Chromatography Forum

I am in the process of adapting an 8260 SIM/SCAN method to make a 524 SIM only method to get the EDB mdl down from the curent 0.18 ppb to 0.02 ppb. I've isolated the individual peaks enough that there are typically only 2-6 masses per group of peaks. Then I realized that in SIM mode the 4-BFB can only "see" 4 peaks regardless of how many peaks for BFB that I specify for that time window.

Just how does a chemist do a BFB check when running SIM? And does meeting the ratios in the BFB standard even have a meaning in a method where the ratios are arbitrary because the chemist can specify different integration times for each mass in a compound?

I suppose its spelled out in the 524.4 method. But it never occurred to me to specifically check.

Don't you just check your BFB in scan mode? See 8260D 11.3.1.2

With the disclaimer that I've never used SIM mode so might not know what I'm talking about...

If it passes in scan mode, your tune is good (lens voltages are adjusted right, etc). And that should be true for SIM as long as you're using the same settings (for each ion, that is: so M/Z 174 for example will be read under the exact same conditions in SIM mode as it was in Scan mode, except for a longer period of time.

Just how does a chemist do a BFB check when running SIM?

To quoth the EPA:

10.1.1 MS TUNE/MS TUNE CHECK– Calibrate the mass and abundance scales of the MS
utilizing calibration compounds and procedures recommended by the manufacturer
with any modifications necessary to meet tuning requirements. Introduce BFB (Sect.
7.5) into the GC/MS system. Acquire a mass spectrum using the same scan range
employed for full scan sample analyses. Use a single spectrum at the apex of the
BFB peak, an average spectrum of the three highest points of the peak or an average
spectrum across the entire peak to evaluate the performance of the system.
Appropriate background subtraction is allowed; however, the background scan(s)
must be chosen from the baseline prior to or after elution of the BFB peak. If the
BFB mass spectrum does not meet all criteria in Table 1, the MS must be retuned to
meet all criteria before proceeding with the initial calibration.

And does meeting the ratios in the BFB standard even have a meaning in a method where the ratios are arbitrary because the chemist can specify different integration times for each mass in a compound?

I feel this way about a lot of EPA method QC


Luckily ever since rev. 3 it only needs to be ran with the iCal.

I feel this way about a lot of EPA method QC

Luckily ever since rev. 3 it only needs to be ran with the iCal.

Benzidine tailing. :\

I'm not looking for it, and the temp ramps that make it better make the analytes I do care about look worse. I'm real glad it doesn't have to be checked every day anymore.

I personally believe we should be evaluating DFTPP or BFB every 12 hour window. DFTPP ion ratios are important for me to maintain not only a tune, but a calibration. Inexperienced analysts will learn more about their systems with a proper daily evaluation like this. A CCV may pass beautifully, but I would be interested to know that DDT is starting to break down, or benzidine tailing is getting worse.

It can act as a preemptive warning that maintenance is coming due.

As mentioned, tune evaluations should be evaluated using full scan data.

I personally believe we should be evaluating DFTPP or BFB every 12 hour window. DFTPP ion ratios are important for me to maintain not only a tune, but a calibration. Inexperienced analysts will learn more about their systems with a proper daily evaluation like this. A CCV may pass beautifully, but I would be interested to know that DDT is starting to break down, or benzidine tailing is getting worse.

It can act as a preemptive warning that maintenance is coming due.

As mentioned, tune evaluations should be evaluated using full scan data.

The problem with one-size-fits all QC rules is that you can't always anticipate how a method is going to be used. I agree that the tune evaluation is a good learning tool, but its usefulness beyond that depends on the use case. I can see a lot of value for a lab that ran a lot of samples and ran them for a lot of analytes.

On the other hand, my last lab was open 24/5, and only ran 1-2 samples per day (we only had in-house GCs because but the desired turnaround time was "now.") Quite often we were only interested in phenol, cresols, and naphthalene.

So once 8270E came out:
If DDT looked great, I'd run my samples.
If DDT was starting to break down, I'd run my samples!

Now, if I knew that the next day I'd be running for the full 8270 list, checking for DDT was a good idea. But then again, my CCV already has compounds that are going to tell me whether I need to do maintenance.

I hope the other EPA methods allow flexibility based on project quality objectives... especially the method defined parameters. The cyanide method requires that you use a 1.0L reaction vessel. There are great distillation setups available commercially that use smaller glassware (and use less reagents, have a smaller footprint, are built more robustly than heating mantles, and are safer to use than traditional setups) and achieve identical results. But, nope, cyanide is an MDP - you aren't allowed to use them.

Well, I set the SIM method to gather masses 95,96,75,50,173,174,175,176,177 at 25ms integration time and BFB evaluates just fine. So not a big deal as long as all the masses are in the SIM table at that retention time.

In SIM mode, the 4-BFB check is used to verify if the instrument can detect specific peaks. Since integration times can be adjusted, ratios from the BFB standard may not apply directly. For details, consult method 524.4.

I had realized that because I was giving EDB 500ms on the 107 peak but only 50ms on the 109 and 187 peaks. The NIST mass library could not identify it. At first I worried about that but realized that I already know precisely what compound is there by having the R.T. and 2-3 masses per peak. So it was then obvious that I had to have all the 4BFB peaks at the same integration time. Also, I found it convenient to include 50ms mass 107 in the preceding DBCM group and the subsequent PERC group. That made the baseline for 107 come out right every time without having to hand integrate.