reagent grade for standards in quantitative analysis

[Edde]

What reagent grade should I use to prepare calibrating standards and QC for a quantitative test for ethylene glycol and diethylene glycol by GC-MS? I've got ACS, spectrophotometric, GC and AR grade reagents and powder form chemical. Is the powder form reagent the best?

What will happen if I use spectrophotometric grade?

Please help. Thanks.

[Peter Apps]

The obvious answer is to use the highest purity that you have, but there are other things to be taken into account.

Do the impurities interfere with the analysis ? - in chromatography this usually implies overlapping peaks, as a crude example 1% of octane in otherwise pure n-hexane would be less of a problem in GC than 0.1% of methylpentane that would probably co-elute or overlap. So your first step would be to run each proposed standard and see if there are any interfering peaks.

How accurate is the purity given on the label ? Many reagents and solvents are guaranteed to have a less than a certain maximum of impurities. Very often they are much better than this minimum specification - for instance a 98% purity reagent may actually be 99.9%. This sounds good, but if you correct your calibration for 98% purity your results will come out 2% low. Certified reference materials (which is what you should use if you can get them) have their purity specified as a value with an uncertainty.

And do you really have either of these glycols as a powder ?

Peter

[Consumer Products Guy]

Are you assaying as is from either water or methanol on a column like the "624" capillaries detailed in the USP glycerin monograph, or are you dissolving in DMF and making trimethylsilyl derivatives and using a non-polar capillary?

Like Peter stated, these are NOT powder form, all liquid. If your solvents don't contain impurities that co-elute, than likely OK to use. But, like Peter also stated: best to use purest solvents you have.

Are you looking at EG and DEG as impurities, or as a possible test for economically-motivated adulteration? Believe me, no one would adulterate a raw material or a product at trace levels, would not be economically feasible.

[Edde]

If I have 2 chemicals, both of which have purity of 99%, one states "spectrophotometric" while the other states "GC" after the purity. Which one should I choose?

In the one with GC stated after the purity, does it mean it has been tested by GC method to be free of impurity that will interfere with or coelute with ethylene glycol in GC?

Likewise, does "spectrophotometric" mean no interference in spectrophotometric method?

There is an "anhydrous, 99.8%" ethylene glycol from Sigma. I think it means a powder form, isn't it?

Thank you very much.

[Peter Apps]

If I have 2 chemicals, both of which have purity of 99%, one states "spectrophotometric" while the other states "GC" after the purity. Which one should I choose? GC

In the one with GC stated after the purity, does it mean it has been tested by GC method to be free of impurity that will interfere with or coelute with ethylene glycol in GC? Yes

Likewise, does "spectrophotometric" mean no interference in spectrophotometric method? Yes
There is an "anhydrous, 99.8%" ethylene glycol from Sigma. I think it means a powder form, isn't it? No, ethylene glycol is a liquid at room temperature

Thank you very much.

[Edde]

Thank you.

How about if I have 2 chemicals, one is 98% GC and the other is 99% spectrophotometric? Should I choose 98% GC for my GC-MS application?

[Peter Apps]

Edde

This could go on for ever !.

Whatever you have, run it on the GC-MS and see for yourself whether you have interfering peaks, and/or extra fragments in the spectrum that point to co-eluting impurities.

Peter

[Edde]

Thank you.