TAN in Lubricants by automated Vis-NIR spectroscopy – Automation saves time and boosts efficiency

Lubricants are petroleum-based products for lubrication of moving machinery parts as well as for metal forming and cutting tools. Acid Number (AN) is a key parameter for monitoring the amount of acidic compounds in such fluids. They
are formed by oxidation or introduced as contaminants, and their concentration correlates with the ageing of the lubricant matrix. Therefore, excessive levels of acidic components can be used as an indicator that the lubricant must be exchanged. AN is usually determined by potentiometric titration (ASTM D664). In many cases, however, Vis-NIR spectroscopy can provide a faster, nondestructive and therefore much easier to use alternative to potentiometric titration. Vis-NIR measurements can be fully automated: For the present application, a Vis-NIR spectrometer with a flow-cell was coupled with a sample changer to perform serial AN measurements completely unattended. Comparison with results obtained from manual measurements confirmed that automated Vis-NIR spectroscopy is a viable solution to save time and boost productivity in the laboratory.