Food Safety Magazine, February/March 2013

Testing(continued from page 15)Figure 1: Chromatograms Obtained in Multiresidue Analyses of More than 300 PesticidesAnalyzed by GC-MS/MS and LC-MS/MSrange of compounds independent oftheir elemental composition and providesimultaneous quantitation and structuralidentification of detected analytes. It alsoadds another degree of separation/selectivityon top of chromatographic separations.These unique features have madeMS the number one choice for detectionand identification/confirmation of tracelevelorganic chemical contaminants inmodern testing laboratories.First, the combination of MS withgas chromatography (GC-MS) has becomepopular for the analysis of volatileand semivolatile compounds, includingmany pesticide residues, PAHs, PCBsand other less-polar POPs. More polar,thermolabile and less volatile analyteswere difficult to analyze until the morerecent introduction of atmosphericionization techniques, such as electrospray,for liquid chromatography-massspectrometry (LC-MS). LC-MS hasopened the door to the direct analysis ofmany more polar contaminants, includingmodern, new-generation pesticides,and the majority of veterinary drugsand toxins, such as mycotoxins. Manyof the emerging and recently identifiedcontaminants, including acrylamide,melamine or Sudan dyes, are analyzedpreferably by LC-MS.Thus, modern food contaminant testinglaboratories utilize both GC-MS andLC-MS to cover the wide polarity rangeof possible organic chemical contaminants.Tandem MS (MS/MS) is typicallyemployed to provide an increased selectivity(especially in LC-MS) that helpsfurther distinguish target compoundsfrom potential matrix interference.Figure 1 shows an example of chromatogramsobtained in a multiresidue analysisof more than 300 pesticides analyzedby GC-MS/MS and LC-MS/MS, demonstratingthe speed and selectivity ofstate-of-the-art instruments that enablethe simultaneous and highly sensitiveanalysis of many compounds.Identification of UnknownChemical Contaminants in FoodDetection and identification ofunknown contaminants is not an easytask, especially if they are present at lowconcentration levels. It requires expertiseand a good analytical strategy that isbased on all gathered information aboutthe sample and potential sources of contamination.Any clues, such as changesin smell, taste or texture, as well as adescription of potential poisoning symptomsmay be important in this respect.Concurrent analysis of control (“good”)samples with suspect samples is often essentialto find differences and eliminatepotential false positives.If a certain compound or a group ofcompounds is suspected, then a targetedsample preparation and instrumentalmethod(s) can be employed (see “TheImportance of Moisture in SamplesPrior to Chemical Analyses,” p. 14).For a truly unknown analysis, differentextraction and separation approachesshould be used to isolate compoundswith a wide range of physicochemicalproperties (polarity, solubility, volatility,etc.). Nontargeted analysis should beperformed, such as MS with full-spectraacquisition. Statistical analysis of theacquired chromatographic and MS dataof contaminated and noncontaminatedsamples may help identify differencesand reduce the number of componentsthat have to be examined. The acquiredMS spectra of suspected contaminantscan be compared with MS spectral librariesand compound databases. In LC-MS,high-resolution/accurate-mass measurements,using time-of-flight (TOF) ororbitrap MS instruments, should beused for added selectivity. In addition,tandem MS should be employed to helpelucidate the structure of unknown contaminants.In the end, strong knowledgeand expertise in both analytical and foodchemistry are typically required to succeedin this task.Current and Future Trends inChemical Contaminant Analysis inFoodThe current and future trends in theanalysis of chemical contaminants areand will be strongly affected by developmentsin analytical instrumentation. Thespeed, sensitivity and selectivity of stateof-the-artMS instruments enable analysisof many compounds in one analyticalrun. Consequently, streamlined samplepreparation approaches, such as QuECh-ERS (Quick, Easy, Cheap, Effective, Ruggedand Safe), can be used that requireminimum extract cleanup without anypreconcentration steps—thus, they can beminiaturized and automated.The advancements in high-resolution/accurateMS instruments and developmentof related software tools showgreat potential to bring this technologyfrom the research environment into testinglaboratories, where it could be employedfor nontargeted testing of knownand unknown chemical contaminants. •Katerina Mastovska, Ph.D., is alead staff scientist at Covance Laboratories.She is actively involved inthe AOAC International as a co-chairof the AOAC Chemical Contaminantsand Residues in Food community.F e b r u a r y • M a r c h 2 0 1 3 65