Chromatography Forum

At the risk of looking absolutely stupid, I'm reaching out to the very informed members of this forum for a simple answer to something which is just not clicking for me.

So I set my proc method to "Average by Amount" and I put the concentration of my Standard in my component editor, I label up standards and samples in sample set, clear calibration, calibrate and quantitate.

For argument, lets just say my Injection volume is 6 mcl and my sample was prepared by weighing out 2g (2000mg). I know Empower takes the area of sample, divides by average area in bracketing standard and multiplies by conc in component editor but how does it take into account the injection vol/sampleweight when calculating final amount?? I use an external standard, linear through zero.

What units do i put my sampleweight into? I cant seem to grasp that last part where the injection volume and sampleweight plays a part.

Thanks in advance.

...For argument, lets just say my Injection volume is 6 mcl and my sample was prepared by weighing out 2g (2000mg). I know Empower takes the area of sample, divides by average area in bracketing standard and multiplies by conc in component editor but how does it take into account the injection vol/sampleweight when calculating final amount?? I use an external standard, linear through zero.

What units do i put my sampleweight into? I cant seem to grasp that last part where the injection volume and sampleweight plays a part.

Amount is the result of using your standard response and associated concentration to determine how much of a given component is in your sample. (y-b)/m=x, which is the amount in the sample injection. This raw amount is divided by sample concentration (as determined by dilution factor entered), bringing you back to your original sample concentration.

If your injection volumes between standard(s) and sample differ, the reciprocal of the ratio of volumes is used to normalize things.

If you want to enter units into your amounts table along with the concentration(s) of standard(s), make sure that their labels start with a "S" and do so in the right-hand column by starting with a < character ("<mg/mL", for example).
Sample amount units are assumed to be the same as standard units (so use the same units for everything). If you enter sample weights, I *think* that they get thrown in as a divisor to what would otherwise be a regular amount calculation so that you end up with a "per unit" amount.

Hope this helps.
It is usually a good idea to play with some of your standard and sample peak areas and dilutions in a spreadsheet to make sure you and Empower "understand each other" when doing anything new.

Thanks very much DR, I have read your reply a few times and its sinking in. I guess I'm trying to account for the weight of standard prepared and the weight of sample prepared. I need to calculate a "%w/w" amount and the formula is:
(Weight Adjusted Peak Area/Weight Adjusted Peak Area of Bracketing Std X Conc of Standard). I presumed you could get an amount from Empower for this, then just multiply the result by your (Theoretical Wt/Actual Wt) for both standard and samples but its not giving me the same result as an Excel spreadsheet, which is odd.

I'm going to have another look at it and see if anything jumps out, thanks again for reply.

Off the top of my head, I'm thinking that you should divide by standard concentration... Play with the cancelling of units to see if that is correct.
The simplest Empower calculation should yield either an amount (weight), concentration (weight/unit vol) or a concentration (also weight per unit volume but without dilutions mucking things up, and only if concentration is chosen over amount in the processing method's Components tab).
Inclusion of a sample weight or a secondary calculation (multiply by 100 and divide amount by label claim or theoretical weight %) is typically what will bring you from an amount to something that you can evaluate in terms of pass/fail - unless you make sample related entries in the amounts table (remember, there are always several ways to get something done in Empower).

Thanks DR. I haven't access to Empower again until next month but I may be over thinking this in terms of software functionality. I remember doing something similar earlier this year and the amount figure (regardless of the units) worked out.

Where I'm getting tangled up is the "weight adjusted" part. My current Excel formula is "Weight adjusted peak area of sample/Weight adjusted peak area of bracketing standard * Correction Factor). Surely Empower DOES provide weight adjusted amounts when you put in the Sampleweight of your sample plus concentration and purity of your standard, unless I'm missing something?? I'm not concerned about the Correction Factor, I can just multiply Amount by Correction Factor. Would I be right in saying that if I put in the conc. (units %w/w) of my standard plus the purity in the component editor and label my sample set as follows ill get weight adjusted amount?

Standard 1 S01 No Sampleweight or Dilution
Sample 1 U01 Sampleweight = 2000 (mg) Dilution of 0.25 (Its a dilution of 5mls stock into 20mls flask)
Standard 2 S02 No Sampleweight or Dilution
Clear Calibration
Calibrate SO1 SO2
Quantitate U01.

Regards.