Theory
Many pesticide multiresidue methods (MRMs) used are complicated, laborious, time-consuming, require high amounts of solvents and are therefore expensive. Considering that the time spent for instrumental analysis is also continuously growing due to the introduction of new analytes and instrument techniques, laboratories are not able to analyze the number of samples they would like to. In addition, some important analytes can not be satisfactorily covered by many common MRMs (e.g. basic, acidic and very polar compounds). In order to cover such analytes, laboratories have to additionally perform laborious single analyte methods, which is often not possible. This results in a large grey area of pesticides which are not routinely monitored by most laboratories.
In the last decade there has been a general trend to develop faster analytical methods. The automated instrument based extraction procedures SFE and ASE, which were introduced in the mid 1990s to speed up extraction, did not succeed to replace traditional multiresidue approaches. Ideally, a multiresidue method should be fast and easy to perform, require a minimum amount of chemicals, provide a certain degree of selectivity to avoid complicated cleanup procedures and still cover a sufficiently broad spectrum of analytes. Analysts accustomed to performing complex traditional analytical procedures often hesitate to switch to simpler ones assuming that a simpler and faster analytical procedure can not be accurate enough and should, if at all, only be used for screening procedures. In reality, however, the more analytical steps a procedure entails and the more complicated it is the more likely is the introduction of systematic and random errors.
During the development of the method the principal aim was to make it as stream-lined as possible by avoiding complicated and time consuming analytical steps.
| Time-Consuming, Complicated or Error-prone Steps |
Simplified Alternatives |
| Sample Processing/HomogenizationSimplified | No Way Around this |
| Blending (e.g. with Ultra-Turrax) | Shaking |
| Filtration | Centrifugation |
| Multiple Partitioning Steps | Single Partitioning (“On-line”-Approach) |
| Separation/Transfers of Entire Extract | Take Aliquots (Use ISTD) |
| Use of a Lot of Glassware | Extraction/Partitioning in Single VesselLarge |
| Evaporation/Reconstitution | Large Volume Injection; Sensitive Instrument |
| Classical StepsClassical SPE with Columns & Manifold | Dispersive SPE |
A schematic view of the analytical procedure is shown below. The entire method was published from Anastassiades and Co-workers in the Journal of AOAC INTERNATIONAL in 2003 (see Literature).
| Working Step | Picture No. |  |
| Weigh 10 g of Sample (50 mL Teflon-Tube) | 1 | |
| Add 10 mL Acetonitrile | 2 | |
| Shake Vigorously 1 min | 3 | |
| Add 4 g MgSO4 and 1 g NaCl | 4 | |
| Shake Vigorously 1 min | 3 | |
| Add ISTD-Solution | 5 | |
| Shake 30 s and Centrifuge | 3 - 6 - 7 | |
| Take Aliquot and Add MgSO4 (and Sorbent) | 8 | |
| Shake 30 s and Centrifuge | 9 - 10 | |
| (Add 0.1% HAc and "Analyte Protectants") | 11 | |
| GC-MSD and LC-MS/MS |
last update: 2011-05-13