If you run HAAs...help!

[JReed]

Hello,
I run epa method 552.2. It seems that lately all I can get out of a column is a month worth of runs, with the last replacement being even before that. I'm on a 5890 II, with RTX-CLP 30m, 0.32mmid, 0.5umdf and an RTX-CLP2 for confirmation (same specs.) Someone suggested that it might be possible that the samples aren't getting completely neutralized, and Restek said if that even the sample being a pH 5 will shorten the life of the column. So I'm wondering if anyone else out there has had a similar problem, and how you deal with it. Or if anyone has any other insight into this problem. Thanks in advance.

[Peter Apps]

Oxygen and water in the carrier gas can also kill columns very quickly.

Peter

[JReed]

My gas line is connected to a moisture/oxygen trap. It might need to be replaced, but there is another instrument that gets it's gas from that trap and it's columns aren't degrading nearly as quickly as mine. Are OP Pesticide columns less susceptable to moisture and oxygen?

[bluejay]

pH - Are you using a saturated enough sodium bicarbonate solution to neutralize the samples? I don't remember exactly what concentration we used, but it was right at the saturation point of sodium bicarbonate in water. You could try adding some extra bicarb solution to a test sample to see if it fizzes more. I also remember it being important to let vent the samples during the neutralization process and to let them sit for long enough to completely react.

Water in samples - It can be difficult to tell if you've gotten water in the MTBE extract that you're putting in the vials for analysis. I found that the easiest way to tell was to put the finished vials into the freezer after extraction and before analysis for a little while (I don't remember how long it took). Even a little water would show up as an ice crystal that was much more visible.

(I was running a DB-1 column on a 6890).

[JReed]

The recipe we use is 60 grams per liter of D.I. and the method dictates the volume of it to use, so I'm not sure how much we can deviate from that. We do shake and vent after adding it.
Since I do have problems with this method frequently, I store the extracts in a freezer. This lengthens the analytical hold time to 14 days. Thanks for your input!

[Peter Apps]

My gas line is connected to a moisture/oxygen trap. It might need to be replaced, but there is another instrument that gets it's gas from that trap and it's columns aren't degrading nearly as quickly as mine. Are OP Pesticide columns less susceptable to moisture and oxygen?

If the two instruments are sharing a gas scrubber it suggests that the scrubber might be further (more pipe connections) from the instrument than is ideal. As a precaution do a very careful leak check aof all the plumbing. You really want the scrubber plumbed straight to the back of the GC. At the rate you are going through columns the price of a scrubber would quickly justify itself.

Peter

[JReed]

I see. I will do a leak check and suggest this to my sup. Thanks!

[bluejay]

Solubility of sodium bicarbonate in water is 78g/L, so you might be able to bump up your concentration a little. (At that level you'd probably have to heat it a bit to get it into solution) I'm not suggesting deviating from the designated amount you add to each sample, just check a test sample to see if the pH has actually been neutralized.

With the 14 day hold time in the freezer I remember not ever being able to hold my samples that long successfully, but I can't exactly remember why (been a few years!). A couple days was fine.

Good luck, HAAs were definitely challenging to successfully analyze.

[JReed]

Ahh I see. Good point. Thanks for your help!

[JReed]

Can anyone tell me about pencil traps? What happens to the chromatography when they're dirty? How often do they need to be changed if at all? Can they be cleaned?

[Peter Apps]

Traps immediately before the inlet are supposed to take out any organics and water that might have got into the carrier gas from the gas control plumbing. If it gets saturated you will see extra peaks on your chromatogram from crud that has trapped on the top if the column.

If you have clean gas going into the GC the pencil traps should last a while - I think that the recommended change out interval on the Varian 450 is a year. But if you have dirty gas coming in the tiny liitle pencil trap will be overwhelmed in a few days.

As far as I know they cannot be cleaned, but they are absurdly expensive, I have replaced mine by Restek split vent traps. The extra volume can challenge the EPC, but with my home made inlet setups that is the least of its troubles !

Peter

[aldehyde]

Yeah I would get the restek assembly that lets you change to the standard larger split vent trap. The older pencil style ones were found to clog more easily, and could definitely be messing with your inlet. I would also check/clean the split vent line.

[Steve Reimer]

When I ran that method I learned the hard way to check the extract with pH paper before analysis. Just a small drop on pH paper will show if the neutralization was complete.

[JReed]

What would you do if you found they were still acidic? I didn't think you could check the solvent pH directly.

[Steve Reimer]

If the pH was still low (no, it isn't anything more than low or neutral on pH paper) I would send it back through the neutralization step. I would not inject it with acid present. Luckily it was a rare event, but I had a splitter on the inlet into two columns so any acid left could be a $1000 event.