been carried out through PARAFAC. The correlation coefficient between the spectra estimated by PARAFAC and the library spectra is 0.96 (hair, SCAN mode) and 1.00 (hair and urine, SIM mode).The Decision 2002/657/EC advocates the use of independent mass fragments to identify banned compounds. These recommendations together with the effect of the number of ions registered on the capability of detection have lead us to select five uncorrelated fragments (86, 243, 262, 264 and 277) from the data set of 210 ions by hierarchical clustering of variables.     

Targeted analysis with benchtop quadrupole–orbitrap hybrid mass spectrometer: Application to determination of synthetic hormones in animal urine

Sensitive and unequivocal determination of analytes/contaminants in complex matrices is a challenge in the field of food safety control. In this study, various acquisition modes (Full MS/AIF, Full MS + tMS/MS, Full MS/dd MS/MS and tSIM/ddMS/MS) and parameters of a quadrupole–orbitrap hybrid mass spectrometer (Q Exactive) were studied in detail. One of the main conclusions has been that, reducing the scan range for Full MS (using the quadrupole) and targeted modes give higher signal-to-noise (S/N) ratios and thereby better detection limits for analytes in matrix. The use of Q Exactive in a complex case, for the confirmatory analysis of hormones in animal urine is presented. A targeted SIM data dependent MS/MS (tSIM/ddMS/MS) acquisition method for determination of eight synthetic hormones (trenbolone, 17α ethinylestradiol, zeranol, stanozolol, dienestrol, diethylstilbestrol, hexestrol, taleranol) and a naturally occurring hormone (zearalenone) in animal urine were optimized to have sensitive precursors from targeted SIM mode and trigger MS/MS scans over the entire chromatograph peak. The method was validated according to EC/657/2002. CCα (decision limit) for the analytes ranged between 0.11 μg L⁻¹ and 0.69 μg L⁻¹ and CCβ (detection capability) ranged between 0.29 μg L⁻¹ and 0.90 μg L⁻¹.     

Simultaneous determination of 11 drugs belonging to four different groups in human urine samples by reversed-phase high-performance liquid chromatography method

A new, accurate, sensitive and fast reversed-phase high-performance liquid chromatography (RP-HPLC) as an analytical method for the quantitative determination of 11 drugs in human urine was worked out, optimized and validated. The objects of analysis were imipenem (IMP), paracetamol (PAR), dipyrone (DPR), vancomycin (VCM), amikacin (AMK), fluconazole (FZ), cefazolin (CFZ), prednisolone (PRE), dexamethasone (DEX), furosemide (FUR) and ketoprofen (KET) belonging to four different groups (antibiotics, analgesic, demulcent and diuretic). For HPLC analysis, diode array (DAD) and fluorescence (FL) detectors were used. The separation of analyzed compounds was conducted by means of a LiChroCART^® Purospher^® C₁₈e (125 mm × 3 mm, particle size 5 μm) analytical column with LiChroCART^® LiChrospher^® C₁₈ (4 mm × 4 mm, particle size 5 μm) pre-column with gradient elution. Analyzed drugs were determined within 20 min. The mobile phase was comprised of various proportions of methanol, acetonitrile and 0.05% trifluoroacetic acid in water. AMK was separated and determined from human urine using ortho-phthaldialdehyde-3-mercaptopropionic acid (OPA-3-MPA) as a fluorescent reagent by RP-HPLC-FL. The following retention times for drugs IMP, PAR, DPR, VCM, AMK, FZ, CFZ, PRE, DEX, FUR and KET in human urine were found: 4.01 min, 4.86 min, 6.71 min, 8.14 min, 9.46 min, 10.01 min, 10.90 min, 13.34 min, 14.06 min, 16.03 min and 18.98 min, respectively. Excellent linearity was obtained for compounds in the range of concentration: 0.35-42 μg ml⁻¹, 0.5-45 μg ml⁻¹, 4.5-38 μg ml⁻¹, 0.25-25 μg ml⁻¹, 0.5-35 μg ml⁻¹, 0.25-22 μg ml⁻¹, 0.03-52 μg ml⁻¹, 0.15-25 μg ml⁻¹, 0.25-28 μg ml⁻¹, 0.05-18 μg ml⁻¹ and 0.15-35 μg ml⁻¹ for IMP, PAR, DPR, VCM, AMK, FZ, CFZ, PRE, DEX, FUR and KET, respectively. The limits of detection (LOD) and limits of quantification (LOQ) for analyzed drugs were calculated in all cases and recovery studies were also performed. Ten human urine samples obtained from patients treated in hospital have been tested. In analyzed samples, one or more drugs from the 11 examined drugs were detected. The concentrations of examined drugs in urine samples ranged between: 1.5-12 μg ml⁻¹ of PAR, 5.2-11.5 μg ml⁻¹ of DPR, 0.13-9.5 μg ml⁻¹ of CFZ and 0.1-8 μg ml⁻¹ of FUR. This method can be successfully applied to routine determination of all these drugs in human urine samples.     

