How to select drug or a combination of drugs for analysis & validation by HPLC?
This is a question posed to some pharmacy and chemistry students. They face it when they wish to take up a small project as a part of their internship or curriculum.
It can turn out to be a worthy project if executed well. So lets see in detail.
HPLC is high performance liquid chromatography and is one of the sophisticated techniques among the available types of chromatography.
Standards of all the drugs and related substances are to be complied as per official books published for the purpose by every industry.
The official books of standards are like United states pharmacopoeia (USP), British pharmacopoeia (BP) etc.
These books give detailed standards of every drug starting from its chemistry, physical properties, identification tests and analysis.
All the drug manufacturing industries comply with either of the books as per the rules of their own nation.
These pharmacopoeias mention different possible methods of analysis in the monograph of each drug.
But very few drugs are recommended for analysis and quality control using HPLC.
So we can have many drugs or combination of drugs which can be evaluated by HPLC.
But before we do, lets see what are the tips considered by committee of pharmacopoeia to prescribe a method of analysis.
1. The method should be accurate and precise to evaluate the said drug.
2. The method should be inexpensive.
3. Should be faster and simple.
4. Results should be reproducible in between labs.
HPLC doesn’t comply with many of the above factors. And to understand the reasons you better read the principles of HPLC first.
The factor which encourage to select a drug or combination of drugs for validation by HPLC include.
a) Drugs with similar chemistry: Like steroids, monoamines etc. Since their chemistry is similar, they cannot be easily identified by UV observation chamber or color reactions.
b) Drugs with small variation in wavelength of absorption. They cannot be identified by UV, visible spectroscopy . This is because they may have similar wavelength of absorption i.e. λmax making it difficult to distinguish in between molecules. See principle of spectroscopy for details.
C) Drugs which have oxido-reducible properties. These molecules undergo reaction during analysis. So they need non-reactive procedures of analysis.
d)Drugs in a combination which are difficult for isolation and evaluation.
How to select drugs for validation by HPLC
1. First list out possible drugs for each alphabet in pharmacopoeia which are not prescribed for HPLC analysis.
2. Select drugs among the list with simple chemistry and possible wavelength of absorbance in UV-visible, flouirmetric range or even oxidisable substances.
3. Also be careful if suitable solvents (for mobile phase) for particular drug or combination of drugs are available. This can be decided by polarity of solvents and also polarity of the compound. Polar drugs are easily isolated by polar solvents and vice-versa.
4. The combination of drugs should be selected such that they have similar chemistry, solubility and absorbance preferably. If not drugs with large differences in chemistry and absorbances can be easily validated by simple spectroscopic methods instead of HPLC.
5. Once you made a selection go for google search for the drug of choice and validation by HPLC. Because someone might have already done the validation for selected drug before you do. They might have published their findings in a some scientific journals. If not you are lucky to find and validate on your own.