CN117470942A - Chemical pretreatment method for analysis of supertrace element content of superbedrock - Google Patents

Abstract

The invention discloses a chemical pretreatment method for ultra-trace element content analysis of ultrabasic rocks, and belongs to the technical field of chemical analysis. It includes the following steps: sample decomposition: pre-digestion with hydrochloric acid-hydrofluoric acid, and then using perchloric acid, hydrochloric acid, and boric acid in sequence to completely decompose the sample to obtain a sample solution of 11±0.5 mol/L hydrochloric acid medium; chemical separation and enrichment: Load the sample solution into an exchange column loaded with UTEVA extraction resin and an exchange column with RE extraction resin, and gradually elute matrix elements such as Ca, Mg, Al, K, Na, Ti, Cr, Ni, Ba, Fe, etc. Trace elements analyzed by 0.24±0.02mol/L hydrochloric acid can be directly tested by mass spectrometry. The method of the invention can separate ultra-trace elements from ultrabasic rocks, has high recovery rate and low process background.

Description

A chemical pretreatment method for ultra-trace element content analysis of ultrabasic rocks

Technical field

The invention belongs to the technical field of chemical analysis, and specifically relates to a chemical pretreatment method for ultra-trace element content analysis of ultrabasic rocks.

Background technique

The mantle, which accounts for about 67% of the Earth's total mass, greatly affects the overall composition of the Earth's materials. The analysis of ultrabasic rock samples from the earth's mantle reveals their geochemical characteristics and can explore the evolution of the mantle. However, so far, there is a lack of high-quality ultra-trace element data in mantle rocks that are recognized as important geochemical tracers, which has seriously affected the study of related mantle evolution processes.

Due to the characteristics of the components, the analysis of ultra-trace elements in mantle ultrabasic rocks has the following difficulties: (1) The abundance of most trace elements in ultrabasic rocks is as low as ppb, making accurate analysis very difficult; (2) This type of sample is rich in refractory minerals such as chromite and spinel, which affects the decomposition of the sample; (3) Ultrabasic rock has a high magnesium content, and a considerable amount of magnesium fluoride will be formed during the evaporation process after the sample is acid-dissolved. Insoluble substances seriously affect subsequent chemical processing.

As far as the current analytical instrument conditions are concerned, it is feasible to achieve ultra-trace element analysis of ultrabasic rocks after the sample is completely decomposed and combined with chemical separation and enrichment technology. As the first step to obtain accurate analytical data, it is crucial to select a reasonable and correct chemical pretreatment method based on the composition characteristics of ultrabasic rocks.

Contents of the invention

In view of the above, the purpose of the present invention is to establish a chemical pretreatment method for ultra-trace element content analysis of ultrabasic rocks, including establishing a reasonable and correct sample decomposition method and ultra-trace element chemical separation and enrichment method. Apply it to the analysis and research of geological samples to achieve the purpose of experimental technology serving scientific research.

The present invention adopts the following technical solutions:

A chemical pretreatment method for ultrabasic rock ultra-trace element content analysis, including the following steps:

(1) Sample decomposition: Add the ultrabasic rock sample into the sample dissolver, moisten it with ultrapure water, add concentrated hydrochloric acid and concentrated hydrofluoric acid, and then keep it at 185-195°C for 45-50 hours for digestion; after natural cooling Then add concentrated perchloric acid and evaporate at 145-155°C. Then add concentrated hydrochloric acid and evaporate at 145-155°C. Raise the temperature to 165-175°C. When white smoke no longer appears, add concentrated hydrochloric acid until white smoke no longer appears. Add boric acid at 145-155°C, evaporate to a wet salt state at 145-155°C, add 11±0.5mol/L hydrochloric acid and extract into a centrifuge tube, centrifuge, take the clear liquid and proceed to the next step;

(2) Chemical separation and enrichment: Place the UTEVA resin column above and the RE resin column below to form a UTEVA-RE double column. Load the clear liquid obtained in step (1) onto the UTEVA resin column, using 11±0.5 mol/L hydrochloric acid to elute matrix elements and interfering elements, then separate the UTEVA resin column and RE resin column, then add 10±0.5mol/L nitric acid to the UTEVA resin column to elute Fe, and then add 0.24±0.02mol/L Analyze Hf, Th, U, Nb, Ta, and Zr with hydrochloric acid and collect it in a clean centrifuge tube. Add the internal standard to the collected eluent, shake it up, and accurately adjust the volume for mass spectrometry; add it to the RE resin column. Decompose REE with 0.24±0.02 mol/L hydrochloric acid and collect it in a clean centrifuge tube. Add the internal standard to the collected eluent, shake it up, and accurately adjust the volume before mass spectrometry measurement.

