High-precision strontium isotope analysis method for trace silk sample

Abstract

The invention relates to the technical field of silk strontium isotope detection, and discloses a high-precision strontium isotope analysis method for a trace silk sample, which comprises the following steps: (1) pretreating a silk sample to obtain a silk residue A1; (2) sequentially carrying out digestion treatment by adopting nitric acid and mixed acid of nitric acid and hydrochloric acid to obtain silk residue B3; (3) separating and collecting a strontium element through a strontium special-effect separation exchange column to obtain a sample C3 to be detected; and (4) preparing a to-be-detected sample C3 into a solution, coating the surface of the high-purity rhenium filament according to a sequence of tungsten silicic acid, the to-be-detected sample C3 solution, tungsten silicic acid and phosphoric acid, drying by distillation after coating each time, heating until the rhenium filament becomes dark red, keeping for 3-5 seconds, and returning the current to 0. According to the method, interference of organic matters and other impurities in the silk sample on experimental data can be removed as much as possible, the recovery rate of the strontium element is increased, the sample consumption is reduced, and the detection and analysis accuracy is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of silk strontium isotope detection, and in particular to a high-precision strontium isotope analysis method for trace silk samples. Background Art

[0002] Traditional methods for tracing the origin of silk cultural relics mostly rely on morphological analysis (such as fabric structure, weaving process) and dye component identification. However, these technologies are difficult to accurately trace the geographical origin of silk raw materials. In recent years, with the rapid development of isotope analysis technology, traceability methods based on stable isotopes have gradually become a research hotspot for identifying the origin of organic cultural relics. Strontium isotopes are considered to be the ecological fingerprint code for origin traceability due to their small fractionation effect. However, because the strontium isotope content in silk is low, to apply this technology to the traceability of organic matter samples of silk cultural relics, the first problem to be solved is to improve the separation and extraction efficiency of strontium elements in silk, so as to achieve the goal of reducing the sample consumption.

[0003] Although the existing strontium isotope experimental methods have strong universality and can test various types of samples such as plants, geology, and bones. For example, the patent with the publication number CN118538319A discloses a method for analyzing the reliability of strontium isotope data of carbonate rocks. The method includes calculating the strontium isotope ratio of acid-insoluble substances ( 87 Sr / 86 Sr) of acid-insoluble substances according to the geological age of the sample collection horizon, and analyzing the reliability of the whole-rock Sr isotope data based on the calculation results. However, the experiment with a sample consumption of hundreds of milligrams is a destructive experiment for silk cultural relic samples and cannot be applied to unearthed silk cultural relics for origin traceability research. The main reason is that the pretreatment methods and spotting methods of traditional strontium isotope analysis technology are mainly for geological and environmental samples. Although trace high-precision detection technologies have been developed for precious samples such as lunar soil, the interference of impurity signals of organic samples has not been considered. And the technologies developed for organic protein samples such as crabs and beef do not consider the amount of sample consumption. Therefore, there is no special optimization for silk samples so far, and an efficient separation and test isotope analysis method for strontium elements in trace silk samples cannot be realized, which affects the application research of this technology in the origin traceability of silk cultural relic samples. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a high-precision strontium isotope analysis method for trace silk samples. By synergistically optimizing the processes of digestion, column passing, spotting, etc., the interference of organic matter and other impurities in the silk samples on the experimental data is removed as much as possible, and the recovery rate of strontium elements in the silk samples is improved, so as to achieve the goal of reducing the sample consumption (the sample consumption can be as low as 15 mg) and improving the accuracy in the strontium isotope analysis experiment of silk.

[0005] The purpose of the present invention is achieved through the following technical solutions: The present invention provides a high-precision strontium isotope analysis method for trace silk samples, comprising the following steps: (1) pretreating a silk sample to obtain a silk residue A1; (2) digesting with nitric acid and a mixed acid of nitric acid and hydrochloric acid in sequence to obtain a silk residue B3; (3) separating and collecting the strontium element by a strontium-specific separation exchange column to obtain a sample C3 to be tested; (4) Prepare the sample C3 to be tested into a solution, and coat it on the surface of the high-purity rhenium filament in the order of tungstosilicic acid-sample C3 solution to be tested-tungstosilicic acid-phosphoric acid. After each coating, evaporate to dryness, then heat until the rhenium filament turns dark red, maintain for 3 to 5 seconds, and return the current to 0.

[0006] In view of the high organic impurities and low strontium content in silk samples, in addition to the usual nitric acid solution for sample digestion, hydrochloric acid solution and nitric acid solution are added for synergistic digestion, which can minimize the interference of organic matter and other impurities in silk samples on experimental data.

