Milestone Srl MA213-003 – DMA-80 EVO – User Manual
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8.5.5 How to increase the reproducibility
After calibration, the reproducibility of the unit should be lower than <1.5% for 5 measurements with
0.1 ml of a solution of 100 ppb ug/Kg (10ng).
If this goal is not achieved with your samples, the cause may be one or more of the following :
Solid/liquid sample contaminated
Repeat the test with new sample.
Solid sample with non-homogeneous
Mix well and increase the sample amount.
Solid/liquid sample with low amount of
Mix well solid and use pre-concentration step up to
satisfactory results.
Old standard liquid solution/liquid
solution with precipitated due to not
Prepare fresh standard liquid solution.
Check balance calibration / Pipette calibration.
DMA-80 unit is not cleaned after high
concentration or “over range”
Cleaning procedure up to blank absorbance < 0.0030
Process parameter too short Increase: waiting (purge) time/ drying time/ decomposition
time.
Leakage of oxygen through the
silicone joint between
cuvette/amalgamator,
amalgamator/catalyst or catalyst/flange
Repair as shown in the “Maintenance of
The DMA-80” manual.
Use only O
2
, 99.50% pure for research, or replace supplier.
The catalyst and or/and amalgamator
Change catalyst and amalgamator and repeat calibration.
Environment contaminated Cleaning procedure up to blank absorbance < 0.0010, if
after this the contamination persists, transfer unit to another
laboratory.
8.6 HOW TO WORK WITH UNKNOWN SAMPLES
Unknown samples can contain high concentrations of Hg, so in order to avoid contamination of the catalyst
we suggest developing the application with a minimum quantity of sample (<5 mg) and then increasing
according the result.
Note: 1500 ng is our highest absolute value of mercury detectable.
For solid samples with concentrations of Hg higher than our range, it is possible to do a premix from 1:1 to
1:200 with inert material, such as previously decontaminated alumina.
For liquid samples with high Hg concentration, it is possible to do a dilution using the same matrix.
8.6.1 How to work with non-homogeneous samples
Non-homogeneous samples can result in poor reproducibility of the results. It is possible to increase the
performance with a sample preparation procedure.
The problem is due to non-homogeneous distribution of Hg in the matrix, or to different sizes of the same
sample—especially for inorganic samples such as soil, sediment, ore, rocks, plastic, etc.
To solve the first problem, mixing well should suffice. For the second problem, you need to reduce the
sample’s particle size to a powder form, normally below 100 um.
Pre-concentration steps may work as an alternative solution.
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