37mm Self Reversal Hollow Cathode Lamp

The Heraeus hollow cathode lamp product range comprises 70 single-element lamps and more than 120 multi-element lamps of the most varied designs to cover almost all appliances.

The Heraeus catalogue includes 70 single-element lamps in standard 37 mm (1.5 inch) and 50 mm (2 inch) diameters to fit almost any AA instrument. All cathode materials are selected from the highest purity available – usually 99.99 % or better – to ensure high spectral line intensity, stability and low noise with good analytical sensitivity. The window material is selected to achieve the optimum transmission of the primary spectral lines of the cathode element. Borosilicate glass is used for wavelengths over 350 nm, and high quality quartz for shorter wavelengths.

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 correction 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 spectrophotometer 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.