[0007] The tungstosilicic acid spotting method in the prior art is mainly aimed at geological samples. The phosphoric acid + tungstosilicic acid + sample spotting method can improve the strontium ionization efficiency by 1-2 orders of magnitude. The silk sample is mainly composed of amino acid macromolecular chains that form a secondary conformation through a β-fold or α-helical structure. Even after column purification, there are still visible protein-like organic residues. According to experiments, the strontium signal in the silk sample is extremely unstable and the ionization efficiency is greatly suppressed when the phosphoric acid-tungstosilicic acid-sample spotting sequence is adopted. The present invention proposes to optimize the silk sample spotting sequence to "tungstosilicic acid + sample + tungstosilicic acid + phosphoric acid". The two layers of tungstosilicic acid wrap the sample to further improve the ionization efficiency. Coating phosphoric acid on the sample can effectively remove the interference of organic matter to produce a stable ion flow.

[0008] Preferably, in step (1), the silk sample is pretreated by cutting the silk sample into pieces and then subjecting it to ultrasonic and centrifugal treatments in sequence.

[0009] Preferably, step (1) specifically comprises the following steps: drying the silk sample and cutting it into pieces, placing it in a centrifuge tube, adding ultrapure water and ultrasonicating it, centrifuging it, discarding the supernatant and drying it to obtain the silk residue A1.

[0010] The silk samples are cut into pieces to homogenize the organic samples without introducing new pollution sources. Since the main component of silk fiber is a large protein molecular chain composed of different amino acids linked together, it has strong toughness and cannot be ground by conventional methods such as liquid nitrogen freezing and grinding or ball mill grinding. However, if the sample is not crushed, the reproducibility of the sample experimental data will be poor.

[0011] Preferably, step (2) specifically includes the following steps: Add nitric acid to the silk residue A1 and react at 110 - 130 °C for 1 - 3 h, then evaporate to dryness. Add nitric acid again and react at 110 - 130 °C for 22 - 28 h, then evaporate to dryness. Then add a mixed acid of nitric acid and hydrochloric acid and react at 110 - 130 °C for 10 - 14 h, then evaporate to dryness. Repeat adding hydrochloric acid twice and evaporate to dryness to obtain the silk residue B3.

[0012] Preferably, the volume ratio of the nitric acid, the nitric acid added again, and the mixed acid of nitric acid and hydrochloric acid is 1:2:3.

[0013] Preferably, the mixed acid of nitric acid and hydrochloric acid contains nitric acid, hydrochloric acid, and ultrapure water in a volume ratio of 1:1:1.

[0014] Preferably, the concentration of the nitric acid is 2 - 4 mol / L; the concentration of the hydrochloric acid is 6 - 8 mol / L.

[0015] Preferably, in step (3), add nitric acid to dissolve the silk residue B3 to obtain solution C1. Repeat passing the solution C1 through a strontium-specific separation and exchange column twice to obtain the test sample C3.

[0016] Preferably, step (3) specifically includes the following steps: a. Wash the strontium-specific separation and exchange column with nitric acid and hydrochloric acid in sequence; b. Balance the resin environment in the strontium-specific separation and exchange column with nitric acid; c. Add nitric acid to dissolve the silk residue B3 to obtain solution C1; d. Transfer the solution C1 to the strontium-specific separation and exchange column for passing through the column, and discard the obtained solution; e. Wash the strontium-specific separation and exchange column with nitric acid, and discard the obtained solution; f. Wash the strontium-specific separation and exchange column with ultrapure water to obtain solution C2; g. Wash the strontium-specific separation and exchange column with hydrochloric acid and ultrapure water in sequence, and discard the obtained solution; h. Repeat the above steps a - g for solution C2 to obtain the test sample C3.

[0017] After repeating passing through the strontium-specific separation and exchange column twice, the interference of other elements is basically removed, and the recovery rate of strontium in the silk sample is improved.

[0018] Preferably, in step (4), the high-purity rhenium filament is first degassed at a current of 1 to 6 A for 1 to 2 hours before surface coating.

[0019] Preferably, in step (4), the solution of the test sample C3 is obtained by dissolving the test sample C3 in hydrochloric acid.

