Identification CF


i am attempting to create a CF for identification of an analyte during routine analysis. the equation is as follows: 

│RT (sa) – RT (st)│/ RT (st) *100


RT (sa) = Retention time of the sample

RT (st) = Retention time of the standard

Our specification is NMT 2.0 % difference. 

Recommendations on a CF setup that would spit out a pass/fail result would be appreciated 


  • How many times do you run the sample and standard per run? Is it just one standard followed by one sample or is it a sample in the middle of bracket standards?
  • gdun
    it is usually samples with brackets throughout the run, we compare the average RT of the standard to the samples 
  • Thanks. First you need a CF to calculate the average RT in standards. So label all your standards as S1, S2, S3 or S0101, S0102 etc, as long as it starts with S. Then create a Peak, Real, Calculated CF called AverageRT_Stds and the formula is S%.%..AVE(Retention Time). Then create a second Peak, Real, Calculated CF called Difference and the formula is ABS(((Retention Time-AverageRT_Stds)/AverageRT_Stds)*100). The ABS stands for Absolute and will report any negative results as positive, so instead of -1.1245 its 1.1245. 

    To add a Pass or Fail to each result, set up a Peak, Bool, Calculated CF called Test_RT and the formula is LTE(ROUND(Difference,-1),2.0) Set it to use as Position and for translation 0 (ie any values of Difference, when rounded to 2 decimal places, which are not LTE 2.0) to Fail or "Outside Spec" whatever suits you. Then set the translation 1 to Pass or whatever you like. I recommened the search order of all above CFs to Result Set Only for ease of use. Plus keep the naming as I advised because any CFs that depend on a summary custom field must have that summary custom field present before it can make the comparison, hence alphabetically calculated before D......then checked for a pass or fail. 

    Then make sure you add the "Summarize Custom Fields" function as the last line of the sample set before processing and your result set will populate results in all the 3 CFs. Good luck.