Development of a New Method for Analysis of Oil Mists

Mineral oils, a complex mixture of chemicals, are primarily used in metalworking processes. Due to different toxicity levels found in mineral oils, two threshold limit values are given for the evaluation of mists of highly and poorly refined mineral oil.
The objective of this study was to explore a new method for the analysis of 2 classes of mineral oils by the FT-IR.
Highly and poorly refined mineral oil samples were prepared by spiking the filters in the range of 10 to 2,250 µg/sample. Samples were extracted with 10 mL of carbon tetrachloride, subsequently analyzed by Fourier Transform Infrared (FT-IR) in the region of 3031 to 2,796 cm-1. Mineral oils (highly and poorly refined) were distinguished qualitatively, according to the FT-IR spectroscopy to determine the presence of formaldehyde using functional groups C = O and C - H, N-Nitroso compounds, and functional groups of N-N and N = O. Method validation parameters, such as precision, accuracy, detection limit and comparison of identical samples with the reference method by NIOSH No.5524 were considered.
According to the FT-IR spectroscopy in this study, highly and poorly refined mineral oil samples were distinguished according to their spectral absorption of the functional groups. The FT-IR spectroscopy analyzed highly and poorly refined mineral oil samples in the linear range of 10 to 2,250 µg/sample. The coefficient variations of inter-day and intra-day were 3.61 and 5.08 for highly refined mineral oil, and 5.23 and 5.18 for poorly refined mineral oil, respectively. The average accuracies for highly and poorly refined oil samples were 1.4% and 0.54%, respectively.
The statistical average differences in the results drawn from the FT-IR method and actual spiked samples were significantly lower than the differences measured by the NIOSH No.5524 method and spiked samples. Therefore, this study demonstrates a viable alternative method for the analysis of mineral oils in future studies.