The calibration issues you are experiencing with the last three compounds (Indeno[1,2,3,c,d]pyrene, Dibenzo[a,h]anthracene, and Benzo[g,h,i,]perylene) in your GC-MS analysis of 16 EPA PAHs could be due to various factors. The decreasing trend in response from the beginning to the last compounds may indicate issues with the calibration curve or the compounds themselves.

To improve these calibration issues, consider the following factors:

Matrix Effects: Matrix effects can impact the linearity and response of compounds in GC-MS analysis. Ensure that your calibration standards and samples have similar matrices to minimize these effects.

Sample Preparation: Proper sample preparation techniques are crucial for accurate analysis. Ensure consistent and thorough sample extraction and clean-up procedures.

Calibration Curve: Check the calibration curve for these compounds. If the linearity is not optimal, consider recalibrating using a wider concentration range or adjusting the calibration method.

Instrument Settings: Verify the instrument settings, such as temperature gradients and MS/MS acquisition parameters, to optimize the resolution and sensitivity for these compounds.

Quality of Standards: Ensure the quality and purity of your standards. Contaminated or degraded standards can affect the calibration and analysis results.

Hello Muhammed Yousuf S,

I would need to know more about your method to be able to answer your question. Basically, the last three PAHs are not so easy to analyze due to their high boiling points. Some system parameters have a significant influence on the quality of the results. The injector temperature should be 350°C, otherwise there is a risk of high-boiling point discrimination. If you are working splitless, you should also adjust the splitless time, i.e. extend it slightly, as the transfer of the analytes to the column takes longer due to the slow evaporation. Unfortunately, the longer split lot time can lead to a peak broadening or tailing; the only thing that helps here is to try it out and find a compromise.

Another point is the column, PAKs tend to tail and this increases with the age of the column. Tailing peaks are difficult to integrate, as the integration limits in the tailing area are constantly shifting. This then leads to high standard deviations. The MS can also contribute to poor analyses. High-boiling analytes tend to contaminate the source, which can lead to ion suppression and poor sensitivity. Here you should take a close look to see if this is contributing to your problems.

I hope I have been able to give you some useful tips and wish you every success with your optimization

Best regards

Joachim Horst