W element separation and high-precision W isotope determination method for ultra-low sample amount rocks

Abstract

The present disclosure provides a method for separating the W element and determining the W isotope of ultra-low sample amount rocks with high precision, comprising: selecting a rock sample to be determined, weighing and dissolving it to obtain a sample solution; using an AG1X8 resin column and a TEVA resin column to perform two-column chemical separation and purification on the sample solution in sequence, separating the W element and obtaining a high-purity W element sample to be determined; establishing a cup structure for determining the W isotope composition and a cup structure for determining the O isotope composition, determining the high-purity W element sample to be determined, and obtaining the W isotope composition of the sample. n WO3 data and all O isotope composition data; n WO3 data is corrected for oxygen removal and W isotope mass fractionation, resulting in highly accurate and precise W isotope ratios. This method reduces chemical process background, improves W recovery, and enhances the accuracy and precision of W isotope measurements.

Description

Technical Field

[0001] The embodiments disclosed herein belong to the technical field of W isotope tracing and dating, and specifically relate to a method for separating the W element in ultra-low sample amount rocks and determining W isotopes with high precision. Background Art

[0002] In cosmochemical and geochemical research, 182 Hf- 182 The W radioisotope system is an important dating and tracing tool. Because its parent element Hf is a strong lithophile element, while its daughter element W is a siderophile element, this special property makes it play an irreplaceable role in the study of the Earth and other planets in the solar system, which is irreplaceable by other isotope systems whose parent and daughter elements are both lithophile (such as Rb-Sr, Sm-Nd, etc.) or siderophile (such as Re-Os, etc.). 182 Hf decays to 182 The half-life of W is only 8.9 Ma, and both Hf and W are trace elements. 182 W / 184 The change in W ratio is less than 10ppm, so 182 W / 184 High-precision determination of the W ratio is particularly important.

[0003] The existing W element separation methods mainly include: 1) using the conventional 2-4 column method to separate W. The 2-4 column separation method is currently commonly used, that is, using anion or cation resins, as well as special resins to gradually separate matrix elements and interfering elements, and finally obtain the purified W element. This method can only achieve high-precision analysis of W isotopes in large sample quantities (the total amount of W is greater than 0.5 micrograms or 1.0 micrograms, and the corresponding rock sample volume requires one to several grams, or even more than ten grams). And the amount of resin and solvent used is large (up to 300

[0004] mL~500mL), the separation process is time-consuming and has high background. For precious extraterrestrial material samples, such as lunar and Martian samples, it cannot meet the requirements of high-precision W isotope determination.

[0005] 2) W is separated using a NaOH alkaline solution precipitation method and a special resin column method. This involves using NaOH to precipitate the matrix elements, evaporating the W-containing supernatant to dryness, and then applying a special resin to further separate the W. This method allows for W separation in small sample sizes (approximately 0.3 g), but it is unable to separate W from major elements such as Na, Mg, and Al. Therefore, for samples with high Na, Mg, and Al content, W isotope determination using TIMS may result in significant matrix interference, affecting the accuracy of W isotope determinations.

[0006] Existing methods for determining W isotopes mainly include: 1) High-precision determination of W isotopes using MC-ICPMS. This method suffers from a strong instrument memory effect, and removing this memory effect when measuring multiple samples is a technical challenge.

[0007] 2) Using conventional thermal ionization mass spectrometry (NTIMS) method, that is, using the traditional 10 11 The Ω amplifier is connected to the Faraday cup and the W 16 The W isotope and interfering element isotope in the form of O3 were determined using 10 12 Ω or 10 13 The Ω amplifier is used to measure the heavy oxygen isotope molecules (W 16 O2 18 This method can only achieve high-precision determination of large sample quantities (the total amount of W is greater than 500 nanograms, and the corresponding rock samples require one to several grams, or even more). For samples that do not meet the requirements, 182 W / 184 The accuracy of W measurement will decrease as the signal intensity of W decreases. In addition, this method can only obtain 18 O / 16 O ratio, and W 16 O2 17 Because the signal is often lower than the detection line, 17 O / 16 O ratio can only be measured by 18 O / 16 The O ratio is calculated based on the assumed O isotope mass fractionation line, and its error and accuracy can lead to 182 W / 184 The precision and accuracy of the W ratio deteriorates.

[0008] In view of the above problems, it is necessary to propose a method for W element separation and high-precision W isotope determination of ultra-low sample amount rocks that is reasonably designed and effectively solves the above problems. Summary of the Invention

[0009] The embodiments of the present disclosure aim to solve at least one of the technical problems existing in the prior art and provide a method for separating the W element and determining the W isotope of ultra-low sample amount rocks with high precision.

[0010] The present disclosure provides a method for separating the W element and determining the W isotope composition of an ultra-low sample amount of rock. The method comprises:

[0011] Selecting a rock sample to be measured and weighing it, and dissolving the weighed rock sample to be measured to obtain a sample solution;

[0012] The sample solution was subjected to two-column chemical separation and purification using an AG1X8 resin column and a TEVA resin column, respectively, to separate and purify the W element, thereby obtaining a high-purity W element sample to be determined;

[0013] The cup structure for determining the W isotope composition and the cup structure for determining the O isotope composition were established respectively, and the isotope thermal ionization mass spectrometry was performed on the high-purity W element sample to be determined, and the W isotope composition was obtained respectively. n WO3 data and all O isotope composition data;

[0014] According to the above-mentioned total O isotope composition data, n The WO3 data were corrected for oxygen removal, and then the W isotope mass fractionation produced during the instrument measurement process was corrected and calculated to obtain W isotope ratios with high accuracy and precision.

