Chromatography Forum

Hi! Our lab recently moved over to a new Agilent 7080 GC using Chemstation, having used Chromcard in the past.

We're having trouble in the 'coding' needed to get chemstation to make custom calculations for us.

Basically from our old software using chromcard the GC would report back area under curves. We would plug these numbers into an excel spreadsheet with the formula

Sample conc = (ISTD conc * (response factor)) / (amount of sample added * slope of calibration curve)

We measure short chain fatty acids from freeze dried faecal material. We'd like to take into account small variations in initial starting material.

I have set up a new calibration table on chemstation. However, this isn’t taking into account varying starting sample amounts.

I see that when generating reports you can add custom columns but I’m struggling to find the ‘coding’ used that what help me recreate this formula.

Its a pain as well with each run generating a separate page/sheet in PDF or excel so we have a macro to view all the runs in a sequence together. I'm sure i'm just using the software wrongly but it isn't obvious how else to do it

Thanks for any help!

What version of Chemstation are you using? A, B or C? Are you using Intelligent Report Editor?

by changing the value under the dilution header in the sequence, it will change concentration calculated by chemstation, eg if you enter a value of 2, it will double the concentration calculated by chemstation.

Thanks for getting back! The version of chemstation is A.02.05.021. Yeah we use intelligent reporting. I've tried playing with the dilution and multiplier field but i'm not sure that's the the answer.

Maybe I need to play with the units; but if I make a calibration table using a series of standards from say 10-300 units (mM)

and then put say 50mg (as our freeze dried sample amount) in the dilution field it'll report much lower concentrations (as its dividing the final concentration by 50)?

If you are using intelligent reporter. The expression used is very similar to Excel. Agilent's manual on Intelligent reporter explained each function pretty well. Creating a good reporting template in OL Chemstation is easy but very time consuming. I would recommend to read the manual first.

I would just use the calibration table for peak naming, and ISTD identification. Other information are entered into sequence table or custom fields.

Take your formula as an example
Sample conc = (ISTD conc * (response factor)) / (amount of sample added * slope of calibration curve)

In your calibration table, add all peaks of interest. Give them a name. Identify the ISTD peak in the calibration table.

ISTD conc - create a compound custom field for ISTD concentration. Enter the ISTD concentration for each sample.

Response Factor - You can either enter it in multiplier cell of the sequence table or create another sample custom field for it. If RF is a static value that never changes, then store the value in the formula that calculate Sample Conc.

Amount of sample added - Enter it in the Sample Weight cell of the sequence table

Slope of calibration curve - Calculate a formula the slope in the template using standard potency, weight/conc, and peak area. Store it as a variable.

This is what the formula may look like.

=((Trim(Choose(2,Split(Compound_CustomField01, "|" ))))*1.23456)/(Sample_Amount*VarSlope)


FYI,
Whenever you made a change to sequence table and calibration table, the data set must be reprocess to apply the change.

In addition you can switch to OpenLAB CDS EZChrom, to which ChromCard was a predecessor. It will do the calculation you require by default.