Chromatography Forum

Can anyone help plz. When my report is generated, the amount is being calculated strangely: When I set up the method, I am using Average Calibration factor to determine the purity of my Sample; so according to the manual, the amount is worked out by Area of Unknown/ Avg Calibration Factor.

But even really low concentration samples (20%) are giving 98% purities.... I think its something in the settings but I have gone over it several times and cant find anything obvious or unusual. Does anyone know what it could be?

Salma

Maybe I don't understand the problem, but I think you have one or more standards and one or more unknown samples (of about 20%, but TC says it's 98%).

In your sequence make sure that "TYPE" of your unknowns is "sample". For your standards use "Cal:Replace" the first time and if you want to use the average of calibrations in various runs use "Cal:Average".

If you have a number of standards in various concentrations be sure you use the correct "Cal Level" in your sequence.

Please let me know if this helped you.

Kevin

Thanks for your reply. You understood it right, it is reporting a 20% sample as 98%. The settings on the sequence are as you suggested.

I have 1 standard which is 100% (We analyse and recover/incinerate waste solvents). Have you any more thoughts.....I thought it had something to do with the settings on the method for data analysis.

Thanks and any help will be gr8...


Salma

Since you have (bad) results, can you send me peak areas (if you want to use area, otherwise send me peakheight) of your 100%-standard and your 20%-sample. If your injection was correct there should be a 5:1 ratio in peak area. If the peak areas are correct there has to be a TC-setting incorrect, which should be easy to find.

Peak areas are fine. I can manually calculate the result but TC is not doing it correctly. Do you still want the areas?

Don't need the areas if they're fine.

I can see only two ways of getting the wrong result from here: either the calibrate-calculation is not OK (for me the most probable) or the report has a wrong calculation.

If the calibration is not OK, i suppose the calibration factor is wrong. I suggest you save your current TotalChrom-method as a backup. Then make a sequence with only your 100%-standard, use Cal:Replace this time. Also inject a 20%-sample and be sure that Sample is selected (not cal:average). Use the current TotalChrom-file.

If this gives a good result: you can delete the backupped TotalChrom-method.

If areas are fine, I think that the problem come from your report. Verify it & try to use Adjusted Amount.

Thank you Reda. I managed to resolved the problem by putting in the correct injection volume in the Global Calibration Information section. Just out of interest, when would you use Adjusted amount?

Also, If I have to increase my Bunching Factor, does that mean i should increase or reduce my Sampling Rate?

Thank you in advance for your advice.

Salma

Hi Salma

First exuse my bad english

Usualy I recomand to customers to use "adjusted amount" in there reports. "Adjusted amount" take all parameters filled in the sequence rows (sample amount, sample volume, dilution factor...etc) in his calculations. For example, if the sample & standard volume are different, "Amount" give you wrong result but "adjusted amount" give you the right one. Why? Simply because when you use "Amount", TotalChrom calculate the amount using the informatios stocked in the method. When you use "Adjusted amount", the software use the new informations intreduced in the sequence. For this reason, when you need to introduce any new parameter (ex:sample volume) do it in the sequence not in the method. I recomand you also to use automatic calibration in the sequence. This way is very usuful especilly when you have lot of samples & an autosampler.

For the BF, you must know that your pic must have at least 20pts to be integrated propely. I don't know if you remember the factor between "Sampling rate" & "suggested BF". In general it is equal to 20. How to choose the right value of BF? Run your sample with the defaults values of BF (1) & sampling rate (20pts/s). After that report the BF value suggested by the software & divied the sampling rate by this value. This will be your new sampling rate. Take care to choose the next higher sampling rate value available in the software. Ex: BF=6, Calculated sampling rate=3.33, Nearst available softwar's values= 2.5 or 5. Choose 5.

I hope that this modest informations will help you , don't hesitate to contact me for any further infos.

Regards

Thanks Reda,

You have been a great help. I did not realize the second part of what you said regarding the bunching factor and sampling rate calculation, so I will work with that information. As for your English, there is nothing wrong with it, you explained very well. Thank you and best regards,

Salma