[serial] paint inspector, I want to say to you (5) - do you have a deep understanding of the content test of harmful heavy metal elements in paint?

1 What are the harmful heavy metal elements in coatings? The harmful elements mainly refer to the elements with significant biological toxicity, such as lead, cadmium, chromium, mercury, etc these elements will accumulate in the body and are not easy to be discharged from the body If they exceed a certain amount, they will have toxic effects on people and animals, and cause pathological changes or dysfunction of biological tissue organs Harmful elements in coatings are usually heavy metals The so-called heavy metal elements generally refer to the metal elements with a density greater than 4.5g/cm3 There are about 45 kinds in the periodic table of elements, including copper, lead, zinc, iron, cobalt, nickel, manganese, cadmium, mercury, tungsten, molybdenum, gold, silver, etc The harmful heavy metal elements in the coating mainly include lead, cadmium, chromium, mercury, etc However, due to the similar harm of arsenic and selenium to organisms and heavy metal elements, they are also tested according to the requirements of heavy metal elements The harmful heavy metal elements in coatings mainly come from pigments, fillers and some additives used in coating production 2 Test methods of harmful heavy metal elements in coatings quantitative analysis of heavy metal elements in coatings can be divided into chemical analysis method and instrument analysis method, specifically can be divided into chemical capacity method, spectrophotometry, atomic absorption spectrometry, inductively coupled plasma emission spectrometry, atomic fluorescence spectrometry, polarography, hydride generation method, X-fluorescence spectrometry, etc At present, AAS, ICP-OES, AFS and XRF are mainly used 3 The test category of harmful heavy metal elements in coatings there are many kinds of harmful heavy metal elements to be tested in coatings The latest green standard GB / T 35602-2017 "green product evaluation coating" specifies the testing of nine heavy metal elements, namely: lead (PB), cadmium (CD), chromium (CR), mercury (Hg), arsenic (as), barium (BA), antimony (sb), selenium (SE), cobalt (CO) Two compulsory national standards GB18582-2008 limits of harmful substances in interior wall coatings and GB 18581-2009 limits of harmful substances in solvent based wood coatings limit the contents of four harmful heavy metals, namely lead (PB), cadmium (CD), chromium (CR) and mercury (Hg) However, with the upgrading of environmental protection policies, more and more elements need to be limited in the coating, which is the general trend of technology development In addition to the heavy metal elements harmful to human body, some product standards of coatings also contain iron (FE), calcium (CA) and other elements that are not harmful to human body This is from the product performance requirements, testing methods and harmful elements are different 4 Classification of harmful heavy metal elements in coatings at present, the content of harmful heavy metal elements in coatings is mainly divided into soluble heavy metal content test and total heavy metal content test The soluble heavy metal content test uses the solution with the same concentration as the human stomach acid Generally, a 0.07mol/l dilute hydrochloric acid solution (pH = 1.12) is prepared to treat the paint dry film (self drying or drying), and then the content of the specified elements is determined by appropriate methods Its essence is to separate the harmful elements by extraction, so that the harmful elements are dissolved in the acid solution The total heavy metal content test refers to the use of appropriate pretreatment methods to remove the organic components of the dried film, to transform all the tested elements into the liquid state suitable for instrument measurement, and then use the appropriate analytical instrument for testing In GB / T 35602-2017, the total content of lead (PB), cadmium (CD), chromium (CR), mercury (Hg), arsenic (as), antimony (sb), selenium (SE), cobalt (CO) is tested, and the soluble content of barium (BA) is tested In GB18582-2008 and gb18581-2009, it is required to test the content of four soluble heavy metals, namely lead (PB), cadmium (CD), chromium (CR) and mercury (Hg) GB 24613-2009 limits of harmful substances in coatings for toys is a test for the content of eight harmful soluble heavy metals 5 Test methods for soluble harmful heavy metals 5.1 main test instruments and equipment: atomic absorption spectrometer; atomic fluorescence spectrometer; hydride generator; inductively coupled plasma emission spectrometer; acidimeter; microporous membrane (aperture 0.45 μ m); agitator; crushing equipment; oven 5.2 prepare the coating and mix the sample to be tested evenly Prepare the mixed sample according to the specified proportion of the product (diluent is not required to be added), and prepare the film with appropriate thickness on the glass plate or polytetrafluoroethylene plate after mixing evenly Under the drying conditions specified in the product manual, after the film is completely dried (if the self drying paint is dried, the temperature shall not exceed (60 ± 2) ℃), remove the film, and crush it with the grinding equipment at room temperature, so that the size of the film is less than 5mm For the film that cannot be crushed by the pulverizer (such as elastic and plastic film), use clean scissors to cut the film to pieces, so that the size of the film is less than 5mm Prepare the test solution directly from the powder sample 5.3 sample treatment weigh 0.5g of crushed sample into a 100ml beaker, and add 25ml hydrochloric acid solution into the pipette After stirring on the stirrer for 1min, measure its acidity with acidimeter If the pH value is greater than 1.5, adjust the pH value between 1.0-1.5 with hydrochloric acid Stir continuously at room temperature for 1h, and then place for 1H Then immediately filter with microfiltration membrane The filtered filtrate is kept away from light, and the analysis and test are completed within one day If the filtrate is kept for more than 1 day before the element analysis test, the concentrated hydrochloric acid shall be used to stabilize it so that the concentration of the preserved solution is about 1mol / L If the sample weight changes, the volume of hydrochloric acid solution added shall be adjusted to 50 times of the sample size The speed of the agitator shall be adjusted throughout the extraction period to keep