Triethyl amine analysis problem

[Narendra]

My problem is Triethylamine detection not possible at 40 ppm. Following is the details about GC Chromatographic condition and std/sample preparation.

Column used - DB 624 Capilary
Inj temp : 150
oven temp : 200
detector temp : 200

split ratio 1:1
carrier gas : nitrogen
injection volume 1 microlitre
I have to determined four solvents which is ethanol+ethyl acetate+methanol+triethylamine.
std prepn : ethanol +ethyl acetate +methanol + triethylamine in Dimethylsulfoxide.
spl prepn : 1 gm API in Dimethylsulfoxide

I am able to detemined other three solvents (ethanol+ethylacetate+methanol) but triethylamine at 40 ppm level not able to detect.

Any suggestion please.

NAV

[aldehyde]

Is it not possible because the peak area is not consistent, the peak is completely absent, or another reason?

Are you able to change your method settings or is it a more restricted environment?

Why are you running a 1:1 split ratio?
What is your flow rate (through the column)?

[Narendra]

triethyl amine peak is not appearing with given concentration and at above concentration peak broadning and blent peak observed.

Method can be changed to within accepatnce criteria

Split ratio kept 1:1 because it is given in API manufacturer STP
flow rate is 10 ml/min nitrogen with column ID 0.5 MM

NAV

[chemistab]

Check if triethylamine reacts with something (probably an acid) in your sample. Add a strong base in order to avoid this problem.

[kalidassa]

Hi This is Kalidass. This is only due to your column problem only change another new column would be better. We also analyzing the Triethylamine in HSGC method we are using N-Methyl pyrrolidone as diluent.In some of old DB-624 column the Triethylamine peak will not elute where all other residual solvent peaks elute and separate well. We are using some what new column for Triethylamine analysis.

Regards
A.Kalidass

[krickos]

Hi

I see a number of potential pitfalls with this analysis, apart from triethylamine being sensitive to active sites in liner or on column (however less likely on a 624 column with a thickness of 1,8-3µm).

First the injection port temperature seems derived from some default headpsace injection, it is too low for liquid injections as DMSO has a boiling point of ~189°C.

Second. Actetates (like ethylacetate) can undergo both basic and acidic hydrolysis, then we have potential matrix issue between API and the amine/acetate aswell. Consequently pH control may be needed and and standard addition calibration is strongly recommended.

Third. Column oven isothermal at 200°C. This is obviously not good from a resolution point of view/peak shape aswell. I would rather start at 40°C for a few minutes and then ramp up with 10°C/min to start with.According to litterature data this approach should resolve all you solvents nicely on that particular column type.

Fourth. Split ratio. Again it seems derived from a headspace method for residual solvent testing. Even if youi now increase injection tport temperature, the realtive huge amount of DMSO on column may smear out you peaks.

Other: I would do a standard first with only DMSO/triethylamine and see if I could get that working first. As mentioned DMSO might not be suiteble another solvent might be needed as DMF, DMI or in worst case N-methylpyrrolidone as mentioned by Kalidass. Kalidass also seems to have a headspace injection procedure that works so changing to headspace injection may also need considering.