Boron and silicon additives play an important role in gear oil as anti-friction and anti-foaming agents respectively. When in use these levels often deplete quickly, which reduces the effectiveness of the lubrication. Hence, B and Si are routinely measured in gear oil. However, ICP-OES levels of these elements is complicated by high viscosity and plasma loading of gear oils that require significant sample dilution. Besides, low sensitivities and unspecific spectral interferences from the organic matrix further add to relatively high matrix-specific detection limits in heavy oil fractions.