Cobalt as internal standard for arsenic and selenium determination in urine by simultaneous atomic absorption spectrometry

The effectiveness of internal standardization for simultaneous atomic absorption spectrometry (SIMAAS) was investigated for As and Se determination in urine. Co and Sn were selected as internal standard (IS) candidates based on the evaluation of some physico-chemical parameters related to the atomization. Correlation graphs, plotted from the normalized absorbance signals (n = 20) of internal standard (axis y) versus analyte (axis x), precision, and accuracy of the analytical results were the supportive parameters to choose Co as the most appropriate IS. The urine samples were diluted 1 + 2 to 1.0% (v/v) HNO₃ + 80 μg L⁻¹ Co²⁺. The mixture 20 μg Pd + 3 μg Mg was used as chemical modifier and the optimized temperatures for pyrolysis and atomization steps were 1400 and 2300 °C, respectively. The characteristic masses for As (47 ± 1 pg) and Se (72 ± 2 pg) were estimated from the analytical curves. The detection limits (n = 20, 3δ) were 1.8 ± 0.1 and 2.6 ± 0.1 μg L⁻¹ for As and Se, respectively. The reliability of the entire procedure was checked with the analysis of certified reference material from Sero AS(Seronorm™ Trace Elements in Urine). The obtained results showed the matrix interference disallowed the instrument calibration with aqueous standards. The best analytical condition was achieved when matrix-matched standards were used in combination with Co as IS, which improved the recoveries obtained for As. Under this experimental condition, eight urine samples were analysed and spiked with 10 and 25 μg L⁻¹ As and Se. The mean recoveries were 96 ± 6% (10 μg L⁻¹ As), 95 ± 6% (25 μg L⁻¹ As), 101 ± 7% (10 μg L⁻¹ Se), and 97 ± 4% (25 μg L⁻¹ Se).     

Quantitative detection of tetracycline residues in honey by a simple sensitive immunoassay

Tetracyclines (TCs) are widely used for prevention and control of infectious diseases and have a great activity against variety of Gram-positive and Gram-negative bacteria. Due to the widespread use of TCs in animal husbandry, it can lead to an increase the risk of TCs remaining in human food. To protect consumers, many countries have set acceptable tolerance levels for these drugs. Therefore, it is necessary to establish a suitable analytical technique with specificity, sensitivity and simplicity.The biotin-avidin mediated ELISA method was performed to determine TC residues in honey quantitatively. By using PBS-EDTA assay buffer at pH 7.2, a honey solution of TC standard was prepared and diluted. And no additional pre-treatment of sample was required in this method. The limit of detection and limit of quantitation of the optimized method were 3.98 × 10⁻¹⁰ M (0.19 μg L⁻¹) and 7.94 × 10⁻¹⁰ M (0.38 μg L⁻¹), respectively, and the dynamic range was from 1.52 μg L⁻¹ to 152 μg L⁻¹ of TC in honey. No cross-reactivity was observed with the structurally similar compounds, and mean percent recoveries of TC spiked in honey ranged from 95% to 101%. Compared to other methods, this method was superior in terms of detection limit, dynamic range, and % recovery with simple sample-preparation.     

