Analytical applications of emulsions. determination of lead in lubricating oils by atomic absorption spectrometry

Lead used in lubricating oils (ca. 0.2%) is determined by direct nebulization of oil-water emulsions into the flame of an atomic absorption spectrometer. The method is as accurate and precise as a similar method involving mineralization of the oil, and has the advantage of simplicity, speed and the use of aqueous standards for calibration.     

Photometric determination of barium and calcium in lubricating oils and lubricating oil concentrates

Summary A rapid and sensitive method for the determination of barium and calcium in lubricating oils is described. It is based on the formation of barium chromate and calcium oxalate and the estimation of barium and calcium by determining chromium and oxalate ions. Results obtained are in close agreement with those obtained by the Standard IP Method.

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Photometrische Barium- und Calciumbestimmung in Schmierölen und Schmierölkonzentraten

Zusammenfassung Die schnelle und empfindliche Methode beruht auf der Fällung der Elemente als Chromat bzw. Oxalat und der photometrischen Bestimmung des Chromats aus der Farbe seiner Lösung und des Oxalats durch Reaktion mit Permanganat. Die Analysenergebnisse stimmen gut mit denen nach der Standardmethode des Institute of Petroleum überein.

     

The determination of trace metals in lubricating oils by atomic spectrometry

The determination of trace metals in lubricating oils using atomic spectrometric methods is reviewed. The importance of such analyses for technical diagnostics as well as the specific sample characteristics related to the analyte form (metallo-organic and metal particles) is discussed. Problems related to sample pre-treatment for appropriate sample introduction and calibration are addressed as well as the strategies to overcome them. Recent trends aimed at simplifying sample manipulation are presented. The applications and scope of AAS, ICP OES and ICP MS techniques for the determination of trace metals in lubricating oil is individually discussed, as well as some present instrumental trends.     

On the direct determination of metals in lubricating oils by ICP

New equipment and procedures are evaluated for the direct analysis of metals in lubricating oils without the need for sample pretreatment or dilution. A modified Babington principle nebulizer equipped with a sample heater is shown to be capable of producing aerosols from undiluted oils, which are suitable for introduction into an inductively coupled plasma atomic emission spectrophotometer. Heating the samples immediately prior to nebulization greatly increases the output of aerosol and reduces output variations in emission intensity due to differences in oil manufacture and viscosity. The type of organometallic complex used in the preparation of standards is shown to be unimportant if the plasma observation region is properly chosen. Performance of a conventional plasma geometry and an inverted torch geometry on analysis of field collected oil samples is presented.     

Testing the thermooxidation of lubricating oils via differential thermal analysis

Two DTA programmes have been developed to differentiate between the thermooxidation stabilities of lubricating oils. Measurements were carried out either by heating the oil sample at a rate of 10 deg/min (direct programme) or by keeping it at 250° (isothermal programme). The selected optimum conditions for these two programmes included the use of 40 mg of sample under oxygen at a flow rate of 150 cm³/min until oxodegradation of the sample. These conditions were found to give precise and repeatable results. The procedures can be recommended as simple and fast quality control methods. Thermooxidation parameters from the DTA curves were correlated with results from the standard routine method IP 306.     

The determination of wear elements in lubricating oils by neutron activation analysis

Used lubricating oil analysis programs are currently employed by both the military and industry in an attempt to minimize some of the costs associated with equipment failure. The periodic determination of water elements in the lubricant of an oil-wetted system can provide very useful information on the condition or health of the system and an early indication of impending failure. In the present study, the application of Neutron Activation Analysis (NAA) to used oil analysis was investigated. The method developed allowed for the determination of fifteen elements (Ag, Al, Cl, Cr, Cu, Fe, In, Mg, Mn, Mo, Na, Ni, Sn, Ti and Zn) associated with engine wear or deterioration. Results obtained for the analysis of used naval diesel oils exhibited good agreement with results obtained by Atomic Absorption Spectrophotometry (AAS) methods. A drawback of the NAA procedure is that the determination of Fe, a major wear element in most systems, involves an analysis time of approximately one week.     

Atomic absorption spectrometric determination of molybdenum in lubricating oils with use of emulsions

Samples (0.1 g) containing molybdenum disulphide are digested with aqua regia or with a (1 + 1) hydrofluoric/nitric acid mixture, without complete destruction of the matrix, and the molybdenum is determined in an air/acetylene flame, after emulsification with a non-ionic surfactant (Nemol K-39). The detection limit is ca. 30 μg Mo g^?1, and the r.s.d. is 2.9% for 6 analyses of a sample containing 6.5 mg Mo g^?1.     

