Different Lubricating Oil Treatments for the Determination of Cu, Cr, Fe, Ni, Sb, Pb, and Zn by HR-CS FAAS

Abstract

Microwave-assisted acid decomposition, direct dilution in kerosene, and oil-in-water emulsion were evaluated as lubricating oil pretreatment procedures for Cu, Cr, Fe, Ni, Pb, Sb, and Zn determination by High-Resolution Continuum Source Flame Atomic Absorption Spectrometry (HR-CS FAAS). For wet digestion, results were compared with those obtained by Flame Atomic Absorption Spectrometry (FAAS). The ultrasound probe used in emulsions sonication contaminated samples with Cr, although better results have been observed for the other six elements in this condition. In general, recovery percentages ranging from 81–106% (Cu), 80–107% (Cr), 85–114% (Fe), 82–116% (Ni), 86–117% (Pb), 85–115% (Sb), and 81–114% (Zn) were obtained. The HR-CS FAAS showed to be faster and more sensitive than FAAS.

Keywords:

• HR-CS FAAS
• lubricating oil
• metals
• sample preparation

The authors thank FAPESP for financially supporting this work and for the research assistance to V.R.A.F and are also grateful to CNPq for the research assistance to J.A.G.N.

Notes

^a Digests analyzed by HR-CS FAAS (contrAA 300).

^b Digests analyzed by FAAS (AAnalyst 100).

^c Oil-in-water emulsion using kerosene analyzed in contrAA 300.

^d Oil-in-water emulsion using n-hexane analyzed in contrAA 300.

^e Oil directly diluted in kerosene analyzed in contrAA 300.

For all information (Linear ranges [mg L⁻¹]): [continuum-source-aqueous medium]: 0.05–1.00 Cu, Fe, Ni; 0.125–2.00 Cr; 0.250–4.00 Sb, Pb; 0.025–0.400 Zn; [line-source-aqueous medium]: 0.2–2.00 Ni; 0.25–4.00 Cu, Fe, Pb; 0.500–4.00 Cr, Sb; 0.025–0.4 Zn; [continuum-source-organometallic standards]: 0.500–2.50 for all elements. LOQ = limit of quantification.

∗Elements determined using wavelength integrated absorbance of 5 pixels.

^a Digests analyzed by HR-CS FAAS (contrAA 300).

^b Digests analyzed by FAAS (AAnalyst 10.)

^a Digests analyzed by HR-CS FAAS.

^b Digests analyzed by FAAS.

^c1 Oil-in-water emulsion using kerosene homogenized with an ultrasound probe analyzed in an oxidizing air/acetylene flame.

^c2 Oil-in-water emulsion using kerosene manually homogenized and analyzed in an oxidizing air/acetylene flame.

^c3 Oil-in-water emulsion using kerosene homogenized with an ultrasound probe analyzed in a fuel-rich air/acetylene flame.

^c4 Oil-in-water emulsion using kerosene manually homogenized, analyzed in a fuel-rich air/acetylene flame.

^c5 Oil-in-water emulsion using kerosene homogenized with an ultrasound probe analyzed in a fuel-rich nitrous oxide/acetylene flame.

^c6 Oil-in-water emulsion using kerosene manually homogenized, analyzed in a fuel-rich nitrous oxide/acetylene flame.

^d1 Oil-in-water emulsion using n-hexane homogenized with an ultrasound probe analyzed in an oxidizing air/acetylene flame.

^d2 Oil-in-water emulsion using n-hexane manually homogenized, analyzed in an oxidizing air/acetylene flame.

^d3 Oil-in-water emulsion using n-hexane homogenized with an ultrasound probe analyzed in a fuel-rich air/acetylene flame.

^d4 Oil-in-water emulsion using n-hexane manually homogenized, analyzed in a fuel-rich air/acetylene flame.

^d5 Oil-in-water emulsion using n-hexane homogenized with an ultrasound probe analyzed in a fuel-rich nitrous oxide/acetylene flame.

^d6 Oil-in-water emulsion using n-hexane manually homogenized, analyzed in a fuel-rich nitrous oxide/acetylene flame.

^e Oil directly diluted in kerosene analyzed by HR-CS FAAS. All emulsions were analyzed only by HR-CS FAAS.

^a,b Aqueous medium used for digests and oil-in-water emulsion analysis performed in contrAA 300 (continuum-source) and in AAnalyst 100 (line source), respectively.

^a1 Aqueous medium used for digests and oil-in-water emulsion analysis performed in contrAA 300 using fuel-rich air/acetylene flame.

^a2 Aqueous medium used for manually homogenized oil-in-water emulsion analysis performed in contrAA 300 (5 pixels) using fuel-rich nitrous oxide/acetylene flame.

^c1,c2,c3 Metallo-organic standard solutions performed in contrAA 300 for oil directly diluted with kerosene in the kerosene/oil proportions 3:1 (w/w), 2.5:1 (w/w), and 2:1 (w/w), respectively, using 3 pixels as line volume.

^c3,c4,c5 Metallo-organic standard solutions performed in contrAA 300 for oil directly diluted with kerosene in the kerosene/oil proportions 3:1 (w/w), 2.5:1 (w/w), and 2:1 (w/w), respectively, using 5 pixels as line volume.

^d Metallo-organic standard solution performed in contrAA 300 for oil directly diluted with kerosene in the kerosene/oil proportion 12.5:1 (w/w). Values in parenthesis in C_o are the ones recommended in the equipment manual. LOD = 3 SD _blank/S; LOQ = 10 SD _blank/S and C_o = standard concentration x 0.0044/absorbance.