Determination of heavy metal elements such as arsenic, lead, chromium and nickel in tobacco and tobacco products - Master's thesis - Dissertation

The harmful effects of heavy metals on smoking in the human body are much higher than those in the digestive tract. When the cigarette is not completely burned, a series of thermal decomposition and thermal synthesis chemical reactions occur, forming a large number of complex organic substances. Studies have confirmed that the temperature of the burning center of cigarettes is as high as 800-900 ° C, and the edge temperature of burning is also 300-400 ° C. The high temperature of tobacco burning converts heavy metals and metalloids in tobacco into soot and mist (aerosol) and enters the human body directly from the respiratory tract. This process includes smokers and passive smokers.

China's tobacco industry currently requires a limited amount of arsenic and lead in cigarette-mounted base paper (YC 170-2009), and gives corresponding detection methods: graphite furnace atomic absorption spectrometry (YC/T 268-2008), inductively coupled plasma Body mass spectrometry (YC/T 316-2009).

For the detection of heavy metal elements in tobacco and its tipping paper, Tianrui Instrument Co., Ltd. has developed a heavy metal detection program for tobacco and tobacco products, in which ICP-MS inductively coupled plasma mass spectrometry can simultaneously detect tobacco and tobacco products. The content of heavy metal elements such as cadmium, lead, arsenic, mercury, chromium and nickel, the test data show that the ICP-MS method has high sensitivity and good accuracy, and has the characteristics of fast and strong anti-interference ability.

The latest inductively coupled plasma mass spectrometer ICP-MS 2000E independently developed by Tianrui has excellent overall performance index and high cost performance. The ICP-MS2000E is equipped with an autosampler to make the test process more automated and improve the test efficiency. The latest collision is adopted. The reaction cell technology can effectively eliminate the interference of polyatomic ions and reduce the detection limit of susceptible elements. ICP-MS2000E can be widely used in food, environmental protection, tobacco, semiconductor, nuclear industry, petrochemical, mineral, medical and physiological analysis. Fields, etc.

1 Experimental method

1.1 Equipment and reagents

ICP-MS2000 inductively coupled plasma mass spectrometer;
WX8000 microwave digestion instrument;
Bs224s type electronic balance;
Millipore Simplicity type ultrapure water purifier;
HNO ₃ (excellent grade pure), H ₂ O ₂ (excellent grade pure);
10 μg/mL Li, Co, In, Ce, U and Bi mixed tuning solution (diluted to 10.0 ng/mL with 1% HNO ₃ before use);
10μg/mL gold, barium, mercury, chromium, nickel, arsenic, selenium, cadmium, lead standard solution;
Pipetting gun (Plender, Germany, 10-100 μL, 100-1000 μL);
The water used in the test was double deionized water (resistance of 18.25 MΩ·cm), and the vessels used were all soaked in 20% HNO ₃ solution overnight;

1.2 Sample Processing and Analysis

The tobacco samples were de-stalked, dried in an oven at 40 ° C for about 14 h, comminuted, and passed through a 40 mesh screen.
Weigh about 0.2g sample (accurate to 0.1mg), placed in a polytetrafluoroethylene digestion tank, add 5mL HNO ₃ , 2mL H ₂ O ₂ and 0.1mL (20μg / mL, 5% HNO ₃ diluted) gold standard solution, Put it into the microwave digestion furnace and digest it according to the program set first. After the digestion is completed, after cooling, the digestion tank is taken out, the sample is transferred to a 50 mL volumetric flask, and the sample tank is rinsed 3 times with ultrapure water, and then 10.0 ng/mL of the internal standard solution (10 μg/mL Rh standard solution) is added. Make up the volume, get the sample solution to be tested, and make the sample blank at the same time, to be tested.

Optimize the working parameters of the instrument with 10.0 ng/mL Li, Co, In, Ce, U and Bi mixed tuning solution to optimize the sensitivity of the instrument and ensure the oxide and double charge yields are less than 3%. The specific operating parameters are shown in Table 1. . Under the conditions of the best working parameters of the instrument, the test was carried out by the internal standard method.

Table 1 Instrument operating parameters

2 Results and discussion

2 .1 detection limit

The Hg standard is a separate group. The Cr, Ni, As, Se, Cd, and Pb standards were diluted to the desired concentration with a standard solution of 10 μg/mL of each element. 0.1 mL of 20 μg/mL gold standard solution was added to prepare the Hg standard solution. The analysis results (Table 2) show that the correlation coefficient of the linear equations of the seven elements is 0.9996 to 1.000, and the detection limit is 0.008 to 0.165 ng/mL.

Table 2. Linear equations and detection limits for standard curves of each element

2 .4 precision and recovery

Accurately weigh 6 tobacco samples, about 0.2g / part, respectively determine As, Cr, Ni, Se, Cd, Hg and Pb, and calculate the relative standard deviation (RSD) according to the measurement results. The results showed that the RSD of Cr, Ni, As, Se, Cd, Hg and Pb were 2.77 %, 3.91 %, 5.52 %, 3.31%, 1.51 %, 9.66 % and 1.89%, respectively. The data is shown in Table 3.

Table 3 Test precision of each element

0.2 g of the test tobacco sample was weighed, placed in a digestion tank, and a certain amount of the standard solution was added, followed by microwave digestion, and the digestion was completed by ICP-MS. The results are shown in Table 4. It can be seen that the recovery rate of the method is between 94.0% and 103.8%, which can meet the requirements of trace analysis of these elements in tobacco.

Table 4 Test recovery rate of each element

3 Conclusion

The contents of Cr, Ni, As, Se, Cd, Hg and Pb in tobacco samples were determined by ICP-MS 2000E. The recovery of the method was 94.0%-103.8%, and the detection limit was 0.008-0.165 ng/mL. The relative standard deviation is 1.51% to 9.66 %; it can meet the requirements of the tobacco industry for the trace analysis of these elements in tobacco samples.