Question

what is HPLC define and explain Describe if it is possible for each technique to distinguish enantiomers and if so, how. Give details about how each technique is used in forensic science.  explaine thoroughly.

Answer 1

Q1 what is HPLC define and explain

Ans High perfomance Liquid Chromatography

High performance liquid chromatography (HPLC) is basically a highly improved form of column liquid chromatography. Instead of a solvent being allowed to drip through a column under gravity, it is forced through under high pressures of up to 400 atmospheres. That makes it much faster. All chromatographic separations, including HPLC operate under the same basic principle; separation of a sample into its constituent parts because of the difference in the relative affinities of different molecules for the mobile phase and the stationary phase used in the separation.

Types of HPLC:

1. Normal Phase HPLC

2. Reverse Phase HPLC

3.Size-exclusion HPLC

4.Ion-Exchange HPLC

Q2. Describe if it is possible for each technique to distinguish enantiomers and if so, how.

Ans Generally there are two techniques that are employed: Synthetically and Post-synthetically.

(1) Synthetically. Avoid racemic mixtures by using chirally pure starting materials (synthons), asymmetric synthesis, chemical catalysis or biocatalysis.

(2) Post-synthetically using chromatography. Chiral stationary phases (HPLC and SFC) can separate racemic mixtures into the individual isomers and can be scaled-up to preparative sizes. The enantiomers can be converted into diastereomers using a chiral derivatization reagent or by using chiral mobile phase additives and then separated using conventional HPLC or GC. However this method is not often used in industry as it requires a chirally-pure derivatization reagent and the rates of reaction with each enantiomer have to be shown to be identical. If Simulating Moving Bed Prep (SMB) is possible, costs fall. New enzymatic (continuous) technologies are becoming available that convert the unwanted isomer back into the racemate for further prep. The most popular method of resolving racemic mixtures for process-scale operations is still the crystallization of diastereomeric salts

Q3..Applications in Forensics
1. Quantification of drugs in biological samples.
2. Identification of steroids in blood, urine etc.
3. Forensic analysis of textile dyes.
4. Determination of cocaine and other drugs of abuse in blood, urine etc.