Sequential Cleanup Research Articles

Multiresidue determination of pesticides in tea by gas chromatography-tandem mass spectrometry

An efficient and reliable GC-MS/MS method for the multiresidue determination of pesticides in tea was developed by modifying the Japanese official multiresidue method. Sample preparation was carefully optimized for the efficient removal of coextracted matrix components. The optimal sample preparation procedure involved swelling of the sample in water; extraction with acetonitrile; removal of water by salting-out; and sequential cleanup by ODS, graphitized carbon black/primary secondary amine (GCB/PSA) and silica gel cartridges prior to GC-MS/MS analysis. The recoveries of 162 pesticides from fortified (at 0.01 mg kg−1) green tea, oolong tea, black tea and matcha (powdered green tea) were mostly (95–98% of the tested pesticides) within the range of 70–120%, with relative standard deviations of <20%. Poor recovery of triazole pesticides was considered to be due to low recovery from the silica gel cartridges. The test solutions obtained by the modified method contained relatively small amounts of pigments, caffeine and other matrix components and were cleaner than those obtained by the original Japanese official multiresidue method. No interfering peaks were observed in the blank chromatograms, indicating the high selectivity of the modified method. The overall results suggest that the developed method is suitable for the quantitative analysis of GC-amenable pesticide residues in tea.

Simultaneous determination of acidic pesticides in vegetables and fruits by liquid chromatography—tandem mass spectrometry

A sensitive and efficient method has been developed for the simultaneous determination of 73 multi-class acidic pesticides, such as phenoxy acid and sulfonylurea herbicides, in vegetables and fruits. The sample preparation procedure was carefully optimized for the efficient removal of co-extracted matrix components. The method involves extraction of acidic pesticides with acetonitrile containing hydrochloric acid, removal of water from crude extract by salting out, and sequential cleanup by octadecylsilyl silica gel and silica gel columns. For samples containing high amounts of pigments, such as spinach, additional cleanup using a graphitized carbon column was performed prior to liquid chromatography–mass spectrometry (LC–MS/MS) analysis. Recovery tests were performed for five times for each sample of cabbage, spinach, potato, eggplant, orange, and apple fortified at 0.01 mg kg−1. Out of the 73 tested pesticides, 70 for cabbage, 67 for spinach, 69 for potato, 67 for eggplant, 64 for orange, and 70 for apple were within the range of 70–120%, with relative standard deviations below 25%. Nitenpyram and pyrasulfotole showed low recoveries for all the samples tested, probably due to low recoveries from silica gel column. The developed method effectively removed co-extracted matrix components and was highly selective, with no interfering peaks found in the chromatograms of blank samples. The overall results indicate that the developed method is suitable for the quantitative analysis of acidic pesticide residues in vegetables and fruits.

Simultaneous determination of polar pharmaceuticals and personal care products in biological organs and tissues

In the present study, a sensitive and accurate isotope dilution method was developed for the simultaneous determination of 17 polar pharmaceutical and personal care product (PPCP) residues (logKow=1.40–5.74), including 14 pharmaceuticals and 3 personal care products, in biological organs and tissues. The proposed method involved enzymatic hydrolysis, followed by sequential clean-up using silica gel chromatography and gel permeation chromatography, and analysis via ultra-high-performance liquid chromatography with tandem mass spectrometry. This method yielded acceptable absolute recoveries (48–88%) and internal standard-corrected recoveries (90–130%) for 17 PPCPs. Method detection limits were between 0.0092 and 3.2ngg−1 wet weight, and the limits of quantification were between 0.020 and 8.7ngg−1 wet weight. The method can be used to readily detect the target compounds at trace levels while minimizing the required sample volume. The developed method was applied to the determination of 17 PPCPs in the liver and kidney of 17 birds collected from Japan and also in the plasma, liver, and brain of 7 cyprinoid fish from an effluent-dominated stream in Japan. Triclosan was detected in 5 of 11 fish-eating birds but not in non-fish-eating birds, suggesting the contamination of prey fish by the chemical. Non-steroidal anti-inflammatory drugs, antibacterial agents, and psychotropic agents were frequently detected in the fish tissues. In addition, 7 of the target compounds were found in fish brain. The median brain/plasma ratios of the psychotropic agents ranged from 1.6 (carbamazepine) to 12 (diphenhydramine), indicating high transportability to fish brain.

Application and validation of a clean-up tandem assay column for screening ochratoxin A in cocoa powder

A rapid antibody-based assay for the detection of ochratoxin A in cocoa powder is described, involving sequential clean-up and visual detection of the toxin (“clean-up tandem assay column”). The screening test was developed to have a cut-off level of 2 µg kg−1 and was shown to have false positive and false negative rates of 10 and 2%, respectively. Analysis of six samples can be carried out in the field in approximately 30 min by untrained workers. Using the proposed rapid screening test, 10 retail cocoa powders were found to contain no detectable levels of ochratoxin A (<2 µg kg−1). These samples were also found to be negative (<2 µg kg−1) when analysed using an LC–MS/MS method.

