Evaluation of six sample preparation methods for determination of trace metals in lubricating oils using inductively coupled plasma-optical emission spectrometry

Abstract

Quantification of trace elements in used lubricating oil forms a vital part in monitoring engine conditions and impact on the environment. In this study, inductively coupled plasma-optical emission spectrometry (ICP-OES) was employed for the determination of Ag, Ba, Cu, Mn and Ni in used lubricating oils. Methodology was developed so as to minimize the oil's carbonaceous matter and its effect on viscosity. Accordingly, six oil sample preparation techniques (xylene dilution, detergent emulsion, microwave digestion, dry-ashing, wet-ashing and ultrasonic extraction) were investigated for their efficiency. Optimization of the factors influencing ultrasonic-assisted extraction and ICP-OES operating parameters enabled quantification of the trace metals in oils. Limits of detection (3S b /m), in the ng g-1 range, were obtained for each element of interest using each method investigated. The validity of the methodologies studied was confirmed through the analysis of quality control (QC) samples. Analyte recoveries, ranging from 48.3 to 106 %, were obtained. Evaluation of the analytical methods studied with regard to accuracy, precision, LOD, linearity, applicability for routine analysis, preparation time and cost was made. Based on these evaluations, ultrasonic extraction has a clear advantage in terms of accuracy, applicability for routine analysis, time and cost of sample preparation.

Dissolution Methods for the Quantification of Metals in Oil Sands Bitumen

“…Results were in agreement with the literature, 15 where a significant drop in the concentration of the analyte was reported with time in organic solutions.…”

“…Conversion of the organic material to recover the metals as an acid aqueous solution avoided the observed sensitivity of the direct dilution method to the nature of the oil. Good performance of sulfated ashing was also reported in the literature. , …”

“…Calibration of the ICP-OES was performed using aqueous/ organic standard solutions in the concentration range 5−40 μg/ g (5,10,15,20,25,30,35, and 40 μg/g) that were prepared in the same medium as was used for the quantification of the metals in the samples. Calibration curves were constructed, and linear regression analysis was performed on each of the calibration curves.…”

“…Liquid samples can be mineralized by ashing before dissolution. , Ultrasonication methods have been used to pretreat samples for spectrophotometric trace metal determination. These methods are proposed to facilitate an accelerated dissolution of metals in solution; − however, some authors argued the poor extraction efficiency as one of the major drawbacks of this approach . Some of the studies reported oil-in-water emulsification as an alternative sample pretreatment methodology. − To alleviate concerns about the nebulizing efficiency of oil-in-water emulsions, microdroplets are created by either addition of a cosolvent (detergentless microemulsification) or by applying heat/centrifugation to break the emulsion (emulsion-breaking). , …”

Determination of Some Heavy Metals in Environment of Bakery and Samoon Furnaces at Erbil City, Kurdistan Region, Iraq

“…The above steps were also applied to digest the collected FB samples. For the kerosene digestion, combined suggested methods were applied with few modifications (Tekie et al, 2015). 10 mL of kerosene sample was added to the crucible and covered with a cap.…”