Using matrix effects as a probe for the study of the charge-transfer mechanism in inductively coupled plasma-atomic emission spectrometry

摘要

A novel method is presented for using matrix effects as a probe for the charge-transfer reaction between analyte atoms and argon ions in inductively coupled plasma-atomic emission spectrometry (ICP-AES).The method is based on the fact that the matrix effect caused by Ca or Ba depends on whether the studied analyte spectral line is from an ion or a neutral atom.Because the charge transfer reaction directly links atomic and high-energy ionic levels of the analyte,ionic spectral lines excited by charge transfer behave more like neutral-atom emission.As a result,quasi-resonant ionic emission lines exhibit a unique matrix effect character and can be easily identified.A commercial simultaneous full UV-Vis wavelength-coverage ICP spectrometer was used to study the responses of a large pool of spectral lines from a total of 22 elements in the presence of Na,Ca and Ba matrices.Candidate elements with charge-transfer character were thereby identified.The results match closely with those reported in the literature.The technique was further used to study charge-transfer reactions exhibited by the fourth-row metals from Sr to Sb.With the exception of Cd,Sr and Mo,all the other studied fourth-row metals showed positive evidence of excitation and ionization by charge-transfer from argon ion.While Sr showed negative results,the charge transfer-character of Cd and Mo could not be confirmed.It was also found that charge transfer can originate from other low-lying atomic analyte levels,in addition to the atomic ground state,and that charge-transfer reactions can occur at an appreciable rate even with a negative energy defect (i.e.negative AE) up to DELTA 1.6 eV.