Milestone Srl MA213-003 – DMA-80 EVO – User Manual
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8.5.4 How to work at standard levels (ppb/ppm)
The aim of this SOP is to provide practical guides to use the DMA-80 evo in our standard working range.
DMA 80 evo is capable to operate both at trace and high levels but in order to achieve such low levels,
the instrument and the operator need to use some additional care.
1. INITIAL INSTRUMENT SETUP
Our standard calibration allows to work at values above 0.1 ng. Nevertheless, to begin the calibration
and work at low levels, the system must be stable and clean. It’s important to have a good calibration and
quality check in the real working range required (for example 1 ng to 100 ng). First of all, it is suggested to
analyze samples with homogeneous mercury content. For example, when the system is clean, it is
advisable to run all the water and low concentration samples and then the samples with a high
concentration of mercury. After that, start the cleaning procedure overnight to get a clean instrument for
the next day, if it is required to work again at low concentrations.
As the blank values lead to non-optimal reproducibility and accuracy at low level, see below how to
achieve good blank values.
2. HOW DO WE GET A GOOD BLANK FOR ROUTINE ANALYSIS?
- Always use quartz boat for calibration and for low level analysis.
- Clean the boats in muffle (900°C for 10’ for the quartz boats, 600°C for 10’ for the metal boats) or
directly into the instrument with the standard method.
- Perform some BV method before working to ensure the right cleanliness of the instrument. The
acceptance of the BV values strongly depends on the user working range. Typically has to be
lower than 0.0030 ABS in the cell 1.
- If the working range start from 0,1 ng, the following cleaning has to be performed: run clean boats
plus 0.3 ml of water with the Water Cleaning method
- The expected ABS value has to be lower than 0.0040 in cell 0
3. CALIBRATION
DMA-80 evo comes with a factory calibration from 0,1 ng up to 1000 ng. A customized calibration is
suggested to match specific needs and working range.
The calibration has to be prepared using the following guidelines:
- Prepare fresh standard solutions according to the working range. For new calibration it is safer to
prepare always new standards.
- Standards have to be stabilized with HCl (2% v/v), in order to avoid mercury evaporation.
- The first calibration point has to be a real blank with the same amount and matrix (water with 2%
v/v of HCl) used for all the other points of the calibration.
- Perform two replicates for each standard
- We suggest a 100 ul of standard for each concentration, especially for low mercury levels. For
higher levels the volume could be reduced.
The calibration has a long lifetime, anyway it is suggested to test it routinely with an external standard
(liquid or solid) in two or more points, based on the working range.
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