GB/T 14506.31-2019Methods for chemical analysis of silicate rocks—Part 31: Determination of 12 components including silicon dioxide etc.—Lithium metaborate fusion-inductively coupled plasma atomic emission spectrometry (English PDF)

Foreword

GB/T 14506 "Methods for chemical analysis of silicate rocks" consists of the following 34 parts.

- Part 1: Determination of hygroscopic water content;

- Part 2: Determination of combined water content;

- Part 3: Determination of silicon dioxide content;

- Part 4: Determination of aluminium oxide content;

- Part 5: Determination of ferric oxide content;

- Part 6: Determination of calcium oxide content;

- Part 7: Determination of magnesium oxide content;

- Part 8: Determination of titanium dioxide content;

- Part 9: Determination of phosphorus pentoxide content;

- Part 10: Determination of manganese oxide content;

- Part 11: Determination of potassium oxide and sodium oxide content;

- Part 12: Determination of fluorine content;

- Part 13: Determination of sulfur content;

- Part 14: Determination of ferrous oxide content;

- Part 15: Determination of lithium content;

- Part 16: Determination of rubidium content;

- Part 17: Determination of strontium content;

- Part 18: Determination of copper content;

- Part 19: Determination of lead content;

- Part 20: Determination of zinc content;

- Part 21: Determination of nickel and cobalt content;

- Part 22: Determination of vanadium content;

- Part 23: Determination of chromium content;

- Part 24: Determination of cadmium content;

- Part 25: Determination of molybdenum and tungsten content;

- Part 26: Determination of cobalt content;

- Part 27: Determination of nickel content;

- Part 28: Determination of 16 major and minor elements content;

- Part 29: Determination of 22 elements including rare earth elements;

- Part 30: Determination of 44 elements;

- Part 31: Determination of 12 components including silicon dioxide etc. - Lithium metaborate fusion-inductively coupled plasma atomic emission spectrometry;

- Part 32: Determination of 20 components including aluminium oxide etc. - Mixed acid digestion-inductively coupled plasma atomic emission spectrometry;

- Part 33: Determination of arsenic, stibium, bismuth and mercury elements content - Hydride generation atomic fluorescence spectrometry;

- Part 34: Determination of loss on ignition - Gravimetric method.

This Part is Part 31 of GB/T 14506.

This Part was drafted in accordance with the rules given in GB/T 1.1-2009.

1 Scope

This Part of GB/T 14506 specifies the method for the determination of silicon dioxide, aluminum oxide, total iron (calculated as ferric oxide), calcium oxide, magnesium oxide, potassium oxide, sodium oxide, titanium dioxide, manganese oxide, phosphorus pentoxide, strontium, barium in silicate rocks, using lithium metaborate fusion followed by inductively coupled plasma atomic emission spectrometry.

This Part is applicable to the determination of silicon dioxide, aluminum oxide, total iron (calculated as ferric oxide), calcium oxide, magnesium oxide, potassium oxide, sodium oxide, titanium dioxide, manganese oxide, phosphorus pentoxide, strontium, barium in silicate rocks, by lithium metaborate fusion-inductively coupled plasma atomic emission spectrometry. It is also applicable to the determination of the aforementioned components in soil and sediment samples.

See Table 1 for the method detection limits and determination ranges.

2 Normative references

The following documents are essential to the application of this document. For the dated documents, only the versions with the dates indicated are applicable to this document; for the undated documents, only the latest version (including all the amendments) is applicable to this standard.

GB/T 6379.2 Accuracy (trueness and precision) of measurement methods and results - Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method

GB/T 6379.4 Accuracy (trueness and precision) of measurement methods and results - Part 4: Basic methods for the determination of the trueness of a standard measurement method

GB/T 6682 Water for analytical laboratory use - Specification and test methods

GB/T 14505 Method for chemical analysis of rocks and ores - General rules and regulations

GB/T 14506.1 Methods for chemical analysis of silicate rocks - Part 1: Determination of hygroscopic water content

JJG 768 Emission spectrometer

3 Principle

The sample is decomposed by fusion with anhydrous lithium metaborate flux; the fused salt is dissolved in an aqua regia solution with the aid of ultrasonic oscillation.