Further, in step (1), 2±0.1mL of concentrated hydrochloric acid and 1±0.1mL of concentrated hydrofluoric acid need to be added for digestion for every 200±1mg of ultrabasic rock sample. Concentrated hydrochloric acid is added in two times, and 0.5±0.1mL is added first. , then add 1.5±0.1mL; when evaporating at 145~155℃, 0.5±0.1mL of concentrated perchloric acid and 0.5±0.1mL of concentrated hydrochloric acid need to be added to every 200±1mg of ultrabasic rock sample; when evaporating at 165~175℃, every 200± 1mg of ultrabasic rock sample needs to be added with 0.5±0.1mL concentrated hydrochloric acid; every 200±1mg of ultrabasic rock sample needs to be added with 1±0.2mL, 0.24±0.02mol/L boric acid; during extraction, every 200±1mg of ultrabasic rock sample needs to be added The sample needs to be extracted by adding 4±0.2mL and 11±0.5mol/L hydrochloric acid, and extracting it twice while hot, 2±0.1mL each time; in step (1), the concentration of concentrated hydrochloric acid is 12±0.5mol/L. The concentration of concentrated hydrofluoric acid is 27.6±0.5mol/L, and the concentration of concentrated perchloric acid is 70% (v/v).

Further, in step (2), UTEVA resin column: the inner diameter of the column is 0.7±0.1cm, the resin amount is 1.5±0.1mL; the UTEVA resin particle size: 50-100μm; the RE resin column: the inner diameter of the column is 0.7±0.1cm, and the resin Volume: 1.5±0.1mL; RE resin particle size: 50-100μm.

Further, in step (2), before use, it is necessary to use high-purity water, 30±0.5mL, 0.05±0.01mol/L hydrochloric acid to pre-clean the resin column, and then use 5±0.1mL, 11±0.5mL mol/L hydrochloric acid to balance the resin column.

Further, in step (2), the amount of supernatant loaded onto the column is 4±0.2mL, and when eluted with 11±0.5mol/L hydrochloric acid, it is divided into three times, each time 2±0.1mL.

Further, in step (2), when adding 10±0.5mol/L nitric acid, add 1.5±0.1mL twice, once.

Further, in step (2), when adding 0.24±0.02mol/L hydrochloric acid to analyze Hf, Th, U, Nb, Ta, Zr and analyze REE, the solution was divided into five times, each time 2±0.1mL.

Further, in step (2), the UTEVA resin and RE resin need to be pre-treated before pre-cleaning. The pre-treatment is to soak in 1.5-2.5 mol/L nitric acid and fully shake, ultrasonic and oscillate for 20-40 minutes to remove Floating objects should be soaked in 1.5~2.5mol/L nitric acid for more than one week and set aside for use.

Further, in step (2), after the UTEVA resin column and RE resin column are used, they are first rinsed with hydrochloric acid with a total volume of 30±0.5mL and a concentration of 0.05±0.1mol/L, and finally with 20±0.1mol/L hydrochloric acid. Elute with 0.5mL ultrapure water.

Further, in step (2), the added internal standard is ¹⁰³ Rh- ¹⁸⁷ Re, and the concentrations of the two internal standard elements in the test solution are both 10ng/mL.

During the sample decomposition process, the sample is first digested with hydrochloric acid-hydrofluoric acid, and then perchloric acid, hydrochloric acid, and boric acid are used to repeatedly digest the sample to completely decompose the sample (including refractory fluorides and refractory minerals), and finally transform It is a sample solution dissolved in 11±0.5mol/L hydrochloric acid medium.

During the decomposition process of the sample, by adding perchloric acid and evaporating by heating, the F in the insoluble magnesium fluoride produced after the high Mg ultrabasic rock is dissolved is volatilized in the form of HF; boric acid is added to form volatile BF ₃ , and To achieve the purpose of fluoride decomposition.

In the chemical pretreatment method, the UTEVA extraction resin and RE extraction resin in the chemical separation and enrichment process are produced by TrisKem International, a French company, with particle sizes of 50-100um; the UTEVA extraction resin exchange column is made of The UTEVA resin homogenate soaked in dilute nitric acid is filled into an empty chromatography column made of PP material with a porous polyethylene gasket. The inner diameter of the column is about 0.7cm, and the resin volume is about 1.5 ml; the RE extraction resin exchange column It is made by filling the RE resin homogenate soaked in dilute nitric acid into an empty chromatography column made of PP with a porous polyethylene gasket. The inner diameter of the column is about 0.7cm, and the resin volume is about 1.5 ml.

The trace elements obtained by the chemical pretreatment were analyzed using a Thermo X Series II inductively coupled plasma mass spectrometer (ICP-MS). For specific mass spectrometry methods, refer to Reference 1.

