Keywords: microwave digestion; hydride atomic absorption method; Pulean tablets; arsenic
Abstract: Objective: To establish a method for determination of trace arsenic in Pule'an tablets. Method: Microwave digestion was used to determine arsenic content by hydride atomic absorption method. Results: The detection limit of this method was 0.045 μg / kg, the coefficient of variation RSD = 5.9%, and the recovery rate was 90% ~ 106%. Conclusion: This method is simple, rapid, and highly sensitive, and can be used as a method for the determination of trace arsenic in Pulean tablets.
CLC number: R927.2. Document identification code: A Article number: 1001-1528 (2005) 01-0031-03
Determination of arsenic in Pule hn Tablet by microwave digestionhydride generation atomic absorption spectrometry
HE Lian-jun, LEI Kai—qin
KEY W ORDS: microwave digestion; HGAAS; Pule hn Tablet; arsenic
ABSTRACT: AIM: To establish a method for the determination of traceamounts arsenic in Pulebaa Tablet (Chinese Cabbage Pollen). MTHODS: Hydride generation atomic absorption spectrometry was used to determine arsenic by microwave digesting sam ple. RESULTS: The detection limit of the method was 0.045 μg / KS, D = 5.9%. the recoverywas in the range of90% ～ 106%． CONCLUSION: The method is simple. rapidand with high sensitivity. and can be applied for the determ ination of trace amounts arsenic in Pule hn Tablet.
Arsenic is a harmful heavy metal element. Frequent intake of trace amounts of arsenic compounds will seriously endanger people's health. Therefore, arsenic is an important element in the hygienic quality control of traditional Chinese medicine preparations. Pulean is a pure rapeseed pollen traditional Chinese medicine preparation. It is used for kidney qi deficiency, waist and knee soreness, residual urine or incontinence after prolapse of urine, prostatitis, and prostate hyperplasia. The traditional sample digestion methods include dry ashing or wet digestion. Dry ashing is easy to operate, but it takes a long time; wet digestion has serious environmental pollution, large acid consumption, and high blank value. Microwave digestion is a new digestion technology developed in recent years. It combines the performance of high-pressure digestion and microwave rapid heating. Compared with the traditional sample dissolution method, it has fast sample digestion, less reagent consumption, and blank. It has outstanding advantages such as low value, avoiding volatile loss and complete recovery. It can also digest many samples that are difficult to digest by conventional methods. It is suitable for the pretreatment of various analytical samples, especially for trace analysis and ultra-pure analysis. Microwave digestion has been widely used to digest foods, alloys, geological samples and cosmetics, but it is rarely reported in the analysis of trace elements in traditional Chinese medicine preparations.
As for the detection method of arsenic, there are silver content method, arsenic spot method, colorimetric method, etc. In recent years, the hydride atomic absorption method has been gradually adopted. It has the advantages of high sensitivity, good selectivity, convenient and fast operation, and little interference. It is suitable for the determination of trace arsenic and trace arsenic.
This article establishes microwave digestion-hydride atomic absorption method for the determination of arsenic in the traditional Chinese medicine preparation Pulean tablets. The method is simple, fast, and highly sensitive. It is an effective method.
1 Instruments, reagents and samples
1.1 Instruments: SOLAAR-S atomic absorption spectrophotometer (U.S. Thermoelectric Company); VP90 hydride generator (U.S. Thermoelectric Company); MK-11I pressure-controlled closed microwave digestion system (Shanghai Xinyi Microwave Chemical Technology Co., Ltd.) .
1.2 Reagents: nitric acid is ultra-pure process; hydrochloric acid and hydrogen peroxide are of high-grade purity; sodium borohydride, sodium hydroxide, potassium iodide, and ascorbic acid are all analytically pure; arsenic standard stock solution is provided by Shanghai Institute of Measurement and Testing Technology.
