Multiresidue Determination and Confirmation of Imidazolinone Herbicides in Soil by High-Performance Liquid Chromatography/Electrospray Ionization Mass Spectrometry

A new multiresidue method was developed to determine 6 imidazolinone herbicides in 5 different soil types, using high-performance liquid chromatography/electrospray ionization mass spectrometry (HPLC/ESMS). Good recoveries and sensitivity were obtained for the compounds investigated at the 2.0 ppb limit of quantitation. A 50 g portion of soil was extracted with 0.5N NaOH. A portion of the extract was acidified to precipitate humic acids, and the supernatant was loaded onto a preconditioned tC-18 solid-phase extraction (SPE) cartridge and eluted with ethyl acetate. Further cleanup was achieved by using a tandem strong-anion-ex- change SPE/strong-cation-exchange (SCX) SPE. Analytes were eluted from the SCX SPE with saturated KCI in methanol. After cleanup, the sample was desalted with an RP-102 SPE cartridge. Quantitation was achieved by monitoring the [M + H]+ ions for each compound, with a time-scheduled selective-ion-monitoring program (positive mode). The extraction and cleanup procedure produced a purified extract for MS confirmation using 3 ions with “in-source” collision-induced dissociation.

Determination of Sulfonylurea Herbicides in Grains by Capillary Electrophoresis

A capillary electrophoresis (CE) method was developed to separate and determine residues of 5 sulfonylurea herbicides in grains (wheat, barley, and corn). This work demonstrated the practicality of using CE for residue analysis of sulfonylureas. The method yielded good recoveries and adequate sensitivities at tolerance levels (0.05–0.1 ppm). The compounds investigated were metsulfuron methyl (Ally), thifensulfuron methyl (Harmony), chlorsulfuron (Glean), rimsulfuron (DPX-E9636), and tribenuron methyl (Express). Acetonitrile extracts of grain samples were partitioned with hexane and then cleaned up with cation exchange solid-phase extraction cartridges. Quantitation was performed by micellar electrokinetic capillary chromatography using a high-sensitivity optical cell. Average recoveries at the 0.05 ppm level ranged from 72.9 to 118.5%. The lower limit of detection was approximately 0.02 ppm, except for rimsulfuron and tribenuron methyl, for which the lower limit of detection was 0.035 ppm. The method was less complicated and showed better sensitivity than current single-analyte liquid chromatographic enforcement methods.

Determination of 22 Triazole Compounds Including Parent Fungicides and Metabolites in Apples, Peaches, Flour, and Water by Liquid Chromatography/TandemMass Spectrometry

A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed for the determination of 14 parent triazole fungicides and 8 of their metabolites found in apples, peaches, flour, raw water, and tap water. The triazole fungicides chosen for this multiresidue method development project included propiconazole, fenbuconazole and its RH-9129 and RH-9130 metabolites, cyproconazole, difenoconazole, tebuconazole and its HWG 2061 metabolite, hexaconazole, bromuconazole (both stereoisomers), epoxiconazole, tetraconazole, triticonazole and its RPA-404886 and RPA-406341 metabolites, triadimefon, triadimenol, and myclobutanil. Of special concern to the U.S. Environmental Protection Agency were the metabolites common to all triazole fungicides: free triazole, 1,2,4-triazole (T), and its 2 conjugates: triazolylalanine (TA) and triazolylacetic acid (TAA). These metabolites were the primary focus of this project. All samples we cleaned up by a combination of C18 solid-phase extraction (SPE), mixed-mode cationic SPE, and mixed-mode anionic SPE columns. A triple-stage quadrupole mass spectrometer, equipped with electrospray ionization in the positive-ion mode, was used to determine the compounds of interest. T, TA, and TAA were quantitated using isotopically labeled internal standards (IS), in which the 1,2,4-triazole ring had been synthesized by using 13C and 15N (IS_T, IS_TA, and IS_TAA). These isotopically labeled internal standards were necessary to correct for matrix effects. The T, TA, and TAA metabolites were quantitated at the 25–50 parts-per-billion (ppb) level in food commodities and at 0.50 ppb in water. Recoveries were 70–101% from apples, 60–121% from peaches, 57–118% from flour, 75–99% from raw water, and 79–99% from tap water.

