Browsing by Author "Fernandes, Paulo J."
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- High-throughput analytical strategy based on modified QuEChERS extraction and dispersive solid-phase extraction clean-up followed by liquid chromatography-triple-quadrupole tandem mass spectrometry for quantification of multiclass mycotoxins in cerealsPublication . Fernandes, Paulo J.; Barros, Nelson; Santo, José L.; Câmara, José S.A simple, reliable, efficient, selective and sensitive QuEChERS-based (quick, easy, cheap, effective, rugged and safe) sample preparation strategy, involving an initial partitioning step using acidified acetonitrile (ACN), MgSO4, NaCl and citrate buffer salts, combined with dispersive solid-phase extraction (d-SPE) clean-up, is proposed for the simultaneous multiclass mycotoxins quantification, including aflatoxins, ochratoxins, fumonisins, trichothecenes and zearalenone, in cereals. The final clear extracts were concentrated under vacuum to near dryness and taken-up with the initial mobile phase (MeOH:H2O;70:30, v/v) previous to reversed-phase liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) analysis. Careful optimization of the LC-ESI-MS/MS parameters was achieved in order to attain a fast separation and increased sensitivity. The detection was carried out on a triple-quadrupole tandem mass spectrometry (MS/MS) by electrospray ionization in positive ion mode (ESI+) with multiple reaction monitoring (MRM). Tandem MS conditions were optimised in order to increase selectivity, selecting the best transitions (parent ion to quantifier and qualifier ions) for quantification and identification. The performance of the method was assessed and compared to European Commission (EC) Regulations, by studying the selectivity, specificity, limits of detection (LOD) and quantification (LOQ), linear dynamic range (LDR), matrix effect, accuracy, precision, and uncertainty. Good linearity (r 2 > 0.9713) was achieved for all mycotoxins investigated, and LODs (S/N = 3) and LOQs (S/N = 10) were below the tolerance levels of mycotoxins set by EC. Recoveries of the extraction process, obtained with different spiked concentrations, ranged from 72.9 to 120.6 %, with relative standard deviations (RSD) lower than 23.0 %. Only in 6 % of all combinations did the RSD values exceed 15 %. Matrix effects were observed by comparing the slope of matrix-matched standard calibration with that of the solvent. The developed method was applied to evaluate the co-occurrence of multiclass mycotoxins in cereals collected at the importation points and consumer habitations at Madeira Island. Samples collected at importation points (15 wheat samples, 4 maize samples and 2 rice samples) showed the presence of DON in three wheat samples, and FB1 and HT-2 in one wheat sample. Three maize samples were detected with FB1 (two samples) and AFG2 (one sample) whereas one rice sample was detected with ZEN. The results revealed the absence of target mycotoxins on the rice samples collected at consumer habitations. None of the studied cereal samples exceeded the maximum permissible limits or indicative levels set by the EC which means that the particular Madeira Island subtropical climate conditions do not represent a major risk for cereal contamination, taking into account the investigated mycotoxins.
- A survey of the occurrence of ochratoxin A in Madeira wines based on a modified QuEChERS extraction procedure combined with liquid chromatography–triple quadrupole tandem mass spectrometryPublication . Fernandes, Paulo J.; Barros, Nelson; Câmara, José S.Over the past years, to ensure food safety, the European Union (EU) has adopted specific legislation concerning the control of mycotoxins residue levels in different kinds of food. In this study, a fast, selective and sensitive reversed-phased liquid chromatography with tandem mass spectrometry (LC–MS/MS) methodology was developed and validated for quantification of ochratoxin A (OTA) in Madeira wines. Sample extraction and purification were performed with a modified QuEChERS-based (quick, easy, cheap, effective, rugged, and safe) procedure. Firstly, the homogenized samples are extracted and partitioned using an organic solvent and salt solution. Then, the supernatant is further extracted and cleaned using a dispersive solid phase extraction (dSPE) technique. Finally clear wine extracts were concentrated under vacuum to near dryness and taken up into initial mobile phase. Careful optimization of the LC–MS/MS parameters was achieved in order to attain a fast separation with the best sensitivity. The detection was carried out on a triple–quadrupole tandem mass spectrometer (MS/MS) by electrospray ionization in positive ion mode (ESI+) with multiple reaction monitoring (MRM). MS/MS conditions were optimized in order to increase selectivity, selecting the corresponding product ions (precursor-to-fragment m/z 404 → 239; m/z 404 → m/z 358) for quantification and identification. The performance of the method was assessed and compared to the European Commission (EC) Regulations, by studying the selectivity and specificity, limit of detection (LOD), limit of quantification (LOQ), linear dynamic range, matrix effect, accuracy, precision, robustness/ruggedness and uncertainty. The validation was performed by analyzing recovery samples at four different spiked concentrations, 0.5, 1.0, 5.0 and 10.0 μg/kg, with four replicates (n = 4) at each concentration. Recoveries ranged from 87.2% to 102.6%, with relative standard deviations below 9% in all cases. The intra-day precision and inter-day precision, expressed as relative standard deviation, were lower than 7% and 14%, respectively. Matrix effects were observed by comparing the slope of matrix-matched standard calibration with that of solvent. Good linearity was achieved at the concentration levels of 0.50–22.5 μg/L. The LOQ and LOD, 0.4 and 0.1 μg/kg, respectively, at the signal-to-noise ratio (S/N) of 10 and 3, were lower than the concentration usually permitted by legislation in wines. The method was successfully applied to evaluate the occurrence of OTA in 30 Madeira wine samples. None of the analyzed samples exceeded the maximum permissible limit for wines (2.0 μg/kg) set by the EC, which confirms that the risk of OTA occurrence in Madeira wines is, as expected, is very low.