[0015] Optionally, the sample solution is subjected to two-column chemical separation and purification using an AG1X8 resin column and a TEVA resin column respectively to separate and purify the W element to obtain a high-purity W element sample to be determined, comprising:

[0016] 2.5 mL to 3.0 mL of AG1X8 resin is loaded into a resin column to obtain the AG1X8 resin column, and the AG1X8 resin column is pretreated;

[0017] The sample solution was evaporated to dryness and redissolved in 0.5 mL to 1 mL of a mixed acid solution of 1 M HCl and 0.5 M HF, and the redissolved sample solution was slowly added to the pretreated AG1X8 resin column;

[0018] Slowly add 6 mL to 7 mL of a mixed acid of 1 M HCl and 0.5 M HF to the AG1X8 resin column to elute the major matrix elements and most of the trace elements;

[0019] Slowly add 6 mL to 7 mL of a mixed acid of 6 M HNO 3 and 0.2 M HF to the AG1X8 resin column to elute some interfering elements and W element;

[0020] The W-containing solution separated by the AG1X8 resin column was evaporated to dryness and then redissolved in 0.3 mL to 0.5 mL of a mixed acid solution of 9 M HCl and 0.02 M HF;

[0021] 0.5 mL to 0.6 mL of TEVA resin is loaded into a resin column to obtain the TEVA resin column, and the TEVA resin column is pretreated;

[0022] Slowly adding the redissolved W-containing solution to the pretreated TEVA resin column;

[0023] Slowly add 2.5 mL to 3.0 mL of a mixed acid of 9 M HCl and 0.02 M HF to the TEVA resin column to elute the remaining interfering elements;

[0024] 2.5 mL to 3.0 mL of a mixed acid of 3 M HCl and 0.02 M HF was slowly added to the TEVA resin column to elute the W element, obtain a high-purity W solution, and complete the separation of the TEVA resin column.

[0025] Optionally, the AG1X8 resin column is pretreated, comprising:

[0026] Slowly add 5 mL to 6 mL of a mixed solution of 6 M HNO 3 and 0.2 M HF to the AG1X8 resin column for the first wash; slowly add 5 mL to 6 mL of a mixed solution of 1 M HCl and 0.5 M HF to the AG1X8 resin column for the second wash;

[0027] Slowly add 5 mL to 6 mL of ultrapure water to the AG1X8 resin column to neutralize the AG1X8 resin column; slowly add 8 mL to 10 mL of a mixed solution of 1 M HCl and 0.5 M HF to the AG1X8 resin column to make the medium of the AG1X8 resin column the same as the medium of the sample dissolution solution.

[0028] Optionally, the TEVA resin column is pretreated, comprising:

[0029] Slowly add 3 mL to 5 mL of a mixed solution of 3 M HCl and 0.02 M HF to the TEVA resin column for the first wash; slowly add 3 mL to 5 mL of a mixed solution of 9 M HCl and 0.02 M HF to the TEVA resin column for the second wash;

[0030] 3 mL to 5 mL of ultrapure water was slowly added to the TEVA resin column to neutralize the TEVA resin column; 3 mL to 5 mL of a mixed solution of 9 M HCl and 0.02 M HF was slowly added to the TEVA resin column to make the medium of the TEVA resin column the same as the medium of the W-containing solution after separation and redissolution of the AG1X8 resin column.

[0031] Optionally, the cup structure established for W isotope composition determination includes:

[0032] 182 WO3 ˉ 、 183 WO3 ˉ 、 184 WO3 ˉand 186 WO3 ˉ The ion beam is connected by the second low cup L2, the first low cup L1, the center cup C and the second high cup H2. 12 Ω amplifier for reception;

[0033] 180 WO3 ˉ The ion beam is connected to the fourth low cup L4 10 13 Ω amplifier for reception;

[0034] 181 TaO3 ˉ The ion beam is connected to the third lower cup L3 10 13 Ω amplifier for reception;

[0035] 185 ReO3 ˉ The ion beam is connected to the first high cup H1 10 11 Ω amplifier for reception.

[0036] Optionally, the cup structure for W isotope composition determination is used to perform isotope thermal ionization mass spectrometry on the high-purity W element sample to be determined, comprising:

[0037] Instrument measurement parameter settings: Measure in the negative ion mode of the TIMS instrument;

[0038] The instrument's baseline is measured once a day before starting measurement, with a pre-wait time of 50 to 60 seconds and a measurement time of 1200 cycles × 1.05 seconds.

[0039] 10 11 Ω, 10 12 Ω and 10 13 The gain of the Ω amplifier is calibrated every three days, and the calibration current is a virtual current of 0.12V;

[0040] The W element of each sample was determined in 40 cycles × 20 blocks, with each data integration period of 16s / 32s, an idle time of 10s to 12s, and peak alignment was performed every 5 blocks;

[0041] During the measurement, the oxygen pressure was maintained at 0.5×10 -7 mbar~1.0×10 -7 mbar, regulated by a micro air valve, each measurement lasts 7.5 to 8 hours, and the evaporation zone temperature is 1300°C to 1350°C during W isotope determination.

[0042] Optionally, the cup structure for determining the O isotopic composition is established, comprising:

[0043] 185Re 16 O4 ˉˉ and 187 Re 16 O4 ˉ The ion beam is connected by the center cup C and the second high cup H2. 12 Ω amplifier for reception;

[0044] 187 Re 16 O3 18 O ˉ The ion beam is connected with the third high cup H3 10 13 Ω amplifier for reception;

[0045] 187 Re 16 O3 17 O ˉˉ The ion beam is received by a secondary ion multiplier (SEM, IC 1C) bound to the central cup C; wherein,

[0046] The position of the cup structure determined by the O isotope composition is the same as the position of the cup structure determined by the W isotope composition.

[0047] Optionally, the cup structure for determining the O isotope composition is used to perform isotope thermal ionization mass spectrometry on the high-purity W element sample to be determined, comprising:

[0048] Before each sample was measured, a Faraday cup was used to statically receive the 185 ReO4 ˉ 、 187 ReO4 - and 187 Re 16 O3 18 O ˉ The SEM peak-jumping method was used to measure the 187 Re 16 O3 17 O ˉ Conducting measurements;

[0049] The analysis parameters for O isotope determination are 20 cycles × 10 blocks, 4 s / 8 s integration, 6 s–8 s idle time, 35–60 min for one measurement, and 700–850 °C evaporation zone temperature for O isotope determination.