Document 1: Sun, Y., Sun, S., Wang, C.Y., Xu, P., 2013. Determination of rare earthelements and thorium at nanogram levels in ultramafic samples by inductivelycoupled plasma-mass spectrometry combined with chemical separation and pre-concentration .Geostandards and Geoanalytical Research,37(1):65-76.

During the decomposition of the sample, by adding perchloric acid and relying on heating and evaporation, the F in the insoluble magnesium fluoride produced after the high Mg ultrabasic rock is dissolved is volatilized in the form of HF; boric acid is added to form volatile BF ₃ to achieve For the purpose of fluoride decomposition, the sample solution is loaded into an exchange column loaded with UTEVA extraction resin and an exchange column loaded with RE extraction resin, and Ca, Mg, Al, K, Na, Ti, Cr, Ni, and Ba are gradually eluted , Fe and other matrix elements, Hf, Th, U, Nb, Ta, Zr and REE trace elements analyzed by 0.24mol/L HCl can be directly tested by mass spectrometry. The method of the invention can separate ultra-trace elements from ultrabasic rocks, has high recovery rate and low process background.

Description of the drawings

Figure 1 is a schematic flow chart of the chemical pretreatment method for trace elements of geological samples according to the present invention.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments.

The invention discloses a chemical pretreatment method for ultra-trace element content analysis of ultrabasic rocks. Referring to Figure 1, a preferred embodiment of the present invention uses an exchange column of UTEVA-RE extraction resin to separate matrix elements and interfering elements from geological samples, and separate and enrich target elements, which mainly includes the following steps:

(1) Decomposition of rock samples

Accurately weigh a certain amount of rock powder sample, place it into the inner cup of the double-layer digestion tank, and add an appropriate amount of high-purity concentrated hydrochloric acid (HCl) and an appropriate amount of high-purity concentrated hydrofluoric acid (HF). After capping, put the inner cup into the outer steel sleeve of the digestion tank and place it in the oven for heating at 190°C for more than 48 hours. After cooling, remove the steel sleeve and take out the inner cup. Add an appropriate amount of high-purity concentrated perchloric acid (HClO ₄ ) to the sample solution in the inner cup, place it on an electric hot plate, and heat it to 150°C to evaporate the sample to nearly dryness; add an appropriate amount of concentrated hydrochloric acid to evaporate the sample to nearly dryness; raise the temperature to 170°C, wait until the perchloric acid has emitted all the white smoke, then add an appropriate amount of concentrated hydrochloric acid to ensure that the white smoke has emitted completely; adjust the electric heating plate to 150°C, add an appropriate amount of boric acid (H ₃ BO ₃ ), and steam until it becomes a wet salt; then add 4 Extract the sample into a clean centrifuge tube using 11 mol/LHCl. The extracted sample is centrifuged and the clear liquid is obtained for the next step of resin column separation and enrichment of trace elements.

The principle of the sample decomposition process is as follows: for the decomposition of ultrabasic rocks, refractory minerals such as chromite and spinel must first be taken into consideration. Usually the sample dissolution temperature is not lower than 190°C. When the sampling amount reaches 200 mg, use HCl-HF for pretreatment, and then use HClO ₄ to dissolve to achieve the dissolution of insoluble minerals. During the heating and evaporation of HF, after the high-Mg ultrabasic rock dissolves, Mg will be converted into a large amount of insoluble magnesium fluoride (MgF ₂ ). If it is not completely decomposed during the post-chemical treatment, the residue will be It will encapsulate those elements that are insoluble in fluoride, such as Sr, Ba and REE, etc., resulting in inaccurate analysis results. At the same time, after multiple condition experiments, it was found that the presence of hydrofluoric acid in the completely dissolved sample solution would affect the adsorption efficiency of hafnium (Hf) element by UTEVA resin. Therefore, before the elemental separation of the sample, the fluorine in _MgF2 is evaporated in the form of HF by adding perchloric acid and relying on heating to evaporate. Then the boric acid complexing method is used to utilize the volatile BF ₃ formed to achieve the purpose of decomposing fluoride. For example, for a 200 mg sample, the final boric acid content is determined to be 1 ml to ensure that the hydrofluoric acid in the dissolved sample is eliminated and the hafnium element is not affected and is completely adsorbed by the UTEVA resin.