Perspective on Advancing FDA Regulatory Monitoring for Mycotoxins in Foods using Liquid Chromatography and Mass Spectrometry (Review)

The presence of mycotoxins (such as aflatoxins, deoxynivalenol, fumonisins, and patulin) is routinely monitored by the U.S. Food and Drug Administration (FDA) to ensure that their concentrations in food are below the levels requiring regulatory action or advisories. To improve the efficiency of mycotoxin analysis, the researchers at the FDA's Center for Food Safety and Applied Nutrition have been evaluating modern LC-MS technologies. Consequently, a variety of LC-tandem MS and LC-high-resolution MS methods have been developed, which simultaneously identify and quantitate multiple mycotoxins in foods and feeds. Although matrix effects (matrix-induced ion suppression or enhancement) associated with LC-MS-based mycotoxin analysis remain, this review discusses methods for managing these effects and proposes practical solutions for the future implementation of LC-MS-based multimycotoxin analysis.

Effect of sample dilution on matrix effects in pesticide analysis of several matrices by liquid chromatography-high-resolution mass spectrometry

This study used two LC columns of different adsorbents and liquid chromatography-electrospray ionization-high-resolution mass spectrometry to study the relationship between matrix effects (ME), the LC separations, and elution patterns of pesticides and those of matrix components. Using calibration standards of 381 pesticides at three dilution levels of 1×, 1/10×, and 1/100×, 108 samples were prepared in solvent and five different sample matrices for the study. Results obtained from principal component analysis and slope ratios of calibration curves provided measurements of the ME and showed the 1/100× sample dilution could minimize suppression ME for most pesticides analyzed. Should a pesticide coeluting with matrix components have a peak intensity of 25 times or higher, the suppression for that pesticide would persist even at 1/100× dilution. The number of pesticides had enhancement ME increased with increasing dilution from 1× to 1/100×, with those early eluting, hydrophilic pesticides affected the most.

Sesquiterpenoid tropolone glycosides from Liriosma ovata

Two new sesquiterpenoid tropolone glycosides, liriosmasides A (1) and B (2), along with two known compounds, secoxyloganin and oplopanpheside C, were isolated from a methanol extract of the roots of Liriosma ovata. The structures of 1 and 2 were elucidated by spectroscopic methods including 1D and 2D NMR and by high-resolution mass spectrometry involving an ultra-high-performance liquid chromatography-quadrupole-orbital ion trap mass spectrometric (UHPLC-Q-Orbitrap MS) method. Compound 1 showed weak inhibitory activity against HIV RNase H.

Determining mycotoxins in baby foods and animal feeds using stable isotope dilution and liquid chromatography tandem mass spectrometry

We developed a stable isotope dilution assay with liquid chromatography tandem mass spectrometry (LC-MS/MS) to determine multiple mycotoxins in baby foods and animal feeds. Samples were fortified with [(13)C]-uniformly labeled mycotoxins as internal standards ([(13)C]-IS) and prepared by solvent extraction (50% acetonitrile in water) and filtration, followed by LC-MS/MS analysis. Mycotoxins in each sample were quantitated with the corresponding [(13)C]-IS. In general, recoveries of aflatoxins (2-100 ng/g), deoxynivalenol, fumonisins (50-2000 ng/g), ochratoxin A (20-1000 ng/kg), T-2 toxin, and zearalenone (40-2000 ng/g) in tested matrices (grain/rice/oatmeal-based formula, animal feed, dry cat/dog food) ranged from 70 to 120% with relative standard deviations (RSDs) <20%. The method provides sufficient selectivity, sensitivity, accuracy, and reproducibility to screen for aflatoxins at ng/g concentrations and deoxynivalenol and fumonisins at low μg/g concentrations in baby foods and animal feeds, without using conventional standard addition or matrix-matched calibration standards to correct for matrix effects.

Determination of multiple mycotoxins in dietary supplements containing green coffee bean extracts using ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS)

An ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method for the determination of 34 mycotoxins in dietary supplements containing green coffee bean (GCB) extracts was developed, evaluated, and used in the analysis of 50 commercial products. A QuEChERS-like procedure was used for isolation of target analytes from the examined matrices. Average recoveries of the analytes were in the range of 75-110%. The precision of the method expressed as relative standard deviation was below 12%. Limits of detection (LODs) and limits of quantitation (LOQs) ranged from 1.0 to 50.0 μg/kg and from 2.5 to 100 μg/kg, respectively. Due to matrix effects, the method of standard additions was used to ensure accurate quantitation. Ochratoxin A, ochratoxin B, fumonisin B1 and mycophenolic acid were found in 36%, 32%, 10%, and 16% of tested products, respectively. Mycotoxins occurred in the following concentration ranges: ochratoxin A, <1.0-136.9 μg/kg; ochratoxin B, <1.0-20.2 μg/kg; fumonisin B1, <50.0-415.0 μg/kg; mycophenolic acid, <5.0-395.0 μg/kg. High-resolution mass spectrometry operated in full MS and MS/MS mode was used to confirm the identities of the reported compounds.