[0050] Optionally, obtaining a high-purity W element sample to be determined includes:

[0051] The W element solution obtained by two separations using the AG1X8 resin column and the TEVA resin column was placed on a hot plate and evaporated to dryness, and redissolved in 1 μL to 2 μL of a mixed solution of 7% M HNO 3 and 4% M HF to obtain the high-purity W element sample to be determined.

[0052] Optionally, the n The WO3 data is corrected for oxygen removal, and then the W isotope mass fractionation produced during the instrument measurement process is corrected and calculated to obtain highly accurate and precise W isotope ratios, including:

[0053] According to the determination of ReO4, the accurate three oxygen isotope compositions are calculated, among which the calculation formula of O isotope composition is: 18 O / 16 O=1 / 4×I( 187 Re 16 O3 18 O - ) / I( 187 ReO4 - ), 17 O / 16 O=1 / 4×I( 187 Re 16 O3 17 O - ) / I( 187 ReO4 - );

[0054] Deduct the isotopic interference of TaO3 and ReO3 on WO3;

[0055] Based on the calculated O isotope composition, deoxygenation correction was performed;

[0056] Perform mass fractionation calibration: Use 186 W / 184 W = 0.92767, corrected by exponential law.

[0057] The method for separating the W element and determining the W isotope of ultra-low sample amounts of rocks in the disclosed embodiments adopts a two-column chemical separation method for chemical separation of the W element, which can completely separate the W element from matrix elements and interfering elements. By simplifying the separation process and reducing the amount of resin and solvent used, it not only reduces the background of the chemical process to as low as 40 pg, but also increases the W recovery rate to more than 97%, making high-precision W isotope determination of small sample amounts (20 mg to 400 mg) possible.

[0058] The method for separating W elements and determining W isotopes with high precision in ultra-low sample amount rocks of the present disclosure is based on the established cup structure for determining W isotope composition and the cup structure for determining O isotope composition. 11 Ω, 10 12 Ω and 10 13 The isotope thermal ionization mass spectrometry method of static measurement with three different types of amplifier combinations is used to statically measure low-content or low-sample rock samples of W, obtaining all five isotopes of tungsten and monitoring the isotopic interferences of tantalum and rhenium; through Faraday cup, 10 12 Ω and 10 13 The combination of two different types of amplifiers and an ion counter (SEM IC 1C) and a rationally designed cup structure for the determination of O isotopic composition was used to determine the ReO4 16 O. 17 O and 18 O all three O isotopes, solve the problem of low W signal in small sample amount and the 17 O abundance is too low (natural abundance is about 16 1 / 2600 of O, 18 The problem that accurate and high-precision measurement data of 1 / 5 of O cannot be obtained is solved, and the high-accuracy and high-precision determination of oxygen isotope composition and the high-precision and high-precision test of W isotope are achieved.

[0059] The method for separating W from ultra-low rock sample amounts and determining its high-precision W isotope composition in this disclosure achieves W isotope composition accuracy comparable to that achieved by conventional methods, even with sample amounts that are only 1 / 10 or less of the conventional amount. This method is particularly suitable for precious samples from the Moon and Mars, enabling high-precision data to be obtained even when large sample quantities are unavailable. This provides technical support for scientific research in my country's current lunar and Mars exploration programs. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 This is a flow chart of a method for separating W from ultra-low sample amount rocks and determining W isotopes with high precision according to one embodiment of the present disclosure;

[0061] Figure 2 This is the elution curve of the MISA multi-element mixed solution in one embodiment of the present disclosure. DETAILED DESCRIPTION

[0062] In order to enable those skilled in the art to better understand the technical solutions of the embodiments of the present disclosure, the embodiments of the present disclosure are further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0063] like Figure 1As shown, the embodiment of the present disclosure provides a method S100 for separating the W element and determining the W isotope of ultra-low sample amount rocks. The method S100 includes:

[0064] S110, selecting a rock sample to be measured and weighing it, and dissolving the weighed rock sample to be measured to obtain a sample solution.

[0065] Specifically, the dissolution of silicate samples (including Earth rocks and meteorites)

[0066] The process can be as follows:

[0067] A plurality of rock samples of different lithologies were selected, wherein each sample had a different lithology and W concentration. 20 mg to 400 mg of each rock powder sample was weighed and placed in a 15 mL Teflon bottle.

[0068] Add 1 mL of concentrated HF and 2 mL of concentrated HNO3 into a Teflon bottle respectively, seal the Teflon bottle, place it on a hot plate, and keep it at 120°C for 2 to 5 days.

[0069] The dissolved sample solution was evaporated at 120° C. until dry; 3 mL of 50% by volume concentrated HCl was added again, and the solution was placed on a hot plate and kept warm at 120° C. for 1 day. After dissolution, the solution was evaporated at 120° C. until dry; 1 mL of a mixture of 1 M HCl and 0.5 M HF was added to redissolve the solution to obtain the sample solution.

[0070] Specifically, the dissolution process for iron meteorite samples (including Earth iron metal minerals) can be as follows:

[0071] Weigh about 30 mg to 100 mg of iron meteorite sample and place it in a 15 mL Teflon bottle.

[0072] Add 2 mL of aqua regia to the Teflon bottle and let it stand at room temperature until no reactive gas is generated. Seal the Teflon bottle, place it on a hot plate, and keep it warm at 120°C for 1 day.

[0073] The dissolved sample solution was evaporated at 120° C. until wet to dry; 2 mL of aqua regia was added again, and the sample solution was placed on a hot plate and kept warm at 120° C. for 1 day. After dissolution, the sample solution was evaporated at 120° C. until wet to dry; 1 mL of a mixed solution of 1 M HCl and 0.5 M HF was added to redissolve the sample solution to obtain the dissolved solution.

