Membrane Desolvation Coupled To ICP-QMS For Accurate Determination Of Rare Earth Elements In Geological Samples

The rare earth element (REE) has a very important role in the geosciences. And accurate and precise determination of REEs is the goal for analytical geochemical workers. Because of the chemical properties of REEs are very similar to each other, only using chemical methods to determine certain elements will be very difficult. X-ray fluorescence(XRF), neutron activation analysis (NAA), inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma-mass spectrometry (ICP-MS) are the most frequently employed analytical techniques for determination of REEs in geological materials. Compare with other analytical methods, the ICP-MS yields simple mass spectra of isotopes and offers better sensitivity and excellent accuracy with the capabilities of rapid multi-elements and isotope measurement. Thus the ICP-MS technology has become a well-established and a powerful instrument for the determination of the REEs. However, determination of low level (ng·g-1) REE concentrations in geological samples is still a challenging goal for the sensitivity of typical quadrupole ICP-MS (ICP-QMS). Additionally, another significant problem is serious spectrometry interferences from the formation of REE or barium oxides (REE-O+, Ba-O+). The use of additional gas plasmas rather than pure argon one to improve sensitivity of ICP-MS is well-known and has been described in various reports. In our study, compare the performances of two introduction system of membrane desolvation and the cooling chamber introduction system when adding nitrogen into the ICP. We found, adding nitrogen with both introduction systems, the ICP could become more robust. However, only using membrane desolvation system with nitrogen, the sensitivity could be improved. And the elements ions distributions also demonstrate the same evidence that the ions density be increased only using membrane desolvation system with nitrogen. For this phenomenon, it maybe water solvent into the ICP and take away a part of energy using the cooling chamber system., in cooling chamber system. The mechanism for elements enhancement could due to the the higher thermal conductivity of the Ar-N2mixed plasma.To reduce the polyatomic ion interference, one effective way is to remove the water solvent before the sample aerosol arrive the plasma. The membrane desolvation introduction system is very effective to and reduces the oxide and hydroxide interferences by removing dissolvent water. In this study, using the membrane desolvation introduction system the ratios of oxides and hydroxides<0.03%for Ce and<0.01%for Ba, which were overwhelmingly lower than these in cooled spray chamber. Membrane desolvation introduction system adding nitrogen was validated by analyzing a series of rock standard reference materials. Under the optimum conditions, the detection limit of REEs proposed were range from0.1to10pg·g-1, and the measurement results are in good agreement with the reference values.The developed method of membrane desolvation introduction system adding nitrogen is suitable for a routine laboratory tasked with the analysis of REEs in geological sample, which is simper than the conventional methods based on pre-concentration, separation and has great potential for the direct determination of REEs in geological.