Trip blank issues

[Bigbear]

We have an issue with finding various amounts of acetaldeyhde, acetone, furfural, and sometimes furfuran ( lib search results) in blanks returning from the field. We run EPA 524.2 using a VOCARB 3000 trap.
We purchase 40 mil VOA vials containing 25mg ascorbic acid. Prepare blanks in batches of 12 by adding sparged DI water followed by 4-6 drops HCL. We analyze 1 from each batch shortly after prep with none of the afore mentioned compounds present. The batches are given to the group selling our VOA sampling kits. We have tested some blanks that were stored in their refrigerator 10-14 days after prep and found none of the compounds.
When analyzing samples, the only ones showing these compounds are the blanks that have been out in the field.
I have run the water, acid, and AA singly and none of the compounds are there.
The only blanks to show the compounds come from the field, and the samples associated with the blanks do not have the compounds!
We have no control over sampling as we sell the kits to the general public. Some kits have been known to have been "out in the field" for up to two years.
This continues to baffle me. It doesn't affect our data as compounds present in samples are not present in the associated blanks. I feel the trip blank's should closely resemble our LRB's.
Any ideas on what I'm missing?

[James_Ball]

I know from our experience that excess HCl can cause problems. We normally use 2 drops of 1:1 HCl with the ascorbic and that will bring the pH down to <2 which is where you want it.

Blanks being out of your control and for such a long period of time it is difficult to discover where contamination would come from. One thing to consider would be if those compounds are absorbed deep into the glass and over time when stored at room temperature they will eventually leach into the water. Try an experiment where you prep the blanks then store them at 40-50C for about three weeks and see if any of those compounds are present, that would help simulate poor storage conditions over a long period of time.

We have had vials in the past that were just not up to par. Calibrations would look bad because of trace amounts of targets present in the "pre cleaned" vials. We could fill them with DI Water, dump it out just leaving the inner surface moist, then pop them in a microwave for a couple minutes, let them cool and they would then be clean. Dan over at EST told me about that trick to test vials

[Peter Apps]

Isn't the idea of a trip blank that the vial gets opened at the sampling site but nothing gets put into it ? So you would expect some contaminants (although probably not the same ones every time). Or are these tip blanks that have never been on a trip, or have been on the journey but not opened ?.

Over periods of months I would certainly expect leaching from cap seals that you might not see over shorter time periods.

James, that microwave trick sounds good - I'm assuming an ordinary kitchen microwave. Can you do lots of vials at a time ?

Peter

[James_Ball]

Isn't the idea of a trip blank that the vial gets opened at the sampling site but nothing gets put into it ? So you would expect some contaminants (although probably not the same ones every time). Or are these tip blanks that have never been on a trip, or have been on the journey but not opened ?.

Over periods of months I would certainly expect leaching from cap seals that you might not see over shorter time periods.

James, that microwave trick sounds good - I'm assuming an ordinary kitchen microwave. Can you do lots of vials at a time ?

Peter

Just using the microwave in the break room and we only did a few at a time but I see no reason you couldn't just fill it up.

Trip blanks are usually unopened and travel with the sample through the whole journey. Blanks that are opened while samples are being taken are usually labeled as Field Blanks since they are exposed to the field conditions. Though I have seen some EPA offices set projects where the Trip Blanks are to be opened, and others where the Field Blanks are to not be opened.

[gurlwithgcms]

Besides excess HCl, the HCl itself could be contaminated. That happened to me, I was getting a couple of peaks in my method blank when using 1-2 drops of 1:1 HCl. I ran some acidified and non acidified samples, and decided it had to be the HCl. I used a different HCl and the problem went away. We have had a small problem in our lab with contamination for various tests, and instead of using a microwave, we use an oven. I believe it is set to 70 degrees C, and we just store glassware in it until the glassware is ready to be cooled and used. I guess it just depends what's easier for you, the oven or microwave. Good luck.

[whdees]

Hi Bear,

interesting problem... "the only ones showing these compounds are the blanks that have been out in the field"... have you considered that these are exposed to significant amounts of sunlight? I doubt this is the problem, but it should be easy to eliminate, just make a batch as usual and set them in bright sunlight for several hours, maybe with a control group in darkness but the same area and same temperature.

Just an idea...good luck!

[01310040231]

Are you able to see if your trip blanks are received intact? We have seen over the years some customers replace the water in the vials!

[Bigbear]

The blanks are received "intact" as we put orange tape that says "do not open" over tha caps. We use amber vials.

[Steve Reimer]

What you are seeing is a known problem with the preservation system. Sorry I don't remember what the actual reaction was but that is one of the reasons that the preservation was changed in 524.3. The other was to eliminate shipping HCl.

[James_Ball]

Thinking back on this I had a problem once that was in all my standards and instrument blanks where I was seeing chloromethane. Turned out someone had used a pipette in the HCl bottle that had also been used in methanol. A drop of methanol in the HCl was being converted to chloromethane and then using the HCl to preserve the CCV and Blanks was contaminating them.

[Bigbear]

We monitor some high sulpher wells that use hyper clorination treatment. We often see chloromethane in those samples.