gc standards for quantitative analysis

[jane bench]

What grade of solvents can be used for quantitave analysis in gas chromatography? Can anyone explane to me difference between reference material,analytical standard, just standard for GC and high purity solent? What is acceptable ito use in pharma QC laboratory for quantification?

[Don_Hilton]

Solvents: use a grade of solvent that is sufficiently free fo contaminatns that you do not get interference with analytes. Depending on the analysis you are preforming, you may be able to use reagent grade solvents or you may need specially purified solvents for your application.

A reference material is a material of known composition and of sufficient quality that it can be expected to give repeatable analytical results of a specified value for anyone properly analyzing a sample of the material.

An analytical standard is a material (often a pure compund) that may be used as a reference for calibrating an analytical instrument. In many cases, the standard may be purcachased already disolved in solution, making preparation of working standards fairly easy.

A high purity solvent is one that has been specially purified to avoid particular interferences. Purity has to do with ability to meet specific specificaitons. GC grade solvents have low leversl of compunds that often interfere with chromatograms.

I will let someone from pharma speak to specific issues for the industry, but as a minimum, you need solvents that will not interfere with analytes of interest by either containing compunds that would react with the analytes or otherwise interfere with the measurement. Purity of solvents must be sufficient that results will be reproducable.

Analytical standards should be of known purity, typically 99% pure or better - and reproducable. Variation in standard materials leads to variation in results. In some cases, compunds can not be obtained at high purity, but can be obtained at a certified level of purity. This can work also.

[krickos]

Hi

Don covered it well, just adding some pharma specific information from a recent FDA Q and A session:

Residual Solvents in ANDAs:
Questions and Answers (October 28, 2008)

Q11: Would it be acceptable to use a high purity solvent in place of the USP reference standard?
A: Yes, a high purity solvent may be used in lieu of the reference standard if suitable documentation (i.e., certificate of analysis) of the purity and source is provided.

[dimxaz]

Hi,

i've used a standard with 50 VOCs (2000 mg/l ).Then i made 7 standards with certain concentrations 10,25,50,100,200,300 ppb to make the calibration.

The problem is that the peaks in the 10 ppb graph are higher than those in the 25 ppb graph which has no sense..The same happenned with 50 and 25 ppb graphs..

Does anyone know what the problem may be??

(I have already checked the standard solutions and the fibber..)

Thank you!

[Peter Apps]

I have an idea, but I would like to look at the data first. Can you post the calibration graph (instructions in a sticky at the top of the LC page) or give us the raw data.

Peter

[dimxaz]

what exactly do you mean by saying "raw data"..??

[chromatographer1]

retention times and most importantly, the area counts of the peaks in question.

Rod

[Peter Apps]

[quote="dimxaz"]Hi,


The problem is that the peaks in the 10 ppb graph are higher than those in the 25 ppb graph which has no sense..The same happenned with 50 and 25 ppb graphs..


quote]

So: 10 ppb is higher than 25 ppb, and 25 ppb is higher than 50 ppb, therefore 10 ppb is higher than 50 ppb.

Are the areas for 10 ppb the same as those for 100 ppb by any chance ?

The raw data that I need to see is the peak areas for each level of standard (i.e. each concentration). To save my time, I would far rather see the calibration plots.

Peter