Multiresidue determination of organochlorine pesticides and polychlorinated biphenyls in milk by gas chromatography with electron-capture detection after extraction by matrix solid-phase dispersion

A multiresidue analytical method based on matrix solid-phase dispersion was developed to analyze liquid milk for 22 organochlorine pesticides (OCPs) and 6 polychlorinated biphenyls (PCBs). Initial extraction is performed by loading 3 mL milk onto a 2.0 g octadecyl (C18)-bonded silica cartridge with n-hexane as the eluant. Neutral alumina column chromatography with sodium sulfate as the drying agent is used for further cleanup. The eluate is concentrated to 0.5 mL, and target analytes are determined by capillary gas chromatography with electron-capture detection. The optimized method was validated by determining accuracy (recovery percentages), precision (repeatability and reproducibility), and sensitivity (detection and quantitation limits) from analyses of milk samples fortified at 10 and 1 microg/L levels. Average recoveries were between 74 and 106% for all residues except beta-HCH, beta-endosulfan, and endosulfan sulfate. Both repeatability and reproducibility relative standard deviation values were < 22% for all residues. Detection limits ranged from 0.02 to 0.12 microg/L and quantitation limits were between 0.02 and 0.62 microg/L. The proposed analytical method may be used as a fast and simple procedure in routine determinations of OCPs and PCBs in milk.     

Trace analysis of polychlorinated dibenzo-p-dioxins, dibenzofurans and WHO polychlorinated biphenyls in food using comprehensive two-dimensional gas chromatography with electron-capture detection

Trace analysis of 2,3,7,8-polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and the 12 WHO-PCBs (four non-ortho and eight mono-ortho congeners that have been assigned toxic equivalence factors, TEFs, by the World Health Organisation) was conducted by comprehensive two-dimensional gas chromatography with a micro electron-capture detector (GC x GC-microECD). Four food matrices (fish oil from herring, spiked cows' milk, vegetable oil and an eel extract) were analysed by two GC x GC laboratories, and four GC-HRMS laboratories generated reference values. The two GC x GC laboratories used different column combinations for separating the target analytes. For the first dimension, non-polar DB-XLB and VF-1 columns were used, and for the second dimension, an LC-50 liquid crystalline column with unique selectivity for planar compounds. The congener-specific and total toxic equivalence (TEQ) data obtained using DB-XLB x LC-50 were in good agreement with results obtained by the GC-HRMS laboratories. The WHO-PCB data obtained with the VF-1 x LC-50 combination was also good, but the PCDD/F concentrations were sometimes overestimated due to matrix interferences. GC x GC-microECD using DB-XLB x LC-50 seems to fulfil the European Community requirements of a screening method for PCDD/F and WHO-PCB TEQ in food.     

Ion-trap tandem mass spectrometry-based analytical methodology for the determination of polychlorinated biphenyls in fish and shellfish. Performance comparison against electron-capture detection and high-resolution mass spectrometry detection

Optimization of the Varian Saturn 2200 ion-trap tandem mass spectrometry (IT-MS/MS) system and comparison of its data quality with two other detection methods [electron-capture detection (ECD) and high-resolution mass spectrometry (HRMS)] was pursued by measuring polychlorinated biphenyls (PCBs) levels in fish and shellfish samples. IT-MS/MS methodology provided limits of detection (LOD) comparable to those obtained by ECD but superior specificity for the detection of a selected number of 39 PCB native congeners and 9 (13)C-labelled PCB standards. The method detection limits (MDLs) established for IT-MS/MS ranged between 1.0 and 5.0 pg/g on a wet weight basis while those obtained by ECD and HRMS were 1.0-4.0 pg/g and 0.1-2.0 pg/g, respectively. Overall, the results obtained in the study demonstrate that gas chromatography (GC) combined with IT-MS/MS provide higher data quality than those achievable by GC-ECD. For this particular set of target analytes the specificity achievable with IT-MS/MS was comparable to that obtained by HRMS and both techniques provided comparable data in terms of accuracy and precision.     