Analysis of phenylurea and propanil herbicides by solid-phase microextraction and liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection

This study examines the application of solid-phase microextraction coupled with high performance liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection (SPME-HPLC-PIF-FD) for the determination of four phenylurea herbicides (monolinuron, diuron, linuron and neburon) and propanil in groundwater. Direct immersion (DI) SPME was applied using a 60 μm polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber for the extraction of the pesticides from groundwater samples. An AQUASIL C₁₈ column (150 mm × 4.6 mm i.d., 5 μm) was used for separation and determination in HPLC. The method was evaluated with respect to the limits of detection (LODs) and the limits of quantification (LOQs) according to IUPAC. The limits of detection varied between 0.019 μg L⁻¹ and 0.034 μg L⁻¹. Limits of quantification ranged between 0.051 μg L⁻¹ and 0.088 μg L⁻¹. These values meet the recommended limits for individual pesticides in groundwater (0.1 μg L⁻¹) established by the EU. Recoveries ranged between 86% and 105% and relative standard deviation values between 2% and 8%.     

NMR investigation of acrolein stability in hydroalcoholic solution as a foundation for the valid HS-SPME/GC–MS quantification of the unsaturated aldehyde in beverages

Acrolein (propenal) is found in many foods and beverages and may pose a health hazard due to its cytotoxicity. Considerable knowledge gaps regarding human exposure to acrolein exist, and there is a lack of reliable analytical methods. Hydroalcoholic dilutions prepared for calibration purposes from pure acrolein show considerable degradation of the compound and nuclear magnetic resonance (NMR) spectroscopy showed that 1,3,3-propanetriol and 3-hydroxypropionaldehyde are formed. The degradation can be prevented by addition of hydroquinone as stabilizer to the calibration solutions, which then show linear concentration-response behaviour required for quantitative analysis. The stabilized calibration solutions were used for quantitative headspace solid-phase microextraction/gas chromatography–mass spectrometry (HS-SPME/GC–MS) determination of acrolein in alcoholic beverages with a detection limit of 14 μg L⁻¹. Of 117 tested alcoholic beverages, 64 were tested positive with the highest incidence in grape marc spirits and whiskey (100%, mean 252 μg L⁻¹), followed by fruit spirits (86%, mean 591 μg/L⁻¹), tequila (86%, mean 404 μg L⁻¹), Asian spirits (43%, mean 54 μg L⁻¹) and wine (9%, mean 0.7 μg L⁻¹). Acrolein could not be detected in beer, vodka, absinthe and bottled water. Six of the fruit and grape marc spirits had acrolein levels above the World Health Organization (WHO) provisional tolerable concentration of 1.5 mg L⁻¹.     

Multi-residue method for the determination of organochlorine pesticides in fish feed based on a cleanup approach followed by gas chromatography–triple quadrupole tandem mass spectrometry

A multi-residue method for the determination of organochlorine pesticides in fish feed samples was developed and optimized. The method is based on a cleanup step of the extracted fat, carried out by liquid–liquid extraction on diatomaceous earth cartridge with n-hexane/acetonitrile (80/20, v/v) followed by solid phase extraction (SPE) with silica gel–SCX cartridge, before the identification and quantification of the residues by gas chromatography–triple quadrupole tandem spectrometry (GC–MS/MS). Performance characteristics, such as accuracy, precision, linear range, limits of detection (LOD) and quantification (LOQ), for each pesticide were determined. Instrumental LODs ranged from 0.01 to 0.11 μg L⁻¹, LOQs were in the range of 0.02–0.35 μg L⁻¹, and calibration curves were linear (r² > 0.999) in the whole range of explored concentrations (5–100 μg L⁻¹). Repeatability values were in the range of 3–15%, evaluated from the relative standard deviation of six samples spiked at 100 μg kg⁻¹ of fat, and in compliance with that derived by the Horwitz's equation. No matrix effects or interfering substances were observed in fish feed analyses. The proposed method allowed high recoveries (92–116%) of spiked extracted fat samples at 100 μg kg⁻¹, and very low LODs (between 0.02 and 0.63 μg kg⁻¹) and LOQs (between 0.05 and 2.09 μg kg⁻¹) determined in fish feed samples.     

