*6.4.2 Vacuum liquid chromatography (VLC)*

The fundamental disadvantage of column chromatography is that it is a time-consuming technique; however, vacuum liquid chromatography can solve this problem. In vacuum chromatography, rather than using pressure, vacuum is employed to improve the flow rate and hence speed up the fractionation process. The stationary phase is usually 40–60 mesh particle size silica or reversed-phase silica, and the crude extracts are separated by gradient elution. TLC is a typical method for examining eluted fractions [43].

*Green Extraction Techniques for Phytoconstituents from Natural Products DOI: http://dx.doi.org/10.5772/intechopen.105088*

#### *6.4.3 Simulated moving bed chromatography (SMB)*

In the pharmaceutical sector, simulated moving bed (SMB) technology is an economical and eco-friendly process for purifying crude extracts and fractions [46]. It has a higher purity and yield than other techniques. A traditional Simulated Moving Bed system has 4–24 columns divided into four zones. In general, a four-column SMB should be sufficient for testing and optimizing purification conditions. Purification of sugars, proteins, monoclonal antibodies, separation of organic solvents, optical isomers, charged molecules, and desalting are all common applications. For the separation of crude medicines, the SMB technique utilizes extremely less solvent. The SMB technique is simple to adapt to a continuous process and can be integrated with other equipment such as evaporation. SMB, on the other hand, necessitates meticulous process control and is less adaptable than traditional elution chromatography.

#### **6.5 Capillary electrophoresis (CE)**

CE provides several advantages, including a smaller sample, high efficiency leads to shorter analysis time, cheap, environmental friendliness, reduced solvent usage, and a powerful tool appropriate for drug discovery [47]. CE is a new method for analyzing different phytochemical groups. Variations in mass to charge ratios are used to separate phytochemicals in capillary electrophoresis. Because borate can form compounds with the flavonoid nucleus' ortho dihydroxyl groups and the sugar's vicinal cis-dihydroxyl groups, borate buffers with a pH of 8–11 and a concentration of 25–200 mM are generally used [48].

Capillary zone electrophoresis (CZE) is the most basic characteristic, and it's been utilized to isolate a variety of target molecules, especially polyphenolic compounds like epicatechin, catechin, quercetin, gentistic acid, caffeic acid, gallic acid, trans-resveratrol, myricetin, and rutin from wine and grape samples. A CZE technique was also used to isolate antioxidants in Ginkgo leaf extracts. For the separation of anthocyanins in wine, a new CZE approach was developed recently [49]. Food analysis, environmental monitoring, clinical diagnostics, and pharmaceutical analysis have mostly used capillary electrophoresis. Since it allows the use of chirality selectors with limited aqueous solubility, nonaqueous capillary electrophoresis can be utilized to separate enantiomeric drugs. Furthermore, the low dielectric constant of organic solvents can let chiral counter-ions that have less selectivity in aqueous environments form ion pairs and therefore increase their selectivity. CE-MS is one of many multidimensional techniques used in the pharmaceutical and biotechnology industries, particularly for drug development. Because high resolution and structural and/or molecular weight information of an analyte may be collected along with using a mass spectrometer as a detector for CE splitting, could be useful. CE has various advantages (for example, high speed, efficiency, and low price); yet, combining CE with MS produces several problems. CE solvents, for example, are not accepted by MS.

#### **6.6 Molecular imprinted technology**

Molecular imprinting knowledge has been a prominent isolation method in the last years because of its distinctive qualities, such as high selectiveness, economical, and ease of preparation. Many correlative cavities with the memory of the template molecules' size, shape, and functional groups are produced when the template molecules

are removed from the molecular imprinted polymer (MIP). As a result, the template molecule and its analogues will be able to recognize the MIP and adsorb it selectively. MIPs have been extensively used in the isolation of phytoconstituents and as sorbents for solid-phase extraction of herbal materials to enrich phytoconstituent components. MIP was made with methyl methacrylate as the monomer, solanesol as the template molecule, and ethylene glycol as the crosslinker by a suspension polymerization method. This technique is used for the purification of enriching in water extract of *Panax notoginseng*, solanesol from tobacco leaves, thermo-responsive magnetic MIP is used to isolate curcuminoids, curcumin, dimethoxy curcumin, and bisdemethoxycurcumin, from the TCM *Curcumae Longa* Rhizoma [50].
