Emitter for trace samples of nickel isotope analysis and its application in thermal ionization mass spectrometry

Abstract

An emitter for nickel isotope analysis of trace samples, its preparation and application are provided, wherein: the emitter is a zirconium hydrogen phosphate emitter; and the zirconium hydrogen phosphate emitter specifically comprises a zirconium hydrogen phosphate suspension and phosphoric acid solution as an auxiliary material. To prepare the zirconium hydrogen phosphate suspension, the zirconium hydrogen phosphate powder must be washed alternately with hydrochloric acid and high-purity water 3 to 4 times to reduce the sample loading blank. The application specifically relates to analytical method, specifically using zirconium hydrogen phosphate suspension as a high-sensitivity emitter to enhance the ionization efficiency of nickel samples, while using phosphoric acid solution to assist ionization, and using high-purity tungsten filament as the sample carrier to determine trace nickel isotope method.

Claims

1. An emitter for trace samples of nickel isotope analysis, wherein: the emitter is a zirconium hydrogen phosphate emitter; and the zirconium hydrogen phosphate specifically comprises a zirconium hydrogen phosphate suspension and a phosphoric acid solution as an auxiliary material.

2. The emitter for trace samples of nickel isotope analysis, as recited in claim 1, wherein the zirconium hydrogen phosphate suspension is prepared by the following process: first alternately washing the high-purity zirconium hydrogen phosphate powder by hydrochloric acid and high-purity deionized water 3 to 4 times to reduce a sample loading blank; then adding deionized water to the treated zirconium hydrogen phosphate powder to prepare zirconium hydrogen phosphate suspension with a certain concentration.

3. The emitter for trace samples of nickel isotope analysis, as recited in claim 2, wherein a concentration of the zirconium hydrogen phosphate suspension is converted according to a dosage of the zirconium hydrogen phosphate emitter required for each analysis and a loading amount of the zirconium hydrogen phosphate suspension, specifically, the dosage of the high-purity zirconium hydrogen phosphate powder required for each analysis, It is 300.2 micrograms, and the loading size of the zirconium phosphate suspension is 1 to 3 L, so the concentration of the zirconium hydrogen phosphate suspension is at a range of 10 to 30 mg/mL.

4. The emitter for trace samples of nickel isotope analysis, as recited in claim 2, wherein a purity of the high-purity zirconium phosphate powder is greater than 99.9%; and a particle size of the high-purity zirconium phosphate powder is less than 75 m.

5. A method for preparing an emitter for trace samples of nickel isotope analysis, wherein the emitter is a zirconium hydrogen phosphate emitter; and the zirconium hydrogen phosphate emitter specifically comprises a zirconium hydrogen phosphate suspension and phosphoric acid solution as an auxiliary material; (1) a preparation method of the zirconium hydrogen phosphate suspension comprising steps of: S1: pre-treating zirconium hydrogen phosphate, comprising: S11: weighing the high-purity zirconium hydrogen phosphate powder and placing in a teflon vial, adding hydrochloric acid in proportion, closing the teflon vial and placing on a hot plate at 80-100 degrees for 1 to 2 hours, shaking the vial during heating time, and cleaning the zirconium hydrogen phosphate with hydrochloric acid powder to reduce the loading blank; S12: then, cooling to room temperature, taking out an upper layer of hydrochloric acid solution, adding high-purity deionized water, closing again and shaking the container for 3 to 4 minutes, standing still for layering, and sucking out the supernatant again; S13: repeating the cleaning process of steps S11 and S12 for 3 to 4 times, and finally obtaining a precipitation phase, which is the pretreated zirconium hydrogen phosphate; S2: weighing the zirconium hydrogen phosphate pretreated in step S13 and adding deionized water to prepare a zirconium hydrogen phosphate suspension of a certain concentration; wherein the concentration of the zirconium hydrogen phosphate suspension is based on the dose of zirconium hydrogen phosphate emitter required for each analysis and the loading volume of zirconium hydrogen phosphate suspension; specifically, the dosage of high-purity zirconium hydrogen phosphate powder required for each analysis is 300.2 g, and the loading volume of zirconium hydrogen phosphate suspension is 1-3 L; the concentration of the zirconium hydrogen phosphate suspension is 10-30 mg/mL; (2) preparing phosphoric acid solution weighing the concentrated phosphoric acid solution, adding deionized water in proportion to prepare a phosphoric acid solution with a concentration at a range of 0.8-1.0 mol/L.

6. The method as recited in claim 5, wherein in step S11, a concentration of hydrochloric acid for cleaning is 2 to 4 mol/L, and an amount of hydrochloric acid for cleaning is 1 ml per (300.2 mg) high-purity zirconium hydrogen phosphate powder; in step S12, an amount of high-purity deionized water used for cleaning is 1 ml per (300.2 mg) high-purity zirconium hydrogen phosphate powder.

7. A method for determining nickel isotopes of trace samples, which is characterized in adopting zirconium hydrogen phosphate suspension as a high-sensitivity emitter to enhance the ionization efficiency of nickel samples, and meanwhile adopting phosphoric acid solution to assist ionization, and adopting high-purity tungsten filament as a sample carrier to determine nickel isotopes.

8. The method for determining nickel isotopes in trace samples as recited in claim 7, which is characterized in specifically comprising steps of: (1) taking an appropriate amount of the emitter composed of zirconium hydrogen phosphate suspension and phosphoric acid solution and coating on the surface of the high-purity tungsten filament; after the emitter evaporates to dryness, loading the nickel sample on the surface of the filament, and tuning the current to 2.2 amperes and evaporating to dryness, then continuing to increase the filament current until the filament turns a dull red glow for 3 to 5 seconds, and then returning the current to zero; (2) installing the sample magazine with nickel sample into the thermal ionization mass spectrometer, and using the thermal ionization mass spectrometer to obtain high-precision nickel isotope data; wherein the temperature of the filament is at a range of 1030-1130 C. during the measurement.