[0074] S120, using an AG1X8 resin column and a TEVA resin column to perform two-column chemical separation and purification on the sample solution in sequence, separating and purifying the W element, and obtaining a high-purity W element sample to be determined.

[0075] Specifically, a two-column method and acids of different concentrations and types were used to chemically separate and purify the dissolved solution. That is, AG1X8 (100-200 mesh) resin was used to separate W from matrix elements, and TEVA (TE-B100-A, 100 μm-150 μm) resin was used to separate W from interfering elements, thereby obtaining a high-purity W sample to be determined.

[0076] Use AG1X8 resin column for the first column separation:

[0077] First, 2.5 mL to 3.0 mL of AG1X8 resin is loaded into a resin column to obtain the AG1X8 resin column, and the AG1X8 resin column is pretreated.

[0078] Specifically, 2.5 ml of AG1X8 (100-200 mesh) resin was loaded into a polytetrafluoroethylene (PFA) resin column with an inner diameter of 0.7 cm to obtain an AG1X8 resin column.

[0079] The specific process of pre-treating the AG1X8 resin column includes:

[0080] (1) Column cleaning. Slowly add 5 mL to 6 mL of a mixed solution of 6 M HNO3 and 0.2 M HF to the AG1X8 resin column for the first cleaning. Slowly add 5 mL to 6 mL of a mixed solution of 1 M HCl and 0.5 M HF to the AG1X8 resin column for the second cleaning.

[0081] In this embodiment, preferably, 5 mL of a mixed solution of 6 M HNO 3 and 0.2 M HF is slowly added to the AG1X8 resin column for the first wash, and 5 mL of a mixed solution of 1 M HCl and 0.5 M HF is slowly added to the AG1X8 resin column for the second wash.

[0082] (2) Column equilibration. Slowly add 5 mL to 6 mL of ultrapure water to the AG1X8 resin column to neutralize the column. Slowly add 8 mL to 10 mL of a mixed solution of 1 M HCl and 0.5 M HF to the AG1X8 resin column to make the medium of the AG1X8 resin column the same as the sample solution.

[0083] In this embodiment, preferably, 5 mL of ultrapure water is slowly added to the AG1X8 resin column to neutralize the AG1X8 resin column; and 10 mL of a mixed solution of 1 M HCl and 0.5 M HF is slowly added to the AG1X8 resin column to make the medium of the AG1X8 resin column the same as the medium of the upper column sample.

[0084] Secondly, after completing the pretreatment of the AG1X8 resin column, add the re-dissolved sample solution to the AG1X8 resin, and then add different concentrations and types of acids to chemically separate and purify the solution. The specific chemical separation and purification steps are as follows:

[0085] (1) Slowly add 0.5 mL to 1 mL of the sample solution into the pretreated AG1X8 resin column.

[0086] In this embodiment, preferably, 1 mL of the sample solution is slowly added to the pretreated AG1X8 resin column to load the sample solution onto the column.

[0087] (2) 6 mL to 7 mL of a mixed acid of 1 M HCl and 0.5 M HF was slowly added to the AG1X8 resin column to elute the major matrix elements and most of the trace elements.

[0088] In this embodiment, preferably, Figure 2 As shown, 6 mL of a mixed acid of 1 M HCl and 0.5 M HF was slowly added to the AG1X8 resin column to elute the major matrix elements and most of the trace elements.

[0089] (3) Slowly add 6 mL to 7 mL of a mixed acid of 6 M HNO 3 and 0.2 M HF to the AG1X8 resin column to elute some interfering elements and W element.

[0090] In this embodiment, preferably, Figure 2 As shown, 6 mL of a mixed acid of 6 M HNO 3 and 0.2 M HF was slowly added to the AG1X8 resin column to elute the W element. At this time, some interfering elements such as Zr, Ti, Hf, Ta, Re and Os were eluted simultaneously with the W element, completing the separation of the AG1X8 resin column.

[0091] The W-containing solution separated by the AG1X8 resin column was placed on a hot plate and evaporated to dryness, and redissolved in 0.5 mL of a mixed solution of 9 M HCl and 0.02 M HF for the second column separation.

[0092] TEVA resin column was used for the second column separation:

[0093] First, 0.5 mL to 0.6 mL of TEVA resin is loaded into a resin column to obtain the TEVA resin column, and the TEVA resin column is pretreated.

[0094] Specifically, 0.5 mL of TEVA (TE-B100-A, 100 μm to 150 μm) resin was loaded into a PFA resin column with an inner diameter of 0.7 cm to obtain the TEVA resin column.

[0095] The TEVA resin column is pretreated, specifically comprising:

[0096] (1) Column cleaning. Slowly add 3 mL to 5 mL of a mixed solution of 3 M HCl and 0.02 M HF to the TEVA resin column for the first cleaning; slowly add 3 mL to 5 mL of a mixed solution of 9 M HCl and 0.02 M HF to the TEVA resin column for the second cleaning.

[0097] In this embodiment, preferably, 5 mL of a mixed solution of 3 M HCl and 0.02 M HF is slowly added to the TEVA resin column for the first washing; and 5 mL of a mixed solution of 9 M HCl and 0.02 M HF is slowly added to the TEVA resin column for the second washing.

[0098] (2) Column equilibration. Slowly add 3 mL to 5 mL of ultrapure water to the TEVA resin column to neutralize the column. Slowly add 3 mL to 5 mL of a mixed solution of 9 M HCl and 0.02 M HF to the TEVA resin column to ensure that the medium of the TEVA resin column is the same as that of the W-containing solution after separation and redissolution of the AG1X8 resin column.

[0099] In this embodiment, preferably, 5 mL of ultrapure water is slowly added to the TEVA resin column to make the TEVA resin column in a neutral state; 5 mL of a mixed solution of 9 M HCl and 0.02 M HF is slowly added to the TEVA resin column so that the medium of the TEVA resin column is the same as the medium of the W element solution after the AG1X8 resin column is separated and redissolved.