Simultaneous analysis of steviol and steviol glycosides by liquid chromatography with ultraviolet detection on a mixed-mode column: application to Stevia plant material and Stevia-containing dietary supplements

Simultaneous separation of steviol and steviol glycosides is challenging because of differences in their polarity and chemical structure. In this study, simultaneous analysis of steviol and steviol glycosides was achieved by LC with UV detection using a mixed-mode RP weak anion exchange chromatography column. Steviol and seven steviol glycosides were analyzed on an Acclaim Mixed-Mode Wax-1 (Dionex) column with a linear gradient of deionized water adjusted to pH 3.00 with phosphoric acid and acetonitrile. The extraction was performed by sonicating dry plant material at 40 degreesC in acetonitrile-water (30 + 70, v/v). LOQ values (mg/g dry weight of plant material) were rebaudioside B, 0.50; steviol, 0.70, dulcoside A, 1.0; steviolbioside, 1.2; stevioside and rebaudioside C, 2.0; rebaudioside D, 3.3; and rebaudioside A, 5.0. The method demonstrated suitable performance for all analytes tested with respect to accuracy (mean recoveries 95-99%), intraday and interday precision for retention times (0.070-0.28% and 0.33-1.0% RSD, respectively), and linearity. The method was used to authenticate steviol glycosides in several samples of Stevia plant material as well as to quantitate steviol glycosides in dietary supplements containing Stevia.

Quantitative determination of cucurbitane-type triterpenes and triterpene glycosides in dietary supplements containing bitter melon (Momordica charantia) by HPLC-MS/MS

Momordica charantia L. (Cucurbitaceae), commonly known as bitter melon, is widely cultivated in many tropical and subtropical areas of the world. It is a common food staple; its fruits, leaves, seeds, stems, and roots also have a long history of use in traditional medicine. In the United States, dietary supplements labeled as containing bitter melon can be purchased over-the-counter and from Internet suppliers. Currently, no quantitative analytical method is available for monitoring the content of cucurbitane-type triterpenes and triterpene glycosides, the major constituents of bitter melon, in such supplements. We investigated the use of HPLC-electrospray ionization (ESI)-MS/MS for the quantitative determination of such compounds in dietary supplements containing bitter melon. Values for each compound obtained from external calibration were compared with those obtained from the method of standard additions to address matrix effects associated with ESI. In addition, the cucurbitane-type triterpene and triterpene glycoside contents of two dietary supplements determined by the HPLC-ESI-MS/MS method with standard additions were compared with those measured by an HPLC method with evaporative light scattering detection, which was recently developed for quantification of such compounds in dried fruits of M. charantia. The contents of five cucurbitane-type triterpenes and triterpene glycosides in 10 dietary supplements were measured using the HPLC-ESI-MS/MS method with standard additions. The total contents of the five compounds ranged from 17 to 3464 microg/serving.

Multiresidue pesticide analysis of agricultural commodities using acetonitrile salt-out extraction, dispersive solid-phase sample clean-up, and high-performance liquid chromatography-tandem mass spectrometry

A multiresidue method analyzing 209 pesticides in 24 agricultural commodities has been developed and validated using the original Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) procedure and high performance liquid chromatography-positive electrospray ionization-tandem mass spectrometry (LC-MS/MS) analysis. Using solvent-only calibration standards (SOCSs) and matrix-matched calibration standards (MMCSs), it was demonstrated that a minimal concentration of 5-10 μg/kg (part per billion, ppb) of analytes in matrix is required for the consistent identification of targeted pesticides with two MRM transitions. Method performance was validated by the precision and accuracy results obtained from fortification studies at 10, 25, 100, and 500 ppb and MMCSs. The method was demonstrated to achieve an average recovery of 100 ± 20% (n = 4) for >75% of evaluated pesticides at the low fortification level (10 ppb) and improved to >84% at the higher fortification concentrations in all 24 matrices. Matrix effects in LC-MS/MS analysis were studied by evaluating the slope ratios of calibration curves (1.0-100 ng/mL) obtained from the SOCSs and MMCSs. Principal component analysis (PCA) of LC-MS/MS and method validation data confirmed that each matrix exerts its specific effect during the sample preparation and LC-MS/MS analysis. The matrix effect is primarily dependent on the matrix type, pesticide type and concentration. Some caution is warranted when using matrix matched calibration curves for the quantitation of pesticides to alleviate concerns on matrix effects. The QuEChERS method with LC-MS/MS was used to identify and quantitate pesticides residues, with concentrations ranging from 2.5 to >1000 ppb in a variety of agricultural samples, demonstrating fitness for screening and surveillance applications.

