Method for determining trace iodine in brine

Abstract

The invention discloses a method for determining trace iodine in brine, which comprises the following steps: step 1, fixing the volume of a sample, dropwise adding sulfuric acid and a sodium nitrite solution, uniformly shaking, and standing, step 2, adding chloroform, carrying out oscillation treatment, and standing for clarification, step 3, separating clarified liquid and transferring a chloroform layer into a colorimetric tube, step 4, heating in a water bath to volatilize the chloroform to obtain pure iodine, 5, determining the intensity by adopting an inductively coupled plasma spectrometry; the trace iodine in the brine is separated by utilizing a sodium nitrite-chloroform extraction method, the operation is relatively simple and convenient, the accuracy is high, the iodine is in a special dark purple color after being dissolved, the observation is convenient, the sample pretreatment is simple and convenient, the influence of matrix salt is eliminated, the chloroform elimination process adopts mild and easy-to-control water bath heating, the system is stable, and the method is suitable for industrial production. The integrity of the sample can be kept.

Description

Technical Field

[0001] The invention relates to the technical field of brine detection, and in particular to a method for determining trace iodine in brine. Background Art

[0002] Iodine is one of the essential trace elements for the human body. When it is deficient or excessive, the body will experience a series of functional, morphological or metabolic disorders, and in severe cases it can cause brain damage.

[0003] At present, the methods for measuring iodine mainly include volumetric method, spectrophotometry, atomic emission method, catalytic kinetic method, reversed-phase ion pair chromatography, gas chromatography, neutron activation analysis, chemical method and the like. However, these methods cannot have the advantages of simple operation and high measurement accuracy. At the same time, it is impossible to observe whether the sample is effectively dissolved during the early stage of sample processing, resulting in complicated detection steps. Therefore, the present invention proposes a method for determining trace iodine in brine to solve the problems existing in the prior art. Summary of the invention

[0004] In view of the above problems, the purpose of the present invention is to propose a method for determining trace iodine in brine. The method for determining trace iodine in brine utilizes sodium nitrite-chloroform extraction to separate trace iodine in brine. The operation is relatively simple and the accuracy is high. After being dissolved, it presents a special deep purple color for easy observation. The preliminary sample treatment is simple and the influence of matrix salt is eliminated. The process of eliminating chloroform adopts mild and easy-to-control water bath heating. The system is stable and the integrity of the sample can be maintained.

[0005] To achieve the purpose of the present invention, the present invention is implemented by the following technical scheme: a method for determining trace iodine in brine, comprising the following steps:

[0006] Step 1: Take 50 ml of the brine solution to be tested, add deionized water to make up to 100 ml and place it in a separatory funnel, then add 0.2-0.5 ml of sulfuric acid and shake well, and finally add 0.15-0.45 ml of sodium nitrite solution and shake well and let stand;

[0007] Step 2: Add 2-9 ml of chloroform to the separatory funnel, add a stopper and shake for 5-50 minutes, then let it stand and wait for clarification;

[0008] Step 3: After the aqueous phase and the organic phase of the solution are completely separated, the chloroform layer is transferred to a colorimetric tube and plugged to obtain an extract, wherein the separated organic phase is dark purple;

[0009] Step 4: Place the extract in a 60°C water bath and heat to evaporate the chloroform until no bubbles are generated in the solution and the solution is in a uniform state, thus separating and obtaining the extract;

[0010] Step 5: Mix the extract with 0.8 mol / L nitric acid and then determine its intensity by inductively coupled plasma spectrometry in a three - level radio - frequency power compensation mode.

[0011] A further improvement lies in that: in Step 1, the sulfuric acid concentration is 10 mol / L, the addition amount is 0.5 ml, the sodium nitrite solution concentration is 0.145 mol / L, and the addition amount is 0.25 ml; after adding sodium nitrite and shaking well, let it stand for 2 min.

[0012] A further improvement lies in that: the chloroform solution in Step 2 is specifically prepared by adding 0.1 - 0.5 wt% of polyoxyethylene ether to pure chloroform; the addition amount of chloroform is 5 ml, and the plug - added oscillation time is 30 min.

[0013] A further improvement lies in that: when the aqueous phase and the organic phase are completely separated in Step 3, the organic phase is dark purple; when transferring the chloroform layer to the colorimetric tube, add 1 - 2 ml of deionized water and shake well.

[0014] A further improvement lies in that: before use, the separating funnel and the colorimetric tube are soaked in a 0.76 mol / L dilute nitric acid solution for 2 h.

[0015] A further improvement lies in that: the three - level radio - frequency power compensation mode in Step 5 is specifically that first, use an 800 W power to stabilize the initial plasma, then use a 1200 W power to detect the iodine signal score range, and finally use a 600 W power to maintain the low - concentration signal. The detected peak - value range wavelength is 200 - 400 nm.

