Chromatography Forum

Hi, all
this is dhruvil.

i have a small query for you all.
for quantifying acetic acid by GC i am suppose to acidify my solution(sample and standard preparations) and i am doing that by adding hydrochloric acid (1 M). now i doubt that this acid will harm column.
will it really ?

i am using Wax column.. can i have any other column that can withstand against this acidic injections ? or is there any make which is providing such columns which will not get damaged upon HCl injections directly in the column ?

Please guide me in this

thanks,
regards
Dhruvil

This is too long an issue to discuss here. Please contact me off-forum.

Rodney George
Senior Research and Development Scientist
Gas Separations Research
Supelco
595 North Harrison Road
Bellefonte, PA 16823

814-359-5737 voice
814-359-5459 fax
rgeorge@sial.com

Dhruvil

You did not contact me so I will let you know that performing an analysis for acetic acid content (especially of a base substance for acetate content) is very difficult and prone to errors.

Most labs perform LC, ion exchange, or NMR to measure acetate or acetic acid. GC can be done but the variability is high and the expectations of a successful analysis (an accurate analysis) is low.

Been there done that for over 25 years.

best wishes,

Rod

Acetic acid can be done more than adequately by GLC unfortunately capillary columns dont fare too well.
Packed column non silanised silica support precoat phosphoric acid and 5% of any methyl silicone.
separation and quantitation of formic acetic propionic and butyric works well.
Acidify sample with phosphoric acid not HCl. HCl vapour does not do stainless tubing any good.

Bob M

One of the best (packed) columns that you can buy for this analysis is made by chromatographer 1 's own company-Supelco; it is 4% Carbowax 20M on Carbopack. If you are extremely careful you can get good results for short chain fatty acids on this column, even for aqueous injections. An advantage of packed columns is the ease of direct on column injections, where the needle actually enters the column and therefore no possibility of loss by adsorption on glass liners or injection ports occurs. Of course you can also do on-column injection with capillary columns, but this introduces another complexity into the procedure due to the narrow bore of such columns. Maybe Rod will let us know if this packing is still available? I agree that HPLC may be a better option.

Thank you, Victor, for your kind comments.

There are times I respond as a Supelco R+D Scientist and there are times I try not to be commercial and respond as an end-user chromatographer. When I respond as Rod, I am trying not to be company specific. I am not asked to do this by my employer, just in case anyone is interested, but if my suggestion deals with a company specific product I try to let the Forum know I work for Supelco.

Yes, this packing is available and is quite useful. Using SP-1000 instead of Carbowax 20M is also an excellent option.

There are times when a packed column will do the job and there are times when no GC column will do the job accurately. Why?

The biggest issue in GC is the matrix in which one is trying to measure acetic acid.

Since I felt Dhruvil might not want to discuss his matrix publicly, I invited him to email me directly to discuss his analysis discreetly.

Formic and Acetic acids can be analyzed by GC but hardware and technique requirements are strict, and some matrices make it VERY difficult. Been there, done that, in petrochemical, pharmaceutical, and industrial/environmental labs.

Sometimes a good NMR is worth its weight in gold, as I once demonstrated to an unbelieving expert in spectroscopy (who knew more and knows more than I will ever learn about NMR), but I prefer Ion chromatography LC as Consumer Products Guy has mentioned in a previous post on another thread on formic acid.

Thanks again, Victor.

Rodney George
Senior Research and Development Scientist
Gas Separations Research
Supelco
595 North Harrison Road
Bellefonte, PA 16823

814-359-5737 voice
814-359-5459 fax
rgeorge@sial.com