VOC/THM problems - Method 524.2

[JI2002]

With 4 min desorb, set up the MS to scan down to m/z 15. My guess is the three trouble compounds come out on or near the shoulder of huge water peak. If that's the case, the possible solution would be longer dry purge if you go with 4 min desorb.

[Omaejel]

We use a 1min desorb for 524 and 502 methods. We had an auditor give us some grief so we tried to go back to 4min but we had a terrible time with it. We finally talked them back into the 1 min desorb.

I was amazed at how much worse it ran with the increased desorb time.

Also, I have seen traps lose a single compound before. I have replaced many traps because MTBE wasn no longer appearing in our chromatograms.

[coombs_ryan]

A couple questions for you guys/girls

About how many samples do you guys run a week for 524 drinking water? Counting everything... BFBs, Blanks, QC, all Calibrations, and of course all samples? Pretty much every vial that runs through the MS?

Are most of youse sparging with 25mL or 5mL? And is your acidification of samples with HCL (1:1)? And if so how many drops are in each sample?

I'm trying to figure out if my Quads are taking a beating more than others and if so why?

Thanks

[jinxwolf69]

I know this post is a little old but to answer your question, we run on average 35 injections per day/per 524.2 instrument. Sometiimes we run up to 45 injections per day depending on how busy we get.

We are currently doing a 25 mL purge and some instruments are running 5 mL purge volumes, 1 min dry purge, and a 2 min desorb (although we have had quite a few auditors complain about us not doing 4 mins). We run all our standards and samples in vials preserved with 1:1 HCL and usually add 2-3 drops per vial.

We do have sporadic problems with some analytes when we run 25 mL purge over time, the 5 mL seems to remain stable for a longer period.

[Bigbear]

coombs_ryan, what makes you think you're beating up the quads? I would sooner suspect the source ( water).
Are you using an Agilent system? If so do you use the 6mm drawout plate?

I do not keep close tabs on the number of samples /week. After working on the problem for about a year with Agilent I can run 200-250 samples between source cleanings. I would be better off if I could convince my auditors to accept 1-2 min of desorb time. I do not want to change to 524.3!

[jinxwolf69]

I would have to agree, 524.3 is looking like a huge pain in the rear, we checked over the method and decided that our organization is going to hold off on switching to 524.3 until our regulators/auditors basically say we have to switch.

As far as getting your auditors to let you switch to 1-2 min desorb, just really depends on who you get and what kind of mood they are in that day. I have gotten two different responses from the same agency on the same issue. We just got lucky so far I think.

[Chroman]

I am still using 524.2.

With purge time higher than 1 minute there is big time tailing. I am keeping it at 0.9 minute and 30 split flow. Tailing is no so bad but responses for some compounds, particularly for MTBE and 1,2 dibromo 3 chloro propane are quite low.

[Bigbear]

I will use 524.2 until I am forced to. The only positive to .3 is building a SIM method for the 504 compounds.

What column are you using Chroman? Also what GC/MS and purge volume?

[Chroman]

Column: Restek RTX VMS, 60 mts, 0.25 mm ID

GC/MS: Perkin Elmer Clarus 500

Purge volume: 25 mL

[Bigbear]

When I was using a 0.25 column I was spliting 50:1. With this size column's flow rate ( 1.5 -2 cc/min) too much water gets transfered to the gc.
If you can I would recommend going to a 20M X 0.18 column. Then you get very good resolution @ about 0.6 cc/min ( I split 75:1 with a 0.18).

[Chroman]

I am using a 1 cc/min flow rate, 0.9 min desorb time and 30 split. I don' t get a lot of water but still I have some tailing around. Thank you for your suggestions, I have been thinking myself about using a different column.

[coombs_ryan]

Big Bear... sorry really meant source... i'm beating them up pretty badly... 200-250 samples between cleanings huh? That sounds about right which is basically about a week for us...

How do you guys go about cleaning your sources? I used to use the Agilent abrasive sheets (the green ones) but have found that they scratch the hell out of the parts and they never seem to work as good after that. I've also tried to use Bar Keepers Friend with a little DI Water and a Qtip and that doesn't seem to scratch the parts as bad...

We here have also tried to implement 524.3 but were having issues with the low MRL coming out consistently... the higher ups here though are pushing on us to make the switch soon so it's just a matter of time before we will most likely have to switch...

As for auditors not letting you change the desorb time... have you showed them the data? I've found that if you can back up your request with superior data they will fold. Also, since 524.3 is already out, at least in my state, they were more lenient to let us switch.

[Bigbear]

Agilent now supports using micro grit powder. Make a thick slury with OFW and clean parts with a wooden Q tip. THe first rinse I use is to run hot tap water through parts in a beaker. Then do 3 ultrasonic rinses of each of the following OFW, acetone, and MeOH. Dry in the oven at not greater than 70C.
I have extended my source cleaning cycle by doing the gas waster thing. Set the gas saver to 100-150 cc/min at 1/2 of your desorb time.
I also hold my oven at the maximum ramp temp ( 220C ) for about 10 min. I played around with the time so that the gc would get to ready just before the P&T gets ready to inject. My system gets to ready durring the last few minutes of dry purge. I DP for 6 min @ 40 cc/min.

[coombs_ryan]

I basically have the same settings as you do BigBear but all of a sudden my Bromoform problem is back to being Quadratic... which is making my recoveries for it low... Just when i thought i solved it, it comes back

It's obviously a water management issue. Really hate this method!

[Bigbear]

Take a deep calming breath we can get through this.

Supelco has a good paper ( bulletin 916) on P&T in which it says problems with bromoform can be caused by:
Active sites
Too slow purge gas rate
Desorb temp too high ( I use 250 with no problem)

You can test if your problem is due to activity by running calibrators from high to low. If bromoform is more linear , you have an active site somewhere.