Grain and oil inspection. Determination of manganese, copper, zinc, rubidium, strontium, cadmium and lead in rice. Rapid extraction-inductively coupled plasma mass spectrometry

This standard was drafted in accordance with the rules given in GB/T 1.

This standard was proposed by the State Bureau of Grain and Material Reserves

This standard is under the jurisdiction of the National Cereals and Oils Standardization Technical Committee (SAC/TC 270)

Drafting organizations of this standard: National Grain and Material Reserve Bureau Scientific Research Institute, National Grain and Material Reserve Bureau Standard Quality Center, Steel Research Nake Testing Technology Co.

The main drafters of this standard: Zhou Minghui, Wang Songxue, Wang Zhengyou, Zhang Yan, Wu Yanxiang, Zhang Jieqiong, Lu Yixin, Chen Xi, Shi Chao, Wu Jing, Wang Jing, Mei Guang, Hong Ling, Liu Jia, Li Xu, Nie Huang , Cheng Ya, Lu Anxiang, Hu Bin, Mao Yongrong, Gao Weiwei, Huang Changjun, Zeng Hua

For more details, please click: " LS/T 6136—2019 Grain and Oil Inspection.

1 Scope

This standard specifies the principles, reagents and materials, instruments and equipment, samples, test procedures, and results processing of inductively coupled plasma mass spectrometry (ICP-MS) for manganese, copper, zinc, rubidium, strontium, cadmium, and lead in rice , Precision and other requirements

This standard applies to the determination of manganese, copper, zinc, rubidium, strontium, cadmium, and lead in rice

2 Normative references

The following documents are indispensable for the application of this document

GB/T 5491 Inspection of Grain and Oilseeds: Sampling and Separating Method

GB/T 6682 Analytical laboratory water specifications and test methods

3 Principle

After the sample is grinded to a certain particle size, the manganese, copper, zinc, rubidium, strontium, cadmium, and lead in the sample can be extracted into the extraction solution after shaking with dilute nitric acid.

4 Reagents and materials

4.

_{Note: Unless otherwise specified, the reagents used in this method are all top grade pure, and the water is the first grade water specified in GB/T 6682}

4.

4.

4.
2 Reagent preparation

4.
2.
1 Nitric acid solution (5 + 95): Take 50 mL of nitric acid, slowly add 950 mL of water, and mix well
.

4.
2.
2 Nitric acid solution (10 + 90): Take 100 mL of nitric acid, slowly add it to 900 mL of water, and mix well
.

4.
3 Standard products

4.
3.
1 Element stock solution (1 000 mg/L) (Mn, Cu, Zn, Rb, Sr, Cd, Pb): Single element or multi-element standard stock solution of certified reference material is used
.

4.
3.
2 Internal standard solution (1 000 μg/L) (Ge): Use a certified internal standard solution
.

4.
4 Preparation of standard solution

4.
4.
1 Mixed standard working solution: draw an appropriate amount of single-element standard stock solution or multi-element mixed standard stock solution, and dilute with nitric acid solution (4.
2.
1) to form a mixed standard solution series.
The mass concentration of each element is shown in the table in Appendix A.
A.
1, according to the mass concentration of the elements in the sample solution, appropriately adjust the mass concentration range of each element in the standard series
.

4.
4.
2 Internal standard solution: Take an appropriate amount of single element stock solution (1 000 mg/L) and mix it with nitric acid solution (4.
2.
1) to prepare a suitable concentration of internal standard solution
.
Refer to Appendix A for the concentration of the internal standard solution
.

5 Apparatus and equipment

5.
1 Inductively coupled plasma mass spectrometer (ICP-MS) 
.

5.
2 Balance: Sensitivity is 0.
1mg
.

5.
3 High-speed centrifuge: with 10 mL centrifugal position, 12 000 r/min
.

5.
4 Grain crusher
.

5.
5 Shaker
.

5.
6 Test sieve: the diameter of the sieve is 0.
38 mm
.

6 samples

6.
1 Sampling and sub-sampling

According to GB/T 5491, during the sampling process, sample contamination should be prevented
.

6.
2 Sample preparation

Crush with a grain crusher (5.
4), all pass through the test sieve (5.
6), mix well and store at room temperature for later use
.
During sample preparation and storage, contamination should be prevented
.

