[The design and evaluation of horizontal pipe mini-flame atomization and ionization synchronous detector in GC/AAS]

Gas chromatography/atomic absorption spectroscopy(GC/AAS) is a good method for the species analysis of organometallic compounds. But the traditional atomizers are not very suitable for this technology and all of them response only to one kind of signal--the concentration of the metallic atoms of the ground state. They can not give any information about the organic group of organometallic compounds and organic compounds which coexist with the former. For GC/AAS we want to design and manufacture a new kind of detector which is much more sensitive and has a much smaller dead volume and will sensitively and synchronously response to the atomization signal of organometallic compound and ionization signal of organic compound. The authors have noticed that the atomization of organometallic compound and ionization of organic compound have been existing in the same hydrogen flame. The question is how to gain and exchange and output the two signals which are completely different in characters. For this purpose we designed and manufactured a new type of horizontal pipe mini-flame atomization and ionization synchronous detector. The key part is a T type glass tube (80 mm x 13 mm x 10 mm i.d.) which covers horizontally on the jet of the mini-flame atomizer and a long pipe stainless steel collector (70 mm x 9.5 mm o.d. x 9 mm i.d.) is tightly inserted in the tube. The light beam of the hollow cathode lamp passes through the hydrogen flame along the axial center of the glass tube and the ground state metallic atoms in the flame diffuses to both ends of the tube along the axial center of the glass tube too. This process enriches the depth of the light absorption and then increases the sensitivity of atomization. At the same time the long pipe collector can enrich the collection efficiency of the ionization and increases the sensitivity and widens the linear range. So the detector can synchronously and sensitively detect the organometallic and organic compounds. The detection limit for atomization of the organometallic compound(diethylmercury) is 2.5 x 10(-11) g.s-1 and for ionization of the organic compound (benzene) is 1.0 x 10(-11) g.s-1. The linear range is 7.0 x 10(2) for atomization of diethylmercury (r = 0.9989) and 2.5 x 10(5) for ionization of benzene (r = 0.9992). The selectivity of the detector to the organic solvent under the optimum operating condition of atomization is 10(4)-10(7). The relative standard deviation (RSD, n = 11) of the peak area in the optimum operating conditions of atomization for the organometallic compound (diethylmercury) and of ionization for the organic compound (benzene) is 1.8% and 1.5% respectively. Under the same operating condition, the atomization and the ionization can not reach the optimum performance at the same time. If the atomization is in the optimum performance state, the performance for ionization is like a chromatographic thermal conductivity detector (TCD). The optimum performance of the atomization and ionization can be quickly adjusted by changing the flow rates of the corresponding gases such as H2, N2 and air.