[Potter Karl]

Hi all,

Here is my question:

I generated a multiple points calibration curve adding increasing concentrations of benzene (synthetic standard) inside multiple Thermal desorption tubes by manual injection (in quadruplicates) and ran them on a TD-GC-MS. Here are the concentrations of the calibration curve:

0.25 ng/ml (4x)
0.50 ng/ml (4x)
1.25 ng/ml (4x)
2.50 ng/ml (4x)
5.00 ng/ml (4x)
10.0 ng/ml (4x)

The R2 of the calibration curve is = 0.9971 (quite good indeed)

Thereafter I loaded 10 thermal desorbion tubes with 500 ml of human breath each and analysed them with the same TD-GC-MS.

I can easily identify the benzene peak and quantify the area under the curve of the peak. How do I use the calibration curve to extrapolate how many ppm of benzene are in each breath sample collected for each tube.


May you please help me with this

Thanks

Karl

[Arkcon]

OK.  You have known values for the standard cure you built, and you say you have good R-squared.  That means you have areas for your results.  How will you compare your unknown samples to your known?

Consider: the 10 ng gives an area of 1000, the 5 ng gives an area of 500, now what?  If your area of the breath sample is 500 or 1000, you'll know exactly what the answers is.  But that's unlikely to happen.

There's more work than this, depending on your level.  But you should be able to start here.

[Potter Karl]

Hi Arkcon,
Thanks for your quick answer....but not sure if this answer my question .

Yes the calibration curve was generated with mass amount of benzene (0.25 ng, 0.50 ng, 1.25 ng and so on....) and quantifier/qualifier EIC m/z are used to measure the area under the curve of the calibration curve...

Hovewer, the breath was collected under pumped monitoring, therefore the relationship between atmospheric concentration and the mass of benzene in a volume of air plays a role in attempting to calculate the breath concentration of the analyte...it is associated with Avogadro's law but cannot figure out the right calculation to go from the calibration curve to the ppm amount in human  breath

 

[hypervalent_iodine]

Hi Arkcon,
Thanks for your quick answer....but not sure if this answer my question .

Yes the calibration curve was generated with mass amount of benzene (0.25 ng, 0.50 ng, 1.25 ng and so on....) and quantifier/qualifier EIC m/z are used to measure the area under the curve of the calibration curve...

Hovewer, the breath was collected under pumped monitoring, therefore the relationship between atmospheric concentration and the mass of benzene in a volume of air plays a role in attempting to calculate the breath concentration of the analyte...it is associated with Avogadro's law but cannot figure out the right calculation to go from the calibration curve to the ppm amount in human  breath

So, were you running your standards as gases or solutions? Presumably if you ran them as gases, the benzene you added to those tubes was added to air, and your blank sample (which I am assuming you ran, but if you didn't, you should) would then have atmospheric benzene taken into account. There might be random errors associated with different air samples I suppose, but you would see this in the precision of your results (and I think it would be negligible anyway).