Nitrous oxide emission spectrum

Figure 16. Comparison of CN flame emission and laser-excited fluorescence spectrum in a nitrous oxide-acetylene slot torch...

Silicate, nickel, and cobalt tend to interfere in the air-acetylene flame, although nickel and cobalt are rarely present in sufficient excess to cause a problem. Silicate interference may be eliminated at modest excesses by the use of lanthanum as a releasing agent or by using a nitrous oxide-acetylene flame. Very careful optimization is sometimes necessary, for example in the analysis of freshwaters, when concentrations are very low. It is important to use a narrow spectral bandpass and to make sure that the correct line is being used, because the hollow cathode lamp emission spectrum of iron is extremely complex. If you have any doubts about monochromator calibration, check the sensitivity at adjacent lines ... 

Since the hollow-cathode lamp spectra used in AAS are relatively simple, spectral bandwidths narrower than 0.1 nm are seldom if ever used. In atomic emission analysis, however, higher resolving power is often essential, particularly when the excitation source (e.g. the nitrous oxide—acetylene flame) is producing a complex spectrum. The instrument should, therefore, provide a wide range of slit settings and a convenient digital display of the wavelength in use for the operator. 

Figure 1 Emission spectrum of the nitrous oxide-acetyiene flame, somewhat rich (red zone 3 mm high). Scan rate 12.5nmmin 25 pm siits. The principai moiecuiar emission bands are iabeied.

The nitrous oxide/acetylene flame is well known for its strong emissions and thus the modified registration scheme was applied to record the spectra. In total, 4 x 50 spectra have been recorded with an individual illumination time of 12 s. For the sample measurements the nitrous oxide / acetylene flame was turned on, while in the case of blank signal registration the flame was turned off. No additional solution was aspirated by the nebulizer to get the pure spectrum of the flame gases. 

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