Chromatography Forum

Does anyone know how to increase the sensitivity of Naphthalene in a low level (0.5 ppb) standard? I am running EPA method 524 for VOCs, and currently seeing only ion 128 and a signal barely above background noise. I am using an Agilent 6890N GC, Agilent 5973inert GC, 25 mL purge volume, inlet temp 130 C, aux temp 200 C, and a split ratio of 1:10. Any suggestions would be greatly appreciated.

Without seeing your other parameters, that inlet temp looks low. What temps are your oven and transfer line at? You want to go low -> high from the sample to the inlet, otherwise you can condense things like naphthalene and the less volatile constituents. We run 524.2 at 100 to 150:1 split ratios and still see down to 0.1-0.2 ppb relatively easily.

For naphthalene all you will see is 128 ( that's why the method does not include a qualifier ion).
25 ml purge with a 1:10 split what size column are you using?
I purge 25 ml, split 150:1 and use a 0.18 column.

Beware water.

On my 5973 I can easily see a .5 ppb std even using the 4 minute desorb (reduced for 524.3) with 5 mL purged and a 50 : 1 split.
A 1 : 10 split with 25 mL purge and a 4 minute desorb will drown your ion source in water.