The concentration is calculated by comparing the peak area of the analyte in the sample with the peak area of the standard of a known concentration. If you have used an internal standard you will use the area ratio between the analyte and the internal standard. I guess you used at least one standard point of a known concentration? How to find the correct area of the correct peak depends on how you have set your mass spectrometer. But if there are many peaks you should be able to filter out only the mass to charge ratios you are interested in.

yes marcus sir is right. for quantification at least you require one known concentration of standard. or you can also go with difference concentration injection and then according to graph equation you can calculate your concentration in sample...

Thank you Marcus sir,But I am totally new to it and very much confused .

I know the concentration of my IS ,i ran on GC/ms but i don`t know which area i have to put in formula to calculate concentrations.Please tell me that what i have to do first and the next during interpretation of my GC/ms chromatogram (step by step ).

The first thing you will have to do is to choose one IS which is a unique molecule and not a mixture of several alkanes.

So first take a pure alkane, for example C20, inject it to determine its retention time.

In a second time you will measure the area, determine the response factor, ...

HI GUPTA ...

If your internal standard is pure, it will give only single peak readily in the chromatogram. If you are using EI souse,  mostly you may not get Molecular ion peak or if its CI you will be getting M+H peak those you can observe in the spectrum. in case of EI you have to know the m/z of the base peak, then go to selected ion chromatogram peak option. there enter the m/z corresponding to ur IS. for that peak you can ask to give Peak area in the peak labeling options, like that you can pick the right peak among many. then by taking peak area ratio, and by plotting the linearity curve you can calculate the concentration. i hope it may be helpful to you. 

BEST REGARDS.

thank you reddy jee,i would do this way.Thanks for your suggestion.

It will not work since you have a mixture of alkanes, and (i) Mw of alkanes are generally not visible in EI), (ii) alkanes have all the same base peak

Moreover you will have to know the exact % of the alkane you will choose in your mixture.

Once you've sorted out exactly what you are using as an internal standard (I agree with the people above, you need one compound of which you add a known amount to your sample) you can use a simple equation as follows:

massunknown = (massIS/areaIS) x areaunknown

If you then need a concentration of the unknown in your original sample you can then divide the answer by the weight of your sample/volume of your sample (depending on what type of sample it was).

I agree with all the earlier responses, but there is another thing you could do. This allows you to standardize your instrumental analysis. You could use an internal standard that has only 1 peak (5-alpha-Androstane) which is commonly used. You can identify this peak's retention time by injecting the standard into solvent and run it for GC (this works as a calibration standard).

So now you know its retention time, so next inject into your sample and run for GC-MS. Once you get it's peaks, you should do an integration for your targeted compound. Once you get the area of your peak, from here you can identify your concentration by linearity slope. Normally, all laboratory that analyses alkanes have a data sheet that allows you to calculate the concentration from the area of peak. If you do not have this sheet, it would be difficult for you to calculate manually.

Also, it applies the same method for your C20-C40 internal standard. You can spike it into solvent and run it for GC. This allows you to identify your peaks well with less disturbance of other peaks. If other peaks are still present, increase the concentration of your internal standards (i.e; 0.1ppm, 1ppm, 10ppm, 50ppm). From this you established a calibration standard analysis. An alternative, you could use GC-FID instead of GC-MS. GC-FID allows you to determine alkane peaks easily too.

thanks Andrew,you really helped me out of the problem.I am now very much clear .Thanks a lot..........such a nice suggestion from you.

Andrew, Please tell me about this alkane data sheet.What is it and how it could be available.

This data sheet should be made by yourself using an excel sheet. Firstly, you should analyze some calibration standards. All with different concentration (i.e; 0.1ppm, 1ppm, 10ppm, 50ppm). So since this is your known concentration, after analysis through GC, you can identify the area of the peak. This area of the peak could be used to calculate the relative response factors (RRF) for each compound in each calibration standard. From the available RRF, you can determine the average RRF for each compound at different concentrations. After running a sample with your GC, you can use the area of individual compound of the sample to divide with your RRF. From this you can determine the concentration of your compound in the sample. However this is the basics for calculation, if you have included some surrogate standards and internal standard in your sample then the calculation method is a little different.

You have to plot every component in C8 to C40 range's conc vs Response factor from the range of conc you prepared. The plot (Calibration curve) and the response factor of the unknown sample can be used to calculate the conc  

Another very easy way to do this is the use of excel sheet to plot area against conc. using  y= mx you can calculate your conc.

secondly the GCMS software can also do it for you. But you will need to specify which type of quantitative method you are using E.g ES- external standard method, IS- internal standard method.....then you can produce a calibration curve and automatically get the conc of each compound...it takes series of steps to do this that is why i suggested the excel sheet 

Hi,

Please , how to calculate response factor and calibration curve by depending on results are obtained from GC-FID

thanks

my email

[email protected]

Hi Sarika,

The first thing you should do is to get help from an experienced GCMS person on site.

From your question and your reactions it seems you don't have a lot of experience with GCMS. GCMS can be a complicated technique, there are many mistakes novice users can make. When you start using a GCMS you should to do this under the guidance of an experienced  user.

Regards, Alex

Hi...

I used micro GC to analyse sample gas and get graph area versus retention time. From the graph, how can I calculate concentration of the gas?

Thank you in advance.