Analysis of estrogens in sediment from a sewage‐impacted urban estuary using high‐performance liquid chromatography/time‐of‐flight mass spectrometry

We describe a highly selective and sensitive method for determination of estrone (E1) and beta-estradiol (E2) in sediments, using high-performance liquid chromatography/time-of-flight (HPLC-ToF) mass spectrometry. The method involved sequential cleanup of sediment extracts over solid phase extraction cartridges, normal phase HPLC, and immunoaffinity extraction, which combine to remove coeluting matrix interferences. Resulting method detection limits (0.03 and 0.04 ng/g for E1 and E2, respectively) are sufficient to determine E1 and E2 in estuarine sediments collected from sewage-impacted Jamaica Bay (New York, NY, USA). The ToF analyzer has a higher resolution (>6,000) than quadrupole mass analyzers and can provide accurate mass estimation to within 2 mDa, which helped in distinguishing steroids from isobaric matrix interferences. The E1 and E2 were internally mass calibrated with respect to their coeluting surrogate standards, and the mass measurement error was between 1.1 and 1.4 mDa. The levels of E1 and E2 ranged between 0.07 to 2.52 and 0.05 to 0.53 ng/g, respectively. The measured concentrations of steroids in sediments correlated closely with other wastewater tracers. Despite the low concentrations of sediment-associated estrogens, their predicted estrogenic potency exceeds that of other measured estrogenic contaminants.

Sample Preparation for Determination of Macrocyclic Lactone Mycotoxins in Fish Tissue, Based on On-Line Matrix Solid-Phase Dispersion and Solid-Phase Extraction Cleanup Followed by Liquid Chromatography/Tandem Mass Spectrometry

A new method based on matrix solid-phase dispersion (MSPD) on-line with a solid-phase extraction (SPE) cleanup process followed by liquid chromatography with tandem mass spectrometry (LC/MS/MS) is presented for the determination of 3 macrocyclic lactone mycotoxins in fish tissues: zearalenone, alpha-zearalenol, and beta-zearalenol. The sample was prepared in a device that used a reversed-phase material (C18) or a normal-phase material (neutral alumina) as a matrix dispersing agent, and a graphitized carbon black cartridge was used for sequential cleanup by SPE. LC/MS/MS was used for selective determination. Isocratic elution with acetonitrile-methanol-water was used for LC separation; for MS/MS, 2 types of interfaces (a pneumatically assisted electrospray ionization interface or an atmospheric pressure chemical ionization interface) were evaluated and compared in terms of the intensity of the total ion current produced by each analyte. The use of highly selective MSPD on-line with SPE for sample preparation before analysis allowed the removal of interfering matrix compounds present in tissue extracts that would otherwise cause severe ionization suppression of zearalenone and its metabolites during the ionization process. Average recoveries at 100 ng/g were between 83 and 103% with C18 and > or = 67% with neutral alumina; the relative standard deviations were < 11% with C18 and < 18% with alumina. The limits of detection ranged from 0.1 to 1.0 ng/g. Sample preparation is simple to perform, no special technical equipment is required, and solvent volumes are minimal.

Optimization of a matrix solid-phase dispersion method with sequential clean-up for the determination of alkylphenol ethoxylates in biological tissues

A modified Matrix Solid-Phase Dispersion (MSPD) method with sequential clean-up has been developed to isolate and purify alkylphenol ethoxylates (APEs) and alkylphenols in biological tissues. Elution profile, sequential clean-up adsorbent and experimental set up were optimized. Octadecylsilica was used as the solid-phase for matrix dispersion. Methanol was found to be the optimal eluting solvent for APEs. Aluminum oxide was quite efficient for removing the coeluting interferences. Quantitative analysis was done by reversed-phase HPLC with fluorescence detection. The optimized procedure was applied to analyze both fish and mussel samples. Average recoveries for all spiked tissue samples were greater than 90%. Typical limits of detection amount to tens of ppbs on a wet weight basis.

Experimental administration of 19-nortestosterone and dexamethasone in cattle: elimination of the two drugs in different biological matrices.

19-Nortestosterone (19-NT) is one of the mostly recurrent anabolic agents on the black market of illicit drugs. Dexamethasone (DEXA) is licensed for therapy in veterinary practice but its misuse, although often suspected, has seldom been demonstrated. The excretion of 19-NT and DEXA is well documented when the compounds are administered independently but poor information is available in literature for instances when both drugs are administered as a mixture. To evaluate a radioimmunoassay (RIA) for anabolic residues in urine, blood and faeces, the effect of the simultaneous administration and the subsequent elimination of the two drugs, two animals were injected (4 times) with 19-NT and another two (4 times) with 19-NT-DEXA. After preparation and a sequential clean-up on C18 and alumina columns, the samples were analysed by means of a specific 19-NT radioimmunoassay kit and an anti-DEXA antibody. Detection limits for both drugs were 0.5 ppb in blood samples and 2.0 ppb in urine and faecal samples. After the final treatment, positive 19-NT results were recorded at 14 and 21 d in urine and faecal samples, respectively. In the same matrices, positive DEXA values were found at 11 and 28 d, respectively. In the same matrices, positive DEXA values were found at 11 and 28 d, respectively. Urinary excretion was the main metabolic path both for 19-NT and DEXA; only 30% of the residues were excreted via the faeces. The simultaneous injection of DEXA and 19-NT increased the urinary excretion of 19-NT; however, the excretion of 19-NT via faecal matter was similar for both groups.