Quantitative moisture measurements in lubricating oils by FTIR spectroscopy combined with solvent extraction approach

Quantitative measurements of moisture in mineral and synthetic polyol ester based lubricating oils using FTIR spectroscopy combined with solvent extraction approach are described. The samples are prepared by mixing dry dimethyl sulfoxide (DMSO) and lubricating oils, and after phase separation, the extracted bottom DMSO layers are analyzed with FTIR. The results from the solvent extraction show that the DMSO is an excellent aprotic solvent for water removal from lubricating oils. The spectroscopic data reveal that near IR region (5400–4800 cm^{− 1}, molecular water) gives the best results for water determination in both mineral and synthetic lubricants, followed by mid-IR region (3800–3200 cm^{− 1}, O―H stretching). However, the water content estimated from the IR region (1800–1550 cm^{− 1}, O―H bending) has the lowest accuracy due to the interference from aminic, phenolic additives and other oxidation products present in the lubricants. The accuracy of the FTIR spectroscopy combined with solvent extraction approach is exemplified by monitoring the water content in mineral oil during oxidation process at 150 °C for 30 days. The quantitative determination of the moisture in the fresh and oxidized oils by the developed approach is shown to be an alternative technique to Karl Fischer titration.     

A multicommuted flow system for the determination of copper, chromium, iron and lead in lubricating oils with detection by flame AAS

In this work, a flow analysis procedure for the determination of copper, chromium, iron and lead in lubricating oils using flame AAS as detection technique is described. The flow manifold was designed to implement the multicommutation approach and it comprised three 3-way solenoid valves controlled by a personal computer. The flow system presented allowed to process the oil samples to determine wear metals without any prior preparation. Aiming to assess accuracy the results were compared with those obtained by manual procedure using flame AAS. Applying the joint-confidence ellipse test, no significant difference at the 95% confidence level was observed. Other profitable features such as a sample throughput of 50 determinations per hour; relative standard deviations (n = 5) below 2% for Cu, and below 8% for Cr, Fe and Pb; and linear responses in the range 0–40 ppm (w/w) (Cu, Fe) and 0–15 ppm (w/w) (Cr, Pb) were also achieved.     

Rapid EDTA determination of lead in binary alloys of lead and tin

Binary alloys of lead and tin were dissolved in nitric acid (1 + 1) containing 10% sodium fluoride. The tin(IV) was effectively masked by the fluoride. The lead was quickly and accurately titrated with EDTA in a hexamine-buffered solution, with Xylenol Orange as indicator.     

Combination of ultrasonic extraction and stripping analysis: an effective and reliable way for the determination of Cu and Pb in lubricating oils

The determination of metals in lubricating oil has been used as an important way to prevent components failures, to provide environmental information and in some cases, to identify adulteration. In this work, an effective and simple procedure is proposed for Cu and Pb determination in lubricating oils. An ultrasonic bath was employed for extraction of these elements from oil samples in a mixture 1:1 (v/v) of concentrated HCl and H₂O₂. A very efficient extraction of Cu and Pb (∼100%) was attained after 30 min of ultrasound, allowing the simultaneous determination of both metals using square-wave anodic stripping voltammetry at thin-film gold electrodes. The extraction procedure was performed in 4 mL polypropylene closed vessels and dozens of samples could be treated simultaneously in the same ultrasonic bath. The regions of the ultrasonic bath, where the maximum efficiency of extraction was attained were evaluated. Over the optimized region, 30 samples can be treated simultaneously. Used lubricating oils from automotive engines were analyzed by using the optimized extraction procedure.     

Automatic determination of insolubles in lubricating oils by flow injection analysis employing an LED-photometer detector

A flow injection system is presented for the determination of the insolubles content in used lubricating oil samples. The system is based on the injection of an aliquot of the sample in a stream of organic solvent where it is dispersed, and measurement of the scattered radiation (measured as apparent absorbance) in the visible range (λ = 640 nm). An LED-based photometer was used for this purpose. The whole system including sample injection and data acquisition was controlled by a personal computer. Calibration curves exhibited good linearity (h = 0.415 ± 0.016C + 0.00 ± 0.03, r² = 0.9995, confidence level of 95%) in the range up to 2.68% (insolubles in pentane). Detection and quantification limits were respectively 0.07% and 0.16% (w/w). The method was validated by analysis of 25 real samples by the proposed method and the FTIR method finding high correlation. Waste generation and reactive consumption is much less than in the official method (ASTM D-893). The proposed method employs 25 mL of kerosene per sample while the official method employs 200 mL of pentane.     

Amperometry with two polarisable electrodes-VII: chelometric determination of indium

Optimum conditions have been found for the chelometric determination of indium by biamperometric titration with EDTA. Two stationary platinum electrodes (Pt-Pt) or two graphite electrodes (C-C) may be used to indicate the end-point of the titration. At pH 1-1.5 the determination is highly selective. The applied potential only influences the absolute value of the current ; the accuracy of the determinations remains constant over a wide interval of applied potential. At a potential of 1.0-1.7 V the change of current during a titration with 0.05 M EDTA solution is of the order of 10 microA. Analytical applications of the method are discussed.     