1.3 Samples: The experimental samples of Pulean tablets are provided by our company.
2 Analysis steps
2.1 Preparation of sample solution: Take appropriate amount of sample, grind it finely, accurately weigh about 0.3-0.5 g into a 60 mL dissolution cup, add 6.0 ～ 10.0 mL of nitric acid, and place it on an electric heating plate Heat up slowly to 150 ° C. After the brownish yellow smoke has exhausted, remove it and let it cool slightly. Then add 1.0ml of 30% hydrogen peroxide and continue to heat it on an electric hot plate at 100 ℃ for 20min. After removing and cooling to room temperature, cover the sealed bowl and dissolve the sample. Put the cup into the digestion tank, put it into the microwave digestion furnace, and adjust the pressure from the first step to the fourth step (2.0 MPa) according to the steps of the digestion furnace. Take it out after 15 minutes of digestion (if the digestion is incomplete, it may be appropriate (Extend the digestion time). After cooling to room temperature, open the lid of the sample dissolution cup, place it on a hot plate at 150 ° C, heat and evaporate until the solution leaves about 0.5 mL, then rinse the inner wall of the sample cup twice with 10 mL of deionized water, and place it on the hot plate Heat at 150 oC to evaporate until the solution remains around 0.5 mL. After cooling, transfer the sample to a 25 mL volumetric flask with deionized water, add 2.5 mL of a 15% potassium iodide-2% ascorbic acid mixed solution, and then add 2.5 mL of hydrochloric acid , Make up to the mark with water, shake well, heat in a 100 oC water bath for 10 min, and do the reagent blank at the same time.
2.2 Preparation of standard solution: Draw an appropriate amount of arsenic standard stock solution with a concentration of 1,000 g / L, dilute with 0.5% nitric acid to make an arsenic standard solution with a concentration of 100.0 g / L, and draw this solution separately 0.0, 0.25, 0.50, 1.0, 2.0 mL in a 25 mL volumetric flask, add 2.5 mL of 15% potassium iodide-2% ascorbic acid mixed solution, and then add 2.5 mL of hydrochloric acid, Dilute to the mark with water and heat for 10 min in a 100 ° C water bath to obtain a standard arsenic solution with a concentration of 0.0, 1.0, 2.0, 4.0 and 8.0 g / L
2.3 Measurement: Atomic absorption spectrophotometer Working parameters: measurement wavelength 193.7 nm, lamp current 9 mA, slit (passband) 1.0 nm, background correction off. Hydride conditions: hydride mode is flame heating, flame is air-acetylene, gas flow is 1.0 L / min, burner height is 15.4mm, stability delay is 80 seconds, return to baseline delay is 80 seconds, argon flow 200 mL / min. Using 10% hydrochloric acid as the carrier liquid, and 1.0% sodium borohydride (stabilized with 0.2% sodium hydroxide solution) as the hydride reducing agent, the absorbance of the arsenic standard solution and the sample solution were measured on the hydride generator, A standard curve was drawn by linear least squares fitting, and the absorbance of the sample was compared with the curve to determine the arsenic content.
3 Results and discussion
3.1 Selection of microwave digestion conditions: For traditional Chinese medicine preparations, there are at least a few flavored medicinal materials and as many as dozens of flavored medicinal materials. The ingredients are complex and difficult to decompose completely, which brings great difficulties to the digestion of the sample, plus the difference The traditional Chinese medicine preparations have different manufacturing methods and can be divided into ointments, tablets, pills, liquids, powders, etc. For liquids or ointments, they are generally easier to digest, while for tablets and pills, etc. Long time and higher pressure digestion.
The choice and amount of digestion solvent have a great influence on the digestion effect. During the digestion process, the decomposition effect should be based on the matrix component of the sample and the nature of the tested element. Whether the soluble salt obtained after the reaction is used. The acid used is introduced into the blank value. Consider the size, rate of reaction and other conditions to fully consider what acid is selected, whether it is a single acid or a mixed acid. In order to increase the oxidizing ability of the oxidant to the sample organic matter, it is necessary to select a suitable mixed acid group and a reasonable mixed acid ratio, because each acid can only effectively decompose the ability of individual components in a matrix, and the mixed acid can achieve complementary It can form a complex with another acid during the sample dissolution process, effectively dissolving the sample. For microwave sample preparation, nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, perchloric acid, hydrofluoric acid, hydrogen peroxide, etc. are commonly used as solvents. In this experiment, ultra-pure nitric acid with a low blank value is used as the digestion acid, and non-polluting hydrogen peroxide is added As a solvent for digesting samples.
