**4. Cleanup techniques**

Sample cleanup is especially important for analytical separations such as GC, HPLC, and electrophoresis. Often, many solid matrices, as soil, biological materials, and natural products, contain hundreds of interferences at higher concentrations than those of the analytes. So, a cleanup step is vital to separate the trace amount of analyte from interferences. On the other hand, some high-boiling materials can cause a variety of problems such as the adsorption of analyte in the injection port or in front of a GC or HPLC column. Therefore, some positive and negative errors can be observed in the retention time of the analyte.

Some other cleanup techniques include gel permeation chromatography (GPC), acid-base partition cleanup, solid-phase extraction (SPE), and column chromatography, which are discussed in the following step [3].

Gel permeation chromatography (GPC) is a size-exclusion method which contained organic solvents (or buffers) and porous gels to separate macromolecules larger than analytes of interest. GPC is used to eliminate lipids, proteins, polymers, copolymers, natural resins, cellular components, viruses, steroids, and dispersed high-molecular-weight compounds from the sample. This method is suitable for both polar and nonpolar analytes [2]. On the other hand, GPC is usually used to remove high-boiling materials which condense in the injection port of a GC or the front of the GC column [28].

Acid-base partition cleanup is a liquid-liquid extraction procedure to separate acids such as organic acids and phenols from the base or neutral analytes like amines, aromatic hydrocarbons, and halogenated organic compounds, by adjusting pH. Also, this cleanup method is applied for petroleum waste prior to analysis [2].

Solid-phase extraction cartridge is a traditional column chromatography which is applied to clean up the biological, clinical, and environmental samples. Some of the SPE application examples are as follows [29]:


As discussed in previous sections, the sufficient amount of a sorbent, which is loaded with the sample extract, has packed the SPE cartridge. Then, the analyte of interest is eluted through the column by an efficient eluting solvent, and the other contaminants are remained on the cartridge. The packing compound may be an inorganic material like either Florisil or one of many stationary phases which are commercially available [30].
