PAH analysis GC-MS

[pah_2015]

Hi everyone! I am performing a Calibration curve with PAH standards 0.005 ppb, 0.01 ppb, 0.1 ppb and 1 ppb, adding to each standard 10 microliters of a 1ppb solution of internal standard, so in each standard (1mL) the concentration of the IS is 0.01 ppb. The chromatogram has too much noise and I cannot perform a proper integration of the peaks. What you would suggest me to do?

[James_Ball]

Hi everyone! I am performing a 4 points Calibration curve with PAH standards 0.005 ppb, 0.01 ppb, 0.1 ppb and 1 ppb, adding to each standard 10 microliters of a 1ppb solution of internal standard, so in each standard (1mL) the concentration of the IS is 0.01 ppb. The chromatogram has too much noise and I cannot perform a proper integration of the peaks. What you would suggest me to do?

I am currently running a similar test and my lowest calibration point is 10ppb for the PAH compounds and I can barely see that level using full scan mode, I can't imagine being able to see 0.005ppb.

I do have better sensitivity using SIM mode and could probably take my concentrations down to 1ppb on some of the PAH analytes, using 2ul injection.

Are these concentrations in the injected solution or in a sample before extraction and concentration?

I am using an Agilent 7000 QQQ running in full scan and SIM modes, and I don't believe I would be able to see those levels. Maybe in MRM mode with the detector gain turned up high possibly.

I have found that in full scan mode, you need to run the electron multiplier voltage as low as possible to eliminate as much noise as possible while still maintaining enough sensitivity to see your target ions. If you try to increase the multiplier voltage to increase your sensitivity, you will also increase the noise in the background, usually faster than you increase the target sensitivity.

[pah_2015]

The calibration standards I am preparing them in volumetric flasks injecting the proper amount of standard in the proper volume of hexane to obtain that particular standard concentration, then i am taking in a vial 1 mL of standard solution to analyse it by GCMSMS. I am using a TSQ 800 triple quadrupole and I am injecting 1 microliter. Should I inject more standard? I am using a detector gain of 2.1E+006.

Hi everyone! I am performing a 4 points Calibration curve with PAH standards 0.005 ppb, 0.01 ppb, 0.1 ppb and 1 ppb, adding to each standard 10 microliters of a 1ppb solution of internal standard, so in each standard (1mL) the concentration of the IS is 0.01 ppb. The chromatogram has too much noise and I cannot perform a proper integration of the peaks. What you would suggest me to do?

I am currently running a similar test and my lowest calibration point is 10ppb for the PAH compounds and I can barely see that level using full scan mode, I can't imagine being able to see 0.005ppb.

I do have better sensitivity using SIM mode and could probably take my concentrations down to 1ppb on some of the PAH analytes, using 2ul injection.

Are these concentrations in the injected solution or in a sample before extraction and concentration?

I am using an Agilent 7000 QQQ running in full scan and SIM modes, and I don't believe I would be able to see those levels. Maybe in MRM mode with the detector gain turned up high possibly.

I have found that in full scan mode, you need to run the electron multiplier voltage as low as possible to eliminate as much noise as possible while still maintaining enough sensitivity to see your target ions. If you try to increase the multiplier voltage to increase your sensitivity, you will also increase the noise in the background, usually faster than you increase the target sensitivity.

[Peter Apps]

Hi everyone! I am performing a 4 points Calibration curve with PAH standards 0.005 ppb, 0.01 ppb, 0.1 ppb and 1 ppb, adding to each standard 10 microliters of a 1ppb solution of internal standard, so in each standard (1mL) the concentration of the IS is 0.01 ppb. The chromatogram has too much noise and I cannot perform a proper integration of the peaks. What you would suggest me to do?

Calculate the mass of each component that you are putting onto the column and into the MS. Compare that with the LOD of the MS.

Peter

[James_Ball]

The calibration standards I am preparing them in volumetric flasks injecting the proper amount of standard in the proper volume of hexane to obtain that particular standard concentration, then i am taking in a vial 1 mL of standard solution to analyse it by GCMSMS. I am using a TSQ 800 triple quadrupole and I am injecting 1 microliter. Should I inject more standard? I am using a detector gain of 2.1E+006.

Hi everyone! I am performing a 4 points Calibration curve with PAH standards 0.005 ppb, 0.01 ppb, 0.1 ppb and 1 ppb, adding to each standard 10 microliters of a 1ppb solution of internal standard, so in each standard (1mL) the concentration of the IS is 0.01 ppb. The chromatogram has too much noise and I cannot perform a proper integration of the peaks. What you would suggest me to do?

I am currently running a similar test and my lowest calibration point is 10ppb for the PAH compounds and I can barely see that level using full scan mode, I can't imagine being able to see 0.005ppb.

I do have better sensitivity using SIM mode and could probably take my concentrations down to 1ppb on some of the PAH analytes, using 2ul injection.

Are these concentrations in the injected solution or in a sample before extraction and concentration?

I am using an Agilent 7000 QQQ running in full scan and SIM modes, and I don't believe I would be able to see those levels. Maybe in MRM mode with the detector gain turned up high possibly.

I have found that in full scan mode, you need to run the electron multiplier voltage as low as possible to eliminate as much noise as possible while still maintaining enough sensitivity to see your target ions. If you try to increase the multiplier voltage to increase your sensitivity, you will also increase the noise in the background, usually faster than you increase the target sensitivity.

Using MSMS will mean lower detection limits since you should be filtering out more noise. As Peter mentioned, if you are below the limit of detection of the instrument itself, you will need to find a way to increase the mass of analyte that goes on column before detection and quantification is possible.