8 Replies Latest reply on Jan 18, 2019 3:09 AM by wydnaa

    Openlab calculation (ISTD)

    tonyyting

      Hi Agilent technical support: I had a question about the calculation of ISTD in openlab. If our ISTD is not pure, maybe 99.1% in purity, shall we multiply the number to correct the final results?@

        • Re: Openlab calculation (ISTD)
          abdur

          Hi tonyyting,

           

          When you build your calibration table you can input what the ISTD concentration is.  Based on that concentration, the software will determine the concentrations of your sample.  If your ISTD amount is different for whatever reason, you should modify that amount in your sequence table, or in the quantitation settings of the report settings.

           

          Please let me know if this answer isn't clear, and provide the revision of openlab you are using.

            • Re: Openlab calculation (ISTD)
              tonyyting

              Hi Abdur,

               

              Appreciate for your prompt reply. However, can you detail specify how to input ISTD concentration which determine the concentration of results? Is the number shall be in calibration table "multiplier" or "multiplier" "dilution factor" in the sequence table?

              Btw, sorry for my miss that to inform you we are using ISTD% method.

              The version number is A.01.05

            • Re: Openlab calculation (ISTD)
              mr.white

              Hello,

               

              The easiest way is to set the multiplier to 0.991.

               

               

              I hope I was right

              • Re: Openlab calculation (ISTD)
                mr.white

                Keep in mind that a Multiplier and Dilution Factor only affect the Concentration not the Amount.

                You also can see this in your processing method. U said you are using a different Version of Open Labs.

                I hope it look similar then this.

                 

                Amount * Multipliers * Dil.Factor = Concentration

                 

                Regards

                White

                • Re: Openlab calculation (ISTD)
                  wydnaa

                  Hello Tony

                   

                  Be careful with this!

                   

                  If the same internal standard, of the same purity, at the same nominal concentration, is used in both samples and standards, then it doesn't really matter what value you put in the internal standard column.  You can simply put the nominal concentration that you're using and all will be well!!

                   

                  Have a look in the help documentation about how internal standard concentration is used in the calculation of amount and concentration.

                   

                  Cheers

                  Andy

                  1 person found this helpful
                    • Re: Openlab calculation (ISTD)
                      mr.white

                      U can change this in your processing method. The multiplier only affect the samples u put a value.

                      If not it just use 1.00

                      Dilution Factor varies, what you selected before.

                       

                      But I also would like to know more how the ISTD is used exactly.

                      A sample calculation would be cool.

                        • Re: Openlab calculation (ISTD)
                          wydnaa

                          Hi Mr White

                           

                          With internal standards, relative response factors and relative amounts are used.  These are well described in the help for OpenLab CDS.  Have a look in the how-to guides in this section:

                           

                          Home > How To > OpenLAB CDS > Data Analysis > Calculations and Background References > Quantitation > Quantitation of calibrated compounds > ISTD calculation

                           

                          The calibration curve is determined by plotting analyte response/ISTD response against analyte amount/ISTD amount.

                           

                          The equation for that line can then be used to calculate the amount ratio of unknowns, which, when multiplied by the amount of ISTD in the samples, gives you the amount of analyte in this sample.  This amount can then be corrected using multipliers and dilution factors.

                           

                          So, back to my original answer, if the same internal standard, same purity and concentration is used in the standards and samples, there is no need to compensate for its purity.

                           

                          I think that makes sense to me

                           

                          Andy