Why is Acetonitrile Used in HPLC?
Acetonitrile together with Methanol are the most commonly used solvents for HPLC and UHPLC Chromatography processes because most substances are easily soluble in both solvents, but not saturated hydrocarbons. Acetonitrile has a low wavelength which means that the solvent will elute first from the column, therefore pressure is reduced on the column. Lower pressure in the column will have the long term effect of prolonging the life of the column, pressure within the column varies depending on the solvent used and the mixture ratio between the solvent and the sample. An Acetonitrile based solution generally has a higher elution strength against the same strength solution using Methanol. Some scientists report that the same retention times can be achieved using acetonitrile with less than half the ratio of methanol. Operator errors can have a significant impact of reproduceable results.
Acetonitrile produces less pressure than Methanol, however the choice between using Acetonitrile against Methanol should not be made on price, (Acetonitrile is generally more expensive than Methanol), choice should be made on performance for your particular instrument and the effect of the chromatography process on the durability of the column. High grade Acetonitrile has a lower absorbance in routine HPLC and UHPLC procedures and causes less interference than other solvents that can be used.
Biosolve solvents, including Acetonitrile, supplied by Greyhound Chromatography, are filtered at 0.1µm and are packed under inert nitrogen gas for longer shelf life, with very low amounts of inorganic metallic contaminants. Acetonitrile is bottled in pure glass containers to minimise leaching and degradation of the solvent. Acetonitrile is a clear colourless liquid with an acidity as low as 0-0.001% depending on the grade. The presence of acid in the solvent improves the chromatographic peak shape. Full certificates of analysis are available to view before selecting the right grade of solvent for your application. Acetonitrile Surpa-gradient grade, available from Biosolve, is the highest-grade Acetonitrile solvent available for HPLC and UHPLC in today's worldwide market.
Acetonitrile is shipped under Dangerous Goods regulations as it is a highly flammable liquid and vapour. Safety procedures should be closely followed for the safe handling of Acetonitrile, including keeping away from sparks and open flames, hot surfaces and heated storage rooms. When handling take reasonable precautions to ensure that it does not go on skin or near eyes. If Acetonitrile does come into contact with clothes, remove the clothing and rinse thoroughly in water. If it comes into contact with the skin, wash cautiously with water. If acetonitrile comes into contact with the eyes, remove contact lenses if they are present, rinse with water for several minutes and seek medical advice.
Is there a need to wash columns frequently during HPLC
It is important to look after your columns to prolong their life and also their integrity. Washing a column is an important process that should be done regularly. Depending on how many samples you are processing and how often you are using them will determine how many times you wash the column. Storage of the cleaned columns should also be considered. It is important to establish a wash cycle in the laboratory, if you do not you will notice a gradual pressure build up and you may experience ghost peaks after the first injection. Ghost peaks are caused by compounds eluting off the column in later runs despite being injected in a previous analysis.
This is the recommendation for a column that is to be stored over a long period. Replace buffers and modifiers at the end of the day, it is recommended that you wash the column with 70% water, 15% methanol and 15% acetonitrile. divert the eluent from the column to waste so as not to contaminate the detectors. Wash the column in 100% methanol and 100% acetonitrile, both for at least 15 minutes. Store the column subject to the manufacturers recommendations, this will preserve the column, which may last for years depending on the number of samples processed and the care you give to your column. For daily use, wash the column in 70% water, without using an acid or modifier, and store overnight subject to manufacturer's instructions.
Historic World Shortage of Acetonitrile
In 2008 there was a world shortage of Acetonitrile, (a by-product from the manufacture of acrylonitrile) because of several factors, including, Chinese manufacture being shut down because China was hosting the Olympics and all industry within China was either closed down or drastically reduced in an attempt to improve the standard of air during the Olympics. Also, during Hurricane Ike in the USA an Acetonitrile factory was damaged in Texas causing further shortages. As Methanol is an acceptable substitute in most HPLC methods the shortage can be overcome. Acetonitrile is seen as a valuable commodity due to the volume used worldwide for a variety of purposes other than Laboratory analysis. There is no anticipated shortage of acetonitrile at this present time.
Susan Massie, Marketing Director
Greyhound Chromatography and Allied Chemicals
Scan for Biosolve Products.