[0016] A further improvement lies in that: the detection limit determined in Step 5 is 0.3 μg / ml.

[0017] The beneficial effects of the present invention are as follows: The present invention uses the sodium nitrite - chloroform extraction method to separate trace iodine in brine. The operation is relatively simple and the accuracy is high. Since its solution shows a special dark purple color, it is convenient for observation. The sample pretreatment is simple, eliminating the influence of matrix salts. The process of eliminating chloroform uses gentle and easy - to - control water - bath heating, and the system is stable, which can maintain the integrity of the sample, avoiding local overheating and sample decomposition that may be brought about by direct flame heating, providing a more accurate method for measuring low - content iodine in brine. Description of the Drawings

[0018] Figure 1 It is the flow chart of the method of the present invention. Detailed Embodiments

[0019] In order to deepen the understanding of the present invention, the following will further elaborate on the present invention in combination with embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0020] Iodine is one of the essential trace elements for the human body. When it is deficient or excessive, the body will have a series of functional, morphological or metabolic disorders, which can cause brain damage in severe cases. my country is an iodine-deficient country. At present, the demand for iodine in my country is 3,000 to 4,000 tons, with an annual growth rate of 20%, but the annual output is only 300 tons. my country has abundant brine resources. Determining the iodine content in brine is of great significance for increasing iodine production.

[0021] In natural brine and salt water, iodine exists in the form of iodide in most cases, but there is also a trace of iodine in the form of organic compound iodate. The iodine ion content in natural brine and salt water varies greatly, ranging from 0.00 to 100 mg / L. The amount of iodine ion content has special significance in geochemistry and prospecting. In some salt deposits, brine and oilfield water, it contains quite high content. In some sodium chloride type water samples, the iodine ion content is very low.

[0022] At present, the methods for measuring iodine mainly include volumetric method, spectrophotometry, atomic emission method, catalytic kinetic method, reversed-phase ion pair chromatography, gas chromatography, neutron activation analysis, chemical method and other methods. However, they cannot combine the advantages of simple operation and high measurement accuracy. At the same time, it is impossible to observe whether the sample is effectively dissolved during the early stage of sample processing, resulting in complicated detection steps.

[0023] Example 1

[0024] according to Figure 1 As shown, this embodiment provides a method for determining trace iodine in brine, comprising the following steps:

[0025] Step 1: Take 50 ml of the brine solution to be tested, add deionized water to make up to 100 ml and place it in a separatory funnel, then add 0.5 ml of 10 mol / L sulfuric acid and shake well, and finally add 0.25 ml of 0.145 mol / L sodium nitrite solution, shake well and let stand for 2 minutes.

[0026] Step 2: Then add 5 ml of chloroform to the separatory funnel, add a stopper and shake for 30 minutes, then let it stand and wait for clarification;

[0027] The chloroform is prepared by adding 0.3 wt % of polyoxyethylene ether into pure chloroform.

[0028] Step 3: After the aqueous phase and the organic phase of the solution are completely separated (the organic phase is dark purple), transfer the chloroform layer to a colorimetric tube and add 1-2 ml of deionized water to shake evenly, then stopper it to prevent chloroform from volatilizing to obtain an extract;

[0029] Step 4: Place the extract in a 60°C water bath and heat to evaporate the chloroform until no bubbles are generated in the solution and the solution is in a uniform state, thus separating and obtaining the extract;

[0030] Step 5: Mix the extract with 0.8 mol / L nitric acid and then determine its intensity by inductively coupled plasma spectroscopy in a three - stage radio frequency power compensation mode;

[0031] Specifically, first use a power of 800 W to stabilize the initial plasma, then use a power of 1200 W to detect the iodine signal score range, and finally use a power of 600 W to maintain the low - concentration signal. The detection peak range wavelength is 200 - 400 nm; the determination detection limit is 0.3 μg / ml.

[0032] Before use, soak the separatory funnel and the volumetric flask with a 0.76 mol / L dilute nitric acid solution for 2 h.

[0033] Example 2

[0034] This example provides a specific experimental process for a method for determining trace iodine in brine.

[0035] Measure 2 portions of 50 ml of the brine solution from Qarhan Salt Lake in Golmud City, Qinghai Province, add water to 100 ml, and place them in 150 - ml separatory funnels respectively;

[0036] To one portion, add 0.5 ml of 10 mol / L sulfuric acid, shake well, then add 0.25 ml of 0.145 mol / L, shake well, and let stand for 2 min;

[0037] Then add 5 ml of chloroform, stopper and shake for 30 min, let stand. After clarification and complete separation of the aqueous phase and the organic phase (at this time the organic phase is dark purple), transfer the chloroform layer into a 25 - ml volumetric flask, and add 1 - 2 ml more of the aqueous solution, stopper to cover the chloroform layer to prevent its volatilization.