Rapid determination of para-phenylenediamine by gas chromatography-mass spectrometry with selected ion monitoring in henna-containing cosmetic products

A rapid method for the determination of para-phenylenediamine (PPD) in cosmetic products, such as henna tattoos has been developed and evaluated. This analytical procedure involved extracting a 10mg test portion of cosmetic product in 10 mL of ethyl acetate, followed by determination by gas chromatography-mass spectrometry in the selected ion monitoring mode (GC/MS-SIM). 1,4-Phenylenediamine-2,3,5,6-d(4) was selected as an internal standard that was added at the beginning of the extraction procedure and used to correct for recovery and matrix effects. The linearity ranged from 1.0 to 1275 μg/mL with a coefficient of determination (r(2)) greater than 0.999. LOQ and LOD were 1.0 and 0.10 μg/mL, respectively. The recovery in a tattoo product containing PPD was 94% and that for a tattoo product containing no PPD reached 105%. Extraction efficiency of 98% was obtained. This method has been successfully applied to henna temporary tattoo and other henna-related cosmetic products for the determination and quantitation of PPD.

Cucurbitane-type triterpenoids from Momordica charantia

One new cucurbitane-type triterpenoid glycoside, momordicoside U (1), together with five known cucurbitane-type triterpenoids and related glycosides, 3β,7 β,25-trihydroxycucurbita-5,23 (E)-dien-19-al (2), momordicine I (3), momordicine II (4), 3-hydroxycucurbita-5,24-dien-19-al-7,23-di-O-β-glucopyranoside (5), and kuguaglycoside G (6), were isolated from the whole plant of Momordica charantia. Their structures were determined by chemical and spectroscopic methods. Momordicoside U (1) was evaluated for insulin secretion activity in an in vitro insulin secretion assay and displayed moderate activity.

Multiresidue pesticide analysis of ginseng powders using acetonitrile- or acetone-based extraction, solid-phase extraction cleanup, and gas chromatography-mass spectrometry/selective ion monitoring (GC-MS/SIM) or -tandem mass spectrometry (GC-MS/MS)

A multiresidue method for the analysis of 168 pesticides in dried powdered ginseng has been developed using acetonitrile or acetone mixture (acetone/cyclohexane/ethyl acetate, 2:1:1 v/v/v) extraction, solid-phase extraction (SPE) cleanup with octyl-bonded silica (C(8)), graphitized carbon black/primary-secondary amine (GCB/PSA) sorbents and toluene, and capillary gas chromatography-mass spectrometry/selective ion monitoring (GC-MS/SIM) or -tandem mass spectrometry (GC-MS/MS). The geometric mean limits of quantitation (LOQs) were 53 and 6 microg/kg for the acetonitrile extraction and 48 and 7 microg/kg for the acetone-based extraction for GC-MS/SIM and GC-MS/MS, respectively. Mean percent recoveries and standard deviations from the ginseng fortified at 25, 100, and 500 microg/kg using GC-MS/SIM were 87 +/- 10, 88 +/- 8, and 86 +/- 10% from acetonitrile extracts and 88 +/- 13, 88 +/- 12, and 88 +/- 14% from acetone mixture extracts, respectively. The mean percent recoveries from the ginseng at the 25, 100, and 500 microg/kg levels using GC-MS/MS were 83 +/- 19, 90 +/- 13, and 89 +/- 11% from acetonitrile extracts and 98 +/- 20, 91 +/- 13, and 88 +/- 14% from acetone extracts, respectively. Twelve dried ginseng products were found to contain one or more of the following pesticides and their metabolites: BHCs (benzene hexachlorides, alpha-, beta-, gamma-, and delta-), chlorothalonil, chlorpyrifos, DDT (dichlorodiphenyl trichloroethane), dacthal, diazinon, iprodione, quintozene, and procymidone ranging from <1 to >4000 microg/kg. No significant differences were found between the two extraction solvents, and GC-MS/MS was found to be more specific and sensitive than GC-MS/SIM. The procedures described were shown to be effective in screening, identifying, confirming, and quantitating pesticides in commercial ginseng products.

