Determination of Trace Mercury in Feed by Cold Atomic Absorption Spectrometry
Key words: cold atomic absorption spectrometry; trace mercury in feed; mass spectrometer ; this article uses mercury atomic vapor generating device in combination with atomic absorption spectrometer to determine trace amounts in feed by cold atomic absorption spectrometry . The detection limit of the method was 0.19 μg/L; the recovery was 95% to 103%: the relative standard deviation was 1.9%. The method is simple, accurate and reproducible. Suitable for the determination of trace mercury in feed. 1 Introduction At home and abroad, there is strict control on the content of harmful heavy metal mercury in feed. The intake of mercury-contaminated feed can cause acute or chronic poisoning. Therefore, it is necessary to establish a method for determining trace mercury in feed. At present, there are many methods for determination, and commonly used are: spectrophotometry, atomic absorption, atomic fluorescence, chromatography, and the like. As a kind of effective trace mercury, cold atomic absorption method has been widely used in practical work. In this paper, mercury atomic vapor generation device is used to measure mercury atomic vapor into the atomic absorption spectrophotometer through carrier gas. The method is simple in operation, strong in anti-interference ability, high in sensitivity and good in reproducibility. The method is used to determine trace mercury in feed, and satisfactory results are obtained. The measured results of the standard sample are in good agreement with the standard values. 2 Experimental part 2.1 Main instrument AA-1800C atomic absorption spectrophotometer, mercury hollow cathode lamp, mercury vapor generating device (including shaker, T-type quartz tube, flow meter), digestion and reflux device. 2.2 main reagent 20% mixed acid: HNO 3 H 2 S0 4 : H 2 O = 1:1: 8. 4o% SnCl 2 : analytically pure; 20% hydroxylamine hydrochloride: analytically pure; mercury standard stock solution: Take 0.1354g of two, dilute with 20% mixed acid, and dilute to a 100ml volumetric flask. The concentration of this solution is 1mg/mL. The nitric acid and sulfuric acid used in the experiment were all pure and pure, and the water was deionized water. 2.3 Instrument operating parameters see Table 1: Table 1 Instrument operating parameters 2.4 Experimental steps 2.4.1 Sample pretreatment Accurately weigh about 1g of feed sample, placed in the conical flask of digestion and reflux device, add 10mL of nitric acid, 2mL sulfuric acid, install the condensation tube, first heat for 1h, after the foaming stops, heat and reflux for 2h until the solution becomes transparent. After cooling, digest the solution into 50ml test tube. 2.4.2 Determination step Accurately remove 5 mL of the above sample digestive solution in a mercury vapor generation bottle, add 3 drops of 20% hydroxylamine hydrochloride, cover the cap, and inject 1.5 mL of 40% SnC12 from the side with an injection needle, shake for 30 s. Nitrogen gas was introduced into the T-type quartz tube under the action of nitrogen gas for cold atomic absorption measurement. 2.4.3 The calibration curve is diluted from the standard stock solution of mercury to 100 μg/L with 20% mixed acid as the standard working solution of mercury, and taken separately: 0.0, 2.0, 4.0, 6.0, 8.0, 10.0 ml, The volume was adjusted to 100 mL, and then 5 mL was taken. The measurement was carried out according to the measurement procedure. The absorbance was read out and the calibration curve was drawn. The curve correlation coefficient was r=0.9998. 3. Results and discussion 3.1 Nitrogen gas used in the carrier gas flow control experiment The mercury vapor in the bottle is introduced into the T-type quartz tube for measurement. Therefore, the flow rate of the gas guide will directly affect the measurement result. The flow rate is too large, the absorption value is reduced, the sensitivity is lowered, the flow rate is too small, and the bee area reading is too short. Long, so this article chooses the best air flow rate is 800LJmin, the reading time is 50s. 3.2 Effects of coexisting elements The main ions present in the feed were determined and the results showed that for 10 μg of mercury (in μg): Ca ?+ (400), Mg2+ (800), K + (200), Na + (200), Fe 3+ (50), Cu 2+ (10) Mn ?+ (50), Zn 2+ (50), the determination of mercury is not sufficient to cause interference. 3.3 Determination of actual sample results and recovery experiments A large number of feed samples were analyzed by this method. The measured results and the spiked recovery experiments are shown in Table 2. Table 2 Actual sample results and spiked recovery experiment 3.4 Method detection limit and precision 6 times parallel determination of blank solution, 3 times the standard deviation of the measured value as the detection limit of the method, detection of mercury The limit was 0.19 g/L; the feed samples were subjected to 6 parallel measurements, and the relative standard deviation of the measurements was taken as the precision of the method, which was 1.9%. 3.5 Control experiment To investigate the accuracy of the method, the national standard reference material GBW08501 and rice GBW08508 were analyzed. The results obtained are listed in Table 3. The analytical results are consistent with the standard values. Table 3 Standard sample analysis results (mg/kg)
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