Usefulness of parallel factor analysis to handle the matrix effect in the fluorescence determination of tetracycline in whey milk

The determination of tetracycline by fluorescence spectrophotometry in complex matrices has some difficulties, because the presence of other compounds in the matrix affects the analytical signal. In this work, the effect of some inorganic species that are present in whey milk on the fluorescence signal of tetracycline is studied using a D-optimal experimental design. Next, an experimental strategy is proposed in conjunction with Parallel Factor Analysis, PARAFAC, modeling that leads to suitably modeling the severe matrix effect in the determination of tetracycline in whey milk. A specific design is performed in such a way that the lack of trilinearity due to the effect of the presence of interferents on the signal is obviated. Then, ten test samples from three brands of milk, spiked with different quantities of tetracycline and measured in 2 days were analysed using this methodology (mean of the absolute value of the relative errors: 5.1%). The developed analytical method fulfils the property of trueness, the relative errors being, both in calibration and prediction, inside the interval set by Commission Decision 2002/657/EC at these concentration levels. Decision limits (CCα) at x₀ = 0 μg L⁻¹ and at x₀ = 100 μg L⁻¹ were 13.2 and 112.4 μg L⁻¹ respectively, for α = 0.05; whereas detection capabilities (CCβ) were 25.9 μg L⁻¹ and 124.4 μg L⁻¹ respectively for α = β = 0.05.     

Determination of the steroid hormone levels in water samples by dispersive liquid-liquid microextraction with solidification of a floating organic drop followed by high-performance liquid chromatography

In this study, the steroid hormone levels in river and tap water samples were determined by using a novel dispersive liquid-liquid microextraction method based on the solidification of a floating organic drop (DLLME-SFO). Several parameters were optimized, including the type and volume of the extraction and dispersive solvents, extraction time, and salt effect. DLLME-SFO is a fast, cheap, and easy-to-use method for detecting trace levels of samples. Most importantly, this method uses less-toxic solvent. The correlation coefficient of the calibration curve was higher than 0.9991. The linear range was from 5 to 1000 μg L⁻¹. The spiked environmental water samples were analyzed using DLLME-SFO. The relative recoveries ranged from 87% to 116% for river water (which was spiked with 4 μg L⁻¹ for E1, 3 μg L⁻¹ for E2, 4 μg L⁻¹ for EE2 and 9 μg L⁻¹ for E3) and 89% to 102% for tap water (which was spiked with 6 μg L⁻¹ for E1, 5 μg L⁻¹ for E2, 6 μg L⁻¹ for EE2 and 10 μg L⁻¹ for E3). The detection limits of the method ranged from 0.8 to 2.7 μg L⁻¹ for spiked river water and 1.4 to 3.1 μg L⁻¹ for spiked tap water. The methods precision ranged from 8% to 14% for spiked river water and 7% to 14% for spiked tap water.     

A sensitive sensor for anthraquinone anticancer drugs and hsDNA based on CdTe/CdS quantum dots fluorescence reversible control