(2) UTEVA-RE resin column separates and enriches trace elements

UTEVA resin column: The inner diameter of the column is about 0.7cm, and the resin volume is 1.5 ml; UTEVA resin particle size: 50 μm ~ 100 μm. RE resin column: The inner diameter of the column is about 0.7cm, and the resin volume is 1.5 ml; RE resin particle size: 50 μm ~ 100 μm. First, use high-purity water and 30 ml of 0.05 mol/L HCl to pre-clean the UTEVA resin column and RE resin column respectively, and use 5 ml of 11 mol/L HCl to balance the resin column. Subsequently, the UTEVA resin column was placed above and the RE resin column was placed below to form a UTEVA-RE double column. Then, load the 11 mol/L HCl solution of the sample to be separated onto the UTEVA resin exchange column, and elute with 6 ml of 11 mol/L HCl to elute Ca, Mg, Al, K, Na, Ti, Cr, Ni, and Ba Like other matrix elements, Fe is strongly adsorbed by UTEVA resin. Subsequently, the UTEVA resin column and the RE resin column were separated. Then, 3 ml of 10 mol/L nitric acid (HNO ₃ ) was added to the UTEVA resin column to separate the matrix interference element Fe, and then 10 ml of 0.24 mol/L HCl was added to analyze Hf, Th, U, Nb, Ta, and Zr. Add ¹⁰³ Rh- ¹⁸⁷ Re standard solution internal standard to the collected eluent and shake well. After the volume is accurately determined, wait for mass spectrometry measurement. Add 10 ml of 0.24 mol/LHCl to the RE resin column to decompose REE and receive it. Add ¹⁰³ Rh- ¹⁸⁷ Re standard solution internal standard to the collected eluent and shake well. After the volume is accurately determined, wait for mass spectrometry measurement. The specific chemical separation and enrichment process is listed in Table 1.

Table 1: UTEVA-RE column trace element chemical separation and enrichment process

The principle of the chemical separation process is as follows: on a UTEVA resin column, under 11mol/L HCl medium conditions, matrix elements such as Ca, Mg, Al, K, Na, Ti, Cr, Ni, Ba and REE are retained very weakly, and Trace elements such as Hf, Th, U, Nb, Ta, Zr and matrix element Fe have extremely strong retention. Therefore, when loading the 11 mol/L HCl sample solution, matrix elements such as Ca, Mg, Al, K, Na, Ti, Cr, Ni, Ba, and REE quickly pass through the resin column, and can then be further eluted with 10 mol/L HNO ₃ Fe. At this time, trace elements such as Hf, Th, U, Nb, Ta, and Zr are strongly adsorbed by UTEVA resin. Thereafter, since the retention of trace elements such as Hf, Th, U, Nb, Ta, and Zr on the UTEVA resin column under the medium condition of 0.24mol/L HCl is very weak, 0.24mol/L HCl can be used for analysis. On the RE resin column, under 11mol/L HCl medium conditions, matrix elements such as Ca, Mg, Al, K, Na, Ti, Cr, Ni, and Ba are also weakly retained and can be eluted, while REE is strongly retained; Under 0.24mol/L HCl medium conditions, REE retention is very weak and can be resolved. Therefore, the separation process of the present invention has a better separation effect of trace elements.

The UTEVA resin and RE resin need to be pre-treated before the pre-cleaning. The pretreatment is to soak in dilute nitric acid (~2mol/L) and shake thoroughly, ultrasonically vibrate for 30 minutes to remove floating matter, and soak in 2mol/L HNO ₃ for more than a week before use.

After use, the UTEVA column and the RE column are washed sequentially with a volume of 30 ml of 0.05 mol/L HCl and 20 ml of H ₂ O.

It is worth noting that since extraction resin column separation is sensitive to the acidity of HCl and HNO ₃ and the amount of resin, the amount of resin loaded should be accurately controlled when filling the resin column, and the acidity of the eluent should be strictly calibrated.

Compared with the traditional trace element chemical pretreatment process for geological samples, this process can achieve the separation and enrichment of ultra-low-content trace elements, with good matrix element separation effect and high trace element recovery rate.

(3) Determination of trace elements by inductively coupled plasma mass spectrometry

The analytical instrument is a Thermo X Series II inductively coupled plasma mass spectrometer (ICP-MS), which uses solution injection. Since parameter settings such as atomizer gas flow rate, detector voltage and instrument resolution have a great impact on the sensitivity of the instrument, the instrument test conditions must first be optimized when the sample is tested on the machine. A mixed solution of 1ng/ml ⁷ Li, ⁵⁹ Co, ¹¹⁵ In, and ²³⁸ U (0.3 mol/L HNO ₃ ) was used for optimization to enter the mass spectrum calibration within the full mass range. The oxide yields in the analysis were <2% and the doubly charged ion yields were <5%. Then measure the standard blank solution and standard solution to fit the calibration curve. Test the quality control sample (international standard reference material or standard solution) every 10 sample solutions to monitor and correct the drift of the instrument. Between each sample analysis, clean the sampling system with 0.3mol/L _HNO3 and ultrapure water.

For specific mass spectrometry measurement and data processing methods, please refer to Reference 1.

