Determination of titanium in high purity sulfuric acid by tandem quadrupole inductively coupled plasma mass spectrometry employing ozone-ion reactions

Determination of titanium in high purity sulfuric acid was investigated to provide a method supporting the application in semiconductor production processes. The measurement was conducted by using tandem quadrupole inductively coupled plasma mass spectrometry (ICP-QMS/QMS), wherein online generated ozone was used as the reaction gas to resolve sulfur-related spectral interferences. Quantum chemical calculations were conducted to investigate the mechanisms of ozone reaction and oxygen reaction with Ti + . In comparison to oxygen reaction, ozone reaction apparently improved the yields of TiO 2 + from Ti + , owing to the much lower relative energy of the transition state. Due to the strong interferences from 32 S 16 O + → 32 S 16 O n + ( n = 1, 2, 3), the measurements of 48 Ti + → 48 Ti 16 O n + ( n = 0, 1, 2) provided insignificant signal to background ratio. By contrast, significant improvements in the reaction Ti + → TiO 2 permitted the measurement of 46 Ti and 47 Ti. Determination of titanium under 10 pg/g in 1/10 ( w /w) diluted sulfuric acid can be achieved with manually diluted samples. Further investigation utilizing on-line dilution provided significantly lower background equivalent concentrations (BECs) and detection limits (DLs) through minimization of adventitious contamination ultimately yielding a BEC and DL for 46 Ti of 0.50 and 0.25 pg/g, respectively. It is notable that the online dilution was achieved by using a T-connector with the flow rate of the diluent controlled by the ICP-QMS/QMS built-in peristaltic pump, i.e. only polytetrafluoroethylene tubes were used for up-taking sulfuric acid to the plasma while peristaltic tube was used only for pure water as the diluent. Ozone reaction permits the highly sensitive determination of titanium in sulfuric acid by measuring Ti + → TiO 2 + , getting rid of the spectral interferences from sulfur-related ions. • Ozone reaction permits the high sensitivity measurement of 46 Ti and 47 Ti as Ti + → TiO 2 + . • Mechanisms of reactions between Ti + and ozone were investigated by quantum chemical calculation. • On-line dilution helps reduce potential contamination of titanium during manual dilution. • Detection limit for titanium under 10 pg/g was achieved for high purity sulfuric acid.