Optimization and application of high-resolution gas chromatography with ion trap tandem mass spectrometry to the determination of polychlorinated biphenyls in atmospheric aerosols

Optimization of the Finnigan GCQ ion trap mass spectrometry (ITMS) system and a clean-up procedure were carried out in order to apply high-resolution gas chromatography-tandem mass spectrometry for the analysis of polychlorinated biphenyls (PCBs) in aerosols. Six ITMS operating parameters, including isolation time, excitation voltage, excitation time, "q" value, ion source temperature and electron energy were adjusted in order to optimize the instrument analytical performance. The adjustment of all parameters substantially increased the sensitivity of ITMS in the MS-MS mode. Changes in isolation time did not particularly affect ITMS sensitivity while ion source temperature had the strongest influence. After optimization, a limit of detection of 600 fg/microl with S/N varying from 8 up to 91 was achieved. The application of the optimized ITMS parameters conjointly with the developed clean-up procedure resulted in method detection limits of 10-20 fg/m3 for the determination of PCBs, in the particulate and gas phase of the atmospheric aerosol of background areas in the Eastern Mediterranean and Sweden.     

Quantitative determination of nitroglycerin in human plasma by capillary gas chromatography with electron-capture detection

A sensitive method for the selective determination of nitroglycerin at concentrations down to 50 pg/ml in human plasma is described. After the addition to plasma of a known amount of butane-1,2,4-triol trinitrate as internal standard, both compounds are extracted into hexane. Nitroglycerin is then quantitated by capillary gas chromatography with electron-capture detection.     

Determination of polychlorinated biphenyls and organochlorine pesticides in human serum by gas chromatography with micro-electron capture detector

A method for determination of concentrations of polychlorinated biphenyl congeners (PCB-28, 52, 101, 118, 138, 153, 156, and 187) and organochlorine pesticides (hexachlorobenzene, alpha-hexachlorocyclohexane, beta-hexachlorocyclohexane, gamma-hexachlorocyclohexane, delta-hexachlorocyclohexane, p,p'-dichlorodiphenyl dichloroethylene, o,p'-dichlorodiphenyl trichloroethane, p,p'-dichlorodiphenyl dichloroethane, p,p'-dichlorodiphenyl trichloroethane, alpha-chlordane, gamma-chlordane, heptachlor, heptachlor epoxide, and aldrin) in human serum is developed. Recovery is assessed with artificial serum, in which PCBs and OCPs could not be detected. The method is then confirmed with pooled human serum. Experiments are performed by adding two concentrations of analytes (0.5 μg/L and 1.0 μg/L) to both matrices. The sample pretreatment process involves denaturing with a mixture of water-1-propanol (v:v, 85:15), extraction with a C-18 cartridge, and cleanup with an Alumina B cartridge. This process required about 2 mL of serum. The limit of detection ranged from 0.05-0.35 μg/L for all the analytes. Recovery of analytes at low and high spiking concentrations varied from 63-122% and 61-124% for artificial serum and pooled human serum, respectively. Relative standard deviation was lower than 16% and 18% for artificial serum and pooled human serum, respectively. Stability of the method, expressed as relative standard deviation, was lower than 14%. The method has been applied in epidemiological research.     

Feasibility of gas chromatography--ion trap tandem mass spectrometry for the determination of polychlorinated biphenyls in food

The different parameters affecting the ionisation and fragmentation of selected polychlorinated biphenyls (PCBs) in an IT detector working in the MS/MS mode, ITD(MS/MS), have been optimised for maximum selectivity and sensibility. The low LODs (in the range 0.03-0.3 microg/L), the satisfactory repeatability (RSDs in general below 11%) and reproducibility (RSDs below 17%) obtained when analysing standard solutions ensured proper determination of the PCBs studied at the concentrations typically found in food samples. Foodstuffs naturally contaminated with varying levels of PCBs have been analysed using the optimised GC-ITD(MS/MS) method. The results obtained compared favourably with those found using more conventional detectors, such as (micro-)electron capture detection (for ortho-PCBs) and high-resolution MS (for non-ortho-PCBs), as well as with the consensus PCB levels established for these particular samples via an international interlaboratory exercise. The relative merits of these three detectors have been discussed.     