Advantages of the present invention: The method established by the present invention can realize the separation of trace elements from sample matrix elements and interfering elements, and has the characteristics of good separation effect, high recovery rate, low process background, etc., and is particularly suitable for carrying out ultra-trace analysis in ultrabasic rocks. High-precision analysis of elements.

The chemical pretreatment method for ultra-trace element content analysis of ultrabasic rocks according to the present invention will be further described below with reference to specific embodiments. Examples of raw materials and equipment selected in the examples are introduced below:

1) Excellent grade pure (GR grade) hydrochloric acid, nitric acid, and hydrofluoric acid: produced by China Sinopharm Chemical Reagent Co., Ltd., all of which have been sub-boiling distilled by Savillex ^TM acid purifier (produced by the American Minnetonka Company, which does not reach the boiling point for distillation and purification) Purify.

2) Perchloric acid: 70% (v/v), produced by Aldrich Company of the United States.

3) Boric acid: The concentration is 0.24mol/L, purified by AG50W-X12 resin.

4) Ultrapure water: prepared by the American Thermo GenPure UV xCAD Plus system, the outlet water resistivity is 18.2MΩ/cm (25℃).

5) Double-layer digestion tank: Produced by Nanjing Zhenghong Company. The outer tank is made of national standard non-magnetic stainless steel and has a circular tongue-and-groove seal design. It is manually screw-fastened and has a vent hole; the inner cup is a 15 ml Telfon sample dissolver. Before use, the sampler must be refluxed and cleaned at 120°C with superior grade pure nitric acid, superior grade pure hydrochloric acid and ultrapure water;

6) UTEVA resin: produced by French TrisKem International (Part.no., UT-B25-S), resin particle size 50~100μm;

7) RE resin: produced by French TrisKem International (Part.no., RE-B25-S), resin particle size 50~100μm;

8) UTEVA resin column: Polyethylene column (Poly-Prep columns, Bio-Rad Laboratories Inc., USA) is 6cm long, with an inner diameter of about 0.7cm, and a porous polyethylene gasket at the lower end, filled with UTEVA extraction resin (particle size 50 -100μm) about 1.5 ml.

9) RE resin column: Polyethylene column (Poly-Prep columns, Bio-Rad Laboratories Inc., USA) is 6cm long, with an inner diameter of about 0.7cm, and a porous polyethylene gasket at the lower end, filled with RE extraction resin (particle size 50 -100μm) about 1.5 ml.

10) Inductively coupled plasma-mass spectrometry (ICP-MS): produced by Thermo-Fisher Company of the United States, model X Series II;

11) Rock standard samples: United States Geological Survey (USGS) JP-1 (peridotite), DTS-2B (dunite), national ultrabasic rock composition analysis standard material DZ∑-2.

12) All sample dissolution and chemical separation experimental operations of the present invention are performed in a Class 100 fume hood and Class 100 clean bench in a Class 1,000 clean room to obtain a low blank background value for elemental processes.

Example 1: Trace element analysis of peridotite international rock standard sample JP-1

(1) Dissolve sample: Accurately weigh about 200 mg of JP-1 peridotite standard sample powder, place it into a polytetrafluoroethylene sample dissolver in a double-layer digestion tank, and add about 0.2 ml of ultrapure water to moisten it. Add purified 12 mol/L concentrated hydrochloric acid and 27.6 mol/L concentrated hydrofluoric acid [volume ratio of concentrated hydrochloric acid: concentrated hydrofluoric acid = 2:1, first add 0.5 ml of concentrated hydrochloric acid dropwise, wait until the sample has no reaction (no longer produced) bubbles), then add 1.5 ml of concentrated hydrochloric acid and 1 ml of concentrated hydrofluoric acid]. After capping, put it into the outer steel sleeve of the digestion tank. Tighten the steel sleeve cover and place it in the oven and keep it at 190°C for 48 hours. After natural cooling, remove the steel sleeve and take out the PTFE sample dissolver. Add 0.5 ml of 70% (v/v) concentrated perchloric acid to the sample solution in the polytetrafluoroethylene sample dissolver and place it on the electric hot plate. Evaporate to nearly dryness at 150°C. Add 0.5 ml of 12 mol/L concentrated hydrochloric acid and evaporate to nearly dryness. Dry. Raise the temperature to 170°C and wait until the perchloric acid has emitted all the white smoke, then add 0.5 ml of 12mol/L concentrated hydrochloric acid to ensure that the white smoke has emitted completely. Add 1 ml of 0.24 mol/L boric acid, steam at 150°C until it becomes a wet salt, add 4 ml of 11 mol/L HCl and extract into a centrifuge tube (extract twice while hot, 2 mL each time). The extracted sample was centrifuged (4000 rpm, 5 minutes) and left to stand overnight until loaded onto the column.