[0020] Preferably, the mass concentration of the hydrochloric acid is 4-6%.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) Using silicotungstic acid and phosphoric acid as emitters, the sandwich-type spotting order of "silicotungstic acid + sample to be tested + silicotungstic acid + phosphoric acid" effectively improved the ionization rate and signal stability of strontium isotope elements in trace organic samples after sampling, effectively reduced the sample consumption of strontium isotope testing experiments of silk samples, and achieved good data reproducibility, thus realizing high-precision strontium isotope analysis of trace silk samples; (2) On the basis of using nitric acid solution to digest the samples, adding hydrochloric acid solution and nitric acid solution for synergistic digestion can remove the interference of organic matter and other impurities in the silk samples on the experimental data as much as possible; (3) After repeated column washing twice using a strontium-specific separation exchange column, the interference of other elements was basically removed, and the recovery rate of strontium in the silk sample was improved; (4) The method of the present invention has the advantages of low sample consumption and high accuracy, and provides technical feasibility for the origin tracing research of movable organic cultural relics such as silk and wool. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 For the samples in Examples 1-6 87 Sr / 86 Test results of Sr ratio.

[0023] Figure 2 Illustration of pervaporation using different spotting sequences. DETAILED DESCRIPTION

[0024] The technical scheme of the present invention is described below with specific examples, but the protection scope of the present invention is not limited thereto. The hydrochloric acid and nitric acid used in the present invention are ultrapure acids obtained by secondary purification of commercially available concentrated hydrochloric acid and concentrated nitric acid.

[0025] Instrument testing and data correction method: Sr isotope analysis was performed using a thermal ionization mass spectrometer (Triton, TIMS) from Thermo Fisher Scientific, USA. The instrument is equipped with 9 Faraday cup receivers, and the amplifier resistance configured for each receiver is 1011 Ω. 84Sr, 85Rb, 86Sr, 87Sr, and 88Sr are received by 5 receiving cups respectively, where 85Rb is used to monitor and correct the isobaric interference of 87Rb on 87Sr.

[0026] First, the filament was heated to 1900 mA at a rate of 300 mA / min, and then increased to 88Sr ~ 50 mV at a rate of 50 mA / min. After focusing, it was continuously increased to 88Sr reaching 2 - 3 V at a rate of 20 - 30 mA / min, and the sampling program was started. Before sampling, focusing, peak centering, and baseline correction were performed. 15 groups (blocks) of data were collected, with 10 cycles in each group and an integration time of 4.19 s. The amplifier rotation was enabled to eliminate the amplification factor differences between amplifiers. The instrumental mass fractionation of Sr isotopes was carried out using the internal standard method. Assuming that the 88Sr / 86Sr in the sample is a fixed value of 8.375219, it was calculated using the exponential fractionation law: where r and R represent the measured value and the true value respectively, and m 88Sr and m 86Sr represent the exact relative atomic masses of 88Sr and 86Sr respectively. The calculation for subtracting the interference signal of 87Rb was performed using the following formula: V 87Sr = V 87 - V 87Rb where V 87 represents the total measured signal, including the interference signal V 87Rb and the target signal V 87Sr . The interference signal V 87Rb can be obtained through the natural abundance ratio r 87Rb / 85Rb of the Rb element and the received 85Rb signal (V 85Rb ): V 87Rb = V 85Rb · r 87Rb / 85Rb where r 87Rb / 85Rb can be obtained through the above instrumental fractionation factor f and the exponential fractionation law. Finally, through the 87Sr signal after interference subtraction, the Sr / 87 Sr ratio of the sample can be obtained using the exponential fractionation law and the fractionation factor f. 86

[0027] The NBS 987Sr standard sample was used as the instrument monitoring standard sample. It was directly spotted onto the instrument, with 0.5 ng spotted each time, and tested together with the samples. The BHVO-2 (basalt) standard sample was used as the whole process monitoring standard sample. Each time, 0.5 ng was taken according to the Sr content and tested by column together with the silk samples.

[0028] Example 1-2 (Silkworm cocoon A, 15 mg) (1) Sample pretreatment: The silkworm cocoon A sample was dried and then cut into pieces with a ceramic scissors to ensure sample uniformity. Weigh 15 mg of the sample into a 10 mL centrifuge tube, add 5 mL of ultrapure water, sonicate for 15 min, then centrifuge. The centrifugation rate was set at 5000 rpm and the centrifugation time was 10 min. After discarding the supernatant, place it in an oven and dry at a temperature of 50 °C to obtain silk residue A1.

[0029] (2) Digestion treatment: a. Place the silk residue A1 in a Teflon vessel, add 1 mL of 3 mol / L HNO3, cover it, and react on a hot plate at 120 °C for 2 h. Then uncover it and evaporate to dryness on the hot plate at 120 °C to obtain silk residue B1; b. Add 2 mL of 3 mol / L HNO3 to the silk residue B1, cover it, and react on a hot plate at 120 °C for 24 h. Then uncover it and evaporate to dryness on the hot plate at 120 °C to obtain silk residue B2; c. Add 3 mL of mixed acid (1 mL of 3 mol / L HNO3 + 1 mL of 7 mol / L HCl + 1 mL of ultrapure water) to the silk residue B2, cover it, and react on a hot plate at 120 °C for 12 h. Then uncover it and evaporate to dryness on the hot plate at 120 °C; d. Finally, repeat adding 0.5 mL of 7 mol / L HCl twice and evaporate to dryness to obtain silk residue B3.

