Chromatography Forum

Hi guys,

I'm facing an issue with the GC-FID, ALS;

I'm getting a good standard repeatability for 6injections, but once after the sample is injected the next standard area is going down to 10% level.

The sample(500mg) is extracted with 4ml of 6N hcl n diluent is DCM(10ml).

I tried with different approaches as follows :
1) by changing split ratio,
2) by changing new column & liner,
3) by changing injection techniques,
4) extra washings for GC syringe.
5) diluent change form DCM to chloroform.

Please help out on the above issue

It almost sounds like your molecular target is unstable in acid. What evidence do you have? Are the standards treated the same as a sample?

Try spiking a sample with the molecular target and make multiple injections. Does the peak area still decrease?

The molecule is already validated by vendor n i have the complete validation data, im just doing the verification.

Acid is using just to break the sodium form the molecule (as the sample is complexes with the sodium).

even i tried by spiking the sample with the impurities also.

Just to confirm

1. good repeatability for 6 injections of standard,
2. Then inject the acidified sample DCM extract of the sodium salt
3. Then inject the standard again and it has only 10% of the original area of 1 above ??

You used the term "complexes with the sodium " ?

But, to avoid more speculating, it would be very helpful if you would post exact details of your target analyte, the sample and the matrix to which you are adding acid along with chromatographic details

Sample : Divalproex sodium,
(Prep - 500mg in 10ml with DCM to this 4ml of 6N hcl);
Organic layer using for injection.

Cc:
Column : DB-FFAP (30M X0. 32MM X 1u film);

Thank you, that is helpful

So

Divalproex sodium is 2-Propylvaleric acid supplied in a mix of free acid and as the sodium salt as a medication.
Valproate (VPA), and its valproic acid, sodium valproate, and valproate semisodium forms

https://en.wikipedia.org/wiki/Valproate

Just to repeat, can you confirm

a. good repeatability for 6 injections of standard,
b. Then you injected the acidified sample DCM extract of the sodium salt
c. Then you injected the standard again and it has only 10% of the original area of (a) above ??

S exactly

I presume that you standards are in DCM, and have not been partitioned against acid ?

Does the area for the standard ever rise again, or does it stay at 10% of the original ?

On the chromatogram of standard with 10% area, do you see any peaks that were not there before ?

Peter

The area is stays at 10% only, but once after cleaning the liner then I will get area which is near to the initial std areas.

There r no other peaks in the chromatogram, but valproic acid peak (main analyst) was showing double response than the expected n remaining impurities were at 10% level only.

Actually the method is validated by vendor, n even I strucked at accuracy parameter, remaining all the verification parameters were completed successfully.

Clearly you are contaminating the inlet with something when you inject a sample. What else is in the samples besides the target analytes ?

Peter

request you to suggest to avoid the same,

request you to suggest to avoid the same,

If you want suggestions you have to answer my question about the samples. The more you don't tell me the more I can't help you.

Peter

Plz ask any thing regarding the conditions n procedure definitely I will reply, Because I'm facing the problem form last 7days. I need a solution n I don't feel any discomfort to gain knowledge.

How many sample injections are you doing between standard injections?

Plz ask any thing regarding the conditions n procedure definitely I will reply, Because I'm facing the problem form last 7days. I need a solution n I don't feel any discomfort to gain knowledge.

What is in the samples besides the target analytes; excipients for example ?

Peter