Page 5 - HCL Brochure EN

50 mm Hollow Cathode Lamp
Data coded hollow cathode lamps incorporate a unique electronic configuration in the base or plug which the instrument recognizes and sets default operating condi- tions for the routine analysis of that element. The parame- ters may be overridden by the operator if desired to suit the specific requirements of the analysis. The electronic configuration of the data coding is also specific to each instrument manufacturer and not interchangeable i.e. a Varian coded lamp will not register in a Thermo instru- ment. Heraeus offers a full range of coded lamps for each manufacturer, the exact range being governed by the software embedded in the instrument.
Self Reversal (Smith-Hieftje) Background Correction lamps
Background correction in atomic absorption spectroscopy commonly uses a Deuterium continuum lamp and on certain instruments the Zeeman method utilising magnetic field polarisation. However, both of these methods have limitations regarding the correction of uniformly distributed background. An alternative method of background correc- tion is the self reversal (Smith-Hieftje) technique in which a high current is momentarily passed through the cathode producing a dense cloud of neutral atoms in front of the cathode, effectively cutting off the stream of photons produced during normal lamp operating low current. This momentarily stops absorption in the flame, the spectro- photometer now reading the background absorption only. At normal operating current the instrument records the sum of the absorption of the element and the background. The spectrophotometer can then electronically subtract the background from the sample signal to solve the analytical problems that may be encountered with other methods of background correction. Heraeus has developed a range
of lamps specifically designed to be used at the currents recommended by the manufacturers of instruments where the self reversal or “Smith-Hieftje” method of background correction is available. These lamps have enhanced insulation to cope with the high voltage pulse used by this background correction method, but may also be used in normal atomic absorption applications. Not all elements are suitable for use with this technique; the available range is included in the lamp listing.
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