Determination of Refractory Elements in Used Lubricating Oil by ICPOES Employing Emulsified Sample Introduction and Calibration with Inorganic Standards

Abstract

The quantitative determination of wear metals in used lubricating oil is an important application for engine and turbine diagnostic purposes, allowing preventive maintenance (oil changes, equipment overhauls and replacement of components) to be made before the collapse of equipment. 1 The wearing of metals causes solid metal debris of different sizes, metal oxides and metallorganic species, from mechanical wear, oxidative corrosion and chemical corrosion, respectivery. 1-3Several analytical methodologies based on atomic spectrometric techniques have been developed for such purposes. Electrothermal atomic absorption spectrometry (ET AAS) has been one of the techniques of choice, since it tolerates samples of high organic load and, in general, allows good sensitivities to be achieved. 2,[4][5][6][7][8] In the case of refractory elements, which can be related to the wearing of specific parts of engines and turbines, 9 AAS methods are not suitable, since those elements have high boiling points and/or tend to form high melting-point carbides and oxides, leading to low sensitivities. 10 For refractory metals, better limits of detection can be obtained using ICPOES because of the efficient atomization, ionization and excitation achieved in the ICP. 11 In addition, ICPOES allows better precision and repeatability, presents wider linear dynamic ranges (4 to 6 orders of magnitude depending on the element) 11,12 and has multielemental detection capability, while ETAAS is basically a monoelemental technique, although sequential procedures can enable fast sequential detection for 2 or 3 elements. 8 Alternatively, a few ICP-MS methodologies for lubricating oils have been reported. Although these methodologies enabled good sensitivities, ICP-MS has a relatively more complex instrumentation and is thus prone to present problems when samples with a relatively high organic load are introduced, when compared to ICPOES. Because of this later limitation, methodologies for lubricating oil samples use either sample vaporization on a electrothermal device 3 or sample emulsification using very diluted surfactant emulsions (1% of oil). 13 In both cases, analyte oil standards have been employed for the calibration procedures.In general, in order to use a spectrometric technique for analysis, it is necessary to submit samples to some kind of treatment in order to make them compatible to the sample introduction systems and atomizers. The choice of such a preparation procedure is critical for the success of the analytical methodology, and several factors must be considered, such as the cost, preparation time and labor, potential for sample contamination and dilution factor. In the case of atomic emission spectrometry with an ICP source, the sample treatment aim is to reduce the organic load of the sample introduced into the plasma, because it affects its stability, reduces the energy available to analyte ionization and excitation and increases the background emission.14 Those factors are intimately related to the sensitivity of the ICPOES me...

Trace Metal Analysis in Petroleum Products: Sample Introduction Evaluation in ICP-OES and Comparison with an ICP-MS Approach

“…Moreover, severe matrix interferences have already been observed during the analysis of organic solutions in ICP-OES due to plasma interactions (Botto, 1987). In order to minimize these problems, five solutions are globally described in the literature with organic injection using micro-nebulisation system (Dreyfus et al, 2005;Botto, 2002), desolvatation using ultrasonic nebulisation and membrane (Botto and Zhu, 1996;Duyck et al, 2002), digestion of the sample (Wondimu et al, 2000;Heilmann et al, 2004, Lopez andMonaco, 2004), microemulsion (Souza et al, 2004;Wang et al, 2003) for introduction of an aqueous phase in the plasma and finally electrothermal vaporization (Resano et al, 2001;Saint'Pierre et al, 2002). Micronebulization and ultrasonic nebulisation are sometimes used in combination with oxygen addition into the plasma, which is particularly recommended with ICP-MS detection.…”

Determination of Wear Metals in Lubrication Oils: A Comparison Study of ICP-OES and FAAS

“…ICP-OES [10][11][12][13] offers the possibility to simultaneously measure almost all metals and some non-metals. Hence, its productivity in the analysis of a large amount of samples is superior to FAAS.…”

Analysis of Lubricating Grease by ICP-OES: A Case Study on Preparation Methodology

“…The emulsification method adopted in the present study was followed from the reported method [15] with a slight modifications in order to analyse the multi-elements present in the lubricating grease samples. This method was carried out with the addition of Triton X-100, which gave acceptable recoveries and stability in emulsion [16]. However to improve the percentage of recovery, Triton X-100 concentration was varied in the range of 1-10 %.…”