Current lamp operating

Figure 1 Schematic representation of the cloud of cool atoms which escapes from the centre of the hollow cathode at high lamp operating currents...

Optimization in Flame AAS Source-related Parameters Effect of Lamp Current Effect of Lamp Warm Up Time Lamp Alignment Lamp Deterioration Choice of Lamp Atomizer-related Parameters Choice of Atomizer Effect of Fuel-to-oxidant Ratio Optimization of Burner Position Burner Design, Warm Up, and Cleanliness Gas Flow Stability Monochromator-related Parameters Choice of Slit Width Choice of Wavelength Optimization in Flame AFS Source-related Parameters Lamp Operating Parameters Lamp Alignment Atomizer-related Parameters Monochromator-related Parameters Optimization in Flame AES... 

Depending on the pressure in the lamp, both line and continuum emission may be observed. Low-pressure lamps operated at low current densities and temperatures produce sharp atomic lines with little or no continuous background. Increasing pressure and temperature cause the lines to broaden and increase the intensity of the background continuum. 

FIGURE 9-16 Emission line profiles for a hotlow-calhode lamp operated at high and low currents. 

The eathode luminous sensitivity" is the eathode current per watt incident light power from a tungsten lamp operated at 2,856 °C. The cathode luminous sensitivity is the integral of the product of the eathode radiant sensitivity and the lamp speetrum. Beeause the lamp has its emission peak in the NIR the cathode luminous sensitivity lets the sensitivity of NIR-sensitive cathodes appear higher than it aetually is. 

Xenon arc lamps operate in a manner similar to deuterium lamps. A passage of current through xenon gas produces intense radiation over the 200-1000 mn range. They provide very high radiation... 

A Perkin-Elmer (PE) Model 603 spectrophotometer equipped with a manual gas control system, a stainless steel nebulizer, a burner mixing chamber, a flow spoiler and a 10 cm. (one-slot) burner head was used in the experimental validation of the flame AAS analytical technique. A PE cadmium hollow cathode lamp, operated at the manufacturer s recommended current setting for continuous operation (4 mA), was used as the source lamp. Instrument parameters are listed in Attachment 1. 

This technique of background correction makes use of the fact that resonant atomic spectral lines emitted by a hollow cathode lamp may display self-reversal when the lamp is operated at high discharge current. A hollow cathode lamp operates during the first part of the measurement... 

The most commonly employed lamps are medium- and high-pressure mercury lamp or xenon arc lamp, having an output covering the whole UV-Visible spectrum range. Xenon arc lamp operated stroboscopically is preferred for its continuous output. The lamp is operated in a current of air to disperse the toxic ozone formed from oxygen on exposure to UV radiation. 

Several types of secondary pyrometer are available. In addition to those that measure by varying lamp current, some pyrometers maintain the lamp at constant current but interpose a wedge of graduated neutral density, whose position is a measure of temperature. Also, automatic pyrometers are available in which the eye is replaced by a detector and the measuring element is operated by a servo. In general, the accuracy of the automatic pyrometer is somewhat less than that achieved manually by a skilled operator. 

---