[0100] Secondly, after completing the pretreatment of the TEVA resin column, the re-dissolved W-containing solution is added to the TEVA resin column, and different concentrations and types of acids are added to the re-dissolved W-containing solution for chemical separation and purification. The specific chemical separation and purification is as follows:

[0101] (1) Slowly add 0.3 mL to 0.5 mL of the W-containing solution after separation and redissolution on the AG1X8 resin column to the pretreated TEVA resin column.

[0102] In this embodiment, preferably, 0.5 mL of the W element solution after separation and redissolution on the AG1X8 resin column is slowly added to the pretreated TEVA resin column to load the W element solution sample onto the column.

[0103] (2) Slowly add 2.5 mL to 3.0 mL of a mixed acid of 9 M HCl and 0.02 M HF to the TEVA resin column to elute the remaining interfering elements.

[0104] In this embodiment, preferably, Figure 2 As shown, 2.5 mL of a mixed acid of 9 M HCl and 0.02 M HF was slowly added to the TEVA resin column to elute interfering elements such as Zr, Ti, Hf, Ta, Re, and Os.

[0105] (3) Slowly add 2.5 mL to 3.0 mL of a mixed acid of 3 M HCl and 0.02 M HF to the TEVA resin column to elute the W element, obtain a high-purity W solution, and complete the separation of the TEVA resin column.

[0106] In this embodiment, preferably, Figure 2 As shown, 2.5 mL of a mixed acid of 3 M HCl and 0.02 M HF was slowly added to the TEVA resin column to elute the W element, obtain a high-purity W solution, and complete the separation of the TEVA resin column.

[0107] The separated W element solution was placed on a hot plate and evaporated to dryness, and redissolved in 1 μL to 2 μL of a mixed solution of 7% HNO 3 and 4% M HF to obtain the high-purity W element sample to be measured, which was then used for TIMS instrument measurement.

[0108] In this embodiment, the chemical separation of the W element adopts a two-column chemical separation method, which can completely separate the W element from the matrix elements and interfering elements. By simplifying the separation process and reducing the amount of resin and solvent used, not only the background of the chemical process is reduced to 40 pg, but also the recovery rate of W is increased to 97%, making high-precision W isotope determination of small sample amounts (20 mg to 400 mg) possible.

[0109] S130, respectively establish a cup structure for determining the W isotope composition and a cup structure for determining the O isotope composition, perform isotope thermal ionization mass spectrometry on the high-purity W element sample to be determined, and obtain the W isotope composition n WO3 data and all O isotope composition data.

[0110] Specifically, as shown in Table 1, different types of receivers (FC, SEM) and different types of amplifiers (10 11Ω, 10 12 Ω and 10 13 Ω) to establish the cup structure for the W isotope composition determination. The cup structure for the W isotope composition determination specifically includes:

[0111] Four more abundant 182 WO3 ˉ 、 183 WO3 ˉ 、 184 WO3 ˉ and 186 WO3 ˉ The ion beam is connected by the second low cup L2, the first low cup L1, the center cup C and the second high cup H2. 12 Ω amplifier for reception.

[0112] 180 WO3 ˉ The ion beam is connected to the fourth low cup L4 10 13 Ω amplifier for reception.

[0113] 181 TaO3 ˉ The ion beam is connected to the third lower cup L3 10 13 Ω amplifier for receiving. Among them, 181 TaO3 ˉ Used for monitoring 180 TaO3 ˉ right 180 WO3 ˉ interference.

[0114] 185 ReO3 ˉ Used to monitor heavy oxides 185 Re 16 O2 17 O ˉ right 186 WO3 ˉ Since W isotope determination uses Re band as carrier, the ReO3 signal may be very high. 185 ReO3 ˉ The ion beam is connected to the first high cup H1 10 11 Ω amplifier for reception.

[0115] It should be noted that configuration 10 12 The maximum limit of the ion beam that the Faraday cup of the Ω amplifier can receive in the negative ion state is 1.2V. In this experiment, no diluent was added to the samples used, and the maximum natural abundance was used. 184 W is calculated when 184 WO3 - When the ion beam intensity is 1.2V, 180WO3 - The ion beam intensity is less than 4.7mV and less than 10 13 The maximum voltage that the Faraday cup of the Ω amplifier can receive in the ion beam is 120mV in the negative ion state.

[0116] Table 1 Cup structure composition determined by W isotopic composition

[0117] Receiver L4 L3 L2 L1 C / SEM H1 H2 ion beam <h2 style=";text-align:left;direction:ltr"><![CDATA[ <h2 style=";text-align:left;direction:ltr"> 180 <h2 style=";text-align:left;direction:ltr"> WO3]]><h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"><![CDATA[ <h2 style=";text-align:left;direction:ltr"> 181 <h2 style=";text-align:left;direction:ltr"> TaO3<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"><![CDATA[ <h2 style=";text-align:left;direction:ltr"> 182 <h2 style=";text-align:left;direction:ltr"> WO3]]><h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"><![CDATA[ <h2 style=";text-align:left;direction:ltr"> 183 <h2 style=";text-align:left;direction:ltr"> WO3]]><h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"><![CDATA[ <h2 style=";text-align:left;direction:ltr"> 184 <h2 style=";text-align:left;direction:ltr"> WO3]]><h2 style=";text-align:left;direction:ltr"> <![CDATA[ 185 ReO3]]> <h2 style=";text-align:left;direction:ltr"><![CDATA[ <h2 style=";text-align:left;direction:ltr"> 186 <h2 style=";text-align:left;direction:ltr"> WO3]]><h2 style=";text-align:left;direction:ltr"> Atomic mass 228 229 230 231 232 233 234 Abundance.(%) 0.12 ˉ 26.5 14.3 30.6 ˉ 28.4 Amplifier (Ω) <![CDATA[10 13 ]]> <![CDATA[10 13 ]]> <![CDATA[10 12 ]]> <![CDATA[10 12 ]]> <![CDATA[10 12 ]]> <![CDATA[10 11 ]]> <![CDATA[10 12 ]]>

[0118] The isotope thermal ionization mass spectrometry determination of the high-purity W element to be determined is performed using the cup structure for W isotope composition determination established in Table 1, specifically including:

[0119] Instrument measurement parameter settings: Measure in the negative ion mode of the TIMS instrument.

