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The invention of drugs ushered a new era in human health. These drugs will only perform their purpose if they are free of contaminants and taken in the correct dosage.
Rather than simple quality control of active components in medicines, complex extraction and derivatization processes are frequently used in bioanalytical procedures and the concentration of trace contaminants in pharmaceuticals. In most cases, quality control of the active component in a formulation involves a straightforward extraction method. If there is an issue with excipient interference after extraction, chromatography can separate the active ingredient from the interference and allow quantification. Low dosage formulations and sophisticated drug delivery formulations, on the other hand, may necessitate more comprehensive sample treatment.
Commonly used excipients in formulations
The primary rationale for extraction before analysis is to remove any elements that may interfere with the analysis. This is a more stringent requirement if chromatographic separation is not performed during the analysis. Some non-chromatographic approaches, such as NIRA, aim to eliminate all sample preparation by screening out interference using powerful computational algorithms. Even if chromatographic separation is used, some form of extraction must be performed before analysis to remove the insoluble tablet matrix elements or oil excipients of ointments and creams.
When monitoring low amounts of pharmaceuticals in biological fluids, extraction techniques may need to be fairly thorough to avoid interference from endogenous substances. This sector briefly discusses the many types of interference used in formulations.
Tablets and capsules
Except in formulations that are high-dose, for example, paracetamol and tablets of other non-steroidal anti-inflammatory medications, where the active component may make up a considerable portion of the formulation, tablets and capsules normally contain a lot of filler. Lactose is the most common filler in tablets, but other sugars or sugar polymers like cellulose, starch, and mannitol are also common. Because these chemicals are polar and will dissolve or swell best in water, extraction methods involving water-soluble drugs should be performed in aqueous solutions to recover the medication efficiently from the sample matrix.
Because the fillers do not absorb UV light, they are unlikely to interfere directly in HPLC methods, where they will elute at the void volume with no modification of the chromatographic baseline, as in routinely used reversed-phase chromatography procedures. They also cause negligible interference in direct UV spectrophotometry analyses. If the medicine isn’t totally water soluble, methanol or ethanol can be employed to extract it because they wet the tablet powder well and dissolve many organic compounds.
Magnesium stearate, stearic acid, and polyethylene glycol are lubricants used in tablet production. They only make up 1–2% of the tablet’s mass. Therefore their ability to interfere is little, especially since their chromophores are weak. When a tablet extract is analysed using GC–FID, the fatty acid lubricants are frequently visible. Sugar polymers that are altered or modified, for example, hydroxypropylmethylcellulose, are frequently used in tablet coatings. These coatings cover around 3% of the tablet’s surface area, are water-soluble, and do not absorb UV radiation.
Because colourants are effective UV/visible radiation absorbers, they have the potential to interfere with the analysis. Colours in tablets and capsules are usually metal oxides or dyes that are organometallic in nature, which is not soluble in any of the extraction solvents and can be filtered out with other insoluble matrix materials. The coloured outer shell of capsules is removed before the contents are taken during analysis.
Suspensions and solutions
Water-soluble colours such as chlorophylls, carotenoids, anthocyanins, and coal-tar-based dyes are utilised in suspensions and solutions. These materials may require more effort to remove interference. Despite the easy extraction of the medication into a solvent of modest polarity may push off such dyes in the phase of aqueous, solid-phase extraction with ion exchange resins may be useful for eliminating anionic or cationic dyes. Antimicrobial preservatives and antioxidants are commonly found in solutions. These are mainly phenols or quaternary amines like benzalkonium chloride, and their chromophores are powerful enough to interfere with drug analysis. Before the examination, these chemicals must be extracted using extraction techniques. Surfactant materials, such as polyethylene glycol-based detergents, are also present in suspensions, although they have low UV absorbance and hence pose little risk of interference.
Creams and ointments
Creams and ointments contain sodium and potassium salts of cationic surfactants, fatty acids, and non-ionic surfactants. As previously stated, these chemicals do not have strong chromophores. Still, if they are not eliminated, they may interfere with chromatography, for example, by adulterating the reverse-phase columns of HPLC. The loss of chromatographic peak morphology is frequently observed when lipophilic compounds contaminate reverse-phase HPLC columns.
Large levels of fatty triglycerides are present in creams and ointments, which must be eliminated to avoid interfering with the chromatographic process. This form of interference can be partially removed by extracting the cream with methanol. The extract can also be partitioned between hexane and methanol or methanol/water combinations, with the highly lipophilic substance being extracted into the hexane layer.
Conclusion
Today, developing effective and selective extraction and isolation strategies for those bioactive natural compounds is critical. This article provides a complete overview of many natural product extraction and isolation methods. This post discussed the benefits, drawbacks, and practical applications of traditional and modern natural product research approaches.
