Chromatography Forum

Dear All

I wanted some information about Purge and trap GC For analysis of halogenated VOC in air .

please help me out

What matrix?

What do you currently have set up or are using for equipment and method?

I have varian CP3800 with GSV for packed column and direct liquid injection port for megabore and packed column.
Right now i am analysing few halogenated compounds by liquid extraction in pentane similar to the analysis of chlorinated disinfection by products in water.

This samples are brought from ocean and esturaine areas contributed bith by anthropogenic and few by biogenic sources.

Now i also wanted to mesure methyl bromide, methyl chloride and methyl iodide .

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best wishes,

Rod

rajdeeproy,

I would be very interested to hear how this works. You are talking about C1 hydrocarbons which means the breakthrough volumes for all but the most tenacious traps are going to be very small (on the order of 15-50 mL) I hope this works out for you.

check out EPA method 524.2, it includes all three compounds you are looking for.

Dear all
At this point i am analysing these few compounds through liquid extraction in pentane and on column injection.
1. chlorofrom
2.dichloromethane
3.carbontetrachloride
4.dibromomethane
5.bromoform
6.diiodomethane
7.iodopropane
I am giving the details below of the method.

Determination of biogenic and anthropogenic volatile halocarbons in sea water by liquid—liquid extraction and capillary gas chromatography • ARTICLE
Journal of Chromatography A, Volume 513, 1990, Pages 39-45
Katarina Abrahamsson and Silke Klick

and now with purge and trap i would like to concentrate on methyl chloride , methyl bromide, and methyl iodide.

As an observation I would add that methyl bromide is one of worst haloalkanes for decomposition on traps containing forms of activated carbon. It may be mitigated by the relatively mild temperatures spoken of in EPA 524.2 (180 C). My experience is with the TO14 mix when I used much higher trap temperatures. The use of internal standards with known response factors which do not decompose is very important.

I have read many papers where the reviewers never noticed that the absolute recovery was not determined. I don't have instant access to the J. Chromatogr. paper so I can't pass comment on their methodology.

Klick article uses ECD, are you using ECD? When I re-read your post, I realized chloromethane, iodomethane, bromomethane,--all doable by purge and trap (EPA 8260, EPA 524, EPA 502.2, etc...) but if you are using an ECD I think the sensitivity will be terrible because they have only one halogen.

Agree with the above on ECD response. I don't have the figures for bromomethanes but if carbon tetrachloride = 1.0 I have found

chloroform = 0.13
dichloromethane = 0.006

I am using ECD for the analysis and I found that sensitivity of CCl4 is much more than any other. I have read many papers where they have used ECD and liquid extraction for these compounds. I have noticed there is some amount of moisture present with the extract which can harm the ECD.
I am not sure if we can use any sodium sulphate anhydrous to remove it. In the paper which i mentioned the sample volume used is 125ml and pentane 1ml but in my practical experience the volume is very small as sometime i the peak height is very small.

I am also having teribble problem with recover percentage study . If somebody can help me through this, it would be nice.

A few suggestions about recovery problem:

Run the calibration using the standards prepared the same way as your samples. Basically you need to extract the standards following liquid-liquid
extraction procedure.

To me sample volume of 125 ml is excessive for 1 ml pentane. Try smaller sample volume, say 30- 50ml. You need to adjust injection volume to your GC to achieve same sensitivity(be aware of overloading the injector).

Make sure you have minimum headspace in the extraction container. Add some kind of salt, like NaCL, to the sample before extraction.

Liquid-liquid extraction procedure only works for less volatile compounds. It's going to be hard to work with very volative chemicals.

with 40 ml samples i tried to extract but there is nothing i am getting. I should teel u that these samples are of marine origin.
Fisrt i thought there must be some problem with extraction but later i tried a tap water samples and i got most of the peaks we get disinfection by product.

Is there any paper on SPME methods for voatiles halocarbons.

thnaks