Milestone Srl MA213-003 – DMA-80 EVO – User Manual
148
ACCEPTANCE LIMITS. Control limits shall be listed on charts for different matrices. Acceptable criteria
should be set through the use of historical analyses. In the absence of historical data this limit should be
set for:
Control standards for checking the stability of the instrument calibration at ±10% of their true value. To do
this use two reference standards with range of interest ( see point 3.5 of EPA Method 7473).
For each batch of samples processed, a method blank must be carried out. A method blank is prepared by
using a volume or weight of reagent water at the volume or weight specified in the preparation method. In
absence of project specifics, if the blank is less than 10% of the lowest sample concentration for each
analyte, then the method blank would be considered acceptable (see point 9.4 of EPA Method 7473).
For each batch of samples processed, a duplicate is carried out to check stability and performance. The
acceptable criteria in absence of historical analysis is set at ±10%.
Matrix Spike/Matrix Spike duplicated at ± 20% of the spiked for precision and ≤ 20 relative percent
difference. After determination of historical data, 20% must still be the limit of maximum deviation for both
percent recovery and relative percent difference to express acceptability (see point 9.3 of EPA Method
7473).
8.5 SAMPLE PROCESSING
8.5.1 Recommendations for preservation of samples
Full preservation of samples—domestic sewage, industrial wastes, natural waters, etc.—is a practical
impossibility. Regardless of the nature of the sample, complete stability for every constituent can never be
achieved. At best, preservation techniques can only retard the chemical and biological changes that
inevitably continue after the sample is removed from the parent source.
The changes that take place in a sample are either chemical or biological. In the former case, certain
changes occur in the chemical structure of the constituents that are a function of physical conditions. Metal
cations may precipitate as hydroxides or form complexes with other constituents; cations or anions may
change valence states under certain reducing or oxidizing conditions; other constituents may dissolve or
volatilize (Hg) with the passage of time. Metal cations may also adsorb onto surfaces (glass, plastic, quartz,
etc.), such as, iron and lead.
Biological changes taking place in a sample may change the valence of an element or a radical. Soluble
constituents may be converted to organically bound materials in cell structures, or cell lysis may result in
release of cellular material into solution. The well-known nitrogen and phosphorus cycles are examples of
biological influence on sample composition.
Therefore, as a general rule, it is best to analyse the samples as soon as possible after collection. This is
especially true when the analyte concentration is expected to be in the low range.
8.5.2 How to clean the DMA-80 boats
Nickel: for solid samples , reusable approx 1000 times. Nickel boats can be cleaned:
- using the DMA-80 with the Clean Procedure method
- using a Muffle at 600°C per 10minutes.
NOTE: Only Hot temperature in order to clean out the Hg!
Quartz: for liquid and semi-liquid samples, reusable approx 2000 times. Quartz boats can be cleaned:
- using the DMA-80 with the Clean Procedure method
- using a Muffle at 900°C per 10 minutes.
To Next Page
Loading...
