This new instrument by Fluitec offers portable TAN, TBN and antioxidant additive measurements. Cliff Mansfield of Texaco R&D puts it to the test.
Fluitec makes the Ruler that can measure total acid number (TAN), total base number (TBN), or antioxidant additive level depending on the solvent system selected. Reagents are supplied in premeasured vials, and the lubricant is added to the reagent using an autopipet. The system uses cyclic voltametry at a glassy carbon electrode. The reagents contain alcohols and ketones and are relatively harmless, especially compared with the strong acids and bases used in the ASTM methods. They can be readily transported and disposed.
Since this system does not depend on a color change for the reaction end point, highly colored oils can be analyzed. Results can usually be obtained in less than three minutes.
The Ruler sells for about $15,000 and is designed for use with an existing computer. This instrument is small and can be used with a portable PC in the field. The reagent vials are approximately $7.50 each.
The Ruler TAN was compared with our laboratory automated D664 method in the analysis of a number of hydraulic fluids. Results are in the chart below.
The main caution with this method is to make sure that the reagent and lubricant are thoroughly mixed and to allow enough time for complete reaction prior to making a measurement. After the addition of the lubricant using an autopipet, the reagent and lubricant should be mixed for one minute on a vortex mixer or by hand with vigorous shaking. After mixing, the vial should stand prior to making a measurement. If this procedure is followed, very repeatable results can be obtained. 
Antioxidant additive levels can also be measured. Results are expressed as the percent of additive remaining as compared to the additive level in the new lubricant. These measurements require reference to the new lubricant first.
This could be a very useful measurement in predicting the remaining useful life of the lubricant. In running this analysis along with the TAN analysis, one can observe that the TAN remains fairly constant until the antioxidant level reaches around 20 percent of its original value. At this point, the TAN starts to increase.
Base number can also be measured with this system. Correlations with existing total base number methods (ASTM D4739 and ASTM D2896) will be reported in a future article.
A precaution that should be noted is that several of the reagents have a shelf life of 3 to 12 months. Planned purchasing should be worked out to limit quantities of reagent so that this shelf life is not exceeded.