After a lot of experimental work, it has been shown that by controlling the appropriate pressure (1.5-3. 0 MPa) and time (5-20min), the nitric acid-hydrogen peroxide system can be used to complex organic The digestion of the ingredients is complete. For a sample of 0.3 to 0.5 g, the digestion system should be 6.0 to 10.0 mL of nitric acid and 1.0 mL of 30% hydrogen peroxide.
3.2 Selection of pre-reducing agent: Arsenic measured by hydride generation method is trivalent arsenic, so pentavalent arsenic must be reduced to trivalent arsenic in advance. With reference to relevant literature, in this experiment, a mixed solution of 15% potassium iodide and 2% ascorbic acid was selected as the pre-reducing agent. The experimental results show that with 10% potassium iodide. The mixed solution of ascorbic acid can obtain satisfactory results.
3.3 The effect of sodium borohydride concentration and acid: The concentration and acidity of sodium borohydride in the reaction system are important factors that affect the full occurrence of hydride. The concentration of sodium borohydride has a great influence on the determination of arsenic. If the concentration of sodium borohydride is too high, the sensitivity will be reduced due to the dilution of arsenic atoms due to a large amount of hydrogen generated by the reaction; Incompleteness reduces the sensitivity. The results show that the sensitivity of arsenic is better when the concentration of sodium borohydride is 1.0%. The hydride reaction should be carried out in an acidic medium. Generally, hydrochloric acid or sulfuric acid is commonly used to adjust the acidity of the reaction system. The experiment uses hydrochloric acid. The test shows that when the concentration of hydrochloric acid is 10%, the conditions for occurrence are the best and the sensitivity of arsenic is better.
3.4 The effect of coexisting cations: As argon gas is carried out with argon, leaving interfering substances in the solution, the effect of coexisting cations is small. For 2 g / L arsenic, 10 mg / L of copper, iron, nickel, lead, cadmium and calcium ions have no effect on the determination.
3. 5 Influence of coexisting acid: If the sample is measured without digesting the acid after digestion, the residual nitric acid can cause iodine to precipitate, polluting the entire measurement system and making the experiment impossible. Therefore, after microwave digestion, the residual nitric acid in the digestive juice must be expelled, otherwise the results will be inaccurate. When the concentration of nitric acid in the measurement solution is less than 0.05 mol / L, it has little effect on the measurement. If it is higher than this concentration, the measurement result will deviate greatly from J.
3.6 Standard working curve: In the concentration range of 0 ～ 8.0μg / L, the standard working curve is drawn with absorbance versus arsenic content, and the regression equation obtained by the least square method is: Y = 0.01346X + 0.0028, r = 0.9983, the linear relationship is good.
3.7 Precision test: Take the same batch of samples (Pulean tablets, 030931 batches), prepare 6 copies in parallel according to the preparation method of the sample solution, and measure the arsenic content on the hydride generator respectively. Results The average content was 0.084 mg / Kg, the standard deviation was 0.0050, and the coefficient of variation was 5.9%.
3.8 Recovery rate test: Weigh accurately 0.4g of a sample with a known content (Pulean tablets, batch 030931), add a control solution of known concentration respectively, process the sample and determine the arsenic by the same method as the preparation of the sample solution The content is shown in Table 1.
3.9 Limit of detection: Calculated by measuring the standard deviation of standard blank solution 11 times, the limit of detection is 0.045 μg / Kg.
3.10 Conclusion: This method is simple, fast, and has a good linear relationship. The precision and recovery rate meet the requirements for trace determination, which provides a good analysis method for the determination of arsenic in the traditional Chinese medicine preparation Pulean tablets.
references:
[1] GB / T 5009.11-1996, the National Standard of the People's Republic of China · Physical and Chemical Part of Food Hygiene Inspection Methods [S].
[2] Pharmacopoeia of the People's Republic of China (1) [S]. Beijing: Chemical Industry Press. 2000, Appendix 51-52.
[3] Hu Wenying, Yin Hongjun, Jiang Xifu. Determination of arsenic in cosmetics by hydride generation atomic absorption method [J]. China Public Health, 1998, 14 (1): 36-37.
[4] Li Xiaoli, Jiang Jinhua. Microwave digestion-hydride atomic absorption method for the determination of arsenic in milk powder [J]. China Dairy Industry, 2000, 28 (4): 30-32.
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