Sample Extraction In Pharmaceutical Analysis

Extraction is a commonly used separation technique in pharmaceutical analysis. It is a process of removal of soluble substances in solution form from an insoluble residue (solid, semi-solid or liquid) by aid of a proper solvent. [1] One of the purposes to carry out sample extraction is to increase sensitivity of analytical measurement method. Sample extraction technique is required to be incorporated into the analytical method when the sample analyte of interest have a very low concentration level which is near or below the detection limit especially for some pharmaceutical residue. By performing this process, the interested analyte level can be enriched to a level which can be more easily detected by analytical technique

[7]

2. Liquid-Liquid extraction (LLE)

Liquid-liquid extraction is also named as partitioning and solvent extraction. In this method, compounds are separated depends on their relative solubility between two immiscible liquids (ie, organic solvent and water). In LLE, a compound is extracted from one to another liquid phase by using a seperatory funnel. Principle – LLE works on principle of partition coefficient or distribution coefficient between solvent and aqueous phase. Partition coefficient, K is defined as the ratio of solubility (concentration) of substances in organic layer to the solubility (concentration) of substances in aqueous layer. Distribution coefficient is used to measure the extent of a compound to be extracted. This method involves mass transfer. [1]

Procedure – When a compound is added into 2 immiscible solvents and shaken, they will distribute themselves in the layer which they are more soluble when equilibrium achieved. Usually, the solvent used is water and organic solvent. Majority of organic compounds will be more soluble in organic solvents than in aqueous solvents.

This technique utilize an extracting phase-coated fiber (polymer liquid or solid sorbent) which extract analytes of different types from either gas or liquid phase. [12] Principle – Its mechanism is similar to that of Solid Phase Extraction except the extraction solvent volume is very small (less than 1 microliter). The main principle of this method is adsorption and desorption. It is a micro-extraction technique utilizing a syringe-like device which protects the sample-coated fiber inside. [13] The amount of adsorbed analyte by the fiber is proportional to the sample concentration in equilibrium and depends on the analytes’ distribution constant and the thickness of coat. Thin coat is apply for semi-volatile compounds while thick coat is apply for volatile compounds. The type of fiber used is depend on the properties of analytes. The time of extraction is not dependent on concentration of analytes. [14] Procedure – The coated fiber is drawn into the needle. Plunger is pressed to immerse fiber into sample or the space above it. The analyte is then adsorbed onto the fiber coating until equilibrium is attained. Then, the fiber is drawn back into the needle and injected (desorbed) into Gas Chromatography (GC) or High Performance Liquid Chromatography (HPLC) injector port for analysis determination.