Subraction of a blank CF

ydan1977

Hi ,

Custom field required : Area_subr = Area-(BL(Area)) taken blank area from blank injection labelled BL then use this in Y-value for quantification (replace Area with Area_Subtr

Works fine in calibration curve but also subtracts blank area from sample - unknowns

If CF type standards only then does not work (assuming since Blank injection is an unknown)

Only want to subtract blank from standards for quantification purposes

Any ideas ?

Empower2019

Can you call the blank a control? Then set the cf to work for only standards and controls?

ydan1977

I tried this but didn't seem to work (no area subtr CF performed)

Summarise CF with a label for standard 'S' perhaps with blank unknown and types just leave as 'All' in CF , would that work?

I am not prepared to process again until confident this will work !

shaunwat

You don't need a custom field to do this. Derive a channel that uses blank subtraction. 

edit: hmmmm... just read past "blank subtraction" and realized you only want this on standards. That's not going to work. You will also be intentionally biasing all of your results if you only correct for standards, which isn't a recommended practice...

ydan1977

I require blank area for quantitation

I was under the impression this was to remove baseline drifts ?!

ydan1977

I think I must be over complicating this , surely correction can be made only on standards for calibration curve (Area_Subtr= y value ) and not for unknowns ? 

Empower2019

If your Y value is set to Area_Subtract then all of the unknowns will be calculated using this calibration curve too, similar to normal area of unknowns using the calibration curve of area in standards.

ydan1977

Hi ,

Think I have it now

Do not include AREA_Subtract as part of calibration curve therefore does quantify and subtract blank twice from unknown using CF 

Dan_Ramlose

Assuming you have no means to improve your chromatography and you have guest peaks adding to your analyte areas, I think the only reasonable strategy is to tick your blank injections, establish the contribution from your matrix/system and subtract it from EVERYTHING. Doing so requires no CFs. 

kneubuem

I'am facing exactly the same problem as ydan1977 described in the initial post.
Can you please tell me, what the final solution to this problem was?

Empower2019

If you derive a channel to subtract the blank then that channel will apply to all standards, samples and controls. Its not good practice to only subtract a blank area from a standard and then use that standard to quantify samples which have not been compensated for such a blank, Your results would be inaccurate.

kneubuem

I need to subtract the Blank Peak only from the standard solutions, as the sample is an organic solvent which is measured undiluted. This means the impurity from the Blank is only in the Standard solutions.
It is for a GC Method.
Is there a way to do that with Empower? 

Jahangir1986

ydan1977 said:

Hi ,

Custom field required : Area_subr = Area-(BL(Area)) taken blank area from blank injection labelled BL then use this in Y-value for quantification (replace Area with Area_Subtr

Works fine in calibration curve but also subtracts blank area from sample - unknowns

If CF type standards only then does not work (assuming since Blank injection is an unknown)

Only want to subtract blank from standards for quantification purposes

Any ideas ?

Which area was used for calculation at excel sheet? Please use area_substr instead of area for standard solution during result verification with empower result. Please process blank & standard together from sample set window only and lock channel them. Then process sample from sample set window. 

I think your problem will be solved completely by following my statement.