Without seeing any of the mass spectra, I would hazard a guess that you have a series of alkanes coming out in order - the pattern seem to be pretty consistent, a new peak roughly every 1.1-1.3 seconds, which would correspond to +2 CH2 groups each peak (I'm guessing +2 since it says this is a plant extract). The problem with the MS for these is that the fragmenting patterns are virtually identical and the mass ion in EI is frequently low or missing altogether making it very hard to distinguish between, e.g. C20H42, C22H46, C24H50 etc. I suspect your system has just gone for library matches and picked the most common spectra and that matches all of them.

Two suggestions for this:

1. Get a couple of analytical standards for a couple, e.g. pentacosane and docosane, see where they come out and match the retention times. From there you can work out the sequence by simply going through the + or - CH2 groups with increasing and decreasing retention time respectively.

2. Run your sample on GC with FI (Field Ionisation) or CI (Chemical Ionisation) rather than the standard EI. You won't get the fragmentation, but you will keep the mass ion peak and from that work out which alkane you have by matching the mass ion to the mass of the compound.

Hi, Sarika. Maybe those names come from an automathic peaks integration method. Have you tried to inject a mix solution of compounds you want determine? In this way you can associate the right name to peaks.

Hi Martina,Thanks for your suggestion.but the results attached is for an alkane standard Mixture Itself. I want to quantify alkanes in my samples that`s why i run this standard and got this type of result.

It is very hard to distinguish between similar alkanes e.g. C20H42, C22H46, C24H50 by means of mass spectrometry. This is because they have nearly identical spectra with no signal for the "molpeak" . You need to compare the chromatographic retention times in order to determine what alkane it is. The "Kovats retention index" may be an appropriate tool to elucidate the exact composition of your compounds.

Hi Sarika. In these chromatograms, there are probably only n-alkanes. But it is very difficult to distinguish them without mass spectra. You have to compare retention times in your sample with retention times in standard.

MS library is a good tool for preliminary identification but not for final identification. You must analyse pure standards. MS library could identify more peaks as one alkane because of similar mass spectra of alkanes.  Parent ions of higher alkanes (correspond to their mass weights) are usually not preserved in EI ionization.

by using MS library ,you can see similarity search (SI) , in that the maximum percent that the component matches  is your answer, acceptable range(80-100)