[0120] The instrument's baseline is measured once a day before starting measurement work, with a pre-wait time of 50 to 60 seconds each time, and a measurement of 1200 cycles × 1.05 seconds. Preferably, a pre-wait time of 60 seconds each time.

[0121] 10 11 Ω, 10 12 Ω and 10 13 The gain calibration of the Ω amplifier is performed every three days, and the calibration current is a virtual current of 0.12V.

[0122] The W element of each sample was measured using 40 cycles × 20 blocks (i.e., 800 data points). Each data point was integrated for 16 seconds / 32 seconds, with an idle time of 10 to 12 seconds. Preferably, each data point was integrated for 32 seconds, with an idle time of 12 seconds. Peak centering was performed every five blocks.

[0123] During the measurement, the oxygen pressure was maintained at 0.5×10 -7 mbar~1.0×10 -7 mbar, regulated by a micro air valve, each measurement lasts 7.5 to 8 hours, and the evaporation zone temperature during W isotope determination is 1300° C. to 1350° C. Preferably, each measurement lasts about 7.5 hours.

[0124] In this embodiment, the cup structure of W isotope composition was determined by using Faraday cup and 10 11 Ω, 10 12 Ω and 10 13The isotope thermal ionization mass spectrometry method for static measurement using three different types of amplifier combinations was used to statically measure low-content or low-sample-amount W rock samples, obtaining all five isotopes of tungsten and monitoring the isobaric interference of tantalum and rhenium, thus achieving low-signal and high-precision static determination of W isotopes.

[0125] More specifically, in this embodiment, the oxygen isotope composition is measured in the form of ReO4. 185 Re 16 O4 (atomic mass 249), 187 Re 16 O4 (atomic mass 251) and heavy oxygen isotopes ( 17 O and 18 Oxide molecules 187 Re 16 O3 17 O 17 O (atomic mass 252) and 187 Re 16 O3 18 O (atomic mass 253) is used to achieve this. Therefore, the structure of the O isotope composition measurement cup shown in Table 2 is established, specifically including:

[0126] 185 Re 16 O4 ˉ and 187 Re 16 O4 ˉ The ion beam is connected by the center cup C and the second high cup H2. 12 Ω amplifier for reception.

[0127] 187 Re 16 O3 18 O ˉ The ion beam is connected with the third high cup H3 10 13 Ω amplifier for reception.

[0128] 187 Re 16 O3 17 O ˉ The ion beam is received by a secondary ion multiplier (SEM, IC 1C) attached to the central cup C.

[0129] As shown in Tables 1 and 2, the position of the cup structure for O isotope composition determination is identical to that for W isotope composition determination. In other words, the positions of all cup structures receiving ReO4ˉ are identical to those receiving WO3ˉ. Therefore, when switching between ReO4ˉ and WO3ˉ measurements, there is no need to adjust or move the Faraday cup position. Instead, the sample can be heated to the lower ReO4 excitation temperature for O isotope determination and then heated to the WO3 excitation temperature for W isotope determination, saving measurement time.

[0130] Table 2 Cup structure composition determined by O isotopic composition

[0131]

[0132] The isotope thermal ionization mass spectrometry determination of the high-purity W element to be determined sample is performed using the cup structure for determination of the O isotope composition shown in Table 2, including:

[0133] Before each sample was measured, the corresponding Faraday cup was used to statically receive the mass numbers 249, 251, and 253 (i.e. 185 ReO4ˉ、 187 ReO4ˉ and 187 Re 16 O3 18 Oˉ) was measured using the SEM peak-jumping method to receive the mass number 252 (i.e. 187 Re 16 O3 17 Oˉ) for determination.

[0134] The O isotope analysis parameters are 20 cycles × 10 blocks (i.e., 200 data points), 4s / 8s integration time, 4s-8s idle time, and a single measurement time of 35-60 minutes. The evaporation zone temperature for O isotope analysis is 700°C-850°C. Preferably, the integration time is 8s, the idle time is 8s, and the single measurement time is 60 minutes.

[0135] In this embodiment, the cup structure for determining the O isotope composition is established in the W isotope determination method to accurately determine the three oxygen isotopes, which is not available in the existing W isotope determination methods. 12 Ω and 10 13 The combined use of two different types of amplifiers and an ion counter (SEM) and the rationally designed cup structure for the determination of O isotopic composition were used to determine the ReO4 16 O. 17 O and 18O all three O isotopes, and take advantage of the convenience of the Re filament used in W isotope determination to obtain high-signal and high-precision O isotope data, solving the problem of low W signal in small sample amounts and 17 O abundance is too low (natural abundance is about 16 1 / 2600 of O, 18 The problem of being unable to obtain accurate and high-precision measurement data for 17O / 18O ratio (1 / 5 of O) is avoided, which avoids the deviation of the 17O / 18O ratio caused by the deviation of the assumption conditions in the past calculation of the 17O / 18O ratio, and realizes the high-accuracy and high-precision determination of oxygen isotope composition and the high-precision and high-precision test of W isotope.

[0136] S140, according to the total O isotope composition data n The WO3 data were corrected for oxygen removal, and then the W isotope mass fractionation produced during the instrument measurement process was corrected and calculated to obtain W isotope ratios with high accuracy and precision.

