Chromatography Forum

Hi, which one is well recongnised test method available for pesticide testing..PAM,AOAC-,DFG S19
in terms of acceptance and reliability

The decision of method for pesticide testing depends in part on what you need to do with the results. Some governmental bodies may have requirements, perhaps written into law or unwritten based on the biases of auditors.

So, next question: To whom will you be reporting data? Do they need to use the results for such things as legal disputes or product certification? And, if so, where?

Hi,
I'm doing pesticide analysis by GC and confirmation by GC-MS in food products. But i'm following lab developed methods. These methods are very useful for day to day work. But if u r going for accreditation then there is lot of problems in following these methods.

In pesticide analysis by GC-MS i'm using a standard mix of 10 compounds.How can i show all the 10 compounds in the chromatogram as in GC. At present i used to search compounds one by one using their base peak.

Thanks & Regards

Seeni

Seeni,

As far as picking a method: First look to see if the target market requires a particular method. Or at least what detection limits are required. You may be able to use the method of your choice as long as you can prove performance - and if you use a published standard method, you will still need to prove performance. If you are trying to become an accredited lab, it involves much more work that selecting a method.

In your question about showing all ten compounds in the GC-MS chromatogram. Your instrument should have some kind of reporting software built in. While you can do things like a display of specific ion traces along a chromatogram, pesticides may be the small peaks between all the other stuff extracted from food. You may want to consider a display of the traces of ions used to quantitate and confirm each compound (analytes and internal standards). This type of report should be part of the standard reporting software.

You describe that you use the base peak for identifying each compound -- which, depending on the compounds and the matrix, may be OK. Some pesticides show a base peak that is common to a number of other compounds that will coelute. And these will show up as interferences at the part per million or part per billion levels. Your chromatographic software should provide some kind of automatic peak identification that will use retention time and multiple characteristic ions to help locate analytes for you. In pesticides containing chlorine or bromine, some of the higher mass ions are not as strong as the base peak, but provide much cleaner signals, since all the other stuff eluting at that point in the chromatogram is lower molecular weight, and will give much lower limits of detection. And, in some types of samples, because of coelution of interfering compounds, there may be a peak present for an ion at the base peak, but there is nothing present for the higher weight ions.

Don

Additional note: I happened to have US EPA method 8270 open on my desk today and noticed that they have recommended ions for a number of pesticides - as well as for many other compounds. - If that helps any. You can find the US EPA methods at the EPA web site or through web sites of many suppliers of analytical standards.