Page 7 - HCL Brochure EN

Getting the best from your Hollow Cathode Lamps
Operating Current
Each hollow cathode lamp has a maximum current which should not be exceeded. Exceeding the limit will consi- derably reduce the usable life of the lamp and may dama- ge the cathode by sputtering off excess material or even melting some of the more volatile alloys and elements.
The current indicated on a 37 mm hollow cathode lamp is the maximum current at which the lamp should be run in an instrument using a modulated power supply typical of most manufacturers.
The current shown on a 50 mm lamp is the maximum cur- rent at which the lamp should be used in an instrument with a continuous power supply typical of most Perkin El- mer instruments. It is possible, with the correct adapters, to run a 37 mm lamp in a Perkin Elmer instrument with
a continuous power supply in which instance the current recommended for 50 mm lamps should be used. Some Perkin Elmer models have a modulated power supply, reference to the instrument user manual will indicate the type of power supply in the instrument. If a modulated supply is present then the lamp should be operated at the current recommended for a 37 mm lamp.
In general lamps should be run at 75% of their maximum current to achieve best precision and 65–75% to achieve their maximum sensitivity. However, the performance of some elements is not materially affected by operation anywhere between 65 and 100%. Lamps should not be operated below 50% maximum current as, in all but a few cases, stability and noise levels deteriorate significantly. Indeed elements with naturally low outputs such as Arse- nic, Tin, Antimony, Bismuth and Selenium would be too noisy for analysis at the detection limit at anything other than maximum current.
Stabilisation
After striking the lamp or following a change in operating current most lamps will require a warm-up period before full stability is obtained. Depending upon the element,
the warm-up time can be between 5 and 30 minutes. If lamps have not been used for a considerable time or have been stored before initial use they may require somewhat longer than usual to stabilise. This period will normally
be around 2 hours but an overnight run may prove to be the most efficient way of restoring full stability. Softer elements with lower melting points such as lead especially benefit from this practise. For optimum performance, on receipt of a new lamp it is also good practice to run it in the instrument to acclimatize the lamp to the particular power supply.
Pb
Se
Typiccal warm up curves
Alignment
Time
A hollow cathode lamp produces a very narrow beam of light; if not aligned correctly the output from the lamp will not fill the entrance slit and there will be an apparent loss in signal and the noise levels will increase. Low output and high noise may indicate that the lamp is misaligned. The lamp should then be re-aligned until maximum signal output is achieved.
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Energy