[0137] Specifically, data processing: Tungsten is measured as trioxide ions in a negative ion state. After the data is exported, it needs to be corrected offline. 1) Based on the determination of ReO4, the accurate tri-oxygen isotope composition is calculated. The calculation formula for the O isotope composition is: 18 O / 16 O=1 / 4×I( 187 Re 16 O3 18 O - ) / I( 187 ReO4 - ), 17 O / 16 O=1 / 4×I( 187 Re 16 O3 17 O - ) / I( 187 ReO4 - ); 2) deduct the isotopic interference of TaO3 and ReO3 on WO3; 3) perform deoxygenation correction on WO3 based on the calculated O isotopic composition; 4) perform W isotope mass fractionation correction: use 186 W / 184 W = 0.92767, corrected by exponential law.

[0138] The following describes the method for separating the W element and determining the W isotope of ultra-low sample amount rocks and the method with high precision in combination with the corresponding embodiments.

[0139] A two-column chemical separation method was designed with a W content of 100 ng and a corresponding sample size of 20 mg to 400 mg.

[0140] The separation process has good reproducibility of elution curves for different earth rocks, stony meteorites and iron meteorites.

[0141] As shown in Table 3, the W element separation and high-precision W isotope determination method S100 for ultra-low sample amount rock of the present disclosure was used to determine the single element W standard solution SRM3163. The total amount of W was about 1000 ng, 100 ng, 50 ng, 30 ng and 10 ng. 184 W 16 O3 - The signal intensities were measured at approximately 0.1 V, 0.25 V, 0.5 V, and 0.1 V, respectively.

[0142] The results showed that when 184 W 16 O3 - The signal strength is 0.5 to 1.0V, 182 W / 184 The ratio and precision of W are 0.864869±6ppm (2RSD, n=21, t=12 months), 184 WO3 - When the signal strength is 0.1 to 0.3V, 182 W / 184 The W ratio and precision were 0.864868±11ppm (2RSD, n=17, t=3 months). When the total W content reached 30ng, the sample size was less than 1 / 10 of that used in conventional methods, yet the best precision of 4ppm to 6ppm (2RSD) achieved with NTIMS equipped with a conventional amplifier for samples over 500ng was achieved in previous studies.

[0143] Table 3 Test data of 3W standard solution and rock sample reference material

[0144]

[0145] As shown in Table 3, a group of earth rock and meteorite samples were measured using the ultra-low sample amount rock W element separation and high-precision W isotope determination method S100 of the disclosed embodiment. The six selected samples were basalts JB-3, BCR-2 and BHVO-2, granodiorite GSP-2, ordinary chondrite-Jilin meteorite and iron meteorite-Nandan meteorite. These rock samples represent typical rock samples of the mantle, crust, stony meteorites, and iron meteorites, covering the W content range of most earth and meteorites (251-1555ng / g), among which JB-3, BCR-2 and BHVO-2, granodiorite GSP-2 are widely reported as international geological reference materials. In order to ensure the homogeneity of the samples in this experiment, about 1 g to 2 g of each sample was weighed for dissolution. Then, the total amount of W was estimated to be about 100 ng (corresponding to 20 mg to 400 mg of rock sample) based on the W content reference value in each sample. The samples were then chemically separated and purified for W, and then subjected to NTIMS determination.

[0146] The results show that within the error range, the μ 182 The W values ​​are consistent with the reported data. 182 The W value is consistent with the reported value for ordinary chondrites of the same type.

[0147] It is understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the embodiments of the present disclosure, but the embodiments of the present disclosure are not limited thereto. Those skilled in the art may make various modifications and improvements without departing from the spirit and essence of the embodiments of the present disclosure, and such modifications and improvements are also considered to be within the scope of protection of the embodiments of the present disclosure.

Claims

1. A method for separating W from ultra-low sample amount rocks and determining W isotopes with high precision, characterized in that: The method comprises: Selecting a rock sample to be measured and weighing it, and dissolving the weighed rock sample to be measured to obtain a sample solution; The sample solution was subjected to two-column chemical separation and purification using an AG1X8 resin column and a TEVA resin column, respectively, to separate and purify the W element, thereby obtaining a high-purity W element sample to be determined; The cup structure for determining the W isotope composition and the cup structure for determining the O isotope composition were established respectively, and the isotope thermal ionization mass spectrometry was performed on the high-purity W element sample to be determined, and the W isotope composition was obtained respectively. n WO3 data and all O isotope composition data; According to the above-mentioned total O isotope composition data, n The WO3 data were corrected for oxygen removal, and then the W isotope mass fractionation produced during the instrument measurement process was corrected and calculated to obtain W isotope ratios with high accuracy and precision.

2. The method according to claim 1, characterized in that The method of using an AG1X8 resin column and a TEVA resin column to perform two-column chemical separation and purification on the sample solution in sequence to separate and purify the W element to obtain a high-purity W element sample to be determined, comprising: 2.5 mL to 3.0 mL of AG1X8 resin is loaded into a resin column to obtain the AG1X8 resin column, and the AG1X8 resin column is pretreated; The sample solution was evaporated to dryness and redissolved in 0.5 mL to 1 mL of a mixed acid solution of 1 M HCl and 0.5 M HF, and the redissolved sample solution was slowly added to the pretreated AG1X8 resin column; Slowly add 6 mL to 7 mL of a mixed acid of 1 M HCl and 0.5 M HF to the AG1X8 resin column to elute the major matrix elements and most of the trace elements; Slowly add 6 mL to 7 mL of a mixed acid of 6 M HNO 3 and 0.2 M HF to the AG1X8 resin column to elute some interfering elements and W element; The W-containing solution separated by the AG1X8 resin column was evaporated to dryness and then redissolved in 0.3 mL to 0.5 mL of a mixed acid solution of 9 M HCl and 0.02 M HF; 0.5 mL to 0.6 mL of TEVA resin is loaded into a resin column to obtain the TEVA resin column, and the TEVA resin column is pretreated; Slowly adding the redissolved W-containing solution to the pretreated TEVA resin column; Slowly add 2.5 mL to 3.0 mL of a mixed acid of 9 M HCl and 0.02 M HF to the TEVA resin column to elute the remaining interfering elements; 2.5 mL to 3.0 mL of a mixed acid of 3 M HCl and 0.02 M HF was slowly added to the TEVA resin column to elute the W element, obtain a high-purity W solution, and complete the separation of the TEVA resin column.