(2) Chemical separation and enrichment: See Table 1 for the chemical separation and enrichment process. UTEVA resin column: The inner diameter of the column is about 0.7cm, and the resin volume is 1.5 ml; UTEVA resin particle size: 50 μm ~ 100 μm. RE resin column: The inner diameter of the column is about 0.7cm, and the resin volume is 1.5 ml; RE resin particle size: 50 μm ~ 100 μm. First, use 20 ml of high-purity water and 30 ml of 0.05 mol/L HCl to pre-clean the resin column, and then use 5 ml of 11 mol/L HCl to balance the resin column. Then, place the UTEVA resin column above and the RE resin column below to form a UTEVA-RE double column. Load the 11 mol/L HCl solution of the sample to be separated onto the UTEVA resin column (volume on the column: about 4 ml), and carefully drip 1 ml (0.5 ml each time, twice) of 11 mol/L HCl along the inner wall of the column tube. , and then rinse with 6 ml of 11mol/L HCl. Subsequently, the UTEVA resin column and the RE resin column were separated. Then, first add 3 ml (1.5 ml each time, divided into 2 times) of 10mol/L HNO ₃ into the UTEVA resin column, and then add 10 ml (2 ml each time, divided into 5 times) of 0.24mol/L HCl to analyze Hf, Th, U, Nb, Ta, and Zr are collected in a clean centrifuge tube. Add ¹⁰³ Rh- ¹⁸⁷ Re standard solution internal standard to the collected eluent and shake well. After accurately determining the volume, wait for mass spectrometry measurement. The concentrations of the two internal standard elements ¹⁰³ Rh- ¹⁸⁷ Re in the test solution are both 10ng/ mL. Add 10 ml (2 ml each time, 5 times) of 0.24 mol/L HCl to the RE resin column to resolve the REE and collect it in a clean centrifuge tube. Add ¹⁰³ Rh- ¹⁸⁷ Re standard solution internal standard to the collected eluent and shake well. After accurately determining the volume, wait for mass spectrometry measurement. The concentrations of the two internal standard elements ¹⁰³ Rh- ¹⁸⁷ Re in the test solution are both 10ng/ mL.

(3) Determination of trace elements by inductively coupled plasma mass spectrometry

The Thermo X Series II inductively coupled plasma mass spectrometer (ICP-MS) uses solution injection. First, a mixed solution of ⁷ Li, ⁵⁹ Co, ¹¹⁵ In, and ²³⁸ U in 0.3 mol/L HNO ₃ with a concentration of 1 ng/ml was used for optimization. Then measure the standard blank solution and standard solution (the blank solution is a 0.3mol/L HNO ₃ solution containing ¹⁰³ Rh- ¹⁸⁷ Re internal standard; the standard solution is Hf, U, Nb, Ta, Zr, REE containing ¹⁰³ Rh- ¹⁸⁷ Re internal standard and Th; the concentration of the two internal standard elements in the blank solution and standard solution is 10ng/mL, and 0.3mol/L HNO ₃ is used as the dissolution medium; the concentration gradient of trace elements in the standard solution is: 0ng/ml, 0.1ng /ml, 1ng/ml, 10ng/ml) to fit the calibration curve. The mass spectrometry scanning mode is peak-shaving mode, each mass integration time is 10 ms, the number of data measurement groups is 5 times, and the number of scans per time is 100 times. The oxide yields in the analysis were <2% and the doubly charged ion yields were <5%. Between each sample analysis, clean the sampling system with 0.3mol/L _HNO3 and ultrapure water. For specific mass spectrometry measurement and data processing methods, please refer to Reference 1.

The trace element determination results of the peridotite international rock standard sample JP-1 are shown in Table 2.

Example 2: Trace element analysis of dunite international rock standard sample DTS-2B

Example 2 is the same as Example 1, except that the geological sample selected in this example is the dunite international rock standard sample DTS-2B, which has an overall lower trace element content than JP-1. The measurement results are shown in Table 3.

Repeatability test results of trace element content of rock standard samples

Table 2: Analysis and determination results of trace element content of rock standard sample JP-1

Table 3: Analysis and determination results of trace element content of rock standard sample DTS-2B

Reference 2: Makishima, A., Nakamura, E., 2007. Determination of major, minor and trace elements in silicate samples by ICP-QMS and ICP-SFMS applying isotope dilution-internal standardisation (ID-IS) and multi-stage internal standardisation. Geostandards and Geoanalytical Research,30(3):245-271.

Reference 3: Barrat, J.A. et al., 2008. Geochemistry of diogenites: Stillmore diversity in their parental melts. Meteoretics And Planetary Science, 43(11):1759-1775.