[0030] (3) Separation and collection of strontium element: The strontium-specific resin was washed 3 times with 6 mol / l HCl, the suspended matter was removed, and it was stored in high-purity water for use. A 1 mL polypropylene (PE) micro-exchange column purchased from Bio-rad was washed with 10% mass concentration of HNO3, then washed with high-purity water and dried. Pipette 1 mL of strontium-specific resin into the column, and the packed column height was 1 cm, finally forming a strontium-specific separation and exchange column.

[0031] a. Column washing: Wash the strontium-specific separation and exchange column successively with 1 mL of 7 mol / L HCl, 1 mL of ultrapure water, 3 mL of 3 mol / L HNO3, and 1 mL of ultrapure water; b. Equilibration: Equilibrate the resin environment in the strontium-specific separation and exchange column with 1 mL of 3 mol / L HNO3; c, Sample preparation: After adding 0.2 mL of 3 mol / L HNO3 to the silk residue B3 to dissolve the sample, solution C1 is obtained; d, Loading: Transfer solution C1 to a strontium-specific separation and exchange column using a pipette for column passing, and discard the resulting solution; e, Elution: Wash the strontium-specific separation and exchange column with 3 mL of 3 mol / L HNO3, and discard the resulting solution; f, Collect strontium element: Wash the strontium-specific separation and exchange column with 3 mL of ultrapure water to obtain solution C2; g, Column washing: Wash the strontium-specific separation and exchange column successively with 2 mL of 7 mol / L HCl and 1 mL of ultrapure water, and discard the resulting solution; h, Repeat the above steps a - g for solution C2 to obtain the sample to be tested C3.

[0032] (4) Spotting: The high-purity rhenium filament (99.99%) purchased from H.Cross Company in the United States is degassed for 1 h at 2 A and 5 A currents respectively to remove impurities. Coating and spotting are carried out on the surface of the high-purity rhenium filament in the order of tungstosilicic acid - sample to be tested C3 solution - tungstosilicic acid - phosphoric acid.

[0033] a, Pipette 2 μL of tungstosilicic acid and coat it on the surface of the high-purity rhenium filament, and evaporate it to dryness at 1 A current; b, Dissolve the sample to be tested C3 in 1 μL of HCl with a mass concentration of 5%, coat it on the evaporated tungstosilicic acid, and evaporate it to dryness at 1 A current; c, Pipette 2 μL of tungstosilicic acid and coat it on the evaporated sample, and evaporate it to dryness at 1 A current; d, Pipette 1 μL of 1 mol / L phosphoric acid and coat it on the evaporated tungstosilicic acid, heat it at 1 A current for 10 s, then increase the current, and raise the current to 2 A within 20 s for evaporation to dryness; e, After evaporation to dryness, slowly raise the temperature until the rhenium filament turns dark red, maintain it for 3 - 5 s, and then reset the current to 0.

[0034] Example 3 (Silkworm cocoon A, 50 mg) (1) Sample pretreatment: Dry the silkworm cocoon A sample and cut it into pieces with a ceramic scissors to ensure the uniformity of the sample; Weigh 50 mg of the sample into a 10 mL centrifuge tube, add 5 mL of ultrapure water, sonicate for 15 min, then centrifuge, set the centrifugation rate to 5000 rpm, and the centrifugation time to 10 min. After discarding the supernatant, place it in an oven and dry it at a temperature of 50 °C to obtain the silk residue A1.

[0035] (2) Digestion treatment: a. Place the silk residue A1 in a Teflon vessel, add 1 mL of 3 mol / L HNO3, cover it, react on a hot plate at 120 °C for 2 h, then uncover and evaporate to dryness on the hot plate at 120 °C to obtain the silk residue B1; b. Add 2 mL of 3 mol / L HNO3 to the silk residue B1, cover it, react on a hot plate at 120 °C for 24 h, then uncover and evaporate to dryness on the hot plate at 120 °C to obtain the silk residue B2; c. Add 3 mL of a mixed acid (1 mL of 3 mol / L HNO3 + 1 mL of 7 mol / L HCl + 1 mL of ultrapure water) to the silk residue B2, cover it, react on a hot plate at 120 °C for 12 h, then uncover and evaporate to dryness on the hot plate at 120 °C; d. Finally, repeat adding 0.5 mL of 7 mol / L HCl twice and evaporate to dryness to obtain the silk residue B3.

