VOC HS-GC-MS / linearity problem

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

4 posts Page 1 of 1
Hello everyone,
I need advice.
I have a problem with the linearity of the curve in the range from 50 to 200 µg. There is no problem with range from 5 to 50 ug.
I have 35 VOCs mix in DMSO.

A calibration curve is only prepared by adding an appropriate amount of standatd mix (DMSO) solution, e.g. 1, 5, 10, 20, 25, 50, 100, 200 µl, And ISTD Toulen-d8 to HS vial.

Response of ISTD is also smaller for higher point.
I suppose the reason could be a larger DMSO volume than the lower points and it's , Am I right?
Do you think that adding 1-2 mL of water can improve resposne ?

HS
Oven: 85*C
Loop: 105*C
Transfer line: 110*C
Time in oven: 35 min.

GC
DB-VRX (60m x 0,25 x 1,4 )
Split 1:40
Inj. 250 *C
no_peak wrote:
Hello everyone,
I need advice.
I have a problem with the linearity of the curve in the range from 50 to 200 µg. There is no problem with range from 5 to 50 ug.
I have 35 VOCs mix in DMSO.

A calibration curve is only prepared by adding an appropriate amount of standatd mix (DMSO) solution, e.g. 1, 5, 10, 20, 25, 50, 100, 200 µl, And ISTD Toulen-d8 to HS vial.

Response of ISTD is also smaller for higher point.
I suppose the reason could be a larger DMSO volume than the lower points and it's , Am I right?
Do you think that adding 1-2 mL of water can improve resposne ?

HS
Oven: 85*C
Loop: 105*C
Transfer line: 110*C
Time in oven: 35 min.

GC
DB-VRX (60m x 0,25 x 1,4 )
Split 1:40
Inj. 250 *C


Unless you are only adding a few microliters of sample, then you should be adding the same amount of DI Water to your standards as you will be adding of the sample. You want to match the matrix of your standards to the matrix of your samples as much as possible. If you normally sample 5ml of water, then add 5ml of clean water to the vial of the standard.
The past is there to guide us into the future, not to dwell in.
James_Ball wrote:

Unless you are only adding a few microliters of sample, then you should be adding the same amount of DI Water to your standards as you will be adding of the sample. You want to match the matrix of your standards to the matrix of your samples as much as possible. If you normally sample 5ml of water, then add 5ml of clean water to the vial of the standard.



Hi James,
it's not a water matrix. The matrix is ground plastic.
no_peak wrote:
James_Ball wrote:

Unless you are only adding a few microliters of sample, then you should be adding the same amount of DI Water to your standards as you will be adding of the sample. You want to match the matrix of your standards to the matrix of your samples as much as possible. If you normally sample 5ml of water, then add 5ml of clean water to the vial of the standard.



Hi James,
it's not a water matrix. The matrix is ground plastic.


Then you may try adding the same amount of DMSO to every vial, including the samples so that the solvent load is the same, it might help the linearity. If you have any known clean plastic that might be good to use as the standard matrix also.
The past is there to guide us into the future, not to dwell in.
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