the specimen in suspension and to avoid splashing as much as possible 5.4 the condition setting of the test instrument shall be tested by atomic absorption spectrometer, inductively coupled plasma emission spectrometer, and mercury shall be tested by atomic fluorescence spectrometer or hydride generator The test of each element usually has multiple spectral lines to choose from The sensitivity of each element and the matrix interference of the tested element solution should be considered in the selection of spectral lines The commonly used spectral lines of the atomic absorption spectrometer (with hydride generator): lead (PB): 283nm; cadmium (CD): 228nm; chromium (CR): 357nm; mercury (Hg): 253nm The ICP-AES usually uses the following lines: lead (PB) 220nm; cadmium (CD) 226nm; chromium (CR) 267nm; mercury (Hg) 194nm; arsenic (as) 197nm; barium (BA) 233nm; antimony (sb) 206nm; selenium (SE) 203nm; cobalt (CO) 238nm Setting of test conditions of ICP-OES: Power: 1.00kw; plasma gas flow: 15L / min; auxiliary gas flow: 1.5l/min; atomized gas flow: 0.75l/min 5.5 preparation of standard solution preparation of standard reference solution of AAS: select appropriate volumetric flask and pipette, use hydrochloric acid solution to gradually dilute the standard solution of lead (PB), cadmium (CD), chromium (CR), mercury (Hg), and prepare a series of standard reference solutions Usually prepared as: The configuration of the standard solution of ICP-AES is usually to purchase the mixed standard solution of multiple elements of certified reference materials for dilution For the mixed standard that cannot be purchased, the standard solution of a single element is usually used for mixing configuration, but it is necessary to ensure that the mixed standard solution will not have chemical reaction or other phenomena leading to the concentration of the standard material Change 5.6 test the content of soluble harmful elements in the extracted solution with an appropriate detection limit analyzer If the relative deviation of the two test results is greater than 10%, repeat the steps in 5.2 5.7 calculation of results the content of soluble harmful heavy metals in the sample is calculated according to the formula: 5.8 correction of results Because the test method of soluble heavy metals is greatly affected by the pH value of the prepared acid solution, the particle size of the film sample, the stirring temperature and other sample pretreatment conditions, it is necessary to get the final analysis results on the basis of the test results after correction That is to say, the value of the result multiplied by the analysis correction coefficient of the corresponding element in the table shall be subtracted from the result calculated according to the formula and reported as the final analysis result of the element The accuracy repeatability of the test method requires that the relative deviation of two test results of the same operator should be less than 20%; the reproducibility requires that the relative deviation of test results between different laboratories should be less than 33% 6 Test of total content of harmful heavy metals 6.1 main test instruments and equipment: atomic absorption spectrometer; inductively coupled plasma emission spectrometer; microwave digestion instrument 6.2 preparation of coating film: mix the sample to be tested evenly, prepare the mixed sample according to the proportion indicated by the product (diluent is not required to be added), and prepare the coating film with appropriate thickness on the glass plate or polytetrafluoroethylene plate after mixing evenly Under the drying conditions specified in the product manual, after the film is completely dried (if the self drying paint is dried, the temperature shall not exceed (60 ± 2) ℃), remove the film, and crush it with the grinding equipment at room temperature, so that the size of the film is less than 5mm For the film that cannot be crushed by the pulverizer (such as elastic and plastic film), use clean scissors to cut the film to pieces, so that the size of the film is less than 5mm Prepare the test solution directly from the powder sample For the samples that can not form film, the test solution is prepared directly after drying 6.3 there are three methods for sample processing: dry ashing, wet acid digestion and closed microwave digestion The method of closed microwave digestion is usually used, which is convenient and fast, and is suitable for the pretreatment of many elements When testing volatile and harmful elements (such as mercury and arsenic), dry ashing method and wet acid digestion method should not be used, but closed microwave digestion method should be used The steps of closed microwave digestion method: weigh about 0.1g-0.2g (accurate to 0.1mg) of crushed sample into microwave digestion tank, add about 6ml of nitric acid and 2ml of hydrogen peroxide respectively Then close the digestion tank, put it into the microwave digestion instrument, and set the appropriate digestion conditions for digestion After digestion, cool the digestion tank to room temperature, open the digestion tank, filter the digestion solution with filter membrane and transfer it to a 50ml volumetric flask Wash the inner wall and the inner cover of the digestion tank with water, collect the washing solution in the same volumetric flask, wash the filter membrane with water at the same time, collect all the solutions in the same volumetric flask, and dilute to the scale with water At the same time, the reagent blank test was done When the sample is digested by the above method, the appropriate digestion conditions can be determined according to the actual situation of the sample, so as to ensure that all the organic compounds in the sample are removed and all the tested elements are dissolved If there is residue in the processed sample, the residue shall be determined by appropriate measurement means (such as weighing the residue after drying for the second digestion), so as to ensure that there is no element to be measured If so, the residue is digested twice, and then the digestion solution is combined 6.4 samples processed in other processes can be tested by atomic absorption spectrometer or inductively coupled plasma emission spectrometer, and standard reference solution shall be prepared for instrument test The concentration range of standard reference solution should be selected to make the test value fall in the middle of the curve The linear coefficient of standard curve is better than 0.999 Formula used in test calculation