The soluble mercury content in the coating was determined by a direct mercury meter

In recent years, with the development of society and the change of people's living concept, the requirements of indoor environment are getting higher and higher, and more and more attention is paid to the quality and safety of interior decoration materials. The quality of coatings directly affects human health, especially the soluble heavy metals (mercury, lead, chromium, cadmium), formaldehyde, volatile organic compounds and other harmful substances, the greatest harm to the human body.
Nate mandatory standard GB 18582-2008 "Indoor decoration materials interior wall coating hazardous substances limit", from the law clearly stipulates that the content of harmful substances in interior wall coating products must meet the limit requirements of the standard, of which mercury content should be ≤ 60 mg/kg
China
. The soluble heavy metal content in GB 18582-2008 is recommended for determination using the method specified in Appendix D.
commonly used methods to detect mercury content are atomic spectroscopy of hydrogenation occurrence, cold atom absorption spectroscopy,sulfur and spectrophotomtum, etc. Atomic spectroscopy of hydrogenation is a rapid development in recent years, and it is also recommended by national standards to detect mercury content. The method is accurate and sensitive, but its main defects are low recovery rate, large pre-treatment loss, long sample processing time, and poor linear regression of the method due to the memory effect of mercury. Using direct mercury meter to determine the soluble mercury content in the coating, with low sampling, high sensitivity, good precision, fast analysis speed, no reagent contamination, can be directly sample determination and other advantages, and achieved satisfactory test results.1 Test Part
1.1 Reagents and Materials
Mercury Standard Substances (1,000 μg/mL), National Standard Substances Research Center; High Purity Oxygen; Nitric Acid, Premium Purity; Potassium Heavy Chromate, Excellent Purity; Ultra-Pure Water for Testing; Liquid Samples, Market Representative Products.
1.2 Test instrument
The DMA-80 direct mercury meter (Milstone, Italy), consists of an automatic sampler, sample furnace, catalytic tube, chihuahua tube, mercury lamp, detector, workstation, nickel boat or quartz sample boat, etc.; ME204E electronic balance (Meitler-Tolido); Miilli-Q ultra-pure water machine (Milibo Corporation of the United States);
1.3 Test Methods and Principles
The liquid sample is removed with a liquid gun and placed in the quartz boat of the mercury meter, and the sample is carried into the mercury meter thermal decomposition furnace through the automatic sampling system. Thermal decomposition, thermal decomposition products are carried by the flowing gas (oxygen) to the decomposition furnace for catalytic reduction, the mercury of various forms into monomer mercury, while other decomposition products containing halogens, nitrogen, sulfur oxides and other decomposition products are captured by the catalytic bed, at the same time is completely decomposed and released. All mercury is carried by gas (oxygen) into the chimer, in which the mercury reacts with gold to form a gold-mercury alloy that is selectively left behind, while mercury-free vapor and decomposition products are removed, after which the chimer is instantly heated and the temperature reaches 9 After 00 degrees C, mercury vapor is released, and the flowing carrier gas (oxygen) carries the mercury vapor through the absorption chamber located in the light path of the single wavelength atomic absorption spectrometer, measuring the absorption value at a wavelength of 253.7 nm. The DMA-80 direct mercury meter works as shown in Figure 1.
the working principle of the DMA-80 direct mercury meter
2 Results and discussion
2.1 Mercury meter operating conditions optimization
drying temperature: 200 degrees C; 60 s; Catalytic temperature: 650 degrees C; Catalysis time: 60 s; Decomposition temperature: 650 degrees C; Decomposition time: 90 s; Wait time: 80 s; Mercury chimeric tube Release time: 12 s; Record measurement signal time: 30 s; Qi temperature: 900 oC; Qiqi time: 12 s; Signal acquisition time: 30 s; Cleaning time: 60 s ; Oxygen pressure: 0.4 MPa; Oxygen flow: 200 mL/min; Light source: low pressure mercury lamp; Detector: silicon UV photoelectctor; wavelength: 253.7 nm.
2.2 Sample sample intake
In order to ensure the service life of the mercury meter and the accuracy of the test results, the appropriate sample size should be selected. If the sample volume is too much, the mercury content is high, affecting the decomposition of the sample, and it is easy to aggravate the damage of mercury in the sample to the catalytic tube, chihuahua tube, shorten the life of the catalytic tube, chihuahua tube; The sample amount is generally 0.05 to 0.5 g during the test.
2.3 Standard Curves and Methods Detection Limit
2.3.1 Standard Curves
Direct mercury meters have two absorption pools, long and short, to test the standard curves of low and high concentration ranges, where mercury vapor is first brought into the long absorption pool and then automatically switched to a short absorption pool for testing. The mercury concentration was low in this test, so a low concentration standard solution series was selected. Absorption of 1,000 μg/mL mercury standard solution diluted by 3% nitric acid step by step to concentrations of 0, 5 μg/L, 10 μg/L, 20 μg/L, A series of standard solutions of 30 sg/L, 50 sg/L and 100 sg/L, with a shift gun to move the standard solution one by one to the built-in sample tray of the automatic mercury meter for determination. The mercury content (absolute value) is represented by the x-axis, and the y-axis represents the peak and high value of the response, and the standard mercury curve is plotted, as shown in Figure 2.
Mercury standard curve
2.3.2 method detection limit
Under the above test conditions, the blank solution was measured 12 times in parallel, the standard deviation of the measurement results was calculated, and the detection limit of this method was found, the results of which are seen in Table 1.
method detection limit
by Table 1 can calculate the standard deviation S is 0.001 084 ng, with 3 times the standard deviation calculation, the detection limit is 0.003 252 ng, the determination of the lower limit is generally ≥ check-out limit 5 times, that is, ≥ 0.016 26 ng.
2.4 Precision and Mark Recovery Test
2.4.1 Precision Test
Under the above-mentioned test conditions, the coating sample was taken, measured in parallel 6 times, and the test results are found in Table 2. Table 2 shows that this method has good repeatability.
Precision Test Results
2.4.2 Recovery Rate Test
Under the above-mentioned test conditions, the coating samples were taken and a certain amount of mercury was added to the mark-up recovery test, and the recovery rate was measured from 87.9% to 105.7%. This shows that the stability and accuracy of the standard-added recovery test of this method are good, and can meet the measurement requirements.
3 conclusion
an analytical method for determining soluble mercury content in coatings using a direct mercury meter. This method does not require pre-sample processing, reduces the system error and the loss of mercury in the process of sample processing, as well as the reagent consumption and environmental pollution during the test process, and guarantees the health of the test personnel.