Based on CdTe/CdS quantum dots (CdTe/CdS QDs) fluorescence (FL) reversible control, a new and sensitive FL sensor for determination of anthraquinone (AQ) anticancer drugs (adriamycin and daunorubicin) and herring sperm DNA (hsDNA) was developed. Under the experimental conditions, FL of CdTe/CdS QDs can be effectively quenched by AQ anticancer drugs due to the binding of AQ anticancer drugs on the surface of CdTe/CdS QDs and photoinduced electron transfer (PET) process from CdTe/CdS QDs to AQ anticancer drugs. Addition of hsDNA afterwards brought the restoration of CdTe/CdS QDs FL intensity, as AQ anticancer drugs peeled off from the surface of CdTe/CdS QDs and embedded into hsDNA double helix structure. The liner ranges and the detection limits of FL quenching methods for two AQ anticancer drugs were 0.33-9 μg mL⁻¹ and 0.09 μg mL⁻¹ for ADM and 0.15-9 μg mL⁻¹ and 0.04 μg mL⁻¹ for DNR, respectively. The restored FL intensity was proportional to concentration of hsDNA in the range of 1.38-28 μg mL⁻¹and the detection limit for hsDNA was 0.41 μg mL⁻¹. It was applied to the determination of AQ anticancer drugs in human serum and urine samples with satisfactory results. The reaction mechanism of CdTe/CdS QDs FL reversible control was studied.     

Enzyme immunoassay for semicarbazide--the nitrofuran metabolite and food contaminant

Semicarbazide (SEM), the marker residue for the banned nitrofuran veterinary antibiotic nitrofurazone (NFZ), has been detected regularly in foods (47% of recent nitrofuran EU Rapid Alerts involve SEM). However, the validity of SEM as a definitive marker for NFZ has been undermined by SEM arising from other sources including azodicarbonamide, a plastics blowing agent and flour treatment additive. An inexpensive screening test for SEM in food matrices is needed—all SEM testing currently uses expensive LC-MS/MS instrumentation. We now report the first production of antibodies against derivatised SEM. A novel carboxyphenyl SEM derivative was used to raise a polyclonal antibody that has been incorporated into a semi-quantitative microtitre plate ELISA, validated according to the criteria set out in Commission Decision 2002/657/EC, for use with chicken muscle. The antibody is highly specific for derivatised SEM, cross-reactivity being 1.7% with NFZ and negligible with a wide range of other nitrofurans and poultry drugs. Samples are derivatised with o-nitrobenzaldehyde and simultaneously protease digested before extraction by cation exchange SPE. The ELISA has a SEM detection capability (CC_β) of 0.25 μg kg⁻¹ when a threshold of 0.21 μg kg⁻¹ is applied to the selection of samples for confirmation (lowest observed 0.25 μg kg⁻¹ fortified sample, n = 20), thus satisfying the EU nitrofurans’ minimum required performance limit of 1 μg kg⁻¹. NFZ-incurred muscles (12) containing SEM at 0.5-5.0 μg kg⁻¹ by LC-MS/MS, all screened positive by this ELISA protocol which is also applicable to egg and chicken liver.     

Transfer assessment of fipronil residues from feed to cow milk

Fipronil, a phenylpyrazole insecticide introduced for pest control on a broad range of crops, can also affect non-target insects such as honeybees. More widely, non-target environment such as milk produced by dairy cows fed with maize silage from treated seeds (=silage T) can be affected. To assess the potential transfer of fipronil residues (sulfone, sulfide, fipronil, desulfinyl and amide), a methodology including gas chromatography coupled with tandem mass spectrometry (GC-MS/MS) analysis was developed and validated according to the 2002/657/EC decision, in order to reach a level of quantification below 0.1 μg L⁻¹ in milk and 0.1 μg kg⁻¹ in plants. Twelve dairy cows were fed with silage T during 4 months. Concentration of fipronil in treated seeds was estimated at 1 g kg⁻¹, whereas silage from these seeds contained 0.30 ± 0.05 μg kg⁻¹ of dry material of fipronil, 0.13 ± 0.03 μg kg⁻¹ of dry material of sulfone. Sulfide residues were below the limit of quantification. Silage from untreated seeds (=silage U) presented traces of fipronil and sulfone, respectively at 0.04 ± 0.06 and 0.02 ± 0.03 μg kg⁻¹ of dry material. Contribution of fipronil residues from supplies was insignificant. During administration of silage T, only sulfone residues were quantified in milk. The average concentration was 0.14 ± 0.05 μg L⁻¹. Before and after administration, sulfone residues were detected but not quantifiable (<0.025 μg L⁻¹). Our results suggest a transfer of fipronil from feed to milk under its sulfone form. Moreover, traces of fipronil residues in maize U, soya, wheat and straw show a diffuse contamination of this pesticide in the environment.     

