High Recovery Area when sample spiked in GC

[dvdthomas345]

I am doing method validation for a Paracetamol Eff tab Methylenechloride content by GC-FID with Headspace.

Sample Placebo with 5ml DMSO in HS vial didn't give any response for MDC (Methylene chloride), but when spiked with known concentration of MDC standard the recovery was about 128% compared to that of standard response.

Can this be because of any matrix effect because of the sample and if yes how can I get rid of it????

[tkubowicz]

Hello

Have you got Standard and spike solution prepared in the same way? Same solvent and additional componds?
It is only my opinion but I think that analyte in STD equlibrates in different way between solution and headspace phase than analyte in spiked solution. That is why you have recovery higher than 100%.

Regards

Tomasz Kubowicz

[dvdthomas345]

Sir thank you for your reply, Yes I have used the same standard for both spiked and standard injection the only change is the spiked contains my sample...
And both the standard as well as spiked sample is injected using the same programme or method.. So I don't think it may be due to different equilibration for the 2 injections.

[tkubowicz]

Hello

Please describe how you prepare:
1.Standard solution
2.Spiked sample
3.Sample

Regards

Tomasz Kubowicz

[Peter Apps]

I am doing method validation for a Paracetamol Eff tab Methylenechloride content by GC-FID with Headspace.

Sample Placebo with 5ml DMSO in HS vial didn't give any response for MDC (Methylene chloride), but when spiked with known concentration of MDC standard the recovery was about 128% compared to that of standard response.

Can this be because of any matrix effect because of the sample and if yes how can I get rid of it????

Yes it is probably a matrix effect, but you do not need to get rid of it since the same matrix effects affect your samples.

Peter

[dvdthomas345]

Thank you for your valuable reply...
FYI

Standard solution : 50mg of Methylene chloride (MDC) to 100ml with DMSO then 5ml to 200ml (12.5ppm) later pipetted out 5 ml of this to 20ml HS vial and crimped.

Sample : 3250mg sample placebo to 20 HS vial + 5ml of DMSO.

Spiked sample : 3250mg of sample to 20 HS vial + 5ml of standard solution.

Here I had no MDC detection in sample whereas in spiked sample the response was higher than that observed in standard solution...

[tkubowicz]

Hello

I think that for your spiked sample you observe "salt effect". In the presence of your sample MDC has different vapor/liquid equilibrium (more in HS phase). That is why you see higher concentration comparing to MDC standard solution.

Regards

Tomasz Kubowicz

[dvdthomas345]

Yes sir may be thats the reason, but can i add additional salt as a part of method in standard as well as sample and spiked sample to get better results???