I would like to know the percentage purity of some impurities in my test sample. The Ref. Standard, i am using has got the same impurities in it. The retention time of the impurities in my sample matched against my Ref. Std. So my question is could i use the percentage area of the relative impurities from my ref. std. for calculating the percentage purity of impurities in my test sample? is it possible? or i have to purchased the Ref. standards for all those impurities instead??
I think you would have to buy each separate impurity reference standard. By using the peak areas alone there is no proof that the RRF (relative response factor) is the same as the API. Thus, the correct %impurity would diverge from the true value that is based on mass.
Thanks for your reply Bruce Neagle. I was little confused, but its all clear now.
You may have to have a small quantity of these impurities manufactured by an outside lab of organic chemists.
Yes, I agree with Bruce, for doing quantification, you need to have authentic standards, maybe you can by from USP, Sigma, Merck or others, best regards
If you accurately know the percentage of the impurity in the reference standard then you can use the peak area to calculate the percentage of the impurity in your sample (note to all: he is NOT using the API for quantification, he is using the impurity peak area). If you do not know the percentage of the impurity in the reference material then you do need to purchase the individual impurity compounds as pure materials.
Thanks for the information Mark Krause. I have one information to share. Lately, I came across a standard purchased from Sigma Aldrich. What's unquie about it was that mostly the reference standards are 99% above purity with very less amount of impurity and has only one main Active ingredient, but this time what I came across the reference standard was the mixture of homologues so the % purity of one homologue was 93.1% and other one was 6% and they have given the total purity of 99% above. So, for finding the percentage purity in technical grade material I can't use 99%. Right because I have two difference RT's in my test sample too. I have to choose 93.1% for one peak with matching R.T and 6% for the other matching R.T. Lastly, I got impressive results. That's why I put up the above question why can't I not use the percentage of impurity present in standard to cross check the percentage impurity in my technical grade sample if they got to have same R.T.
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