[0036] (3) Separate and collect strontium: Wash the strontium-specific resin 3 times with 6 mol / l HCl, remove the suspended matter, and store it in high-purity water for later use. Wash a 1 mL polypropylene (PE) micro-exchange column purchased from Bio-rad with 10% (mass concentration) HNO3, then wash it with high-purity water and dry it. Pipette 1 mL of the strontium-specific resin into the column, and the filling column height is 1 cm to finally form a strontium-specific separation and exchange column.

[0037] a. Wash the column: Wash the strontium-specific separation and exchange column successively with 1 mL of 7 mol / L HCl, 1 mL of ultrapure water, 3 mL of 3 mol / L HNO3, and 1 ml of ultrapure water; b. Equilibrate: Equilibrate the resin environment in the strontium-specific separation and exchange column with 1 mL of 3 mol / L HNO3; c. Sample preparation: Add 0.2 mL of 3 mol / L HNO3 to the silk residue B3 to dissolve the sample to obtain solution C1; d. Loading: Transfer solution C1 to the strontium-specific separation and exchange column with a pipette for column passing, and discard the resulting solution; e. Elution: Elute the strontium-specific separation and exchange column with 3 mL of 3 mol / L HNO3, and discard the resulting solution; f. Collect strontium: Elute the strontium-specific separation and exchange column with 3 mL of ultrapure water to obtain solution C2; g. Wash the column: Wash the strontium-specific separation and exchange column successively with 2 mL of 7 mol / L HCl and 1 mL of ultrapure water, and discard the resulting solution; h. Repeat the above steps a - g for solution C2 to obtain the test sample C3.

[0038] (4) Spotting: The high-purity rhenium filament (99.99%) purchased from H.Cross Company in the United States was degassed for 1 h at 2 A and 5 A currents respectively to remove impurities. The high-purity rhenium filament surface was coated and spotted in the order of tungstosilicic acid - test sample C3 solution - tungstosilicic acid - phosphoric acid.

[0039] a. Pipette 2 μL of tungstosilicic acid and coat it on the surface of the high-purity rhenium filament, and evaporate to dryness at 1 A current; b. Dissolve the test sample C3 in 1 μL of HCl with a mass concentration of 5%, coat it on the evaporated tungstosilicic acid, and evaporate to dryness at 1 A current; c. Pipette 2 μL of tungstosilicic acid and coat it on the evaporated sample, and evaporate to dryness at 1 A current; d. Pipette 1 μL of 1 mol / L phosphoric acid and coat it on the evaporated tungstosilicic acid, heat it at 1 A current for 10 s, then increase the current, raise the current to 2 A within 20 s, and evaporate to dryness; e. After evaporation to dryness, slowly raise the temperature until the rhenium filament turns dark red, keep it for 3 - 5 s, and then set the current back to 0.

[0040] Example 4 - 5 (Silkworm cocoon B, 15 mg) (1) Sample pretreatment: Dry the silkworm cocoon B sample and cut it into pieces with a ceramic scissors to ensure sample uniformity; Weigh 15 mg of the sample into a 10 mL centrifuge tube, add 5 mL of ultrapure water, sonicate for 15 min, then centrifuge, set the centrifugation rate to 5000 rpm, and the centrifugation time to 10 min. Discard the supernatant and place it in an oven, set the temperature to 50 °C for drying to obtain silk residue A1.

[0041] (2) Digestion treatment: a. Place the silk residue A1 in a Teflon vessel, add 1 mL of 3 mol / L HNO3, cover it, and react on a hot plate at 120 °C for 2 h. Then uncover it and evaporate to dryness on the hot plate at 120 °C to obtain silk residue B1; b. Add 2 mL of 3 mol / L HNO3 to the silk residue B1, cover it, and react on a hot plate at 120 °C for 24 h. Then uncover it and evaporate to dryness on the hot plate at 120 °C to obtain silk residue B2; c. Add 3 mL of mixed acid (1 mL of 3 mol / L HNO3 + 1 mL of 7 mol / L HCl + 1 mL of ultrapure water) to the silk residue B2, cover it, and react on a hot plate at 120 °C for 12 h. Then uncover it and evaporate to dryness on the hot plate at 120 °C; d. Finally, repeat adding 0.5 mL of 7 mol / L HCl twice and evaporate to dryness to obtain silk residue B3.

