Chromatography Forum

Hello all,

I am attempting to quantify Class 3 solvents using USP 467.

In section 9 of USP 467 it says

"In that case, the procedures described in this chapter, with appropriate adjustments, are to be applied wherever possible and USP Reference Standards, where available, should be used in these procedures. Such procedures should be properly validated as described in 〈1467〉"

After trying to use mimic the procedure used for class 1 and class 2 my results haven't been looking very great.

Does anyone have experience making the appropriate adjustments?

How much can we alter/deviate from procedures described earlier in the chapter? (i.e changing column length, adding internal standard, etc.)

When you say your "results are not looking great", I assume you mean poor resolution. USP<621> Chromatography, list the acceptable changes to the method. USP<467> has Procedure A or B which gives you the option of a Wax phase or a Cyanopropyl phase.

What solvents in particular are you trying to quantify? Could you post your GC conditions and chromatogram if possible?

I am having problems with 1-pentanol and 3-methyl-1-butanol. I am adding 2,5,10,20,30 ul of 5000ppm class 3 usp solvent std into a 2 ml headspace and at 20 & 30 ul injection the peaks shape begins to distort. I need those injection volumes to make my calibration curve and I am already at the maximum split ratio possible in my given column and flow rate.

Are you validating a method from scratch, or performing a method transfer?

Injecting different volumes seems like an unconventional approach for headspace analysis by <467> , unless it has been updated in the last few years. Which conditions of 467 are you following exactly? Or are you validating a method with conditions that differ from those in the USP 467?

For instance, USP 467 recommends injecting 1.0ml. I would make up solutions at different concentrations for a calibration curve and add the same amount to each headspace vial (and also inject the same amount) rather than injecting different amounts. Plus if you have a fixed loop headspace system you can't change injection volume.

Also bear in mind you'll have to prepare solutions with respect to sample - so if your sample concentration is 500mg dissolved in 1mL of solvent, you will have to adjust your standard concentrations accordingly to get a mid-range standard that corresponds to 5000ppm with respect to sample preparation.

Also - are you using 10mL or 20mL headspace vials?

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When I perform 5-30 uL injections of the Class 3 mixture from stock (5000 ug/ml), I can see all the peaks as expected from the supplier CoA.

If I choose to dilute the stock with DMF, which is what the stock is already in, and inject 1 mL of the working standard using headspace, both chromatography and retention times start changing drastically. The chromatography no longer resembles the chromatography in the CoA.

I am having problems with 1-pentanol and 3-methyl-1-butanol. I am adding 2,5,10,20,30 ul of 5000ppm class 3 usp solvent std into a 2 ml headspace and at 20 & 30 ul injection the peaks shape begins to distort. I need those injection volumes to make my calibration curve and I am already at the maximum split ratio possible in my given column and flow rate.

Are you only putting 2,5,10,20 and 30 ul into a 2ml vial then injecting from the headspace?

Normally you make standards so that all of them have the same volume of solvent and are in a 10 or 20ml vial, and you draw 1ml headspace from that large vial. If you are pulling from a 2ml vial you will be making a vacuum in the vial and that will cause different amounts of the analytes to evaporate into the headspace.

Your solvent volume and injection volume should remain constant through all injections. Changing injection volume onto the column would require a different inlet setting for each amount so that it would be optimized and would be considered a different method for each volume injected.

Thanks. You helped me a lot.

Hi MadelineThom,

Were you able to analyze class 3 solvents? If so, could you describe your preparation?