[0038] To the other portion, add 10 μg of iodine, add 10 drops (0.5 ml) of 10 mol / L sulfuric acid, shake well, then add 5 drops (0.25 ml) of 0.145 mol / L sodium nitrite solution, shake well, and let stand for 2 min;

[0039] Then add 5 ml of chloroform, stopper and shake for 30 min, let stand. After clarification and complete separation of the aqueous phase and the organic phase (at this time the organic phase is dark purple), transfer the chloroform layer into a 25 - ml volumetric flask, and add 1 - 2 ml more of the aqueous solution, stopper to cover the chloroform layer to prevent its volatilization.

[0040] Use a water bath (60 °C) to heat to volatilize the chloroform and separate out the iodine until there are no bubbles in the solution and it is in a uniform state. Control a 5% nitric acid medium system and measure on the machine.

[0041] Study on the addition amounts of sulfuric acid and sodium nitrite

[0042] The oxidation of iodine by sodium nitrite must be carried out in a certain acidity system and have good oxidizability. If the acidity is not reached, the oxidation is incomplete. If the amount of sodium nitrite is too large, the iodine generated by oxidation will be further oxidized into iodate, resulting in a loss of iodine and failing to achieve the expected effect. See Table 1 for specific data.

[0043] Table 1 Effect of the amount of sulfuric acid and sodium nitrite added

[0044]

[0045] Note: m / μg indicates the mass of iodine in every 100 ml of brine sample, m indicates the mass of iodine, and μg indicates the unit of iodine mass.

[0046] As can be seen from Table 1, an appropriate amount of sodium nitrite forms nitrous acid under strong acidic conditions, which can oxidize iodine ions to elemental iodine, but cannot oxidize elemental iodine to iodate, making the system more stable. However, excessive sodium nitrite will further oxidize iodine, turning elemental iodine into iodic acid, making it impossible to observe stratification with the naked eye, reducing the amount of iodine extracted, or even making it impossible to obtain iodine.

[0047] Study on the amount of chloroform added

[0048] In the sodium nitrite-chloroform extraction method, chloroform is used as an extractant, and its main function is to utilize its strong solubility and high efficiency separation performance to extract the target substance iodine from the brine. The selection of the addition amount to ensure the extraction effect is shown in Table 2 below.

[0049] Table 2 Selection of chloroform addition amount

[0050] Chloroform addition volume / ml Iodine addition amount m / μg Iodine measured value m / μg Iodine recovery rate / % 2.0 10.0 3.90 39.0 3.0 10.0 6.58 65.8 4.0 10.0 8.47 84.7 5.0 10.0 9.52 95.2 6.0 10.0 9.45 94.5 7.0 10.0 9.50 95.0 8.0 10.0 9.35 93.5 9.0 10.0 9.49 94.9

[0051] Note: m / μg indicates the mass of iodine in every 100 ml of brine sample, m indicates the mass of iodine, and μg indicates the unit of iodine mass.

[0052] It can be seen from Table 2 that the addition amount of chloroform at 5 ml can ensure sufficient contact and extraction, which is economical and can achieve the desired effect.

[0053] Study of Oscillation Time

[0054] Oscillation can fully mix the components in the solution and increase the contact area, thereby improving the extraction efficiency. Through oscillation, iodine can be more effectively transferred from the aqueous phase to the organic phase (chloroform). Oscillation helps to break the interfacial tension between the two phases, making it easier for iodine molecules to pass through the interface from the aqueous phase into the organic phase. This step is crucial to achieve efficient interphase transfer from the aqueous phase to the organic phase. Specific experimental data are shown in Table 3 below.

[0055] Table 3 Effect of oscillation time on enrichment efficiency

[0056] Oscillation time / min Iodine addition amount m / μg Iodine measured value m / μg Iodine recovery rate / % 5 10.0 6.08 60.8 10 10.0 7.05 67.5 15 10.0 8.25 78.0 20 10.0 8.57 82.5 25 10.0 9.01 91.5 30 10.0 9.51 101.5 35 10.0 9.49 101 40 10.0 9.50 100.5 45 10.0 9.48 100 50 10.0 9.39 100

[0057] Note: m / μg represents the mass of iodine contained in every 100 ml of the brine sample, m represents the mass of iodine, and μg represents the unit of iodine mass.

