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| Analysis of Ultra-Trace Metal Impurity Elements in Proprylene Glycol Monomethyl Ether Using Inductively Coupled Plasma Tandem Mass Spectrometry |
| LI Tan-ping, LI Ai-yang |
| New Building Materials Academy, Hunan Institute of Technology, Hengyang 421002, China |
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Abstract Based on inductively coupled plasma tandem mass spectrometry (ICP-MS/MS), an analytical method for the accurate determination of ultra-trace metal impurity elements in propylene glycol methyl ether (PGME) was established, and mixed reaction gas was used to eliminate the spectral interference. The challenging ultra-trace metal elements including Na, Mg, Al, Ti, V, Cr, Fe, Ni, Cu, and Zn in diluted PGME were determined directly by ICP-MS/MS. In the MS/MS mode, the mixed gas NH3/He/H2 was selected as the reaction gas. Ti+, Cr+, Fe+, Ni+, Cu+, Zn+ and NH3 undergo mass shift reactions. Among the large number of cluster ions formed, Ti(NH3)+6, Cr(NH3)+2, Fe(NH3)+2, Co(NH3)+2, Ni(NH3)+3, Cu(NH3)+2, Zn(NH3)+ have high abundances and interference-free, Ti+, Cr+, Fe+, Ni+, Cu+, Zn+ can be transferred to the corresponding cluster ions for determination by NH3 mass shift method. H2 can react with the adducts —NH and —NH2 to form —NH3. Increasing the concentration of —NH3 in the collision/reaction cell (CRC) will help to improve the analytical sensitivity of Ti, Cr, Fe, Ni, Cu, Zn. Mg+, Al+, K+, V+ can hardly react with NH3, and the interference ions can react with NH3 to form cluster ions. The NH3 on-mass method can be used to determine the contents of Mg, Al, K, and V. Argide ions react with H2 at a relatively fast rate, while nearly all elemental ions exhibit low reactivity with H2. Therefore, the addition of H2 to the reaction gas can quickly and completely eliminate the spectral interference caused by Argide ions, which is beneficial to the determination of Mg, Al, K, and V. The cluster ions Sc(NH3)+5 generated by the reaction between Sc+ and NH3 were selected as the standard internal ions of Ti(NH3)+6, Cr(NH3)+2, Fe(NH3)+2, Ni(NH3)+3, Cu(NH3)+2, and Zn(NH3)+. The cluster ions Be(NH3)+4 generated by the reaction between Be+ and NH3 were selected as the standard internal ions of Mg+, Al+, K+, and V+. The matrix effect caused by the difference of physical and chemical properties between sample solution, standard solution and the blank solution was corrected to ensure the stability of the analytical signal. The developed method was applied to the spike recovery experiment of real samples, and the accuracy was evaluated by comparing and analyzing with sector field inductively coupled plasma mass spectrometry (SF-ICP-MS). The results show that the limit of detection is 0.52～61.5 ng·L-1, the spiked recovery is 95.6%～104.2%, and the relative standard deviation (RSD) is ≤4.5%. At the 95% confidence level, there is no significant difference between the analysis results of analytes and that of SF-ICP-MS, which verifies the accuracy and precision of this analysis method. The method shows great potential for determining the ultra-trace metal impurity elements in PGME, and has the advantages of rapid, interference-free and high sensitivity.
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Received: 2019-12-26
Accepted: 2020-03-19
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