Reference 4: Babechuk, M.G., Kamber, B.S., Greig, A., Canil, D., Kodolányi, J., 2010. The behavior of tungsten during mantle melting revisited with implications for planetary differentiation time scales. Geochimica etCosmochimica Acta, 74( 4):1448-1470.

Reference 5: Rospabé, M., Benoit, M., Candaudap, F., 2018. Determination oftrace element mass fractions in ultramafic rocks by HR-ICP-MS: a combined approach using a direct digestion/dilution method and preconcentration bycoprecipitation. Geostandards and Geoanalytical Research,42(1):115-129.

Reference 6: Robin-Popieul, C.C.M.et al., 2012. A new model for Barbertonkomatiites: deep critical melting with high melt retention. Journal of Petrology, 53(11): 2191-2229.

Reference 7: Debret, B. et al., 2019. Shallow forearc mantledynamics and geochemistry: New insights from IODP expedition 366. Lithos: An International Journal of Mineralogy, Petrology, and Geochemistry, 326-327(22):230-245.

Rock standard samples with different trace element contents were used to test the reliability and reproducibility of the measurement results, as shown in Table 2-3. The results showed that the trace element content determination results of JP-1 and DTS-2B were consistent with the published data. The precision of repeated measurement results for most elements is better than 10%. The UTEVA-RE resin combination of the present invention can perform high-efficiency chemical separation of trace elements on geological samples with ultra-low trace element content, and the solution obtained by separation can be directly analyzed by ICP-MS for high-precision element content.

Sample recovery, blank background value and detection limit

In the embodiment of the present application, in the process of establishing a chemical separation process experiment, an elution curve experiment was conducted using the ultrabasic rock component analysis standard material DZ∑-2 and the trace element mixed standard solution. The major elements of the elution curve were measured by inductively coupled plasma spectrometry (ICP-OES) (IRISAdvantage ICPOES produced by Thermo-Fisher Scientific Company of the United States), and the trace elements were measured by inductively coupled plasma mass spectrometry (produced by Thermo-Fisher Scientific Company of the United States, model X Series II) determination. After loading the sample, use 6 ml of 11 mol/L HCl to elute, and matrix elements such as Ca, Mg, Al, K, Na, Ti, Cr, Ni, Ba, etc. can be completely eluted. The UTEVA single column uses 3 ml of 10 mol/L HNO ₃ to further elute Fe, and 10 ml of 0.24 mol/L HCl can completely resolve Hf, Th, U, Nb, Ta, and Zr. RE single column can completely resolve REE using 10 ml of 0.24mol/L HCl. The recovery rates of each element are shown in Table 4.

Table 4: Recovery rate, full process blank and detection limit of the chemical pretreatment method for trace elements of geological samples according to the embodiment of the present invention

As can be seen from Table 4, the recovery rate of Hf, Th, U, Nb, Ta, and Zr is >94%, and the recovery rate of REE is >95%.

In summary, the separation process of the present invention has the characteristics of good separation effect and low process background, and is particularly suitable for ultra-trace sample analysis. In addition, since the extraction resin is made by coating the extraction agent on an inert carrier material, long-term use of the exchange column may cause the loss of the extraction agent on the resin, resulting in changes in the elution curve. At the same time, the resin may have a memory effect, and repeated use may cause cross-contamination between samples. Therefore, it is recommended to review the elution profile and recovery rate regularly.

The above descriptions are only preferred embodiments of the present invention. It should be noted that those skilled in the art can make improvements or changes based on the above descriptions, and all these improvements and changes should belong to the appended claims of the present invention. scope of protection.

Claims (10)

