Simultaneous Determination of Iron, Manganese and Lead in Motor Gasoline by Inductively Coupled Plasma Atomic Emission Spectrometry with Direct Dilution Injection

In order to solve the problems of flameout, ignition failure and unstable results in the determination of iron, manganese and lead in motor gasoline by inductively coupled plasma atomic emission spectrometry (ICP-AES), the diluent, dilution ratio the mass ratio of sample to 5 mg·L^-1 cobalt internal standard working solution (with kerosene as the diluent) and quantitative mode were optimized, and the title method was proposed. An aliquot (5 g) of motor gasoline sample was mixed with 45 g of 5 mg·L^-1 cobalt internal standard working solution at dilution ratio of 1∶9. After mixing evenly, the mixture was introduced by organic matter sampling system. The intensities of iron, manganese and lead at 238.204, 257.610, 220.353 nm were measured at radio frequency power of 1 300 W, cooling gas flow rate of 16.0 L·min^-1, auxiliary gas flow rate of 1.1 L·min^-1, and atomizing gas flow rate of 0.4 L·min^-1. The internal standard method was used for quantification. It was shown that linear relationships between values of the mass fractions of the 3 target elements and the corresponding spectral line intensity ratio were kept in the range of 0.20-5.00 mg·kg^-1, with detection limits (3S/N) in the range of 0.04-0.06 mg·kg^-1. The spiked recovery test was conducted on blank gasoline samples at the 3 concentration levels, giving recoveries ranging from 93.8% to 106%, and results of tests for repeatability and reproducibility were within the repeatability limit and reproducibility limit. The proposed method was applied to the analysis of the 6 actual samples, and the relative error absolute values of detection amounts of the 3 target elements and results obtained from standard methods of GB/T 8020-2015 (detection of lead), SH/T 0711-2019 (detection of manganese), and SH/T 0712-2002 (detection of iron) were within 6.5%.