Cadmium is accurately added as an internal standard element, to eliminate the effects of instrument fluctuations and matrix effects. After nebulization, the sample solution is introduced by a carrier gas into an argon plasma torch; atoms of the analyte and the internal standard element are excited and emit characteristic spectra. Within a certain concentration range, the concentration of the analyte in the sample solution is directly proportional to the intensity of its characteristic spectral line; the quantity of the analyte in the sample is calculated by measuring the signal intensity of the characteristic spectral line.

4 Test conditions

Test conditions such as temperature, humidity, voltage, frequency during detection using the inductively coupled plasma atomic emission spectrometer shall comply with the relevant requirements of JJG 768.

5 Reagents or materials

Unless otherwise specified in this Part, reagents confirmed to be of analytical grade are used in the analysis.

5.1 Water. GB/T 6682, Grade 2.

5.2 Aqua regia. Mix 3 parts hydrochloric acid (rho = 1.19 g/mL) with 1 part nitric acid (rho = 1.42 g/mL); prepare immediately before use.

5.3 Aqua regia solution (5 + 95).

5.4 Nitric acid solution (1 + 1).

5.5 Anhydrous lithium metaborate. Take hydrated lithium metaborate (LiBO2·8H2O); dehydrate it in a platinum dish at approximately 700 °C for 7 ~ 10 minutes. Once the moisture has been driven off, grind the material and store it in a bottle for later use. Commercially available anhydrous lithium metaborate may also be used.

5.6 Cadmium standard stock solution [rho(Cd) = 5.000 mg/mL]. Accurately weigh 0.5710 g of high-purity cadmium oxide (CdO); place it in a beaker; add 20 mL of nitric acid solution (5.4); heat until dissolved. After cooling, transfer the solution to a 100 mL volumetric flask; dilute to the mark with water; mix well. A commercially available certified cadmium standard solution may also be used.

5.7 Cadmium internal standard solution [rho(Cd) = 100 µg/mL]. Pipette 20.00 mL of the cadmium standard stock solution (5.6) into a 1000 mL volumetric flask; dilute to the mark with aqua regia solution (5.3); mix well for later use.

5.8 Preparation of calibration standard solutions. Select at least 5 national primary certified reference materials (CRMs). These shall have a matrix similar to the samples to be tested, with concentration values falling within the determination range of this method (ideally bracketing the expected sample values) and distributed across a suitable concentration gradient. Subject these CRMs to the same chemical treatment as the samples, to prepare CRM solutions for use as calibration standards.

5.9 Calibration blank solution. Weigh 0.2 g (to the nearest 1 mg) of anhydrous lithium metaborate (5.5); dissolve it in a 50 mL volumetric flask; accurately add 5.00 mL of the cadmium internal standard solution (5.7); dilute to the mark with aqua regia solution (5.3); mix well for later use.

5.10 Argon gas. phi(Ar) >= 99.996%.

6 Instruments and equipment

6.1 Inductively coupled plasma atomic emission spectrometer (ICP-AES).

6.2 Analytical balance, with a readability of 0.1 mg.

6.3 Muffle furnace. maximum temperature 1000 °C, temperature control accuracy ±10 °C.

6.4 Ultrasonic cleaner. Operating at room temperature.

6.5 Graphite crucible. Machined from spectrally pure graphite rods; see Appendix A for specific dimensions. Commercially available similar products may also be used.

6.6 Test instruments and equipment shall be verified or calibrated and within their validity period.

7 Samples

7.1 In accordance with the relevant provisions of GB/T 14505, the particle size of the processed sample shall be less than 74 µm.

7.2 The sample shall be pre-dried at 105 °C for 2 h ~ 4 h, then placed in a desiccator and cooled to room temperature.

7.3 For rocks that readily absorb water, use an air-dried sample; simultaneously with weighing the sample for the test, determine the adsorbed water content in accordance with GB/T 14506.1; report the calculated results on a dry-mass basis.

7.4 Weigh 0.1 g of the sample, to an accuracy of 0.1 mg; this constitutes the test sample.

8 Test procedure

9 Processing of test data

The content of the analyte i in the sample is expressed as a mass fraction wi (in percentage, %); calculate it using formula (1).

When expressed in micrograms per gram (µg/g), calculate it using formula (2). In formulas (1) and (2). rhoi - Mass concentration of the analyte in the sample measurement solution, in micrograms per milliliter (µg/mL);

rhoi0 - Mass concentration of the analyte in the blank test solution (8.2), in micrograms per milliliter (µg/mL);

V0 - Total volume of the sample solution, in milliliters (mL);

V1 - Volume of the aliquot of the sample solution, in milliliters (mL);

V - Volume of the sample measurement solution, in milliliters (mL); m - Mass of the sample used for the test, in grams (g).