1. A chemical pretreatment method for ultrabasic rock ultra-trace element content analysis, which is characterized by including the following steps: (1) Sample decomposition: Add the ultrabasic rock sample into the sample dissolver, moisten it with ultrapure water, add concentrated hydrochloric acid and concentrated hydrofluoric acid, and then keep it at 185~195°C for 45~50 hours for digestion; after natural cooling Then add concentrated perchloric acid, evaporate at 145~155℃, then add concentrated hydrochloric acid, evaporate at 145~155℃, raise the temperature to 165~175℃. When white smoke no longer appears, add concentrated hydrochloric acid until white smoke no longer appears. Add boric acid at 145~155℃, evaporate to wet salt form at 145~155℃, add 11±0.5 mol/L hydrochloric acid and extract into a centrifuge tube, centrifuge, take the clear liquid and proceed to the next step; (2) Chemical separation and enrichment: Place the UTEVA resin column above and the RE resin column below to form a UTEVA-RE double column. Load the clear liquid obtained in step (1) onto the UTEVA resin column, using 11±0.5 mol/L hydrochloric acid to elute matrix elements and interfering elements, then separate the UTEVA resin column and RE resin column, then add 10±0.5 mol/L nitric acid to the UTEVA resin column to elute Fe, and then add 0.24±0.02 mol/L Analyze Hf, Th, U, Nb, Ta, and Zr with hydrochloric acid and collect it in a clean centrifuge tube. Add the internal standard to the collected eluent, shake it up, and accurately adjust the volume for mass spectrometry; add it to the RE resin column. Decompose REE with 0.24±0.02 mol/L hydrochloric acid and collect it in a clean centrifuge tube. Add internal standard to the collected eluate, shake well, and accurately adjust the volume before mass spectrometry measurement. 2. The chemical pretreatment method for ultra-trace element content analysis of ultrabasic rocks according to claim 1, characterized in that in step (1), 2±0.1 mL of concentrated hydrochloric acid needs to be added for every 200±1 mg of ultrabasic rock samples. , 1±0.1mL concentrated hydrofluoric acid for digestion, concentrated hydrochloric acid is added in two times, first add 0.5±0.1mL, then add 1.5±0.1mL; when evaporating at 145~155℃, every 200±1 mg of ultrabasic rock sample is required Add 0.5±0.1mL concentrated perchloric acid and 0.5±0.1mL concentrated hydrochloric acid; when evaporating at 165~175℃, add 0.5±0.1mL concentrated hydrochloric acid for every 200±1 mg of ultrabasic rock sample; for every 200±1mg of ultrabasic rock sample The sample needs to add 1±0.2mL, 0.24±0.02mol/L boric acid; during extraction, every 200±1mg ultrabasic rock sample needs to add 4±0.2mL, 11±0.5mol/L hydrochloric acid for extraction; in step (1) , the concentration of concentrated hydrochloric acid is 12±0.5 mol/L, the concentration of concentrated hydrofluoric acid is 27.6±0.5 mol/L, and the concentration of concentrated perchloric acid is 70% (v/v). 3. The chemical pretreatment method for ultra-trace element content analysis of ultrabasic rocks according to claim 1, characterized in that in step (2), UTEVA resin column: the inner diameter of the column is 0.7±0.1cm, and the resin amount is 1.5± 0.1mL; UTEVA resin particle size: 50-100μm; RE resin column: column inner diameter is 0.7±0.1cm, resin volume 1.5±0.1mL; RE resin particle size: 50-100μm. 4. The chemical pretreatment method for ultra-trace element content analysis of ultrabasic rocks according to claim 3, characterized in that in step (2), before use, 20±1mL high-purity water, 30±0.5mL, 0.05 Pre-clean the resin column with ±0.01mol/L hydrochloric acid, and then balance the resin column with 5±0.1 mL and 11±0.5 mL mol/L hydrochloric acid. 5. The chemical pretreatment method for ultra-trace element content analysis of ultrabasic rocks according to claim 1, characterized in that in step (2), the amount of clear liquid loaded onto the column is 4 ± 0.2 mL, and 11 ± 0.5 is used. When eluting with mol/L hydrochloric acid, divide it into three times, 2±0.1 mL each time. 6. The chemical pretreatment method for ultra-trace element content analysis of ultrabasic rocks according to claim 1, characterized in that in step (2), when adding 10 ± 0.5 mol/L nitric acid, add 1.5 mol/L nitric acid twice and once. ±0.1mL. 7. The chemical pretreatment method for ultra-trace element content analysis of ultrabasic rocks according to claim 1, characterized in that in step (2), 0.24±0.02mol/L hydrochloric acid is added to analyze Hf, Th, U, and Nb , Ta, Zr and when analyzing REE, it was divided into five times, 2±0.1 mL each time. 8. The chemical pretreatment method for ultra-trace element content analysis of ultrabasic rocks according to claim 1, characterized in that in step (2), the UTEVA resin and RE resin need to be pre-treated before pre-cleaning, The pretreatment is to use 1.5~2.5 mol/L nitric acid to soak and fully shake and ultrasonic vibrate for 20~40 minutes to remove floating matter, and then soak in 1.5~2.5 mol/L nitric acid for more than a week before use. 9. The chemical pretreatment method for ultra-trace element content analysis of ultrabasic rocks according to claim 1, characterized in that in step (2), after using the UTEVA resin column and RE resin column, first use the total Elute with hydrochloric acid with a volume of 30±0.5mL and a concentration of 0.05±0.01 mol/L, and finally rinse with 20±0.5mL of high-purity water. 10. The chemical pretreatment method for ultra-trace element content analysis of ultrabasic rocks according to claim 1, characterized in that in step (2), the added internal standard is ¹⁰³ Rh- ¹⁸⁷ Re, and the two internal standard elements The concentrations in the test solutions are all 10ng/mL.