Dechlorination of polychlorinated biphenyls in electron-capture negative-ion chemical ionization mass spectrometry

The electron-capture negative-ion chemical Ionization mass spectra of 36 ³⁵Cl mono- and di-labelled penta- and hexachlorobiphenyls were studied. Under the conditions of the analyses, the dechlorination of these congeners probably proceeds through electrophilic hydrogen atom attachment followed by rapid loss of the chlorine atom at the same position. These dechlorination reactions occur regioselectively. When present, ortho-chlorines are lost preferentially to meta- and para-chlorines. The extent of the dechlorination reaction, as seen by the relative abundance of the [MH ? Cl]^? ions, decreases with increasing number of ortho-chlorines.     

Trace determination of alpha- and beta-endosulfan and three metabolites in human serum by gas chromatography electron capture detection and gas chromatography tandem mass spectrometry

Endosufan, alpha and beta, and three conversion products, sulphate, ether and lactone, were simultaneously determined in human serum by means of an analytical procedure which combines extraction with organic solvents, clean-up with H(2)SO(4) and by liquid column chromatography, and detection by gas chromatography (GC) using electron capture detection (ECD) and tandem mass spectrometry (MS/MS). The procedure was validated and the values of some merit figures, such as linear range, detection and quantitation limits, accuracy, precision and recovery, obtained with the GC/ECD and the GC/MS/MS methods, were compared. The lower limits of detection in GC/ECD and GC/MS/MS were 0.03 and 0.05 microg I(-1), respectively. The recovery of the pesticides at the 20 microg I(-1) concentration level was 60-65%, with the exception of endosufan alpha. Recovery studies at higher levels (100 and 200 microg I(-1)) were independent of pesticide concentration in serum samples. The application of the proposed analytical methodology to the determination of endosulfans and their metabolites in real samples was tested by analyzing serum samples from a population living in agricultural areas of Almeria (Spain). The results show the advantage of MS/MS over the ECD detector in the analysis of serum samples where matrix interferences can be confused with target pesticides.     

Estimation of measurement uncertainty of pesticides,polychlorinated biphenyls and polyaromatic hydrocarbons in sediments by using gas chromatography–mass spectrometry

The evaluation of the uncertainty associated to analytical methods is essential in order to demonstrate quality of a result. However, there is often lack of information about uncertainty of methods to estimate persistent organic pollutants concentration in complex matrix. Current work has thoroughly evaluated uncertainty associated to quantification of several organochloride pesticides, PCBs and PAHs in sediments. A discussion of the main contributions to the overall uncertainty is reported, allowing authors to establish the accuracy of results and plan future improvements. Combined uncertainties ranged between 5–9% (pesticides), 4–7% (PCBs) and 5–10% (PAHs), being uncertainty derived of calibration the main contribution. Also, the analytical procedure was validated analysing a standard reference material (IAEA-408).     

Determination of polychlorinated biphenyls in ambient air by gas chromatography coupled to triple quadrupole tandem mass spectrometry

A multiresidue method for determining 22 polychlorinated biphenyls (PCBs) in air has been developed and validated by gas chromatography (GC) coupled to tandem mass spectrometry (MS/MS) using a triple quadrupole analyzer (QqQ). The method was validated in terms of both steps of sampling and analysis. The sampling method, which is based on active sampling using polyurethane foam (PUF) as adsorbent, was validated by generating standard atmospheres. The retention capacity of this sampling sorbent allows up to 5 m³ of air to be sampled without any breakthrough for most compounds. Two solvent extraction methods were compared: sonication and Soxhlet extraction with a mixture of n-hexane:diethyl ether (95:5 v/v). Both extraction methods yielded similar results, but the first one required less solvent and time. The method exhibited good accuracy (80.3–99.8%), precision (2.2–15.2%) and lower limits that allowed quantification and confirmation at levels as low as 0.008 ng/m³. Finally, the method was applied to the analysis of PCBs in the air in areas near to a municipal solid-waste landfill and directly above the refuse in the landfill, where it indicatedd the presence of some of the target compounds. Figure General chemical structure of polychlorinated biphenyls     

Broad-spectrum determination of pesticides in groundwater by gas chromatography with electron capture detection, nitrogen-phosphorus detection, and tandem mass spectrometry.

