Separation and analysis of pharmaceuticals in cold drugs using green chromatography

Exploring the green frontier: Subcritical water chromatography for sustainable analytical practices

Water in the subcritical state is characterized by properties significantly different from water under standard conditions. These include low viscosity, low surface tension, and a much lower dielectric constant, increasing the solubility of nonpolar substances. For this reason, it can provide an alternative solvent and be used in chromatographic techniques-subcritical water chromatography (SBWC). SBWC appears to be one of the greenest analytical techniques until we unravel chromatography with pure water at room temperature. The versatility of SBWC is explored through its applications in the separation and analysis of a wide range of compounds, including pharmaceuticals, natural products, etc. The use of subcritical water as a mobile phase requires suitable stable stationary phases and special apparatus. Still, it makes it possible to conduct analyses without using organic solvents. When using this technique, it is important to remember that it suits the analysis of thermally stable substances. The following work is a critical review of developments in SBWC.

Stability and Extraction of Vanillin and Coumarin under Subcritical Water Conditions

In order to facilitate the development of the green subcritical water chromatography technique for vanillin and coumarin, the stability of the compounds under subcritical water conditions was investigated in this work. In addition, their extraction from natural products was also studied. The stability experiments were carried out by heating the mixtures of vanillin and water or coumarin and water at temperatures ranging from 100 °C to 250 °C, while subcritical water extractions (SBWE) of both analytes from vanilla beans and whole tonka beans were conducted at 100 °C to 200 °C. Analyte quantification for both stability and extraction studies was carried out by HPLC. After heating for 60 min, vanillin was found to be stable in water at temperatures up to 250 °C. While coumarin is also stable at lower temperatures such as 100 °C and 150 °C, it undergoes partial degradation after heating for 60 min at 200 °C and higher. The results of this stability study support green subcritical water chromatographic separation and extraction of vanillin and coumarin at temperatures up to 150 °C. The SBWE results revealed that the extraction efficiency of both analytes from vanilla beans and tonka beans is significantly improved with increasing temperature.

Separation and Analysis of Aspirin and Metformin HCl Using Green Subcritical Water Chromatography

Organic solvents are widely used in pharmaceutical and chemical industry for chromatographic separations. In recent years, subcritical water chromatography (SBWC) has shown ability in replacing hazardous organic solvents used in traditional high-performance liquid chromatography (HPLC). In this work, a pain killer—aspirin—and an antidiabetic drug—metformin HCl—were successfully separated on an XBridge C18 column using no organic solvents in the subcritical water chromatography mobile phase. Both traditional HPLC and subcritical water chromatography were used for comparison purposes. SBWC separation of metformin HCl and aspirin were achieved at 95 °C and 125 °C, respectively. The recovery for both active pharmaceutical ingredients (APIs) obtained by SBWC is 99% in comparing with the stated content of each drug. The relative standard deviation is less than 1% for SBWC assays developed in this work. This level of accuracy and precision achieved by SBWC is the same as that resulted by the traditional HPLC analysis.

Greening Reversed-Phase Liquid Chromatography Methods Using Alternative Solvents for Pharmaceutical Analysis

The greening of analytical methods has gained increasing interest in the field of pharmaceutical analysis to reduce environmental impacts and improve the health safety of analysts. Reversed-phase high-performance liquid chromatography (RP-HPLC) is the most widely used analytical technique involved in pharmaceutical drug development and manufacturing, such as the quality control of bulk drugs and pharmaceutical formulations, as well as the analysis of drugs in biological samples. However, RP-HPLC methods commonly use large amounts of organic solvents and generate high quantities of waste to be disposed, leading to some issues in terms of ecological impact and operator safety. In this context, greening HPLC methods is becoming highly desirable. One strategy to reduce the impact of hazardous solvents is to replace classically used organic solvents (i.e., acetonitrile and methanol) with greener ones. So far, ethanol has been the most often used alternative organic solvent. Others strategies have followed, such as the use of totally aqueous mobile phases, micellar liquid chromatography, and ionic liquids. These approaches have been well developed, as they do not require equipment investments and are rather economical. This review describes and critically discusses the recent advances in greening RP-HPLC methods dedicated to pharmaceutical analysis based on the use of alternative solvents.

Surface-enhanced Raman spectroscopy and microfluidic platforms: challenges, solutions and potential applications

The review provides an overview of the development in the field of surface-enhanced Raman spectroscopy combined with microfluidic platforms.