Chromatography Forum

Hi all,

I'm setting up a method for PAHs in air (TO-13) on a 7890A/5975C with a gerstel PTV inlet installed. I'm injecting 5uL of dichloromethane solutions into a baffled liner using the solvent vent mode, and my trouble is with one of our extraction surrogates, nitrobenzene-d5. I get very little response, if any. I've tried varying initial inlet temps from 30 down to -30, altering the vent time and flowrate to best vent the dichloromethane, but no appreciable difference in recovery. We're about to get rid of nitrobenzene-d5 altogether and substitute another surrogate that won't be problematic. I hope that I'm not missing something very important setting this method up. With a boiling point of approximately 210, I don't see why this compound should be such a problem.

Is the problem specific to deuterated nitrobenzene ?, are there other similar compounds that you can detect.

If it is compound specific it could be soomething as simple as a SIM mass set slightly wrong.

Peter

I am seeing response for 1,4-dichlorobenzene-d4 which elutes just before nitrobenzene-d5 in full scan mode. I've made this standard fresh twice now, and now considering rebuilding the inlet..perhaps nitrobenzene-d5 is adsorbing?? More tests to be done...thank you for suggestions.

Adsorption is certaialy possible - can you see ordinary nitrobenzene, which should suffer in exactly the same way ?. If you extract an ion for D5-nitrobenzene from the TIC you might see a distorted, tailed peak sitting under the TIC baseline.

A slightly unlikely possibility is that 5 ul is too much liquid for the injector - those baffles do not hold onto much sample, so that the sample runs down to the active metal surfaces below the liner. What happens if you inject 1 ul of a 5 x concentration ?

Peter

I will try exactly that, injecting 1uL first and see how response compares..I'm pretty certain we have injection speed/vent flow/vent time/injection amount pretty solid, we did tests and showed that with a solvent vent flow of 40mL/min we could only inject 5uL slowly..10uL would "leak" out the bottom of liner before solvent evaporates..I also need to try a new liner, something I'm still waiting to have delivered. I'll let you know what I find..

I also try ptv inlet thanks for suggestions cjm