Quantitative Analysis of Pesticides in QuEChERs Extracts Using APGC/MS/MS Douglas Stevens1, Dominic Roberts2 , Ramesh Rao2 1 Waters Corporation, 34 Maple Street, Milford, MA 01757, USA. 2Waters Corporation, Altrincham Road, Wilmslow, UK. INTRODUCTION METHODS RESULTS & DISCUSSION Since the sensitivity of this system is well beyond Each sample type, including matrix matched stan- regulatory requirements, a practical application of this Pesticides are widely used in the production of fruit and Strawberry, were Analysis of 20 GC amenable pesticides, difficult to analyze dards and replicates, was analyzed on three different performance is to dilute samples, thereby, further vegetables homogenized using a domestic food blender. The in EI due to excessive fragmentation, was performed days. Figure 2 shows a typical calibration curve and reducing matrix effects on chromatography samples were then extracted using the QuEChERS using source residuals plot for endosulfan sulphate generated from minimizing conditions either charge exchange or protonation can be the triplicate injection of the matrix matched calibra- column. This in turn reduces the frequency of column selected for an APGC analysis. For the analysis of tion standard in strawberry extract. The response is trimming, extends the useful life of the column and pesticides, protonation provides more efficient ionization linear from 0.05 to 50 ng/mL with a correlation coeffi- increases the interval between source cleanings which mixed pesticide standard in acetonitrile to each than charge exchange. Therefore, a vial of water was cient R2 of 0.994. All of the residuals are less than is already measured in months. The net effect of all of matrix. To test the repeatability at low concentration, added to the source to promote protonation. The MRM transitions with optimized cone voltages and collision these factors is increased up-time and utilization for in a diverse range of food commodities. As there are each matrix was fortified with the pesticide mix at 1 15% demonstrating excellent linearity and repeatabil- currently in excess of 1000 pesticides in use, laboratories µg/kg energies are shown in Table 1. Two transitions were ity. The limits of detection and linearity achieved for the system. are under increasing pressure to broaden the range of deuterated pesticides determined in ever shorter turnaround times. added to give a fixed concentration of 2 ng/mL to Therefore, the analytical methods they employ need to each vial prior to analysis and was used as an use injection standard to correct for injection volume across the globe. Governments, food producers and food retailers have a duty to ensure they are not present in final products for consumption. Most countries have regulations governing pesticide residues in food. For pesticides in food products, legislation imposes Maximum Residue Limits (MRLs) which lead to the requirement for analytical techniques that are sensitive, selective and reproducible. Multi-residue pesticide analysis is challenging due to the low limits of detection required efficient but low selectivity sample preparation methods combined with high selectivity and sensitivity MS/MS methods. Typically, this analysis is carried out using a dedicated GC-MS/MS system with an EI source. As shown by fragmentation Portoles of some et 1 al , EI causes pesticides leading extensive to poor sensitivity and selectivity. APGC is a soft ionization technique which generates high relative and absolute pear and spinach samples (CEN method 15662 DisQuE #186004831) protocol to generate blank matrix extract in acetonitrile. A nine point calibration range from 0 to 50 ng/mL (equivalent to µg/kg) was prepared by addition of a (1ppb final internal concentration standard, in aliquot). chrysene-d12, A was positive monitored for ion each MRM mode. pesticide By to varying increase method specificity. The high intensity of the precursor/molecular ion generated by APGC makes it possible to use specific of detection ranged from 0.01 to 0.5 ng/mL with ex- the low level spike in each matrix was analyzed ten MRM transitions used with EI MS/MS use lower m/z, less limits and is applicable to routine quantitative analy- times using the Waters® Xevo TQ-S with the APGC specific fragment ion as the precursor. The inherent sis. source using the conditions described below. specificity provided by use of the molecular ion as the selective MRM transitions. Furthermore, the APGC source simplified, generic sample preparation technique. precise, accurate and reproducible across different sitivity and overall performance characteristics of enabling a single MS instrument to be used for the APGC on Xevo TQ-S currently exceeds existing regu- interchangeable with the LC electrospray analysis of both LC and GC amenable pesticides. lations related to pesticide residue analysis. In this study, we demonstrate sensitive, accurate and repeatable results for the analysis of pesticides on  Soft ionization provided by this technique produces abundant molecular ions for selective and sensitive MRM transitions  Routine and sensitive multi-residue pesticide analysis of QuEChERS extracts from fruit and vegetables, using the same workflow used for LC/ MS/MS analysis of pesticides, is possible with this system  System can covert between GC and LC operation in minutes allowing comprehensive analysis of both GC and LC amenable pesticides on a single instrument sample matrices analyzed on different days. The sen- source is injected APGC on Xevo TQ-S is sensitive, accurate and reproducible for pesticides that are difficult to analyze using conventional EI GC/MS/MS good at < 5%. This demonstrates that the method is ion results in more confident detection of lower levels of analytes even in these complex matrices prepared with a material  Table 2. Mean concentration of each pesticide (n=10) in the three sample matrices The %RSD for all pesticides is also shown to be very precursor in an MRM transition over the use of a fragment abundance molecular ions resulting in highly sensitive and of CONCLUSION cellent linearity (R2 >0.99) for all. This demonstrates that the method can easily achieve the regulatory GC Conditions amount all 20 pesticides are summarized in Table 1. The limits and sensitive MRM transitions. In contrast, many pesticide variation. All standards were analyzed in triplicate and the and in QuEChERS extracts of strawberry, pear and spinach below Figure 2. Typical matrix matched calibration curve for endosulfan sulphate in strawberry matrix the regulatory limits. References To assess the accuracy and precision of the method 1. Portoles, Tania, Laura Cherta, Joaquim Beltran, and Felix Hernandez. "Improved gas chromatography–tandem mass spectrometry determination of pesticide residues making use of atmospheric pressure chemical ionization." Journal of Chromatography A 1260 (2012): 183-192 each sample matrix was spiked at 1 µg/kg (10 times MS Conditions below the blanket MRL of 10 µg/kg) and ten replicate injections made. The concentration of each pesticide 2. Young, Michael, Tran, Kim Van, Shia, Jeremy C. “Multi-Residue Pesticide Analysis in Ginseng Powder”. Waters application note #720005006EN (2014) was calculated using matrix matched calibration curves. Table 2 shows the mean calculated concentrations for each pesticide in all three samples matrices. The accuracy of the method is excellent with all Table 1. Summary of the 20 pesticides analyzed, MRM conditions and method performance results Figure 1. Photo of UPLC and APGC on Xevo TQ-S TO DOWNLOAD A COPY OF THIS POSTER, VISIT WWW.WATERS.COM/POSTERS measured concentrations within 5% of the true con- Figure 3. Mean calculated concentration of pesticides spiked at 1 μg/kg in 3 different food matrices (n=10) 3. Giroud, Barbara, Antoine Vauchez, Emmanuelle Vulliet, Laure Wiest, and Audrey Bulete. "Trace level determination of pyrethroid and neonicotinoid insecticides in beebread using acetonitrile-based extraction followed by analysis with ultra-highperformance liquid chromatography–tandem mass spectrometry." Journal of Chromatography A 1316 (2013): 53-61 centration. ©2014 Waters Corporation