Large Volume Liquid Injection is Back

GC has always had a problem with the narrow range of sample volumes that can be accommodated (0.1-2ul). This means that most methods involve either a dilution or concentration step. Large volume injection, using a PTV injector has always held the promise to extend this range to 100ul and beyond, enabling concentration steps to be eliminated altogether in many cases. This would remove a significant source of error and offer the potential of simpler, faster and cheaper sample preparation.

With the current trend toward faster chromatography, operating a GCMS in SIM can, with complex samples, become nigh on impossible and so being able to work in scan mode and still meet LOD requirements - by injecting a bit more, is also very attractive.

The problem has been that LVI hasn't always lived up to its promise. While some labs have got excellent results, it has required a degree of skill and knowledge that hasn't always been available and it has not been sufficiently universal in the range of jobs it can do.

Two recent developments are significant in this respect; the first is the availability of packed PTV liners that are intrinsically inert - so that virtually any compound can run without losses. The second is better near-ambient temperature control - this keeps the solvent elimination step reproducible.

In the Anatune applications lab, we have been able to get excellent results very easily using a Peltier cooled, GERSTEL CIS4+ with our new P type liner. We have run more than 400 semi-volatile components and investigated DCM, ethyl acetate, hexane and Iso-octane as solvents - all of which work fine. Losses are minimal (and broadly similar for all compounds) and the results are reproducible - sub 5% RSD for most things (substituted phenols are the only real exception, but these are still less than 10% RSD). Work continues to add other common solvents to this list.

What is more, we have been able to deliver fully crafted solutions to a number of environmental and water labs that have proved their worth running real samples.

I am now strongly of the view that we have LVI to a point where it is ready to take its place as routine, universal and useful technique. We have found that we can now deliver robust LVI solutions economically. This means that we can work-up the LVI method for you as part of the package of instrumentation that you buy, all at a sensible cost.