Raw material testing

Chromatography Forum: GC Archives: Raw material testing
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Thursday, September 7, 2000 - 04:26 am:

I have a procedure to analyze TNBP for impurities. TNBP must be > or equal to a certain percentage. In order to see the impurities there is a split flow and the sample is also diluted. But, the TNBP peak is still overloaded. How do I determine system suitability (tf, res, k', plate #) for this method when my analyte is overloaded?
Thanks for any suggestions.

Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Tuesday, September 19, 2000 - 12:33 pm:

I have no clue what TNBP is. I assume it must be the latest gasoline additive.

This is also a problem for pesticide manufacturers. I have some familiarity with the problem, but I'm not an expert. They must identify and quantitate impurities down to something like 0.01% (or some other low level) on defined manufacturing processes.

In the cases I know about, it was necessary to 'write off' the major peak in the impurity analysis. You're right--when you get the major peak to chromatograph properly, the impurities are too small to see. So, the suitability criteria (resolution, etc.) was based on the expected impurities. Peak overload in these cases did not affect the impurity peaks. These chemists used 30M capillary GC columns with 1 hour run times to separate their samples. It was quite impressive.

In a separate analysis, the major peak was analyzed against a high-purity standard to make sure it met concentration requirements.

The solution to your problem may be somewhere between these extremes.

Let's not talk about identifying and quantitating all those tiny peaks that are suddenly going to become very large if you actually try this.

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