Points for Attention in Determination of Mercury and Arsenic by Atomic Fluorescence Spectrometry

1.

(1) The laboratory temperature is 15～30℃, and the humidity is less than 75%

(2) It should be equipped with a precision regulated power supply and the power supply should be well grounded

(3) The rear of the instrument table should be 50cm away from the wall to facilitate the installation and maintenance of the instrument

(4) The purity of argon gas is greater than 99.

(5) Glassware should be cleaned, soaked in acid, and used exclusively for atomic fluorescence

(6) The purity of the reagents should meet the requirements, and generally require superior grade purity

(7) The standard stock liquid should be replaced regularly, and the standard liquid and reducing agent should be used and prepared

(8) Be sure to turn off the power of the host when replacing the element lights

(9) Note that the order of starting up is computer, instrument host, sequential injection or dual pumps

(10) Before using the instrument, check whether there is water in the secondary gas-liquid separator (water seal)

(11) The instrument should be preheated for 1 hour before measurement.

(12) The sample must be clarified, must not contain impurities, and cannot enter too high concentrations of standards and samples (As concentration is less than 100ug/mL, Hg concentration is less than 10ug/mL)

2.

(1) During sample pretreatment, according to the characteristics of the sample, the type and amount of acid can be appropriately reduced or increased, and the pretreatment method suitable for the sample can be selected

(2) Pay attention to check the reagent blank of the whole procedure during the detection process, and re-test if reagent or utensil contamination is found

(3) greater than the aqua regia solubility single acid, can effectively dissolve the mercury sulfide, formulated aqua regia, hydrochloric acid and nitric acid ratio may be adequately adjusted, wherein hydrochloric acid and nitric acid of 9: 1 ratio of better treatment, because In the presence of hydrochloric acid, a large amount of Cl- interacts with Hg ^{2+ to} form a stable [HgCl ₄ ] ₂ ^- complex ion, which can inhibit the adsorption and volatilization of mercury
.

(4) During the pre-treatment, cover the digestion.
The temperature of the open digestion should not exceed 110℃.
If conditions permit, the microwave digestion can be used to prevent the loss of mercury by volatilization in the form of chloride
.

(5) When the sample contains more organic matter, the amount of aqua regia can be increased appropriately.
Due to the influence of environmental factors and the limitation of the stability of the instrument, a calibration curve must be drawn at the same time for the determination of each batch of samples.
Standard samples can be purchased from national standards.
Use after diluting step by step
.

(6) When the mercury content in the sample is high, it cannot be directly measured.
The sample weight should be appropriately reduced, or the sample should be diluted and then tested on the machine
.

(7) The sample should be determined as soon as possible after digestion.
Generally, it is only allowed to be stored for 2 to 3 days, and a preservation solution should be added to prevent the loss of mercury
.

(8) During the test, the excited state mercury atoms collide with certain atomic compounds (oxygen, nitrogen, carbon dioxide, etc.
) to produce energy transfer and "fluorescence quenching".
Therefore, inert gas high-purity argon or high-purity nitrogen is required as The carrier gas is passed into the fluorescent cell to help improve the sensitivity and stability of the test.
During operation, air and water vapor should be avoided from entering the fluorescent cell
.

(9) Substances that can strongly absorb the 235.
7nm mercury line and emit fluorescence (such as aromatic compounds such as benzene and toluene) will cause serious interference to the test.
Avoid introducing such interfering substances during the test
.

3.
Precautions for atomic fluorescence measurement of arsenic

(1) During the pretreatment process, the temperature should not be too high.
When the temperature is high, the arsenic element may be volatilized by high temperature, which will affect the measurement result.
The temperature should not exceed 110°C
.

(2) After the sample is decomposed by pretreatment, arsenic generally exists in a high-valence state.
The high-valence arsenic must be reduced to a low-valence state to effectively generate arsine .
Therefore, hydrochloric acid and thiourea must be added for pre-reduction and pre-reduction.
Affected greatly by acidity, the concentration of hydrochloric acid is selected between 10% and 20%
.

(3) After the sample is pre-treated, most of the elements in the soil can be decomposed into the test solution.
Among them, Cu ²⁺ , Co ²⁺ , Ni ²⁺ , Cr ⁶⁺ , Hg ^2+, etc.
will interfere with the determination.
Add sulfur Urea can eliminate these interferences
.

(4) Each batch of sample testing needs to draw a standard curve.
The concentration range of the standard curve should be selected according to the conditions of the instrument and the arsenic content in the sample.
The standard sample can be used after being diluted stepwise by purchasing the national standard
.