Analysis of samples with high mercury content - a smooth transition from ppb to ppm
Apr 19 2018 Read 786 Times
The new software algorithm offered by Lumex expands the upper limit above 10,000 ng Hg in a sample to simplify the analysis of high variations of mercury content, sorbent traps (when a sample is unique) and samples with unknown mercury concentration.
Very often laboratory specialists who analyse mercury in solid samples (such as contaminated soil, sorbents and sorbent traps, waste water, etc,) have to address the problem of high variations of mercury content in the samples that are analysed. It is not unusual to have to clean the mercury analyser or manually readjust the instrument’s settings/parameters in order to be able to switch from analysis of mercury contents at ppm level to ppb level. Not to mention a headache when the sample is unique (like analysis of sorbent traps), and one risks getting an invalid result for a sample with unknown mercury concentration which might be out of the calibration range.
Commonly, when working with conventional gold-trap analysers, the sample in such cases is homogenized and divided into several independently analysed subsamples to avoid saturation of the analytical signal. Such an approach increases measurement error.
Analysing samples with the high variation of mercury content has never been a problem for the users of Lumex Instruments RA-915M/Pyro-915+ analyser due to a very wide dynamic range of the analyser and linearity of the calibration in this range. But with the recent addition of the new algorithm for RAPID software, it is now extremely easy to handle even samples with the mercury content of thousands of ppm.
A novel approach for the analysis upper limit expanding (above 10,000 ng Hg in a sample) is based on atomising temperature control depending on a rise/decay of analytical signal: Closed-Loop Control System (CLCS).
If the analytical signal exceeds a pre-set level L1 during analysis and the signal increases faster than a pre-set value R, the sample heating is automatically decreased and switched on when these values drop back below the prescribed levels. So in case of high mercury content in a sample, CLCS keeps the analytical signal between the specified levels L1 and L2, controlling the atomisation temperature and thereby avoiding the signal overflow. For a sample with “common” concentration, when the signal does not exceed the L1 value, atomization follows standard temperature scenario with the overall time of analysis within 1 - 3 min
The CLCS automated control shows excellent linearity of the calibration graph obtained in a range of three orders of magnitude. Some Lumex Instruments customers have already tested the new technique for the analysis of solid samples by thermal decomposition and direct analysis by AAS following standard methods like, for example, EPA 7473, or ASTM 7622.
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