ViewpointThe determination of trace metals in lubricating oils by atomic spectrometry☆
Introduction
Engine and turbine components undergo continual wear under normal operating conditions; this is minimized by the use of lubricating oils. Lubricating oils from petroleum are mainly composed of paraffinic, naphthenic and, to a lesser extent, aromatic hydrocarbons. Several additives, including metallo-organic ones, are also part of the final composition of commercial lubricating oil. Wear has both physical (friction between metallic parts, high temperature and pressure) and chemical (corrosion) sources. Chemical wear may produce not only metallic particles but also soluble metallo-organic species, whereas physical wear generates metallic particles of varying sizes (up to a few micrometers) [1], [2]. Part of the metallic debris is not retained by filters and collectors, remaining in the lubricating oil and being transported through the whole system [3]. Increasing amounts of some key elements in the lubricating oil may indicate the extent of the wear of wetted components. For instance, an abrupt increase of Ni, Sn or Cr indicates corrosion in bearings, valves and pistons, Fe indicates corrosion in various parts, Na indicates oil contamination with anti-freeze fluids and so on [4], [5]. The diagnosis based on elemental analysis of used lubricating oils may indicate the need for preventive maintenance of engines and turbines before irreversible damage occurs. Besides bringing economic benefits, such diagnoses save lives. The Spectroscopy Oil Analysis Program (SOAP) of the United States Air Force was the pioneer program based on this type of monitoring [4].
Elements such as Ag, B, Ba, Bi, Ca, Cd, Co, Cr, Fe, Hg, Mg, Mo, Ni, P, Sb, Se, Sn, Ti and Zn, are also deliberately introduced in small portions to lubricating oils to address requisites for special applications [4]. In these cases, metallo-organic compounds containing these elements act as additives, improving lubricating capability and properties such as antioxidant, anticorrosive, dispersing, antiwear, and others. The improvement of performance of the oil is dependent upon the amount of the additive introduced; therefore, these amounts must be strictly controlled.
Sensitive techniques are required for analysis of used lubricating oils since the capability of monitoring small concentration changes in the key elements is needed. The complexity of the oil matrix, its viscosity and the high organic load impose serious difficulties for elemental analysis. Such determinations are also an analytical challenge because all wear metals (solid particles of different sizes and metallo-organic species) must be accurately determined for information purposes [4], [6].
Apart from the existence of a few electroanalytical [7], [8], [9], [10], [11] and XRF [12] methods for the determination of Zn, Cu, Pb, Fe, Cr, Ni, As and Cd in lubricating oils, the majority of analytical methods reported in the literature are based on atomic spectrometric techniques such as FAAS, ET AAS, DC or ICP OES, ICP MS and AFS.
Section snippets
Sample pre-treatment, introduction and analyte calibration
Despite advances in sample introduction utilizing a minimum of previous treatment (solid sampling, electrothermal vaporization, laser ablation, etc.), most methods based on atomic spectrometric techniques still require some sample pre-treatment. In the case of viscous complex oil-based organic materials, major problems arise due to the difficulty in introducing them directly into the atomizers and selecting proper calibration standards [13]. As a consequence, proper preparation of oil samples,
Atomic fluorescence and atomic absorption methods
Pioneering work within the SOAP program used AFS for the determination of Ag, Cu, Fe, Mo and Mg in jet engine oils [36], [37], [38], [39]. Sample atomization from a graphite rod or in a low-quenching H2–Ar or Air–C2H2 flame was employed. Because of low-radiance light sources, resonance fluorescence schemes were chosen; therefore, a high stray and scattering background environment was expected. Limits of detection at the μg g− 1 level were reported. Determinations of Pb, Cr and Ni were plagued by
Final remarks
Table 1 summarizes the referenced analytical procedures for determination of metals in lubricating oils. In spite of the difficulties of this type of analysis caused by sample heterogeneity and matrix complexity, modern instrumentation in combination with a proper sample pre-treatment, has greatly improved the reliability of trace metal results. FAAS remains as an important technique for metal determination in lubricating oil due to its lower costs and robustness in relation to interferences
Acknowledgements
The authors thank CNPq (Brazil) for scholarships and Petrobras for research funding. FINEP (Brazil) is also acknowledged.
References (70)
- et al.
Simultaneous determination of copper and lead in ethanol fuel by anodic stripping voltammetry
Microchem. J.
(2004) - et al.
Combination of ultrasonic extraction and stripping analysis: an effective and reliable way for the determination of Cu and Pb in lubricating oils
Talanta
(2006) - et al.
Determination of metals in lubricating oils by X-ray fluorescence spectrometry
Talanta
(2001) Determination of trace metals in petroleum and petroleum products using an inductively coupled plasma optical emission spectrometer
Spectrochim. Acta Part B
(1983)- et al.
Determination of metallo-organic species in lubricating oil by electrothermal vaporization inductively coupled plasma mass spectrometry
Anal. Chim. Acta
(1996) - et al.