Gas chromatography with electron capture detector (ECD), nitrogen-phosphorus detector (NPD), and tandem mass spectrometry (MS/MS) was used to identify 36 pesticides, widely used to control various pest and diseases in vegetables, in water after a preconcentration step on C18 cartridges. The recoveries obtained ranged from 70 to 135% at a fortification level of 100 ng/L with relative standard deviations of <36.2%. The limits of detection and quantitation were < or =48 and < or =160 ng/L, respectively. Important advantages of MS/MS over ECD and NPD in the determination of pesticides are also presented. The proposed analytical methodology was applied to the determination of pesticides in groundwater samples from an agricultural area, the Campo de Dalías (Almería, Spain). The most frequently encountered pesticides were endosulfan sulfate and metalaxyl, whereas the pesticide found at the highest concentration was fenamiphos.     

Multiresidue determination of pesticides in fruit and vegetables by gas chromatography/tandem mass spectrometry

Pesticide residues in fruit and vegetables were determined by gas chromatography/tandem mass spectrometry (GC/MS/MS). Electron impact (EI)/MS/MS and chemical ionization (CI)/MS/MS were developed for 80 compounds, including organochlorine, organophosphorus, organonitrogen, and pyrethroids, providing unambiguous spectral confirmation for these complex matrixes. Residues were extracted from samples with acetone followed by a mixture of dichloromethane-petroleum ether. Two injections per sample were required for analysis of the entire pesticide list by EI/MS/MS and CI/MS/MS. Initial steps involving cleanup and concentration of extracts were eliminated. The excellent selectivity and good linearity allowed quantification and identification of low levels of pesticides in the most difficult matrixes. The method has been used for routine analysis of many vegetables.     

Comparison of gas chromatography-ion-trap tandem mass spectrometry systems for the determination of polychlorinated dibenzo-p-dioxins, dibenzofurans and dioxin-like polychlorinated biphenyls

Two gas chromatography-mass spectrometry systems equipped with an ion-trap mass analyzer working in tandem mode (GC-MS-MS) were evaluated for the determination of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (PCBs) in food samples. The performance of the two ion-trap instruments, which dispose of an external ion source (ThermoFinnigan GCQ/Polaris) and internal ionization (Varian Saturn 2,200), have been compared in terms of linearity, repeatability, limit of detection and long-term precision. Both instruments provided similar run-to-run and day-to-day precisions, ranging from 2% to 8% and between 2% and 13%, and instrumental limits of detection between 0.09 and 0.36 pg injected for PCDD/Fs and from 0.03 to 0.09 pg injected for dioxin-like PCBs. Although both instruments seem to be suitable for food analysis, only the use of external ionization allowed to achieve reliable results for PCDD/F determination at concentrations close to the maximum residue levels established by the EU for foods. Internal ionization provides high limits of detection (from 10- to 30-fold higher) and worse precision (RSD, 14-43%). In contrast, for dioxin-like PCBs both instruments allowed to obtain excellent results with precisions lower than 15%.     

Multi-residue determination of pesticides in tropical fruits using liquid chromatography/tandem mass spectrometry

Monitoring pesticide residues in tropical fruits is of great interest for many countries, e.g., from South America, that base an important part of their economy on the exportation of these products. In this work, a LC-MS/MS multi-residue method using a triple quadrupole analyzer has been developed for around 30 pesticides in seven Colombian tropical fruits of high commercial value for domestic and international markets (uchuva, tamarillo, granadilla, gulupa, maracuya, papaya, and pithaya). After sample extraction with acetonitrile, an aliquot of the extract was diluted with water and directly injected into the HPLC-MS/MS system (electrospray interface) without any cleanup step. The formation of sodium adducts—of poor fragmentation—was minimized using 0.1% formic acid in the mobile phase, which favored the formation of the protonated molecule. However, the addition of ammonium acetate made the formation of the ammonium adducts in some particular cases possible, avoiding the presence of the sodium adducts. The highest sensitivity was observed in positive electrospray ionization for the wide majority of pesticides, with a few exceptions for acidic compounds that gave better response in the negative mode (e.g., 2,4-D, fluazinan). Thus, simultaneous acquisition on the positive/negative mode was applied. Two MS/MS transitions were acquired for each compound to ensure a reliable quantification and identification of the compounds detected in samples, although for malathion a third transition was acquired due to the presence of interfering isobaric compounds in the sample extracts. A detailed study of matrix effects was made by a comparison of standards in solvent and in matrix. Both ionization suppression and ionization enhancement were observed depending on the analyte/matrix combination tested. Correction of matrix effects was made by the application of calibration in matrix. Three matrices were selected (uchuva, maracuya, gulupa) to perform matrix calibration in the analysis of all seven fruit varieties studied. The method was validated by recovery experiments in samples spiked at two levels (0.05 and 0.5 mg/kg). The data were satisfactory for the wide majority of analyte/matrix combinations, with most recoveries between 70% and 110% and the RSD below 15%. Several samples collected from the market were finally analyzed. Positive findings were confirmed by evaluating the experimental Q/q ratios and retention times, and comparing them with those of reference standards.     

