Chromatography Forum

Hi!
I am starting my work with blood analysis for alcohol determination. Unfortunately I do not have Head-Space with my GC, so I have decided to choose the method of direct injection with packed GC column. I am asking you for the advice which column should I use. I have been thinking about:

1. 10% Carbowax 20M on Chromosorb W-HP, 80/100 or
2. 10% OV-1 on Chromosorb W-HP, 80/100 or mabye:
3. Porapak Q, 80/100
(these I found in the literature)

Which one is the best choice?

I also would like to ask you about any comments to this "old-fashioned" method of direct injection on packed column.

Thanks!

rady

Besides working as a chemist, I also worked one year as a toxicologist at a hospital.

The method that had been used for years was direct injection onto a Porapak Q packed column. You get a wide separation of methanol and isopropanol from ethanol with this packing, which is not always true for the Wax column and as long as the column is not loaded with 'junk' the tailing will be minimal, which is not always the case for the silicone column.

I suggest glass tubing or a fused silica coated SS column.

A replaceable precolumn would be advisable if you are performing this analysis routinely.

Inject as little as possible and beware of overloading the injector with sample deposits.

Isothermal oven at 160-200°C is recommended with 20-40 cc/min carrier flow.

best wishes,

Rodney George
consultant

Tenax-GC or Tenax-AT packed columns also work well for alcohols. Since you'll likely be using internal standard with this (most use n-propyl alcohol internal standard, but USP 611 details acetonitrile), should work fine.

There can be difficulties if you use acetonitrile as an Internal Standard.

n-Butanol or n-propanol should work well as an internal standard, besides acetone or MEK.

Many commercially packed columns may have voids in the packing bed after column conditioning which will cause tailing of the ethanol under the acetonitrile peak. I worked on this problem prior to my time at Supelco and solved the problem independently while I worked at Mallinckrodt. I had purchased columns from several commercial sources and they all had the voids problem. The solution I discovered was implemented at Supelco and any complaints about this column were greatly reduced in number (they almost disappeared entirely) and their cover letter explaining the issue became superfluous.

(Note: I don't work for Supelco today)

I would suggest a OV-1301 phase packed column but there could be a potential resolution problem with ethyl ether and ethanol.

best wishes,

Rodney George
consultant

Note that USP 611 IIB uses acetonitrile internal standard BUT on a G43 capillary, not a packed column. n-propyl alcohol works fine with those same USP conditions and seems a more natural internal standard, but (to quote Yogi) "the USP is the USP".

So follow what Rodney George states.

to rady:

Direct injection without sample preparation is not good choice. If you want determine EtOH (and other Alk-OH) in blood samples: EtOH + NaNO2 + H3O+ (TFA) => Et-O-NO +... (20-25 oC) injection of vapor phase - you may use standart autosampler and 100-500mkl syringe (gas-tight). Sorbent: 10% dinonylphtalate on Chromosorb W. IS: i-PrOH or n-PrOH. Detector: TCD (FID)

other way: centrifugation and... injection of liquid sample... Sorbent: Porapak Q. Detector: FID

Best regards, Alex.

Thank you all for all the comments!

Any other suggestions are welcome!

Best regards for all!
rady