The obtained results are expressed in accordance with GB/T 14505 as. ××.××%, ×.××%, 0.×××%, ××× µg/g, ××.× µg/g, ×.×× µg/g, 0.×× µg/g, 0.0×× µg/g.

10 Precision

10.1 Statistical results regarding the method precision data (repeatability and reproducibility) of the method-lithium metaborate fusion, followed by inductively coupled plasma atomic emission spectrometry (ICP-AES) for the determination of 12 components (including silicon dioxide) in silicate rocks, which is obtained according to the procedures specified in GB/T 6379.2, are presented in Table 2 and the relevant clauses of Appendix C.

10.2 Under repeatability conditions, the absolute difference between two independent test results obtained within the concentration ranges specified in Table 2 shall exceed the repeatability limit (r) in no more than 5% of cases; the repeatability limit (r) is calculated using the equations listed in Table 2.

10.3 Under reproducibility conditions, the absolute difference between two independent test results obtained within the concentration ranges specified in Table 2 shall exceed the reproducibility limit (R) in no more than 5% of cases; the reproducibility limit (R) is calculated using the equations listed in Table 2.

11 Trueness

Using the procedure specified in GB/T 6379.4, the trueness data for the method as obtained by determining 12 components (including silicon dioxide) in silicate rocks, via lithium metaborate fusion and inductively coupled plasma atomic emission spectrometry (ICP-AES), is as shown in the relevant clauses in Appendix C.

12 Quality assurance and control

12.1 For each batch of sample analysis, it shall concurrently perform 2 blank tests, parallel test analyses on 20% ~ 30% of the samples (or 100% parallel test analysis if the total number of samples is 5 or fewer), verification tests using one or two certified reference materials (CRMs) of the same lithology.

12.2 The sample mass used for analysis shall be as close as possible to the mass of the reference material used to prepare the calibration standard solutions.

12.3 To minimize wear on the graphite crucibles, the crucibles containing the weighed sample and flux shall be placed in the muffle furnace, only after the furnace temperature has reached 1000 °C.

12.4 If the melt cannot be completely poured out of the graphite crucible (i.e., residue adheres to the bottom), the sample mass may be reduced, or the amount of lithium metaborate flux increased, to raise the flux-to-sample weight ratio.

12.5 Accurately add the same volume of cadmium internal standard solution (5.7), to equal volumes of the calibration blank, calibration standard solutions, sample solutions.

12.6 Analysts shall be proficient in operating the ICP-AES instrument, understand matrix and background interferences, be capable of performing correct corrections.

12.7 The correlation coefficient gamma for the linear fit of the calibration curve shall be >= 0.999.

12.8 Analysts shall monitor the internal standard signal intensity and the ratio of the analyte signal intensity to the internal standard signal intensity, throughout the sample analysis process. The absolute value of the internal standard signal shall remain within 80% ~ 120% of the initial signal intensity of the calibration blank. If this range is exceeded, the cause shall be analyzed and identified.

12.9 Under repeatability conditions, the absolute difference between two measurement results shall be less than the repeatability limit r given in Table 2; under reproducibility conditions, the absolute difference between single measurement results from different laboratories shall be less than the reproducibility limit R given in Table 2. Otherwise, the cause shall be investigated; the test analysis shall be repeated after correcting the error.

12.10 This Part is applicable to the determination of 12 major components (SiO2, Al2O3, Fe2O3, CaO, MgO, K2O, Na2O, TiO2, MnO, P2O5, Sr, Ba) in silicate rock samples. By separately determining the loss on ignition (LOI), a complete analysis result for the sample can be obtained; the sum of the mass fractions of the major components can reach 99.3% ~ 100.7%.

Appendix A (Informative) Graphite crucible

Appendix B (Informative) Reference operating conditions for the instrument

Taking a specific inductively coupled plasma atomic emission spectrometer as an example, the reference operating conditions for the instrument are shown in Table B.1.

See Table B.2 for the wavelengths, intensities, background correction positions selected for the determination of each element.

Appendix C (Informative) Statistical results of inter-laboratory collaborative tests on accuracy

The repeatability limit and reproducibility limit of the measurement method, as well as the bias of the analytical method, are determined in accordance with GB/T 6379.2 and GB/T 6379.4; the statistical results are presented in Tables C.1 ~ C.12. […]