Multiresidue determination of pesticides in honey by matrix solid-phase dispersion and gas chromatography with electron-capture detection

A multiresidue method was developed for the determination of 15 pesticides (organochlorines, organophosphorus compounds, pyrethroids, and other acaricides) in various commercial honeys (eucalyptus, lavender, orange, rosemary, and multifloral). The analytical procedure is based on the matrix solid-phase dispersion of honey in a mixture of Florisil and anhydrous sodium sulfate; the mixture is placed in small plastic columns and extracted with hexane-ethyl acetate (90 + 10, v/v). The pesticide residues are determined by capillary gas chromatography with electron-capture detection. Recoveries with the method at concentrations between 0.15 and 1.5 microg/g ranged from 80 to 113%, and relative standard deviations were <10% for all the pesticides studied. The pesticide detection limits were within the range 0.5-5 microg/kg for organochlorines, around 3 microg/kg for the chlorinated organophosphorus pesticides studied, near 15 microg/kg for fluvalinate, and about 3 microg/kg for the other pyrethroids.     

Pesticide trace analysis using solid-phase extraction and gas chromatography with electron-capture and tandem mass spectrometric detection in water samples

Gas chromatography (GC) with electron-capture detection (ECD), mass spectrometry (MS) and tandem mass spectrometry (MS-MS) were employed for the identification of 12 pesticides in water samples. For this purpose, a solid-phase extraction procedure with C18 cartridges was used, optimising the breakthrough volume and the saturation concentration. In GC-MS-MS, the lowest detectable concentrations for the pesticides were between 2 and 26 ng l(-1), recoveries ranged from 70 to 133% in water samples spiked at 100 ng l(-1) and the relative standard deviations were in the range 5.3 to 17.4%. The proposed analytical methodology was applied to analyse pesticides in wetland samples from Almería (Spain).     

Separation of seventeen 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins and dibenzofurans and 12 dioxin-like polychlorinated biphenyls by comprehensive two-dimensional gas chromatography with electron-capture detection

Comprehensive two-dimensional gas chromatography (GC x GC) with electron-capture detection (ECD) has been optimized for the separation of seventeen 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins and dibenzofurans and 12 dioxin-like polychlorinated biphenyls, with emphasis on the selection of the first- and second-dimension, commercially available, columns. When eight second-dimension columns were subsequently combined with a 100% methylpolysiloxane stationary phase (DB-1) in the first dimension to create orthogonal conditions, a complete separation of all congeners with different TEF values was obtained with two column combinations, DB-1 x VF-23 and DB-1 x LC-50. When other types of first-dimension columns were used (and orthogonality was partly sacrificed), a DB-XLB column combined with 007-65HT, VF-23 and LC-50 was found to provide a complete separation of all 29 priority congeners. Next, the potential of these three column combinations for real-life analysis was preliminarily studied. With a spiked and fractionated milk extract, DB-XLB x LC-50 was found to be the most powerful column combination, because of the good separation of the 29 priority congeners from each other as well as from the matrix constituents. Quantitative performance (close to three-order linearity; LODs, 30-150 fg injected; R.S.D.s, 1.5-6.5% (n = 10)) was satisfactory.