[gaschroking]

Hello everyone,

 I am new to this forum and this is my first post. I am  novice to gas chromatography. I am trying to determine the ability of my bacterial samples to degrade phenanthrene and hexadecane.  After 10 days of incubation I will extract phenathrene and hexadecane using  dichloromethane and then analyze by  GC FID. May I know what  internal standards are appropriate for the two chemicals that I use? What amount, How and when do we add internal standards?

Many thanks to your replies

[chiralic]

Hello gaschroking:

Before to suggest some ideas about your "bacterial samples", I have some questions:

1) Do you have a chromatogram of your "bacterial samples" extract? Could you post it for us?

2)How is COMPLEX your chromatogram of your "baterial samples" extract? Is clear? a lot peaks?

3) Did you identify your TARGET PEAKS in your "bacterial samples" extracts chromatographed?

4) Do you run your "bacterial samples"extracts in isothermal mode or programming mode?
   (Temperature into the Oven)

5) What kind of column are you using or you will think use?

The Internal Standard Compound is selected according to the following criteria:

- The peak of the standard should be located in a section of the chromatogram where
  overlapping with the peaks of the other components does not occur.

- The retention of the standard should not be too different from those of the components
  to be quantitated

- The volatility of the standard should not be too different from that of the significant sample
  components; this is important for the application of sample introduction techniques the
  performance of which is influenced by "discrimination" according to volatility; it may happen
  that compounds of the same boiling point are eluted with different retentions, because they
  have different chromatographic polarities.

- The concentration of the standard within the sample should be of the same order of
  magnitude as those of the analyte components; the signals of both the standard and the
  sample component should fit into the linear dynamic range of the detection system (for
  you is Flame Ionization Detector); Response Factor calibrations with the standard should be
  performed under the same conditions and in the same range of concentrations.

- Structural the standard maybe SIMILAR to structure of your Target Components


I saw a chromatogram on a reference (book) and I got these data:

Column: 5% phenyl polysiloxane or SE-54 (equivalent in commercial phases= DB-5 (former J&W); Ultra-2 (HP today Agilent); SPB-5 (Supelco); RTx-5 (Restek) or CP-Sil-8CB)

Temparature Programing from 90 ºC to 175 ºC, programming rate 30ºC/min,hold by 5 min, then
rate 3ºC/min to 260 ºC

Suggestions: n-decane, or similar...Also you must check "the cost" and "availability"

My best regards and I wish you a Happy New Year

Chiralic

[gaschroking]

Thank you so much chiralic for the inputs. A prosperous New Year too.