AnsweredAssumed Answered

Sample amount clarification for methods with internal standards

Question asked by jherpel on Oct 18, 2018
Latest reply on Oct 19, 2018 by ryoboyle

My lab runs D4815 on a 7890 using Open Lab CDS and I noticed a discrepancy between our method and what is described in ASTM D4815 in regards to the sample amount. Internally, it looks like our techs measure 0.5ml of internal standard into a 10ml flask, record the mass, then fill to volume with sample and record the overall mass of sample + ISTD.  According to ASTM, they should be recording the mass of the ISTD, taring the flask, then recording the mass of the sample separately.  In the software, they are entering the sample amount as "mass of sample +ISTD" and then ISTD as "mass of ISTD."  I'm trying to get a clarification in regards to whether or not they are entering this value correctly, or should they only be entering the mass of the sample alone instead of the mass of the overall mixture.  I'm not clear on the math that is going on in the background of the software.