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Dear All
I would appreciate your help in method development of diltiazem
(Benzothiazapines ) in LCMS,
1. Its pKa =8.1, we are also determining its 2 metabolites in plasma.
Mobile phase = ACN : Ammonium acetate (80:20), column = X terra 4.6*5.
2. The sample prep is SPE using HLB, Loading in basic condition and
elution in methanol and reconstitution in Acn: water (80:20).
The problem we are facing is that In aqueous sample (in Acn: water
80:20) area (both drug and IS) is stable , but in processed sample,
area drops (both Drug and IS) and stabilizes after 20-30 injections.
The area of processed sample drops almost to 50% in 20 injections and
stabilizes.
I believe the problem is Processing method, but I am not able to pin-
point.
I would appreciate your help in this matter.
regards
Ranvijay
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Dear Ranvijay, I dont feel the problem is with the extraction
procedure. You can inject a system suitability test with the extracted
samples to pin the problem. If your system suitability fails then
there is some problem with the instrument and if it passes then relook
into extraction procedure required (Especially look for Matrix effect)
Dr. Mandar Mote
Sr. Manager
Bio-analyticalBio-equivalence Division
Macleods Pharmaceuticals Ltd.
Mumbai.
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Dear Ranvijay,
I remember that a lot of time ago (early 90') we quantified Diltiazem
and two main metabolites (des-acthyldiltiazem and des-
methyldiltiazem), this is reported in
"Bernasconi R et al. - Pharmacokinetics of diltiazem and a new
analogue, LR-A/113, in the conscious rat. Eur J Drug Metab
Pharmacokinet. 1992 Oct-Dec;17(4):269-74
"
At that time we used a double step liquid extraction to clean
compounds from matrix (quantification was by HPLC-UV).
I remember the second step in extraction (back-extraction) was very
useful to avoid matrix effects and overall recovery was excellent.
I suppose that now this approach with back-extraction is obsolete to
apply LC/MS/MS!
Best regards
Stefano
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