Chromatography Forum

Don, you are soooo right: and I shouldn't criticise people who had to work with oversized desk-calculators. The first computer I ever used had 512 bytes of user memory! Not much room for an extensive library there...

Peter Aps, at risk of making another assertion I can't back up, I agree with you. Every day I am grateful to synthetic chemists. Non-analysts rarely appreciate how difficult it is to make a meaningful analysis of something present at minute levels in a complex biological sample when you can't get a reasonably pure standard.

I agree with Peter Apps as to an approach to the ID of a commercially available substance like a pesticide and the ID of unknowns where no authentic standard is available. I just finished one of these where a substance was isolated as an attractant for a weevil that attacks tequila cactus. The compound had never been identified. After obtaining integer EI mass spectra, we used the DART AccuTOF to get an exact mass of the protonated molecule. We then synthesized what we believed the structure to be. We used IR and proton and C-13 NMR to verify the structure with a confirmed elemental composition using the DART AccuTOF. The material was added to the sample and shown to have the same retention time as the unknown and the mass spectrum did not change. The only thing we did not do was the biological testing.

And, yes Don, I remember when spectra were condensed to the two most intense peaks in 14 m/z unit windows. But we used minicomputers (not microcomputers) which were the size of a large breadbox (Oops, probably most of this crowd is too young to know what a breadbox is. I guess I should have said a kitchen microwave oven). Anyway, they were 19” wide x 10” high and about 30” deep and in a 6’ high rack. They had four sets of three large toggle switches on the front where you had to key in the 4-digit instructions (about 100 or so octal commands) for the computer (a Digital Equipment Corp. PDP-8e with 8K words of Core memory) to talk to a tape drive (and later a 1.25 megabyte disk which was about 17” dia.), teletype, and incremental plotter. Library searches were only possible if you had two of the disk drives, one for the library of ~12K condensed spectra with no structures) and one for the data and software. Those were the days.

This is called space-charging, and reduces resolution, while also distorting the peak-shape in a spectrum. The distortion can move the middle of the peak away from the correct mass.











-------------------------------------
plc training in chennai
pdms course in india