Multiresidue pesticide analysis in fresh produce by capillary gas chromatography-mass spectrometry/selective ion monitoring (GC-MS/SIM) and -tandem mass spectrometry (GC-MS/MS)

A multiresidue method for the analysis of pesticides in fresh produce has been developed using salt-out acetonitrile extraction, solid-phase dispersive cleanup with octadecyl-bonded silica (C(18)), and graphitized carbon black/primary-secondary amine (GCB/PSA) sorbents and toluene, followed by capillary gas chromatography-mass spectrometry in selected ion monitoring mode (GC-MS/SIM) or -tandem mass spectrometry (GC-MS/MS). Quantitation was determined from calibration curves using matrix-matched standards ranging from 3.3 to 6667 ng/mL with r(2) > 0.99, and geometric mean limits of quantitation were typically 8.4 and 3.4 microg/kg for GC-MS/SIM and GC-MS/MS, respectively. Identification was determined by using target and qualifier ions and qualifier-to-target ratios for GC-MS/SIM and two ion transitions for GC-MS/MS. Fortification studies (10, 25, 100, and 500 microg/kg) were performed on 167 organohalogen, organophosphorus, and pyrethroid pesticides in 10 different commodities (apple, broccoli, carrot, onion, orange, pea, peach, potato, spinach, and tomato). The mean percent recoveries were 90 +/- 14, 87 +/- 14, 89 +/- 14, and 92 +/- 14% for GC-MS/SIM and 95 +/- 22, 93 +/- 14, 93 +/- 13, and 97 +/- 13% for GC-MS/MS at 10, 25, 100, and 500 microg/kg, respectively. GC-MS/MS was shown to be more effective than GC-MS/SIM due to its specificity and sensitivity in detecting pesticides in fresh produce samples. The method, based on concepts from the multiresidue procedure used by the Canadian Food Inspection Agency and QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe), was shown to be efficient in screening, identifying, and quantitating pesticides in fresh produce samples.

Emerging pesticide residue issues and analytical approaches

The 46th Annual Florida Pesticide Residue Workshop of 2009 (FPRW 2009) held in St. Pete Beach, FL, is the latest in an annual tradition drawing scientists from U.S. federal and state government laboratories, industry, and other laboratories worldwide. In 2009, selected FPRW presenters were invited to contribute to this special issue of the Journal of Agricultural and Food Chemistry with a section devoted to emerging pesticide residue issues and analytical approaches. What follows is the written record of what should become a scientific conversation launched at FPRW 2009. There are two distinct approaches to organic residue analysis: instrumental methods and assays. In much of the world, scientists primarily rely on laboratories equipped with instrumentation for analysis, usually gas chromatography and liquid chromatography with some type of selective detector. In the discussion of instrumental approaches, the focus is on chromatography with mass spectrometry as a detection method. Approaches such as biomonitoring and assays fall outside the traditional instrumental method approach to residue analysis. Assays that do not require laboratory equipment are of greater interest for screening and are well-suited to field use. Regardless of the analytical method, the success of multiresidue analysis relies on the appropriate choice of sample preparation and cleanup methodologies. Many new sample preparation and cleanup approaches used for pesticide and other small molecule contaminant residue analyses in a variety of complex sample matrices are discussed in this special issue. The goal of these approaches is to reduce overall analysis time and solvent consumption without compromising the analytical results.

Multiresidue pesticide analysis of wines by dispersive solid-phase extraction and ultrahigh-performance liquid chromatography-tandem mass spectrometry

A multiresidue pesticide method is described for the determination of 72 pesticides in wines. Pesticides were extracted using acetonitrile saturated with magnesium sulfate and sodium chloride, followed by solid-phase dispersive cleanup using primary-secondary amine and graphitized carbon black sorbents. Analysis is performed by ultraperformance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-MS/MS). The limits of quantitation (LOQs) for most of the pesticides ranged from 0.3 to 3.3 μg/L with the exception of cyromazine, fenhexamid, and acibenzolar S-methyl (LOQ > 10 μg/L), and quantitation was determined from calibration curves of standards containing 5.0-2500 μg/L with r(2) > 0.99. Recovery studies were performed by fortifying wine samples with the pesticides to concentrations of 10, 100, and 1000 μg/L, resulting in recoveries of >80% for most of the pesticides. Lower (<70%) and higher (>120%) recoveries were most likely from complications of pesticide lability or volatility, matrix interference, or inefficient desorption from the solid-phase sorbents. The method was used to analyze 10 wines collected from a market basket survey, and 19 different pesticides, primarily fungicides, were present at concentrations ranging from <1.0 to 1000 μg/L.