[0042] (3) Separate and collect strontium element: After cleaning the strontium-specific resin three times with 6 mol / L HCl, remove the suspended matter and store it in high-purity water for later use. After cleaning a 1 mL polypropylene (PE) micro-exchange column purchased from Bio-rad with 10% (mass concentration) HNO3, wash it with high-purity water and dry it. Pipette 1 mL of the strontium-specific resin into the column, with a packed column height of 1 cm, finally forming a strontium-specific separation and exchange column.

[0043] a. Column washing: Wash the strontium-specific separation and exchange column successively with 1 mL of 7 mol / L HCl, 1 mL of ultrapure water, 3 mL of 3 mol / L HNO3, and 1 mL of ultrapure water; b. Equilibration: Equilibrate the resin environment in the strontium-specific separation and exchange column with 1 mL of 3 mol / L HNO3; c. Sample preparation: After adding 0.2 mL of 3 mol / L HNO3 to the silk residue B3 to dissolve the sample, obtain solution C1; d. Loading: Transfer solution C1 to the strontium-specific separation and exchange column with a pipette for column passing, and discard the resulting solution; e. Elution: Elute the strontium-specific separation and exchange column with 3 mL of 3 mol / L HNO3, and discard the resulting solution; f. Collecting strontium element: Elute the strontium-specific separation and exchange column with 3 mL of ultrapure water to obtain solution C2; g. Column washing: Wash the strontium-specific separation and exchange column successively with 2 mL of 7 mol / L HCl and 1 mL of ultrapure water, and discard the resulting solution; h. Repeat the above steps a - g for solution C2 to obtain the sample to be measured C3.

[0044] (4) Spotting: The high-purity rhenium filament (99.99%) purchased from H.Cross Company, USA, is degassed for 1 h at 2 A and 5 A currents respectively to remove impurities. Coat and spot on the surface of the high-purity rhenium filament in the order of tungstosilicic acid - sample to be measured C3 solution - tungstosilicic acid - phosphoric acid.

[0045] a. Pipette 2 μL of tungstosilicic acid and coat it on the surface of the high-purity rhenium filament, and evaporate it to dryness at 1 A current; b. Dissolve the sample to be measured C3 in 1 μL of 5% (mass concentration) HCl, coat it on the evaporated tungstosilicic acid, and evaporate it to dryness at 1 A current; c. Pipette 2 μL of tungstosilicic acid and coat it on the evaporated sample, and evaporate it to dryness at 1 A current; d. Pipette 1 μL of 1 mol / L phosphoric acid and coat it on the evaporated tungstosilicic acid, heat it at 1 A current for 10 s, then increase the current, and raise the current to 2 A within 20 s for evaporation to dryness; e. After evaporation to dryness, slowly raise the temperature until the rhenium filament turns dark red, maintain for 3 - 5 s, and then return the current to 0.

[0046] Example 6 (Silkworm Cocoon B, 50 mg) (1) Sample pretreatment: Dry the silkworm cocoon B sample and then cut it into pieces with a ceramic scissors to ensure the uniformity of the sample. Weigh 50 mg of the sample into a 10 mL centrifuge tube, add 5 mL of ultrapure water, sonicate for 15 min, and then centrifuge. Set the centrifugation rate to 5000 rpm and the centrifugation time to 10 min. Discard the supernatant and place it in an oven at a temperature of 50 °C for drying to obtain silk residue A1.

[0047] (2) Digestion treatment: a. Place the silk residue A1 in a Teflon vessel, add 1 mL of 3 mol / L HNO3, cover it, and react on a hot plate at 120 °C for 2 h. Then uncover it and evaporate to dryness on the hot plate at 120 °C to obtain silk residue B1; b. Add 2 mL of 3 mol / L HNO3 to the silk residue B1, cover it, and react on a hot plate at 120 °C for 24 h. Then uncover it and evaporate to dryness on the hot plate at 120 °C to obtain silk residue B2; c. Add 3 mL of mixed acid (1 mL of 3 mol / L HNO3 + 1 mL of 7 mol / L HCl + 1 mL of ultrapure water) to the silk residue B2, cover it, and react on a hot plate at 120 °C for 12 h. Then uncover it and evaporate to dryness on the hot plate at 120 °C; d. Finally, repeat the addition of 0.5 mL of 7 mol / L HCl twice and evaporate to dryness to obtain silk residue B3.

[0048] (3) Separation and collection of strontium element: Clean the strontium-specific resin 3 times with 6 mol / l HCl, remove the suspended matter, and store it in high-purity water for later use. After cleaning a 1 mL polypropylene (PE) micro-exchange column purchased from Bio-rad with 10% (mass concentration) HNO3, wash it with high-purity water and dry it. Pipette 1 mL of strontium-specific resin into the column, and the packed column height is 1 cm to finally form a strontium-specific separation and exchange column.

