2 Replies Latest reply on May 7, 2018 1:12 PM by ryoboyle

    How to calculate RPD between compound amount sums


      We analyze PCBs on a dual column with two uECD detectors. We are required to check the RPD between the two signals and I would like to add this into the sample report. I am currently using a report that has a table with the compounds grouped by signal and the amounts summed. I'd like to get the RPD of those two summed amounts but I can't figure out how to make this happen. We are using Openlab CDS Chemstation Edition, Ver C.1.05 [35]


      I could also separate the tables by signal and have two tables per sample where the the entire row for the compound amount is summed, but I am not sure how to get the RPDs for those values either. I have attached the report I am currently working on.


      Any help is appreciated! Thank you.


        • Re: How to calculate RPD between compound amount sums

          Hello Brittany,


          Before I dive into answering your question, I would just like to point out that the RPD calculation is built into MSD ChemStation Enviroquant reports as well as Environmental MassHunter Quantitative Data Analysis reports. These software packages are generally better equipped than OpenLAB ChemStation for the type of analysis you are performing.


          In an intelligent report, there are a few ways you could set up this calculation. If you want to keep your current layout and want to avoid splitting the results for your dual ECDs into two separate tables, you will need to make a couple hidden tables in order to define some aggregators.


          Each table only needs one column, that being the Amount column. You then want to set up a filter on the tables so that one contains only the front detector results and the other contains only the back detector results. Below is an example of setting up a filter base on Signal Description in the table properties:


          Then, to prevent these new tables from showing up on your report, you can make them invisible by going to the Advanced tab in the Table Properties and un-checking the Visible checkbox:


          In order to set up the aggregators that can then be used to calculate RPD, you will need to edit the Amount Column Properties. Then, enter the Expression Editor from the Value tab and click on the option to 'Save Expression Result As'. In the resulting pop-up window you can choose to save the expression as an Aggregator and assign the Aggregator a name, as shown below:



          Once you have aggregators defined for the front and back signal amounts, you can then use these aggregators to calculate the RPD. Below is the equation for RPD and, if I am understanding your question, I believe you want to define C1 as the sum of your front detector amounts and C2 as the sum of your back detector amounts:


          You can create a custom field on your report to calculate RPD. In the below expression, I defined my front detector amount aggregator as FrontDet and my back detector amount aggregator as BackDet:



          NOTE: The field where you calculate RPD must be further down on your report than the hidden tables where you define the aggregators.


          Hopefully this helps.

          • Re: How to calculate RPD between compound amount sums

            Hello Brittany,


            I just wanted to follow-up with you to see if you needed any further assistance. Please let us know if you do and we would be happy to continue working with you. If the previous reply answered your question, it would be appreciated if you returned to this thread and marked a Correct Answer to increase its visibility to other users.