Rapid and reliable determination of elevated blood lead levels

Summary For the control of lead exposed persons the most important parameter is the blood lead (PbB) level. Since for PbB in various countries maximal permissible threshold levels exist, analytical methods with high precision and accuracy are required. During the continuous control of a lead exposed collective two in principle well suited methods have been compared: graphite furnace AAS (GFAA), evaluation against control samples with known lead contents, and staircase stripping voltammetry directly applied in dilute blood, evaluation against calibration solutions. The GFAAS procedure obtained on average, depending on the number of subsamples and firings per sample, an imprecision from about 2.5 to about 5%, the voltammetric procedure one of 5%. Sample throughput is comparable at the same imprecision. Accuracy of both procedures could be checked by mass spectrometric isotope dilution analysis (MS-IDA) and differential pulse anodic stripping voltammetry (DPASV) after complete digestion and was found to be quite satisfactory.

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Rasche und zuverlässige Bestimmung erhöhter Blutbleispiegel

Zusammenfassung Bei der Überwachung bleibelasteter Personen ist die Ermittlung der Blutbleikonzentration (PbB) der wichtigste Parameter. Da für PbB in zahlreichen Ländern maximal zulässige Konzentrationen festgelegt wurden, müssen hohe Anforderungen an Präzision und Richtigkeit der angewandten Analysenverfahren gestellt werden. Bei der laufenden Überwachung eines bleibelasteten Kollektivs konnten zwei prinzipiell hierfür besonders geeignete Methoden miteinander verglichen werden: Graphitofen-AAS (GFAAS), Auswertung gegen Kontrollproben mit bekanntem Bleigehalt, und Staircase-Stripping-Voltammetrie direkt im verdünnten Blut, Auswertung gegen zwei Eichlösungen. Das GFAAS-Verfahren erreicht im Mittel eine Unpräzision von ca. 2,5 bis ca. 5% abhängig von der Zahl der Aliquote und Einzelmessungen pro Probe, das voltammetrische Verfahren eine Unpräzision von ca. 5%. Der Probendurchsatz ist bei vergleichbarer Unpräzision etwa gleich. Die Richtigkeit beider Verfahren wurde mit Hilfe der Isotopenverdünnungs-Massenspektrometrie (MS-IDA) sowie der differentiellen anodischen Pulsinversvoltammetrie (DPASV) nach vollständigem Aufschluß überprüft; sie ist recht zufriedenstellend.

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Dedicated to Prof. Dr. W. Fresenius on the occasion of his 70th birthday     

离子色谱-抑制型电导检测法同时测定食品级润滑油中的3种无机阴离子

建立了离子色谱-抑制型电导检测同时测定食品级润滑油中Cl^-、NO₃^-、SO₄^2- 3种代表性无机阴离子的方法。样品经50%(v/v)甲醇水溶液超声提取,离心后所得下层水相用0.22 μm混合纤维过滤膜净化,以15 mmol/L KOH溶液为淋洗液,采用抑制型电导检测器进行检测,外标法定量。在上述条件下,Cl^-、NO₃^-、SO₄^2- 3种无机阴离子在0.10~20.00 mg/L范围内具有良好的线性关系(R²>0.999);检出限(S/N=3)为0.01~0.03 mg/kg;在1.00、5.00、10.00 mg/kg添加水平下,实际样品中3种阴离子的加标回收率为90.0%~103.6%,相对标准偏差为2.8%~5.7%。结果表明,该方法无需燃烧、灰化油相基质等繁琐耗时的前处理过程,可以快速、准确定量测定食品级润滑油中Cl^-、NO₃^-、SO₄^2- 3种无机阴离子的含量,适用于润滑油等油品中痕量无机阴离子的同时分离与测定。     

Rapid determination of lead in steel by flameless atomic absorption spectrometry

A method for the determination of 1–100 p.p.m. of lead in high- and low-alloy steels by flameless atomic absorption is described. The sample was dissolved in aqua regia. and 2 μl of the diluted solution were pipetted into a Massmann-type furnace. Ashing of the sample at 625°C eliminated influences from hydrochloric acid. Fe, Cr and Ni gave similar negative interferences, which were compensated for by using low-alloy steel with standard additions. An interlaboratory comparison showed that this method gave the same result as extraction with TOPO in MIBK. The procedure could also be applied to commercial instruments. The time for a complete analysis including dissolution was 15 min.     

A versatile kit of additives to lubricating oils

Various mixtures of imidazolines, copolymers of methacrylic acid esters, and trithiolanes were examined as additives to motor oils for diesel fuels or to cutting fluids.