Benefits and pitfalls of the application of screening methods for the analysis of pesticide residues in fruits and vegetables.

The goal of this study was to expand knowledge on the performance of screening methods based on accurate mass measurements using a liquid chromatography electrospray quadrupole time-of-flight mass spectrometry (LC-ESI-QTOF-MS) system operating in full scan mode and with automatic identification based on the use accurate-mass databases. The study involved the analysis of 97 pesticides, in five matrices (tomato, pepper, zucchini, orange and leek) and at three concentration levels (20, 50 and 100 µg kg(-1)). Aspects concerning optimization of the search parameters, sensitivity, matrix effects, efficiency of the algorithm search, usefulness of fragment ions, etc., are evaluated in deep. Sensitivity requirements have been identified as the main obstacle affecting the automatic identification of pesticides, especially in complex matrices, where the ionization suppression reduces the detectability of analytes. In addition, we have detected some failures in the software used for automatic data processing in terms of analysis of isobaric compounds, use of isotopic clusters, spectral deconvolution and data processing speed that hamper the correct identification in some pesticide/matrix combinations. These drawbacks should be improved in the future for its effective implementation in routine residue analysis.

Evaluation of relevant time-of-flight-MS parameters used in HPLC/MS full-scan screening methods for pesticide residues.

An automatic screening method based on HPLC/time-of-flight (TOF)-MS (full scan) was used for the analysis of 103 non-European fruit and vegetable samples after extraction by the quick, easy, cheap, effective, rugged, and safe method. The screening method uses a database that includes 300 pesticides, their fragments, and isotopical signals (910 ions) that identified 210 pesticides in 78 positive samples, with the highest number of detection being nine pesticides/sample. The concentrations of 97 pesticides were <10 microg/kg, 53 were between 10 and 100 microg/kg, and 60 were at a concentration of >100 microg/kg. Several parameters of the automatic screening method were carefully studied to avoid false positives and negatives in the studied samples; these included peak filter (number of chromatographic peak counts) and search criteria (retention time and error window). These parameters were affected by differences in mass accuracy and sensitivity of the two HPLC/TOF-MS systems used with different resolution powers (15 000 and 7500), the capabilities of which for resolving the ions included in the database from the matrix ions were studied in four matrixes, viz., pepper, rice, garlic, and cauliflower. Both of these mass resolutions were found to be satisfactory to resolve interferences from the signals of interest in the studied matrixes.

Accurate-mass databases for comprehensive screening of pesticide residues in food by fast liquid chromatography time-of-flight mass spectrometry.

Because of the international trade of fruits and vegetables and the lack of harmonized regulations on the use of pesticides worldwide, the development of comprehensive screening methods for analyzing hundreds of pesticides and other banned chemicals is very convenient. This work reports the development and evaluation of a rapid automated screening method for determining pesticide residues in food using liquid chromatography electrospray time-of-flight mass spectrometry (LC-TOFMS) based on the use of an accurate-mass database. The database created includes data not only on the accurate masses of the target ions but also the characteristic in-source fragment ions (over 400 fragments included) and retention time data. This customized database was associated to commercially available software which extracted all the potential compounds of interest from the LC-TOFMS raw data of each sample and matched them against the database to search for targeted compounds in the sample. This automatic screening method requires a careful optimization of the accurate-mass window and retention time tolerances, which play a determinant role on the selectivity, accuracy, and throughput of the whole procedure. Values of 10 mDa for preliminary screening and 1 mDa/5 ppm for confirmation along with a +/-0.15 min retention time window were found to be optimum for the compounds and samples tested. The optimized methods enable the automated screening of ca. 300 compounds in less than 20 min including the LC-MS run and data processing. The proposed method was applied to 60 real samples, and the results of the positive findings compared well with those obtained using a liquid chromatography tandem mass spectrometry (LC-MS/MS) method (triple quadrupole). The rates obtained on the identification of compounds in spiked and real samples in an automated fashion at different concentration levels were over 95% of the compounds, thus revealing as a convenient tool for the large-scale screening of pesticides in foodstuffs.

Solid-phase extraction followed by liquid chromatography-time-of-flight-mass spectrometry to evaluate pharmaceuticals in effluents. A pilot monitoring study.

The present work provides a multi-residue analytical method for determining a selection of 20 pharmaceuticals from diverse therapeutical classes in hospital effluent wastewater. The method is based on the simultaneous extraction of the target compounds by solid phase extraction (SPE), followed by liquid chromatography-time-of-flight-mass spectrometry (LC-TOF-MS) analysis. Using TOF-MS, accurate mass measurements within 2 ppm error were obtained for most of the pharmaceuticals studied. Empirical formula information can be obtained by this method, allowing the unequivocal identification of the target compounds in the samples. Validation studies showed that LC-TOF-MS analysis is a valuable new tool for identification and quantification of pharmaceuticals in wastewater. Recoveries, using Oasis HLB cartridges at pH 7, were higher than 75% for all pharmaceuticals, except for ranitidine, 4-methylaminoantipyrine (4-MAA), cefotaxime and omeprazole, which needed specific pH conditions for their extraction. Linearity of response over two orders of magnitude was demonstrated (r > 0.99). Matrix effects resulting in suppression of the response were observed. For most of the compounds ion suppression was less than 39%, except for metronidazole, carbamazepine 10,11-epoxide, naproxen and erythromycin, where the signal suppression was 42%, 59%, 46% and 95%, respectively. A simple and effective approach to minimize or avoid matrix interferences was the 1 : 4 dilution of the SPE extracts. Method detection limits (MDLs) and quantification limits (MQLs) ranged between 4-115 ng l(-1) and 14-384 ng l(-1), respectively. The precision of the method, calculated as relative standard deviation (RSD), ranged from 1.1-19.8% and 1.7-21.7% for intra- and inter-day, respectively. The developed analytical method was applied to the analysis of hospital effluent wastewater during a survey study. 18 of the 20 pharmaceuticals studied were detected at concentration levels of microg l(-1), reaching in some cases concentrations over 100 microg l(-1), and in the case of the analgesic and antipyretic dipyrone metabolite, higher than 1000 microg l(-1).

Feasibility of LC/TOFMS and elemental database searching as a spectral library for pesticides in food.

Traditionally, the screening of unknown pesticides in food has been accomplished by GC/MS methods using conventional library-searching routines. However, many of the new polar and thermally labile pesticides are more readily and easily analysed by LC/MS methods and no searchable libraries currently exist (with the exception of some user libraries, which are limited). Therefore, there is a need for LC/MS libraries that can detect pesticides and their degradation products. This paper reports an identification scheme using a combination of LC/MS time-of-flight (accurate mass) and an Access database of 350 pesticides that are amenable to positive ion electrospray. The approach differs from conventional library searching of fragment ions. The concept consists of three parts: (1) initial screening of possible pesticides in actual market-place fruit extracts (apple and orange) using accurate mass and generating an accurate mass via an automatic ion-extraction routine, (2) searching the Access database manually for screening identification of a pesticide, and (3) identification of the suspected compound by accurate mass of at least one fragment ion and comparison of retention time with an actual standard. Imazalil and iprodione were identified in apples and thiabendazole in oranges using this database approach.