The determination of wear metals in used lubricating oils by flame atomic absorption spectrometry using sulphanilic acid as ashing agent
Talanta
(1997) - et al.
Determination of metals in used lubricating oils by AAS using emulsified samples
Talanta
(1998) - et al.
Determination of the total iron content of used lubricating oils by atomic-absorption with use of emulsions
Talanta
(1983) - et al.
Organised surfactant assemblies in analytical atomic spectrometry
Spectrochim. Acta Part B
(1999) - et al.
Graphite rod atomization and atomic fluorescence for simultaneous determination of silver and copper in jet-engine oils
Anal. Chim. Acta
(1973)
Wavelength-modulated continuum-source excited atomic fluorescence spectrometric system for wear metals in jet engine lubricating oils using electrothermal atomization
Anal. Chim. Acta
Determination of insolubles in diesel lubricating oil by FIA-visible spectrometry
Talanta
Determination of lead in petroleum and petroleum products by atomic absorption spectrometry with a carbon rod atomizer
Anal. Chim. Acta
Determination of aluminum by electrothermal atomic absorption spectroscopy in lubricating oils emulsified in a sequential injection analysis system
Talanta
On the direct determination of metals in lubricating oils by ICP
Spectrochim. Acta Part B
Quantitative determination of wear metals in engine oils using laser-induced breakdown spectroscopy: a comparison between liquid jets and static liquids
Spectrochim. Acta Part B
Quantitative determination of wear metals in engine oils using LIBS: the use of paper substrates and a comparison between single- and double-pulse LIBS
Spectrochim. Acta Part B
Speciation analysis of volatile and non-volatile vanadium compounds in Brazilian crude oils using high-resolution continuum source graphite furnace atomic absorption spectrometry
Anal. Chim. Acta
Uses and applications of inductively coupled plasma mass spectrometry in the petrochemical industry
Spectroscopy
Analytical methods for the analysis of petroleum products
Spectroscopy
Oil Debris Monitoring, Avionics Magazine
Analysis of petroleum and petroleum products by atomic absorption spectroscopy and related techniques
Prog. Anal. At. Spectrosc.
Comparison of results for determination of wear metals in used lubricating oils by flame atomic absorption spectrometry and inductively coupled plasma emission spectrometry
Atom. Spectrosc.
Spectrometric oil analysis. Detecting engine failures before they occur
Anal. Chem.
Determination of zinc in lubricating oil by polarography of emulsified samples
Fresenius J. Anal. Chem.
Potentiometric stripping analysis for simultaneous determination of copper and lead in lubricating oils after total digestion in a focused microwave-assisted oven
Microkhim. Acta
Electroanalysis of trace metals in lubricating oils
Bull. Electrochem.
Determination of trace metals in crude oil by inductively coupled plasma mass spectrometry with micro-emulsion sample introduction
Anal. Chem.
Determination of lead and copper in kerosene by electrothermal atomic absorption spectrometry stabilization of metals in organic media by a 3-component solution
J. Anal. At. Spectrom.
Use of silica gel in the preparation of used lubricating oil samples for the determination of wear metals by flame atomic absorption spectrometry
Analyst
Simultaneous determination of wear metals in lubricating oils by inductively-coupled plasma atomic emission spectrometry
Anal. Chem.
Simultaneous determination of metals in oil by inductively coupled plasma emission spectrometry
Anal. Chem.
Determination of heavy metals in waste lubricating oils by inductively coupled plasma-optical emission spectrometry
Intern. J. Anal. Chem.
Trace element determination in crude oil and its fractions by inductively coupled plasma mass spectrometry using ultrasonic nebulization of toluene solutions
Spectrochim. Acta Part B
Determination of wear metals in marine lubricating oils by microwave digestion and atomic absorption spectrometry
Microkhim. Acta
Cited by (121)
Progressively narrow the gap of PM<inf>2.5</inf> pollution characteristics at urban and suburban sites in a megacity of Sichuan Basin, China
2023, Journal of Environmental Sciences (China)Seasonal variation of driving factors of ambient PM<inf>2.5</inf> oxidative potential in Shenzhen, China
2023, Science of the Total EnvironmentMeasurement of moisture content in lubricating oils of high-speed rail gearbox by Vis-NIR spectroscopy
2020, OptikCitation Excerpt :Therefore, it is very necessary to monitor the condition of the lubricating oil to guarantee the safety of the high-speed rail. In recent years, more and more researchers pay attention to the detection of contaminants in lubricating oil [5–14]. Water is one of the most destructive contaminants in lubricants.
Copper particle contamination detection of oil-immersed transformer using laser-induced breakdown spectroscopy
2020, Spectrochimica Acta - Part B Atomic Spectroscopy
- ☆
This paper was presented at the 9th Rio Symposium on Atomic Spectrometry, held in Barquisimeto, Venezuela, 5–10 November 2006, and is published in the special issue of Spectrochimica Acta Part B, dedicated to that conference.