Regards,

Izdiharr

This is a nice paper on relative response factors (RRF):

Rome, K. & McIntyre, A. Intelligent use of Relative Response Factors in Gas Chromatography-Flame Ionisation Detection Chromatography, 2012

As thumb rule for GC calculations

• First you run pure standard with known concentration and note down retention time and peak area.
• Now run sample and note down the chromatographic area of peak appear at same retention time as that of standard. Ignore other peaks.
• Calculate concentration= sample Area of sample divided by area of standard multiply by conc. of standard
• It gives same units  as that of standard

Also, you can make a calibration curve and from that, you can find the concentration of your sample.

first, make at least three (maximum can be many) known concentration series from your standard. 

then run each standard and record the peak area against the different concentration of the STD.

then plot a graph concentration Vs area. 

then run your sample and record the area of the corresponding peak. 

finally, you can find the concentration fit with this area in the calibration curve. 

Whatever method you are using - calibration curve or internal standard - you need to do it fresh each day as the response from any detector is not always uniform.  An internal standard needs to be internal to the sample i.e. added to the sample not in advance.  You can then use the equation I gave earlier to work out your sample concentrations.  A calibration curve should really be run each day or each time you start a new batch of samples as each time you retune the mass spectrometer (which should be every day or between batches of samples) the response will vary slightly and in any case will alter slowly over time as the ion source gets dirtier.  You do not need to calculate a response factor to do this.  If you are using GC-MS it should also be easy to identify your internal standard from the mass spectrun.  The only problem will be if the compound you are using as an internal standard is also present in the sample - in which case you will have a problem as the peak will be a combination of internal standard and sample and your quantification will be inaccurate.

https://www.youtube.com/watch?v=9j65SIlv4hM

check the site. it would solve your problem. Cheers

I recommend Duru's answer

Best Regards

Thank you very much !

Might be a naive question, but can a GC calibration curve for an internal standard be made irrespective of the method used (assuming same column and consumables are being used throughout)?

In answer to Austin, you can always generate a calibration curve for an internal standard (provided it will elute under the conditions used) but you must use the same methods and exactly the same conditions as those used for your samples. As I said above, ideally you should create a new calibration curve each day if you want really accurate quantification. This is particularly true for GC-MS as the mass spec will slowly get dirty and the response for each compound will fall off as this happens.

as Jaspal Singh Hundal

• irst you run pure standard with known concentration and note down retention time and peak area.
• Now run sample and note down the chromatographic area of peak appear at same retention time as that of standard. Ignore other peaks.
• Calculate concentration= sample Area of sample divided by area of standard multiply by conc. of standard
• It gives same units  as that of standard

@Valerie Steel please is it applicable to GC-FID? Is it possible to use the calibration curve and analyse products with concentrations higher than the standard concentrations used for the curve?

Hello Sarika, first if you want to perform quantitative analysis for my system SHIMADZU GCMS QP2010 plus has six ways to do this.. But the most common is the external standard method: where you prepare a serial dilution of your std run them and prepare a calibration curve.

*But since you have only retention time I need to ask the area is it from a std? If yes then you can use excel sheet to prepare your calibration curve and deduce the unknown conc.

@Ammaru Ismaila yes you can use this method with GC-FID. However really your callibration curve should cover at least most of the concentrations you are going to measure in your sample. You can extrapolate a concentration curve, but the further away you get from the actual, measured curve the less accurate the results are, especially if the curve is not linear. If you have lots of peaks at higher concentrations than your standard I would re-run the standard at a different range of concentrations. You should in any case re-run the calibration regularly to compensate for the inevitable, and quite normal, variations in the performance of your machine.

thank you @ Valerie...

Thank you @ Valerie.

I am using GCMS to sample ambient air and get isoprene concentration. But I am using different sample volumes of air for the standard (5ml) and the sample (3000ml). Will this affect the way the concentration is estimated. I suppose I can divide the resulting concentration by the volume relation but I am not sure

The calculation depend on the retention time for each compound in the standard solution(that appear as peak) that injected firstly in the device and after inject the sample, each peak has retention time thus each retention time that approximately with retention time for compounds in standard represent the same compound.the concentration is calculate by the ratio between retention times for compounds in standard and sample and some factors such as the volume of sample injected and the volume of standard.

thank you

Based on the peak area and retention time, you can easily calculate the concentration of the desired analytes. In order to calculate the concentration of your desired analytes, you have to inject the CRM along with the samples in which you are intended to calculate the concentrations. Then, You have to apply the following formula:

The peak area obtained from samples divided by the peak area obtained by the injected CRM * concentration in the injected CRM

Good Luck

Use peak area of standard sample containing same compounds as your product

There are two aspects which one has to address while calculating the concentration using GC-MS.

There are two ways by which you can calculate the concentration.

1. By adding an internal standard (Deuterated Alkane or Aromatic compound).

2. By obtaining a calibration curve using an external standard at varying concentrations (C8-C40 alkane mix, PAHs mix, EPA-phthalate mix and etc.).

Now comes the tricky part and i.e., The Response Factor.

Response factor for the compounds vary. So you have to be extra cautionary while using internal standards.

For example; You can not use an alkane standard to calculate the concentration of aromatic hydrocarbons, cyclic isoprenoids and etc.

The response factor for homologous alkanes do not vary significantly and thus you may use an internal standard like dodecane to calculate the abundance of long-chain alkanes.

Now if you want to calculate the abundance of PAH having Coronene, pyrene and other compounds as well in the solution, you may not use naphthalene as an internal standard. The aromatic hydrocarbons have relatively different response factors and that is why you need to obtain a calibration curve for each and every compound with respect to its external standard.

I hope my answer clears some confusion of yours.

Please I need some help,

How can I calculate mass fraction from GC analysis results? The only values I have are the relative abundance, Peak area in %, and the retention time

Share the few samples pick area value and standard samples pick area value on my email ([email protected]). A template will be provided to you by email. @Sonia Nkongho