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Simultaneous Determination of Impurity Elements in N-Methyl-2- Pyrrolidone (NMP) with Direct Injection Inductively Coupled Plasma Optical Emission Spectrometry.

An analytical method for simultaneous determination of 12 impurity elements including Mo, Cr, Zn, Pb, Ni, Mn, Fe, Cu, Ca, Al, Na and K in N-methyl-2-pyrrolidone (NMP) was established with inductively coupled plasma optical emission spectrometry (ICP-OES). The NMP without decomposing was acidized with nitric acid and analyzed directly, avoiding the risk of error introducing during sample pretreatment. The load of plasma on organic solvent was decreased by optimizing the plasma parameters and ensuring the stability of plasma. The optimized and adopted nebulizer gas flow rate was 0.4 L·min-1 and RF power was 800W. The whole signals during the sample atomization or ionization have been obtained with axially viewed ICP-OES which increases the sensitivity and decrease the detection limits. The interferences of spectral lines and background were eliminated by selecting analysis spectral lines, removing the carbon by adding oxygen and background correction method. Furthermore, standard addition method was employed to overcome the matrix effect, counteracting the ionization interference of high concerned organic matrix to easily ionizable elements. The results showed that the correlation coefficients of the calibration curve were in the range of 0.999 5～1.000 0, the detection limits were in the range of 3.8～106.4 ng·g-1, and the recoveries were in the range of 92.0%～108.0%. The relative standard deviation (RSD, n=11) were larger than 4.8% of the analytes. The method is simple without complex sample pretreatment. It is a fast analysis method with high accuracy which can satisfy completely the requirements of control analysis in mass production. This method can be applied to determine impurity elements in NMP products.