Chromatography Forum

Hi, dear all,

Recently I'm developing a pestcides residual analysis method, but I have not many experience on GC analysis, so someone give me some information on development.

Another question is: when performing LC development, an initial gradient run is recommended for isocratic or gradient elution prediction in next step, so I want to know whether there is a simiar guideline in GC development, i.e, an initial programmed temperature GC run for next isothermal elution is appropriate? Thanks in advance!:)

For GC, a temperature-programmed run is a good idea to "scout". I usually start with a more-concentrated standard, and establish retention time v. blank solvent, then go to my analyte as "use levels". Then I scout my sample to see if other components or my analyte elute at this time. If OK, then I go to making my conditions simpler, faster, more efficient, etc.

Isocratic is generally "faster" because there's no equilibration times between injections, but often a temperature program is continued to higher temperatures so higher-boiling componds (of no quantifying interest) can get off the column.

Another place to try is to search the column manufacturers website for test chromatograms. You can look for the class of analytes on the phase you use. It should give you a ramp and flow rate. I use these as a starting point.

Take a look for existing methods. There are may already developed for residual pesticides in food, water, soil and such. The first source that comes to mind are the methods developed by the US EPA - and these are available on line at no charge. While you can look for them on the US EPA website, I always find them faster on the AccuStandard web site: http://accustandard.com/asi/epa_downloads.php3