Chemical modification in atomic emission: Determination of V in lubricant oils by tungsten coil atomic emission spectrometry

A procedure based on the use of chemical modifiers to determine V in lubricant oil samples by tungsten coil atomic emission spectrometry (WCAES) is described. Cobalt, Ni and Pd were evaluated as chemical modifiers, and the best sensitivity and limit of detection were obtained with the latter. As previously described for Cr, signal enhancements may be related to charge-transfer and electron recombination reactions in the gas phase. Using Pd as a modifier, calibration curves in the 0.25-10.0 mg L− 1 V range, with R2 > 0.999 and relative standard deviations better than 5.6% were obtained. Accuracy was checked by determining V in a certified reference material of lubricating oil. Results were in agreement with reference values at a 95% confidence level (t-test). The procedure was also applied to two samples of unused, and five samples of used lubricant oil submitted to acid digestion. The V content found in these samples was between 20.5 and 67.4 mg kg− 1. Some of these concentrations were below the limit of detection for determinations without chemical modification (30 mg kg− 1). A 10-fold improvement of the limit of detection was obtained by employing Pd as the chemical modifier (3 mg kg− 1).