[0049] a. Wash the column: Wash the strontium-specific separation and exchange column successively with 1 mL of 7 mol / L HCl, 1 mL of ultrapure water, 3 mL of 3 mol / L HNO3, and 1 mL of ultrapure water; b. Equilibrate: Equilibrate the resin environment in the strontium-specific separation and exchange column with 1 mL of 3 mol / L HNO3; c. Sample preparation: After adding 0.2 mL of 3 mol / L HNO3 to dissolve the sample in the silk residue B3, obtain solution C1; d. Loading: Transfer solution C1 to the strontium-specific separation and exchange column with a pipette for column passing, and discard the resulting solution; e. Elution: Use 3 mL of 3 mol / L HNO3 to elute the strontium-specific separation and exchange column, and discard the resulting solution; f. Collect strontium element: Use 3 mL of ultrapure water to elute the strontium-specific separation and exchange column to obtain solution C2; g. Wash the column: Sequentially use 2 mL of 7 mol / L HCl and 1 mL of ultrapure water to elute the strontium-specific separation and exchange column, and discard the resulting solution; h. Repeat the above steps a - g for solution C2 to obtain the test sample C3.

[0050] (4) Spotting: The high-purity rhenium filament (99.99%) purchased from H.Cross Company, USA is degassed at 2 A and 5 A currents for 1 h respectively to remove impurities. Coating and spotting are carried out on the surface of the high-purity rhenium filament in the order of tungstosilicic acid - test sample C3 solution - tungstosilicic acid - phosphoric acid.

[0051] a. Pipette 2 μL of tungstosilicic acid and coat it on the surface of the high-purity rhenium filament, and evaporate to dryness at 1 A current; b. Dissolve the test sample C3 in 1 μL of HCl with a mass concentration of 5%, coat it on the evaporated tungstosilicic acid, and evaporate to dryness at 1 A current; c. Pipette 2 μL of tungstosilicic acid and coat it on the evaporated sample, and evaporate to dryness at 1 A current; d. Pipette 1 μL of 1 mol / L phosphoric acid and coat it on the evaporated tungstosilicic acid, heat at 1 A current for 10 s, then increase the current, raise the current to 2 A within 20 s, and evaporate to dryness; e. After evaporation to dryness, slowly raise the temperature until the rhenium filament turns dark red, keep it for 3 - 5 s, and then set the current back to 0.

[0052] Example 7 (using a different spotting order from Example 1) (4) Spotting: The high-purity rhenium filament (99.99%) purchased from H.Cross Company, USA is degassed at 2 A and 5 A currents for 1 h respectively to remove impurities. Coating and spotting are carried out on the surface of the high-purity rhenium filament in the order of phosphoric acid - tungstosilicic acid - test sample C3 solution.

[0053] a. Pipette 1 μL of 1 mol / L phosphoric acid and coat it on the surface of the high-purity rhenium filament, and evaporate to dryness at 1 A current; b. Pipette 2 μL of tungstosilicic acid and coat it on the evaporated phosphoric acid, and evaporate to dryness at 1 A current; c. Dissolve the test sample C3 in 1 μL of HCl with a mass concentration of 5%, coat it on the evaporated tungstosilicic acid, heat at 1 A current for 10 s, then increase the current, raise the current to 2 A within 20 s, and evaporate to dryness; d. After evaporation to dryness, slowly raise the temperature until the rhenium filament turns dark red, keep it for 3 - 5 s, and then set the current back to 0.

[0054] Take two different silkworm cocoons, A and B. After degumming and drying in a pure water water bath, cut them into pieces. Take 3 portions from each silkworm cocoon, for a total of 6 portions. Samples with different masses, as shown in Table 1, are respectively implemented according to Examples 1-6.

[0055] Table 1 Example Sample Number Sample Material Sample Quantity (mg) Example 1 A1 Silk 15 Example 2 A2 Silk 15 Example 3 A3 Silk 50 Example 4 B1 Silk 15 Example 5 B2 Silk 15 Example 6 B3 Silk 50 Table 2 As shown in Table 2 and Figure 1 The measured results of strontium isotope ratios of 6 samples in Examples 1-6 are shown. For the same silkworm cocoon sample, the standard deviation of the data of the strontium isotope test results of the 15 mg sample and the 50 mg sample is less than 1×10 -4 , indicating good data reproducibility. The method in the present invention can achieve high-precision analysis of strontium isotopes in trace silk samples (the sample amount ≥ 15 mg is sufficient).

