Ion ratio

hi,I am doing for drugs, benzos, maphetamines and opiates, analysis and in the criteria of aceptance I can add Ion ratio.  I did put of each compounds the value that was given to me while infusion and further analysis, but now I realize that I have variation on my Ion ratio.  I made up a formula that calculte the difference between the expected Ion ratio and the actual one and I have a lot of variation between -20 to 20%.  When i am looking into the processing method in QuantLynx, the software suggest 5% variation, so I am wondering if I am supposed to have about 5% variation and why my variation is about  plus or minus 20%.  I am using the same method with the same std and the same mobile phase with the same injection volume, same injection mode, basically same everything.ThanksChristine

Answers

  • I believe most clinical labs use 15-20% as a frame of reference for their ion ratio acceptance criteria

  • Hi Christine, my lab works in the food security field and we use ion ratios for confirmation in all our analysis. We are currently using the ratio variation guidelines stated in the EU legislation. This legislation allows different levels of variation depending on the relative abundance of the MRM transitions. For example, if the second transitions is less than 10% of the most abundant one, the allow variation is 50 %. To be more precise, the ratio of a transition which is 5% of the most intense one can vary from 2.5% to 7.5% for a sample to be considered "positive". For comparison we always use a "reference" sample in the sample batch which is a spiked sample at a desired concentration. We update the "reference" ion ratio for each sample batch since those ratios do change with column lifetime, source cleanness, ...

    Hope it helps

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