This method specifies the determination method of iodine content in geochemical samples.
This method is suitable for the determination of iodine content in river sediments and soil samples.
The detection limit (3s) of this method 3S):0.2 μ g/g iodine.
The determination range of this method is 0.6 μ g/g ~ 500 μ g/g iodine.
2 normative reference documents
In this part of this method, the clauses in the following documents become clauses of this part by reference.
The latest version of the following undated reference documents is applicable to this method.
Compilation rules of GB/T 2000 1.4 Standard Part 4: Chemical analysis methods.
GB/T 14505 general rules for chemical analysis methods of rocks and ores.
Precision of GB 6379 test method The repeatability and reproducibility of standard test method are determined by interlaboratory tests.
GB/T 14496—93-93 geochemical exploration terms.
3 method summary
The sample was mixed with mixed reagent (Na2CO3∶ZnO=3∶2), sintered and leached with water. After a large number of matrices (cations) were separated by static exchange with hydrogen cation exchange resin, the iodate was reduced to iodine ions with ascorbic acid, and the sample solution was injected into the instrument, which was carried by [C (Nano3) = 0.0 15 mol/L] sodium nitrate eluent. In the separation column, iodine ion is separated from other anions by elution and exchange, and then the current value generated by the oxidation reaction of iodine ion on the silver working electrode is measured by electrochemical detector. The recorder records the peak height value of iodine ion concentration, and at the same time measures the peak height value of each iodine ion concentration on the working curve, respectively finds the iodine content in the test solution on the corresponding working curve, and calculates the iodine amount.
4 reagent
Unless otherwise specified, only analytically pure reagents and deionized water (conductivity < 1 μ s/cm) are used in the analysis.
4. 1 anhydrous ethanol
4.2 sodium carbonate and zinc oxide mixed reagent
Sodium carbonate (excellent grade pure) and zinc oxide (excellent grade pure) are fully mixed according to the ratio of 3: 2 for standby.
4.3 sulfuric acid (ρ1.84g/ml)
4.4 sulfuric acid solution [c (1/2h2so4) = 2mo1/l]
Take out 42 ml of sulfuric acid (4.3) and slowly add it into 700 ml of water, and stir it evenly for later use.
4.5 Type 732 cation exchange resin (50 ~ 100 mesh)
Soak in water first and wash it several times. Then, the resin was put into a glass column with a diameter of about 1.5cm and a length of about 30cm, and the top end was connected with a pear-shaped separating funnel. Add 150mL sulfuric acid solution (4.4) into the separatory funnel and flow through the exchange column at a flow rate of about 1.5ml/min. Water flows through the exchange column at the same flow rate until the effluent is washed without sulfate. Vacuum filter the regenerated resin to dryness and bottle it for later use. The cation exchange resin statically exchanged by this method is collected and can be regenerated by the above steps, and then continuously used.
4.6 Ascorbic acid solution [ρ (C6H8O) = 15g/L]
Weigh 0. 15g ascorbic acid and dissolve it in 10mL water. Prepare in time.
4.7 sodium hydroxide solution [c (NaOH) = 0. 1 mol/l]
Weigh 4.0g sodium hydroxide and dissolve it in 100mL water. Prepare in time.
4.8 sodium nitrate solution [c (nano3) = 0.0 15mol/l]
Weigh 1.275g sodium nitrate [containing Ag < 100 ng] and dissolve it in 1000mL water. Prepare in time.
4.9 iodine standard solution
4.9. 1 iodine standard solution I [ρ (I-) = 1000mL g/ml] weigh 0. 1308g of high-purity potassium iodide dried at 105℃/h and put it in a 250mL beaker.
4.9.2 Transfer iodine standard solution II [ρ (I-) =10 μ g/ml] 10.0mL iodine standard solution I (4.9.1), put it in a 100mL volumetric flask, and add/kloc-
4.9.3 Transfer iodine standard solution III [ρ (I-) =1.0 μ g/ml] 10.0mL iodine standard solution II (4.9.2), put it in a 100mL volumetric flask, and add1.0. Prepare in time.
5 Instruments and materials
5. 1 DIONEX-2020i ion chromatograph
5.2 DIONEX separation tower
HPIC-AG5(4 mm× 50 mm), HPIC-AS5(4 mm× 250 mm)
5.3 amp detector
5.4 Silver working electrode
5.5 recorder
The measuring range is1mv ~10mv.
Six analysis steps
6. 1 sample
The sample size should be less than 0.097mm, dried at 60℃ for 2 hours, and put in a dryer for later use.
The sample size is 0. 1g~0.5g ~ 0.5g, and the precision is 0.0002g.
6.2 blank experiment
Two blank tests were carried out in the whole process of sample analysis.
6.3 Quality control
Select 2 ~ 4 samples of the same type of river sediments or soil first-class reference materials and analyze them synchronously with the samples.