Rapid and sensitive methodology for determination of ethyl carbamate in fortified wines using microextraction by packed sorbent and gas chromatography with mass spectrometric detection

This work presents a new methodology to quantify ethyl carbamate (EC) in fortified wines. The presented approach combines the microextraction by packed sorbent (MEPS), using a hand-held automated analytical syringe, with one-dimensional gas chromatography coupled with mass spectrometry detection (GC–MS). The performance of different MEPS sorbent materials was tested, namely SIL, C2, C8, C18, and M1. Also, several extraction solvents and the matrix effect were evaluated. Experimental data showed that C8 and dichloromethane were the best sorbent/solvent pair to extract EC. Concerning solvent and sample volumes optimization used in MEPS extraction an experimental design (DoE) was carried out. The best extraction yield was achieved passing 300 μL of sample and 100 μL of dichloromethane. The method validation was performed using a matrix-matched calibration using both sweet and dry fortified wines, to minimize the matrix effect. The proposed methodology presented good linearity (R² = 0.9999) and high sensitivity, with quite low limits of detection (LOD) and quantification (LOQ), 1.5 μg L⁻¹ and 4.5 μg L⁻¹, respectively. The recoveries varied between 97% and 106%, while the method precision (repeatability and reproducibility) was lower than 7%. The applicability of the methodology was confirmed through the analysis of 16 fortified wines, with values ranging between 7.3 and 206 μg L⁻¹. All chromatograms showed good peak resolution, confirming its selectivity. The developed MEPS/GC–MS methodology arises as an important tool to quantify EC in fortified wines, combining efficiency and effectiveness, with simpler, faster and affordable analytical procedures that provide great sensitivity without using sophisticated and expensive equipment.     

Sensitive and ultra-fast determination of arsenic(III) by gas-diffusion flow injection analysis with chemiluminescence detection

A novel chemiluminescence gas-diffusion flow injection system for the determination of arsenic(III) in aqueous samples is described. The analytical procedure involves injection of arsenic(III) samples and standards into a 0.3 mol L⁻¹ hydrochloric acid carrier stream which is merged with a reagent stream containing 0.2% (w/v) sodium borohydride and 0.015 mol L⁻¹ sodium hydroxide. Arsine, generated in the combined carrier/reagent donor stream, diffuses across the hydrophobic Teflon membrane of the gas-diffusion cell into an argon acceptor stream and then reacts with ozone in the flow-through chemiluminescence measuring cell of the flow system. Under optimal conditions, the method is characterized by a wide linear calibration range from 0.6 μg L⁻¹ to 25 mg L⁻¹, a detection limit of 0.6 μg L⁻¹ and a sample throughput of 300 samples per hour at 25 mg L⁻¹ and 450 samples per hour at 25 μg L⁻¹.     

Determination of trace bisphenol A in complex samples using selective molecularly imprinted solid-phase extraction coupled with capillary electrophoresis

The highly selective, fast and effective sample pretreatment technique molecularly imprinted solid-phase extraction (MISPE) can overcome the low sensitivity of the highly efficient capillary electrophoresis-UV method (CE-UV). In this work, narrowly dispersible bisphenol A (BPA)-imprinted polymeric microspheres with a high capacity factor of k′ = 6.8 and an imprinted factor of I = 6.53 were investigated as selective solid-phase extraction (SPE) sorbents for use in extraction of BPA from different sample matrices (tap water, wastewater, Yangtze River water, soil from the Yangtze River, shrimp and human urine). Washing and eluting protocols of MISPE were optimized. Under optimal conditions, recoveries of MISPE were investigated. Recoveries were basically constant and the relative standard deviation (RSD) was lower than 5.8% when loading volumes changed from 1 to 50 mL. Recoveries ranged from 71.20% to 86.23% for different sample matrices. Compared with C18 SPE, MISPE had higher selectivity and recovery for BPA. BPA was determined with good accuracy and precision in different complex samples using CE-UV coupled with MISPE. Spiked recoveries ranged from 95.20% to 105.40%, and the RSD was less than 7.2%. Because a large loading volume was achieved, the enrichment efficiency of pretreatment and the sensitivity of this method were improved. The limits of detection of this MISPE-CE-UV method for BPA in tap water, wastewater, Yangtze River water, soil from the Yangtze River, shrimp and human urine were 3.0 μg L^− 1, 5.4 μg L^− 1, 6.9 μg L^− 1, 2.1 μg L^− 1, 1.8 μg L^− 1 and 84 μg L^− 1, respectively.     