[0058] Study on the linear relationship

[0059] Gradually dilute the iodine standard solution of 1 mg / L to 10 μg / L;

[0060] Determine that the salt content in the sample is 15 g / 100 ml. According to this content, prepare a salt solution of the required volume with sodium chloride and distilled water, and prepare a salt solution of the required volume with sodium sulfate and distilled water;

[0061] Use a micro pipette to separately take 0, 0.25, 0.5, 1.5, 2.0, 2.5 ml of the iodine standard solution containing 10 μg / L into two 100 ml volumetric flasks. Add the sodium chloride-type salt solution to 100 ml in one flask, and add the sodium sulfate-type salt solution to the other flask. Transfer the solution to a 150 ml separating funnel and operate according to the steps of the test method. This series corresponds to the sodium chloride-type series with iodine contents of 0, 2.5, 5.0, 10.0, 15.0, 20.0, 25.0 micrograms and the sodium sulfate-type series with iodine contents of 0, 2.5, 5.0, 10.0, 15.0, 20.0, 25.0 micrograms.

[0062] Determine the iodine standard solution series according to the instrument operating conditions. Iodine shows a linear relationship in the range of 0 - 25 μg / L, and the linear relationship is as follows:

[0063] Sodium chloride type: Intensity = 17.30644493 * Concentration + 3.00913954, and the correlation coefficient is 0.99998.

[0064] Sodium sulfate type: Intensity = 21.97627127 * Concentration + 3.96106142, and the correlation coefficient is 1.00000.

[0065] Relative standard deviation

[0066] Continuously determine the 0.00 mg / L standard series points 11 times, and the relative standard deviation is 1.77%, as shown in Table 4 below.

[0067] Table 4 Values of 11 blank determinations

[0068]

[0069]

[0070] Analysis of different samples

[0071] Take 250 ml of brine samples from different mining areas, and add a quantitative iodine standard solution to one of them. Process and measure according to the test method. The sample measurement results and spike recovery rates are shown in Table 5 below.

[0072] Table 5 Analysis Results of Samples

[0073]

[0074] Through the above research and analysis, the optimal usage amounts of various reagents and operating conditions in the present invention are determined. The sulfuric acid dropping amount is 0.5 ml, the sodium nitrite solution dropping amount is 0.25 ml, the chloroform addition amount is 5 ml, and the oscillation duration after adding chloroform is 30 min.

[0075] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for determining trace iodine in brine, characterized in that, It includes the following steps: Step 1: Take 50 ml of the halogenated aqueous solution to be detected, dilute it to 100 ml with deionized water, place it in a separatory funnel, then add 0.2 - 0.5 ml of sulfuric acid and shake well. Finally, add 0.15 - 0.45 ml of sodium nitrite solution, shake well and let it stand still; Step 2: Then add 2 - 9 ml of chloroform to the separatory funnel, stopper it, shake for 5 - 50 min, and then let it stand still until it becomes clear; Step 3: After the aqueous phase and the organic phase of the solution are completely separated, transfer the chloroform layer to a colorimetric tube, stopper it to obtain the extract. The separated organic phase is dark purple; Step 4: Place the extract in a water bath at 60 °C to heat and volatilize the chloroform until there are no bubbles in the solution and it becomes homogeneous, then the extract is separated; Step 5: Mix the extract with 0.8 mol / L nitric acid and then use inductively coupled plasma spectrometry to measure its intensity according to the three - stage radio frequency power compensation mode.

2. The method for determining trace iodine in brine according to claim 1, wherein: In Step 1, the concentration of sulfuric acid is 10 mol / L, the addition amount is 0.5 ml, the concentration of sodium nitrite solution is 0.145 mol / L, and the addition amount is 0.25 ml; after adding sodium nitrite and shaking well, let it stand still for 2 min.

3. The method for determining trace iodine in brine according to claim 1, characterized in that: The chloroform solution in Step 2 is specifically prepared by adding 0.1 - 0.5 wt% of polyoxyethylene ether to pure chloroform; the addition amount of chloroform is 5 ml, and the shaking time after stoppering is 30 min.

4. The method for determining trace iodine in brine according to claim 1, wherein: When the aqueous phase and the organic phase are completely separated in Step 3, the organic phase is dark purple; when transferring the chloroform layer to the colorimetric tube, add 1 - 2 ml of deionized water and shake well.

5. The method for determining trace iodine in brine according to claim 1, wherein: Before use, the separatory funnel and the colorimetric tube are soaked in a 0.76 mol / L dilute nitric acid solution for 2 h.

6. The method for determining trace iodine in brine according to claim 1, wherein: In Step 5, the three - stage radio frequency power compensation mode is specifically to first stabilize the initial plasma with a power of 800 W, then use a power of 1200 W to detect the iodine signal score range, and finally use a power of 600 W to maintain the low - concentration signal. The peak detection wavelength range is 200 - 400 nm.

7. The method for determining trace iodine in brine according to claim 1, characterized in that: The detection limit measured in Step 5 is 0.3 μg / ml.

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