6.4 decision
6.4. 1 Weigh the sample (6. 1) and put it in a porcelain crucible filled with 1.5g mixed flux of sodium carbonate and zinc oxide (4.2) in advance, stir it evenly, and cover it evenly with 1.5g mixed flux of sodium carbonate and zinc oxide, then put it in a muffle furnace, and raise the temperature from low temperature to 750. Pour the glass frit into a 100mL beaker, clean the crucible with hot water, add a few drops of anhydrous ethanol and 20mL of water, boil and cool, move the solution and precipitate together into a 50mL colorimetric tube, dilute it to scale with water, shake it evenly, and let it stand for clarification.
6.4.2 Suck 5.0mL of clear liquid (6.4. 1) and put it in a 50mL dry beaker, add 0. 1mL ascorbic acid solution (4.6) and shake it evenly, then add 5g of cation exchange resin (4.5). In the process of static exchange, it is necessary to shake it for 2 ~ 3 times until the solution is slightly acidic, and then let it stand for 30min (about 2 hours in total).
6.4.3 Suck out 3mL of the preparation solution (6.4.2) after static exchange with a syringe, put it in a small dry beaker of 10mL, and adjust the test solution to pH 7-8 with sodium hydroxide solution (4.7) (about 0. 15 ml sodium hydroxide).
6.4.4 Debug the instrument according to its working conditions (see Appendix A). After the baseline is stable, suck 1.0mL clear solution (6.4.3) with a syringe, inject it into the instrument (injection valve), pass through the exchange column, and flow through the amperometric detector. The recorder records the peak height of iodine ion concentration and measures the peak height of each iodine ion concentration on the working curve. Find the corresponding iodine amount from the working curve.
Note: After testing five kinds of test solutions, check whether the peak height of a certain iodine concentration on the measurement curve is deviated, so as to monitor the stability of the instrument and improve the accuracy of measurement.
6.4.5 Draw the working curve. Transfer 0.0mL, 0.25mL, 0.50mL, 1.00mL, 1.50mL, 2.00mL and 2.50mL iodine ion standard solutions (4.9.3) respectively, put them in a group of 50mL volumetric flasks, add 0.20mL sodium hydroxide solution (4.7) and dilute them with water. The following operations shall be carried out according to (6.4.4). After the measurement, the working curve of iodine is drawn with iodine ion concentration as abscissa and peak height as ordinate.
7 Calculation of analysis results
Calculate the iodine content according to the following formula:
Analysis method of regional geochemical exploration samples
Where: ρ —— the concentration of iodine in the sample solution found from the working curve, ng/ml; ρ0—— The concentration of iodine in the blank test solution is found from the working curve, ng/ml; V—— total volume of prepared solution, ml; M—— sample quality, g; 1.07—— Dilution coefficient (volume change of measuring liquid caused by adding ascorbic acid and sodium hydroxide in 6.4.2 and 6.4.3).
8 accuracy
See table 1 for the accuracy of iodine content.
Table 1 accuracy [W (I-), 10-6]
Annex a
(Information Appendix)
A. 1 instrument working conditions
See table A. 1.
Table A. 1 instrument working conditions
A.2 electrode activation step
Firstly, the separation column is removed from the chromatograph, then the outlet pipe of the eluent is connected with the inlet pipe of the electrochemical cell through a coupler, and 5mL of iodine ion standard solution ρ(I)= 10.00 mg/L is injected into the instrument twice with a syringe to bring the eluent into the electrochemical cell. The interval between the two is 5 minutes.
Note: Electrode activation is required only after polishing.
Additional record b
(Information Appendix)
B. 1 Statistical data and other data obtained from inter-laboratory test results
See table B. 1.
The precision collaborative test data of this method is obtained by statistical analysis of the results provided by collaborative research of methods in several laboratories.
Table B. 1 does not need to list all the data of each concentration, but at least three or more parameters are listed.
B. 1. 1 lists the number of laboratories with acceptable test results (i.e. laboratory data out of bounds except for the mean and variance tests).
B. 1.2 lists the relative error parameters of the method, and the calculation formula is, in which the average values of several laboratory measurements are given; X0 is the standard value of the first-class reference material.
B. 1.3 lists the precision parameters of the method, and the calculation formula is, where SR is the repeated standard deviation and Sr is the recurring standard deviation. In order to be consistent with the naming of the parameters listed in GB/T2000 1.4, the precision table of this method is called "repeated coefficient of variation" and "repeated coefficient of variation".
B. 1.4 lists the relative accuracy parameters of this method. Relative accuracy refers to the percentage of the measured value (average value) to the true value.
Table B. 1 I Statistical Results Table
additional information
This method was put forward by China Geological Survey.
This method is under the technical centralized control of Wuhan Rock and Mineral Comprehensive Testing Center.
These Measures were drafted by Anhui Institute of Geological Experiment.
The main drafter of this method is She Xiaolin.
The precision collaborative test of this method was organized and implemented by Jiang Baolin and Ye Jiayu of Wuhan Rock and Mineral Comprehensive Testing Center.