[0056] As Figure 2 shown, the ionization efficiency obtained by the traditional spotting method of "phosphoric acid - tungstosilicic acid - sample" in Example 7 is 3.64 - 4.30%, while the ionization efficiency obtained by the "tungstosilicic acid - sample - tungstosilicic acid - phosphoric acid" sandwich spotting method in Example 1 of the present invention is 7.93 - 10.1%. It shows that wrapping the sample with two layers of tungstosilicic acid can further improve the ionization efficiency, and coating phosphoric acid on the sample can effectively remove the interference of organic substances, thus generating a more stable ion current compared with the traditional spotting method.

[0057] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made using the specification of the present invention, or directly or indirectly applied in other related technical fields, is equally included in the patent protection scope of the present invention.

Claims

1. A high-precision strontium isotope analysis method for trace silk samples, characterized in that: The steps include: (1) Pretreatment of silk samples to obtain silk residue A1; (2) digesting with nitric acid and a mixed acid of nitric acid and hydrochloric acid in sequence to obtain a silk residue B3; (3) Separating and collecting strontium elements through a strontium special separation exchange column to obtain a sample C3 to be tested; (4) Prepare the sample C3 to be tested into a solution, and coat it on the surface of the high-purity rhenium filament in the order of tungstosilicic acid-sample C3 solution to be tested-tungstosilicic acid-phosphoric acid. Evaporate to dryness after each coating, then heat until the rhenium filament turns dark red, maintain for 3-5 seconds, and return the current to 0.

2. The high-precision strontium isotope analysis method for trace silk samples according to claim 1, characterized in that: In step (1), the silk sample is pretreated by cutting the silk sample into pieces and then subjecting it to ultrasonic and centrifugal treatments in sequence.

3. The high-precision strontium isotope analysis method for trace silk samples according to claim 1, characterized in that: Step (2) specifically comprises the following steps: adding nitric acid to the silk residue A1 at 110-130° C. for reaction for 1-3 hours and then evaporating to dryness; adding nitric acid again at 110-130° C. for reaction for 22-28 hours and then evaporating to dryness; adding a mixed acid of nitric acid and hydrochloric acid at 110-130° C. for reaction for 10-14 hours and then evaporating to dryness; repeating the addition of hydrochloric acid twice and evaporating to dryness to obtain the silk residue B3.

4. The high-precision strontium isotope analysis method for trace silk samples according to claim 3, characterized in that: The volume ratio of the nitric acid, the re-added nitric acid, and the mixed acid of nitric acid and hydrochloric acid is 1:2:

3.

5. The high-precision strontium isotope analysis method for trace silk samples according to claim 3 or 4, characterized in that: The mixed acid of nitric acid and hydrochloric acid contains nitric acid, hydrochloric acid and ultrapure water in a volume ratio of 1:1:

1.

6. The high-precision strontium isotope analysis method for trace silk samples according to claim 3 or 4, characterized in that: The concentration of the nitric acid is 2-4 mol / L; the concentration of the hydrochloric acid is 6-8 mol / L.

7. The high-precision strontium isotope analysis method for trace silk samples according to claim 1, characterized in that: In step (3), nitric acid is added to the silk residue B3 to dissolve it to obtain a solution C1, and the solution C1 is repeatedly passed through a strontium special separation exchange column twice to obtain a sample C3 to be tested.

8. The high-precision strontium isotope analysis method for trace silk samples according to claim 7, characterized in that: Step (3) specifically includes the following steps: a. Use nitric acid and hydrochloric acid to clean the strontium special separation exchange column in sequence; b. Using nitric acid to balance the resin environment in the strontium special separation exchange column; c. Add nitric acid to the silk residue B3 and dissolve it to obtain solution C1; d. Transfer solution C1 to a strontium special separation exchange column for column separation, and discard the resulting solution; e. Using nitric acid to elute the strontium special separation exchange column, and discarding the resulting solution; f. Using ultrapure water to elute the strontium special separation exchange column to obtain solution C2; g. Use hydrochloric acid and ultrapure water to wash the strontium special separation exchange column in turn, and discard the resulting solution; h. Repeat the above steps a to g with solution C2 to obtain the sample C3 to be tested.

9. The high-precision strontium isotope analysis method for trace silk samples according to claim 1, characterized in that: In step (4), the high-purity rhenium filament is first degassed at a current of 1 to 6 A for 1 to 2 hours, and then surface coating is performed.

10. The high-precision strontium isotope analysis method for trace silk samples according to claim 1 or 9, characterized in that: In step (4), the test sample C3 solution is obtained by dissolving the test sample C3 in hydrochloric acid.

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