Determination of aluminium in water samples by adsorptive cathodic stripping voltammetry in the presence of pyrogallol red and a quaternary ammonium salt

A fast, sensitive and selective method for the determination of aluminium based on the reaction of the metal with pyrogallol red (PR) in the presence of tetrabutylammonium tetrafluoroborate (TBATFB) to form an Al(PR)₃x9TBATFB complex which is adsorbed on the mercury electrode is presented. Under these conditions complexation of aluminium is rapid and no waiting period or heating of the sample is required. The reduction current of the accumulated complex is measured by scanning the potential in the cathodic direction. The variation of peak current with pH, adsorption time, adsorption potential, ligand and quaternary ammonium salt concentration, and some instrumental parameters, such as stirring rate in the accumulation stage, and step amplitude, pulse amplitude and step duration while obtaining the square wave voltamperograms were optimized. The best experimental parameters were pH 8.5, (NH₄Ac-NH₃ buffer), C_PR = 25 μmol L⁻¹, C_TBATFB over 75 μmol L⁻¹, t_ads = 60 s, and E_ads = −0.60 V versus Ag/AgCl. A linear response is observed over the 0.0-30.0 μg L⁻¹ concentration range, with a detection limit of 1.0 μg L⁻¹. Reproducibility for 9.0 μg L⁻¹ aluminium solution was 2.3% (n = 6). Synthetic sea water and sea water reference material CRM-SW were used for validation measurements. Aluminium in urine samples of a volunteer who ingested 800 mg of Al(OH)₃ was analyzed.     

Quantitative selenium speciation in human urine by using liquid chromatography–electrospray tandem mass spectrometry

A liquid chromatography–electrospray-tandem mass spectrometry (ES-MS/MS) method was developed for the speciation analysis of four organic selenium species of relevance to human urinary metabolism, namely trimethylselenomium ion (TMSe⁺), selenomethionine (SeMet) and the two selenosugars, methyl 2-acetamido-2-deoxy-1-seleno-β-d-galactos/-glucos-amine (SeGalNAc and SeGluNAc, respectively). Their chromatographic separation was achieved by using a cation exchange pre-column coupled in-series with a reversed-phase high-performance liquid chromatography column, along with an isocratic mobile phase. Online detection was performed using ES-MS/MS in selective reaction monitoring mode. SeGalNAc was detected as the major human urinary metabolite of selenium in the samples analysed, whereas TMSe⁺ was detected in the urine of one volunteer before and after receiving a selenium supplement. SeMet was not detected as a urine excretory metabolite in this study. Spiking experiments performed with the urine samples revealed significant signal suppression caused by coeluting matrix constituents. To overcome such interferences, isotopically labelled ¹³CD₃⁸²SeGalNAc was used as an internal standard, whereas in the absence of an isotopically labelled internal standard for TMSe⁺, the standard addition method was applied. Quality control for the accurate quantitation of TMSe⁺ and SeGalNAc was carried out by analysing spiked human urine samples with appropriate selenium standards over a concentration range of 10–50 μg Se L⁻¹. The method has achieved a limit of detection in the presence of urine matrix comparable to that of HPLC-inductively coupled plasma-mass spectrometry for the four selenium species: 1.0 μg Se L⁻¹ for TMSe⁺, 5.6 μg Se L⁻¹ for SeMet, and 0.1 μg Se L⁻¹ for both SeGalNAc and SeGluNAc.