3. The method according to claim 2, characterized in that The AG1X8 resin column is pretreated, comprising: Slowly add 5 mL to 6 mL of a mixed solution of 6 M HNO 3 and 0.2 M HF to the AG1X8 resin column for the first wash; slowly add 5 mL to 6 mL of a mixed solution of 1 M HCl and 0.5 M HF to the AG1X8 resin column for the second wash; Slowly add 5 mL to 6 mL of ultrapure water to the AG1X8 resin column to neutralize the AG1X8 resin column; slowly add 8 mL to 10 mL of a mixed solution of 1 M HCl and 0.5 M HF to the AG1X8 resin column to make the medium of the AG1X8 resin column the same as the medium of the sample dissolution solution.

4. The method according to claim 2, characterized in that The TEVA resin column is pretreated, comprising: Slowly add 3 mL to 5 mL of a mixed solution of 3 M HCl and 0.02 M HF to the TEVA resin column for the first wash; slowly add 3 mL to 5 mL of a mixed solution of 9 M HCl and 0.02 M HF to the TEVA resin column for the second wash; 3 mL to 5 mL of ultrapure water was slowly added to the TEVA resin column to neutralize the TEVA resin column; 3 mL to 5 mL of a mixed solution of 9 M HCl and 0.02 M HF was slowly added to the TEVA resin column to make the medium of the TEVA resin column the same as the medium of the W-containing solution after separation and redissolution of the AG1X8 resin column.

5. The method according to claim 1, characterized in that The cup structure established for the W isotope composition determination includes: 182 WO3 ˉ 、 183 WO3 ˉ 、 184 WO3 ˉ and 186 WO3 ˉ The ion beam is connected by the second low cup L2, the first low cup L1, the center cup C and the second high cup H2. 12 Ω amplifier for reception; 180 WO3 ˉ The ion beam is connected to the fourth low cup L4 10 13 Ω amplifier for reception; 181 TaO3 ˉ The ion beam is connected to the third lower cup L3 10 13 Ω amplifier for reception; 185 ReO3 ˉ The ion beam is connected to the first high cup H1 10 11 Ω amplifier for reception.

6. The method according to claim 5, characterized in that The cup structure for W isotope composition determination is used to perform isotope thermal ionization mass spectrometry on the high-purity W element sample to be determined, comprising: Instrument measurement parameter settings: Measure in the negative ion mode of the TIMS instrument; The instrument's baseline is measured once a day before starting measurement, with a pre-wait time of 50 to 60 seconds and a measurement time of 1200 cycles × 1.05 seconds. 10 11 Ω, 10 12 Ω and 10 13 The gain of the Ω amplifier is calibrated every three days, and the calibration current is a virtual current of 0.12V; The W element of each sample was determined in 40 cycles × 20 blocks, with each data integration period of 16s / 32s, an idle time of 10s to 12s, and peak alignment was performed every 5 blocks; During the measurement, the oxygen pressure was maintained at 0.5×10 -7 mbar~1.0×10 -7 mbar, regulated by a micro air valve, each measurement lasts 7.5 to 8 hours, and the evaporation zone temperature is 1300°C to 1350°C during W isotope determination.

7. The method according to claim 1, characterized in that The cup structure for determining the O isotopic composition is established, including: 185 Re 16 O4 ˉˉ and 187 Re 16 O4 ˉ The ion beam is connected by the center cup C and the second high cup H2. 12 Ω amplifier for reception; 187 Re 16 O3 18 O ˉ The ion beam is connected with the third high cup H3 10 13 Ω amplifier for reception; 187 Re 16 O3 17 O ˉˉ The ion beam is received by a secondary ion multiplier bound to the central cup C; wherein, The position of the cup structure determined by the O isotope composition is the same as the position of the cup structure determined by the W isotope composition.

8. The method according to claim 7, characterized in that The cup structure for determining the O isotope composition is used to perform isotope thermal ionization mass spectrometry on the high-purity W element sample to be determined, comprising: Before each sample was measured, a Faraday cup was used to statically receive the 185 ReO4 ˉ 、 187 ReO4 ˉ and 187 Re 16 O3 18 O ˉ The SEM peak-jumping method was used to measure the 187 Re 16 O3 17 O ˉ Conducting measurements; The analysis parameters for O isotope determination are 20 cycles × 10 blocks, 4 s / 8 s integration, 6 s–8 s idle time, 35–60 min for one measurement, and 700–850 °C evaporation zone temperature for O isotope determination.

9. The method according to any one of claims 1 to 4, characterized in that The method of obtaining a high-purity W element sample to be determined comprises: The W element solution obtained by two separations using the AG1X8 resin column and the TEVA resin column was placed on a hot plate and evaporated to dryness, and redissolved in 1 μL to 2 μL of a mixed solution of 7% M HNO 3 and 4% M HF to obtain the high-purity W element sample to be determined.

10. The method according to any one of claims 1 to 4, characterized in that The n The WO3 data is corrected for oxygen removal, and then the W isotope mass fractionation produced during the instrument measurement process is corrected and calculated to obtain highly accurate and precise W isotope ratios, including: According to the determination of ReO4, the accurate three oxygen isotope compositions are calculated, among which the calculation formula of O isotope composition is: 18 O / 16 O=1 / 4×I( 187 Re 16 O3 18 O ˉ ) / I( 187 ReO4 - ), 17 O / 16 O=1 / 4×I( 187 Re 16 O3 17 O - ) / I( 187 ReO4 - ); Deduct the isotopic interference of TaO3 and ReO3 on WO3; Based on the calculated O isotope composition, deoxygenation correction was performed; Perform mass fractionation calibration: Use 186 W / 184 W = 0.92767, corrected by exponential law.

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