EPA Method 624

[mjh32586]

I am currently working on gaining accreditation for EPA Method 624. Can anyone out there help me with some pointers? We currently have 524.2 accreditation and my understanding is they are very similar. What are the main qc differences with method 624? Can someone send me what their typical daily batch would look like including all QC? I'm not sure I understand the acceptance criteria in Table 5 of 40 CFR. Also, how do you determine what the acceptance criteria should be for your surrogates? For 524.2, I always go with +/-30% recovery on all my qc and +/-20% recovery on surrogates.

Thanks!

[dperk527]

I use the following as acceptance criteria for 624:

Gases, Acrolein/Acrylonitrile, 2-CEVE: +/-40%
Surrogates: +/-20%
All others: +/-30%

As far 624 being similar to 524, only in that many of the same compounds are analyzed. Water as a matrix is clean and purges well. Wastewater is a different story. Matrix interference is a problem with 2-CEVE in Matrix Spikes.

As far as QC goes, I run a Calibration Check, Method Blank, and Laboratory Check Standard, along with a Matrix SPike and Matrix Spike Duplicate. The 524 method has more extensive QC requirements since it is for drinking water.

Hope this helps.

[mjh32586]

What split ratio range is generally used for this method? I am currently running a split of 30 for drinking water.

[Steve Reimer]

Split ratio will depend upon the column used.

[Bigbear]

Run the highest split that you can in order to limit the amount of water getting to the mass spec. Run your reporting limit standard at different ratios and use the highest that still gives good peaks in your standard.

[mjh32586]

I am using Restek's RXI-624 Sil MS column (30 m x 0.25 mm ID x 1.4um film). I am only using a 0.5 minute desorb and tried calibrating with an 85 split and then a 100 split. Both curves looked good for all analytes except bromomethane and cis-1,3-dichloropropene. I would venture to guess that bromomethane is being affected due to water management but what would cause a poor calibration curve and low recovery for cis-1,3-dichloropropene?

[Bigbear]

Probably, do you dry purge? If so for how long and at what rate. Or it could be as simple as your trap is worn.
I have good luck with P set @ 40 cc/min for 6 min. with my condensor @ 20C ( Stratum).

[Bigbear]

DO you have a copy of this?

http://www.sigmaaldrich.com/etc/mediali ... p/4542.pdf

[mjh32586]

Big Bear,

No, I do not use dry purge because I am using an OI #10 trap (tenax, silica gel, cms) which does not require a dry purge. My trap may need replaced. I installed it on 3-22-12 but since I have the long desorb time (3.5 min) for 524.2, I bake it for 15 minutes between samples which shortens its lifetime. I have also read that sodium thiosulfate can cause degradation of these two particular analytes. What preservative to you use for your vials for 624 and do you add sodium thiosulfate and 1:1 HCl to all your calibration vials? Someone also told me that I may be looking at a linearity issue. These calibrations are from 5-200 ppb. What cal range and points do you use for your calibration?

[Bigbear]

I run 524 and use ascorbic acid and HCl. Would you consider switching to a Vocarb 3000 trap? Most folks use this trap for 524, it's hydrophobic and you can dry purge it. Using silica gel in your trap you must be putting lots of water in your source.