7 Test procedure

7.
1 Sample preparation

Accurately weigh 0.
2 g of rice sample (6.
2) (accurate to 0.
0001 g) into a 10 mL centrifuge tube, add 5 mL of nitric acid solution (4.
2.
2), shake on a shaker for 15 minutes, use a high-speed centrifuge for 12 000 r Centrifuge for 5 min at /min, take 1 mL of the supernatant, dilute 5 to 10 times with primary water for use, and make a reagent blank at the same time
.

7.
2 Instrument reference conditions

7.
2.
1 Optimize the operating conditions of the instrument so that the sensitivity, oxides and double-charged compounds meet the determination requirements
.
Refer to Appendix B for the operating reference conditions of the inductively coupled plasma mass spectrometer
.

7.
2.
2 Measurement reference conditions: After the tuning instrument meets the measurement requirements, edit the measurement method, select the isotope of each element to be tested and the selected internal standard element, and sequentially introduce the reagent blank, standard series, and sample solution into the instrument for measurement
.
Isotope selected analyte and the internal standard elements in Appendix C
.

For instruments that do not have a suitable interference elimination mode, the measurement results can be corrected using interference correction equations.
The instrument software generally contains interference correction equations.
Refer to Appendix D for the isobaric interference correction equations for lead, cadmium, and arsenic
.

7.
3 Preparation of standard curve

Inject the standard series of working solutions into the inductively coupled plasma mass spectrometer to determine the signal response value of the corresponding element.
The concentration of the corresponding element is used as the abscissa, and the response ratio of the corresponding element to the selected internal standard element is the ratio of ion counts per second.
As the ordinate, draw a standard curve
.

7.
4 Determination of sample solution

The sample solution is injected into the inductively coupled plasma mass spectrometer to obtain the corresponding signal response ratio, and the concentration of the corresponding element in the test solution is calculated according to the standard curve
.

8 Results processing

The content of the element to be tested in the sample is calculated according to formula (1):

Where:

X——The content of the element to be tested in the sample, the unit is milligram per kilogram or milligram per liter (mg/kg or mg/L);

c——The mass concentration of the measured element in the sample solution, in milligrams per liter (mg/L);

c ₀ ——The mass concentration of the measured element in the sample blank solution, in milligrams per liter (mg/L);

V-a constant volume of the sample digestion solution, the unit is milliliters (mL);

n——The dilution factor of the sample;

m The weighing mass or pipetting volume of the sample, the unit is grams or milliliters (g or mL):

The calculation result is expressed as the arithmetic mean of the two independent determination results obtained under the repeatability condition.
If the content is less than 1 mg/kg, the result retains two significant digits; if the content is greater than 1 mg/kg, the result retains three significant digits
.

9 Precision

When the content of each element in the sample is greater than 1 mg/kg, the absolute difference between the two independent determination results obtained under repeatability conditions shall not exceed 10% of the arithmetic mean; when it is less than or equal to 10 mg/kg and greater than 0.
1 mg/kg , The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 15% of the arithmetic mean; when less than or equal to 0.
1 mg/kg, the absolute difference between two independent determination results obtained under repeatability conditions Must not exceed 20% of the arithmetic mean
.

10 other

The rice sample is calculated with a constant volume of 0.
2 g to 50 mL.
The detection limits, quantification limits and related parameters of each element in this standard are shown in Table 1
.

Table 1 (continued)

Appendix A (informative appendix)

Standard series solution mass concentration

A.
1 The mass concentrations of the standard series of 7 elements are shown in Table A.
1
.

A.
2 Because different instruments use peristaltic pump tubes with different inner diameters to add internal standards online, the concentration of internal standards entering the sample is different, so when preparing the concentration of the internal standard solution, the reference concentration of the internal standard element in the sample solution should be considered as 0.
025 mg/L~0.
05 mg/L
.

Appendix B (informative appendix)

Reference conditions for sample determination

B.
1 The operating reference conditions of inductively coupled plasma mass spectrometer are shown in Table B.
1
.

B.
2 The element analysis mode of inductively coupled plasma mass spectrometer is shown in Table B.
2
.

Appendix C (informative appendix)

Recommended isotope and internal standard elements

The selected isotopes and internal standard elements of the elements to be tested are shown in Table C.
1
.

Appendix D (informative appendix)

Recommended interference correction equation

The isobaric interference correction equation is shown in Table D.
1
.