Chromatographic analytical procedures are analysed by two types of method there are
1. External Standard methods
2. Internal Standard methods
External Standard methods:
An external standard method is used when the standard is analyzed on a separate chromatogram from the sample. Quantitation is based on a comparison of the peak area or height (HPLC or GC) or spot intensity (TLC) of the sample to that of a reference standard of the analyte of interest.
The external standard method is more appropriate for samples as follows:
1. Sample with a single target concentration and narrow concentration range, e.g., acceptance and release tests.
2. Simple sample preparation procedure.
3. Increased baseline time for detection of potential extraneous peaks, e.g., impurities test.
1. Sample with a single target concentration and narrow concentration range, e.g., acceptance and release tests.
2. Simple sample preparation procedure.
3. Increased baseline time for detection of potential extraneous peaks, e.g., impurities test.
Internal Standard Methods:
With an internal standard method, compound of known purity that does not cause interference in the analysis is added to the sample mixture.
Quantitation is based on the response ratio of compound of interest to the internal standard vs the response ratio of a similar preparation of the reference standard (HPLC or GC).
This technique is rarely used for TLC methods.
This technique is rarely used for TLC methods.
The internal standard method is more appropriate for samples as follows:
1. Complex sample preparation procedures, e.g., multiple extractions.
2. Low concentration sample (sensitivity being an issue), e.g., pharmacokinetics studies.
3. Wide range of concentrations expected in the sample for analysis, e.g., pharmacokinetics studies.
2. Low concentration sample (sensitivity being an issue), e.g., pharmacokinetics studies.
3. Wide range of concentrations expected in the sample for analysis, e.g., pharmacokinetics studies.
HPLC methods for release and stability and TLC methods use external standards; and methods for biological fluids and GC methods use internal standards.
ReplyDeleteI would like to thank Ultimate Life Clinic for reversing my father's Amyotrophic Lateral Sclerosis (ALS). My father’s ALS condition was fast deteriorating before he started on the ALS Herbal medicine treatment from Ultimate Life Clinic. He was on the treatment for just 6 months and we never thought my father will recover so soon. He has gained some weight in the past months and he is able to walk with no support. You can reach them through there website www.ultimatelifeclinic.com