Chromatography Forum

My client states... "The Risk Based Screening Levels (RBSLs) the state requires us to be under to make a groundwater sample "clean" for the following chemicals
are:
1,2-DCA 0.38-5 ug/L
Benzene 5 ug/L
EDB 0.02- 0.05 ug/L"

By running 8260 in SIM/Scan and using SIM to quatitate I have these MDL's respectively for water matrix...
1,2-DCA 0.18 ppb or by Scan mode without SIM... 0.59 ppb
Benzene 0.20 ppb or by Scan mode without SIM... 0.48 ppb
1,2-EDB 0.19 ppb or by Scan mode without SIM... 0.49 ppb

Am I right in thinking I cannot get any lower for 1,2-EDB without going with an ECD detector method?

My current SIM/Scan 8260 method cal curve is from 20 ppb to 480 ppb. I used a 50X dilution of the CCV standards to run a 0.8 ppb and a 4.0 ppb check standard each day I ran 8260. I used student's T test on the averages and standard deviations of of each level taken from 16 different runs to get the MDLs' I cite above (c.f. CFR 136B how to determine an MDL).

If you want to run that low on EDB you're probably going to need a SIM only second injection and it's just going to throw your 8260 curve off faster. Not sure why they want drinking water limits for 8260 samples but we just run 504.1 when a 524 samples comes back with high BTEX.

Current 504.1 instrument hasn't had to curve in the last two years, but you aren't going to pick up benzene on it.

Method 524,3 says that running straight SIM can get the MDL's down by a factor of 10 from SIM/Scan mode (5973 inert fastscan sideboard).

What do you mean "it's just going to throw your 8260 curve off faster"?

Do you mean wear and tear on the source / detector?

Yeah, back when I ran To-15 we had scan only and SIM/scan instruments for clients with lower detection limit needs. Scan instruments would hold tunes longer and you could get by without cleaning the source for about twice as long vs the sim instruments.

We only report down to the CFR 141 MCL for EDB/DBCP for 524 and if we see a sample with significant BTEX hits send out a 504 sample for collection to get down to the enhanced monitoring trigger levels.

20-50 parts per quadrillion?!?
Yeah - that's pretty low...
Are you allowed to extract from larger volumes? Might require an internal standard, but that's the "other" way to get lower... if method allows it. (I'm not an environmental chemist and glad of it).

0.02 ppb is 20 ppt. In SIM/SCAN mode I am giving it 500 ms per peak for 107, 108, 188. Maybe that will give a lower MDL but maybe one only gets the lowest detection in a SIM method.

We are going to convert our current SIM/SCAN method into a SIM method and run EPA524 in SIM for a shorter list of compounds. Hopefully the very much lower top end and SIM only will get us the lower MDL.

I'm happy to report that I get an excellent calibration which I am still refining. I'm using my regular 8260 P&T conditions with a 40:1 inlet split ratio. I'm using the 8260 ISS at 5000 ppt. Calibration curve from 1000 ppt to 40 ppt. Average Response Factor for 1,2-EDB is 0.157 with a 9.33% RSD. We have 942 counts at 40 ppt.