I'm a student from Belgium who's working with a GC. This GC uses a micro Thermal Conductivity Detector (TCD).Does anyone know what it is? How it works? What it looks like?

Sure, a thermal conductivity detector is a universal detector (responds to everything), but not necessarily very sensitive. It is based on a Wheatstone bridge, where the sample gas passes over one resistance element and a reference gas over another. The difference in thermal conductivity changes the resistance in the circuit and it becomes imbalanced. This imbalance is converted to a signal to the recording device. The detector can give either positive or negative peaks depending on the relative thermal conductivity of the sample stream vs the reference stream.

Micro TCD is having least dead volume and principally it same as TCD. It is used for high sensitivity <20-50<100which is common for TCD.

Can anyone suggest a web site address that will help me with some homework that I need to do for college. The content needs to be of a basic nature into the process of gas chromatography.
i.e. setup of equipment, what gas to use as a carrier, etc..
Especially for the use in detecting accelerants in the case of arson.
Thankyou

Iam working in the lab and ihave GC Ineed to develop a method to analyze the oil lubricant
Ihave FID detector and carrier gas is nitrogen can any body help me on this .
thank you

I am very new to gas chromatography and was recently informed that response factors could be plotted on a chart to check the linearity of the thermal detector. Is this true? If so, how is this done?

Hello,my name is joyqing.I am working in the analysis lab. Recently I find there is something wrong with my NPD detecter. The baseline sigal of it is too low although I adjusted the power of the bead and I have tried aging the column and detecter.
Another question is I can not seperate the two organo-phosporus material: malathion and para-ethyl,by using DB-5 15m*0.53um*1.5um.

Hello everyone. I have taught myself gas chromatography as part of my PhD work but need to measure formaldehyde using my Shimadzu GC-14B. Is the FID sensitive to formaldehyde, or must I use the TCD? If using the TCD, do I need to use a packed column, or is it possible still to use my DB-WAX capillary (30m X 0.32mm X 0.15um) column (enough flow rate)? Any advice on column selection would be very helpful. I need to measure formaldehyde concentrations of, I suspect, low ppmv or even ppbv without the benefit of purge-and-trap methods. Please don't laugh!

Paul,
A Haysep-N, 1/8 ID, 3 meters long, ev of HCHO is around 11.2, I use a PID LiFl window 11.8 ev.
Carrier He @ 10 cc/min.

Thank you very much for your advice, Richard. I don't have a PID and cannot afford one. Is it true that a FID is insensitive to HCHO? Would the TCD be sensitive enough? How do you calibrate on HCHO? Using formaldehyde? Your advice is most helpful.
Paul

I might be wrong but an FID an a TCD are just about useless for the amount of CH2O you are attempting to detect but try it you may have better luck than I had. The first thing you have to do is determine the exact amount of CH2O available. Look up DeJonje and DeJonge(J. Recuel Trav. Chim. Pays-Bas, DeJonge, J.I., DeJonge, 71, 643-60 (1952)). This is a titration procedure that is essential. After you determine the amount of CH2O in a diluted solution 1:100 of stock CH2O (37%)calculate 2mcg up to 15 mcg in 20 ml vials and run. The detector should top off @ 15mcgs. Temp should be in the range of 65C or above depending on your requirements.

Another question: what about using an ECD for formaldehyde analysis? Is is sensitive down to the levels I am likely to encounter with in-flame measurements, say low ppmv, high ppbv? I think there's another GC with an ECD in it which I have access to. Thanks in advance! Regards, Paul.

Paul:
I have not tried to measure formaldehyde on an ECD, but I would be amazed if it did not work. You do not say exactly what the matrix is, but suspect it is water, or maybe air. Both are a problem since both water and oxygen will cause huge peaks on an ECD and swamp out the formaldehyde.

It would be a bit more complex, but you might try a valved, multi-column approach, to separate most of the water and/or air from formaldehyde, but send the water/air out to a vent and let only the formaldehyde into the detector. Talk to Valco Instruments for valve advice, and Hayesep for column selection.

In order to measure formaldehyde concentration and perhaps those of some chlorinated compounds within a coal flame, I need to purchase a new detector. Advice leads me towards either the ECD or the PID type. I have two questions:

1. Does the ECD have a more limited linear dymanic range than the PID, or vice-versa?

2. Would the ECD actually detect formaldehyde? Has anyone out there tried to measure HCHO with one of these?

Any further advice would be much appreciated.

A PID has a linear dropoff at 15mcg of HCHO and can detect much lower conc. than the ECD. The only downside is that the lamp you buy has to have a LiFl window. OI makes a good detector. I would stay away from HNU if possible. I'm sure that the ECD would detect HCHO however Bill is correct in that water and air may very well mask what you are searching for.

Good luck

Hi Richard, Paul and Bill. By the looks, you all are very special cromatographers. I like the level of the objects. Maybe I could help you Paul!. Look for methods that determine formaldehyde in water, that uses cromotropic acid reaction,. More references, refer to NIOSH and OSHA methods, look for their web page.This method refers to VIS - espectrometry!

Identify yourselves cromathografers!, I need to improve my English, and contacts to excelent people like you!