HPLC Tips & Tricks: Getting Greener in HPLC

Egidijus Machtejevas, Lead Expert

Merck

Article from Analytix Reporter - Issue 15

INTRODUCTION

Liquid chromatography is a widely used analytical technique in various fields such as pharmaceuticals, biotechnology, food and beverage, environmental monitoring, and more. The most popular type of liquid chromatography is reversed phase (~>75%). Up until now, the technique often employs acetonitrile and relatively large columns (the most used column dimension still is 250 x 4.6 mm). However, there are a few options for adjusting the mobile phase to improve the sustainability of chromatography without compromising its performance.

Use eco-friendly solvents

One of the biggest environmental impacts of liquid chromatography is the use of solvents. Replacing hazardous solvents with more environmentally friendly options such as water, ethanol, or other organic solvents that are bio-renewable, safe, non-toxic, and biodegradable can significantly reduce the environmental impact. Green solvents are an important component in making liquid chromatography more sustainable in general. However, higher viscosity/ backpressure, UV cut-off, and temperature limits of the used solvent system might need to be considered. Here are some examples of green solvents potentially to be used in liquid chromatography.

• Water: Water is the most commonly used solvent in liquid chromatography, especially in reversed-phase chromatography. This solvent can be considered one of the greenest solvents. Hot water (superheated water from 75 to 180 °C) has been already proven to have the potential to reduce the organic solvent percentage in the mobile phase.¹
• Ethanol: Ethanol is typically a bio-based solvent that can be produced from renewable sources such as fermentation of bio-waste. This solvent is non-toxic, biodegradable, and has a low environmental impact.
• CO₂: Supercritical CO₂ is a green solvent that is used in supercritical fluid chromatography (SFC). This solvent is non-toxic, non-flammable, and can be easily recycled.
• Other bio-based solvents: Bio-based solvents such as terpenes or lactic acid for sample extraction, and glycerol² or dimethyl carbonate³ are gaining attention in liquid chromatography workflows. These solvents are derived from renewable sources and have low toxicity and a low environmental impact.

However, it is important to note that not all green solvents are suitable for every chromatographic application, so users should carefully consider the specific properties and requirements of their method before selecting an alternative green solvent. Also, for validated methods, it is not allowed to make any changes in mobile phase composition according to Pharmacopoeias without full re-validation.

Other approaches to get greener in HPLC

Another set of improvements is related to the method setup and different instrumental solutions.

• Optimized methods: HPLC method optimization can significantly reduce the consumption of solvents and the generation of waste. The environmental impact of an HPLC method can be reduced by reducing the column dimensions, in particular the column inner diameter, reducing the injection volume, using different gradient conditions, and/or reducing the run time. The most significant reduction in solvent consumption can be achieved by using shorter columns with smaller inner diameters. The loss in separation efficiency of a shorter column can be compensated by more efficient smaller particles or superficially porous particles to still obtain accurate and reliable results. (see an example for peptide mapping)
• Use “greener” equipment: Modern liquid chromatography equipment is designed to be more energy-efficient. Using systems that recycle solvents and/ or using a lower flow split ratio can help reduce solvent consumption and waste generation.
• Recycle waste: Instead of discarding the waste generated during the chromatographic process, it could be (partly) recycled or reused for other applications, thus reducing the overall environmental impact. This approach so far is only applicable for isocratic runs.
• Choose sustainable suppliers: It is important to select suppliers who prioritize sustainability and offer environmentally friendly products. This fact includes suppliers who use recycled materials, source raw materials sustainably, and prioritize energy- and raw material-efficient production methods. Look out for e.g., high EcoVadis rating or Environmental, Social, Governance (ESG) rating from MSCI.
• Consider alternative methods: In some cases, alternative analytical techniques such as capillary electrophoresis, supercritical fluid chromatography, or sensorics-based methods may be more sustainable and have a lower environmental impact than liquid chromatography while still providing the needed analytical answer.

Conclusion

By considering and adopting the above mentioned strategies, in particular, the reduction of column dimensions, liquid chromatography can be made more sustainable, reducing its environmental impact and contributing to a more sustainable future.

To read more about our sustainability efforts and more sustainable chemistry products, visit us at SigmaAldrich.com/sustainable-chemistry

References

1. Huang G, Smith RM, Albishri HM, Lin J. 2010. Thermal Stability of Thiazide and Related Diuretics During Superheated Water Chromatography. Chroma. 72(11-12):1177-1181. https://doi.org/10.1365/s10337-010-1789-1

2. Habib A, Mabrouk MM, Fekry M, Mansour FR. 2021. Glycerol as a novel green mobile phase modifier for reversed phase liquid chromatography. Microchemical Journal. 169106587. https://doi.org/10.1016/j.microc.2021.106587

3. Lajin B, Goessler W. Introducing dimethyl carbonate as a new eluent in HPLC-ICPMS: stronger elution with less carbon. J. Anal. At. Spectrom.. 36(6):1272-1279. https://doi.org/10.1039/d0ja00525h