Is it a good idea to replace HPLC solvents with greener alternatives with low performance capabilities? Christopher Welch and his colleagues at Merck Research Laboratories in Rahway, New Jersey, US, think so.

High performance liquid chromatography is the most widely-used analytical technique in the pharmaceutical industry and acetonitrile is by far the preferred HPLC solvent. 'A pharma company could have over a thousand instruments in operation,' explains Welch, who adds, 'While the amount of waste generated by an individual HPLC is small, the cumulative volume is substantial.'

Recent improvements in HPLC technology mean that greener, but less effective, solvents such as ethanol can be used without a significant loss in analytical capacity. Improved UV detector design has led to an enhanced signal-to-noise ratio and lower-volume mixing has improved the speed of experiments. 'More importantly, there has been a revolution in column packing materials that has led to dramatically improved peak sharpness. The smaller the particles packed into the chromatography column, the better the chromatographic efficiency,' says Welch.

Welch tested the solvents with a range of sample mixtures and conditions. He found that while acetonitrile undoubtedly delivers outstanding performance as a HPLC solvent, greener alternatives perform reasonably well, and may be suitable replacements.

'Many analysts are uncomfortable with the idea of giving up any performance, preferring to have as much firepower as possible available for handling whatever scenario may arise,' comments Welch. 'While justifiable in some settings, the fact remains that every bit of excess performance delivered by modern HPLC technology is probably not needed in most cases. As the cost of acetonitrile and the resulting cost in waste disposal continue to escalate, the ethanol alternative becomes increasingly compelling.'

Michael Spencelayh

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