Hi Yohana,

May be information you provided is insufficient here, but i would suggest you to taken up or follow this simple steps to ensure your procedure.

• Post-run analysis- is just to make comparison of  between samples and nothing to do with quantifying the peak. You need to establish the limit of detection (LoD) and limit of quantification (LoQ)for particular compound (in your case it is toluene) for your MS system. Based on this limits you will be able to identify the compounds in MS methods.
• If the toluene concentration you detected is above or equal to mark of  LoD of your MS detection system, then the you can interpret the compound detected is toluene, if not you can't support the identified as toluene.
• procedures or steps?-  you can spike the known amount of standard toluene in your sample to ensure the presence of toluene and there on you can back calculate the amount or intensity of toluene in samples.

All the best with further experiments

You have not mentioned what column you are using. A 60 meter VOCOL or DB-624 is designed to separate volatile compounds. If you are using a non-volatile column, you could be observing co-eluting compounds. Also, after you create a calibration curve, analyze your sample plus matrix spike and matrix spike duplicate.

For increased sensitivity, you can choose selected ion monitoring (SIM) and scan for three largest ions - 92, 91, and 65.

For further help, read Method 8260B - Environmental Protection Agency on the internet.

Headspace is all about equilibrium! Anything in your sample could affect how the toluene "transfers" to the headspace.

 If you are doing SPME (fibre) or using a needle to sample the headspace you should be adding labelled toluene (deuterium or carbon) as internal standard to both your stanards and sample solutions. Calculate using the Stable Isotope Dilution Assay (SIDA) method.

Good Luck!

For Raghava Thimmappa

Thanks for your valuable comments. We have quantified toluene which is below the LoD. But in the peak integration process, target ion and reference ions were separated clearly by the software. So, can you comment whether we are able to consider such peaks (below LoD) for quantification process.

For Thomas Furnish

Thanks a lot your valuable comments. Actually, we are using Rtx 624 capillary column ( length – 20 m , Internal diameter – 0.18 mm , 1 µm ) which is capable of detecting 62 VOCs including toluene. As you said, we use 92, 91 and 65 as the target and reference ions. Can we quantify the toluene peaks which are below the LoD (limt of detection)?  steps which we followed in experiment given in attached document (step in GCMS)