9. The method as recited in claim 8, wherein step (1) The coating process of the emitter is as follows: taking 1-2 L of phosphoric acid solution with a concentration of 0.8-1.0 mol/L and applying on a surface of high-purity tungsten filament, tuning the filament current to evaporate the phosphoric acid solution to dryness, and then taking 1-3 L of a certain concentration of zirconium hydrogen phosphate suspension to cover on the evaporated phosphoric acid coating, after the zirconium hydrogen phosphate suspension is evaporated to dryness, loading the nickel sample on the surface of the W filament.

10. The method, as recited in claim 8, wherein in step (1), an amount of nickel sample is at a range of 200-1000 ng.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0057] In order to better illustrate the content of the present invention, the following further verification of the present invention is carried out through specific embodiments.

[0058] It is hereby explained that the embodiments are only to describe the present invention more apparent, they are only a part of the present invention and cannot constitute any limitation to the present invention.

[0059] In the following examples, the selected source of raw materials is:

[0060] Premium grade pure zirconium hydrogen phosphate (purity: 99.9%, Sinopharm Chemical Reagent Co., Ltd.)

[0061] MOS pure hydrochloric acid (purified by sub-boiling distillation once purified, Sinopharm Chemical Reagent Co., Ltd)

[0062] Ultra-pure water (Millipore Simplicity type ultra-pure water system, outlet water conductivity 18.2 M/cm)

[0063] Nickel isotope standard NIST 986 (National Institute of Standards and Materials, 1000 g mL-1)

Example 1

1. Preparation of Emitter

[0064] 1) Weigh 1500.2 mg of zirconium hydrogen phosphate powder into a teflon sample vial, then add 3 mL 2 mol/L hydrochloric acid, and then closed sample vial in a hot plate at 100-degree for 1 to 2 hours, shaking the sample vail frequently to clean the zirconium hydrogen phosphate powder, reducing the sample loading blank.

[0065] 2) After the sample vial is cooled to room temperature, use a pipette to take out the upper hydrochloric acid solution, add 3 mL of high-purity deionized water, close the sample vial and shake the vial for 2 to 3 minutes, and let it stand for 3 minutes before use pipette to suck out the upper layer of solution.

[0066] 3) Repeat the cleaning process of steps 1) and 2) 4 times, wash the high-purity zirconium hydrogen phosphate powder alternately with hydrochloric acid and deionized water, and the precipitate phase is the final used zirconium hydrogen phosphate powder.

[0067] 4) Add 5 mL of high-purity deionized water to the zirconium hydrogen phosphate powder obtained in step 3) to prepare a zirconium hydrogen phosphate suspension with a concentration of 30 mg/mL for use as a nickel isotope ionization enhancement emitter.

2. Prepare Phosphoric Acid Solution

[0068] Add deionized water to saturated phosphoric acid (14.63 mol/L) in order to obtain 0.8 mol/L phosphoric acid solution, which is used as the auxiliary material of the emitter and is ready for use.

3. Sample Analysis Evaluation

[0069] The sample loading analysis evaluation is as follows:

[0070] 1) Take 1 L of 0.8 mol/L phosphoric acid solution and apply it on the surface of the high-purity tungsten filament, tune the filament current to evaporate the phosphoric acid solution to dryness first, and then take 1 L of 30 mg/mL zirconium hydrogen phosphate suspension to cover the evaporated phosphoric acid coating. After the zirconium hydrogen phosphate suspension is evaporated to dryness, the international standard NIST 986 is loaded onto the surface of the tungsten filament, the current is tuned to 2.2 ampere, and the nickel sample is evaporated to dryness, and then the filament current is heated to a dull red glow and kept 3-5 seconds, then return the current to zero.

[0071] 2) Install the sample magazine into the Triton Plus thermal ionization mass spectrometer, and use the Triton Plus thermal ionization mass spectrometer to determine international standard NIST 986 with loading different sample size. The filament temperature during the measurement is 1030 to 1130 degrees.

[0072] 3) Use .sup.62Ni/.sup.58Ni=0.05338858 for mass fractionation correction, the correction method is exponential law, 200 cycles of data are inquired, and .sup.60Ni/.sup.58Ni results are recorded.

[0073] The concentration of phosphoric acid solution, the concentration of zirconium hydrogen phosphate suspension and the loading size of NIST986 in each example are listed in Table 1 and as follows:

TABLE-US-00001 TABLE 1 Data of the concentration of phosphoric acid solution, the concentration of zirconium hydrogen phosphate suspension and the loading size of NIST986 in Examples 1 to 5 Phosphoric Zirconium hydrogen acid solution phosphate suspension Loading size Concen- Loading Concen- Loading of NIST986 Groups tration size tration size (ng) Example 1 0.8 mol/L 1 L 30 mg/mL 1 L 1000 Example 2 0.8 mol/L 1 L 30 mg/mL 1 L 800 Example 3 0.8 mol/L 1 L 30 mg/mL 1 L 500 Example 4 0.8 mol/L 1 L 30 mg/mL 1 L 400 Example 5 0.8 mol/L 1 L 30 mg/mL 1 L 200

[0074] The analytical results are as follows in Table 2-6:

TABLE-US-00002 TABLE 2 Analysis results of 1000 ng international standard NIST 986 in Example 1 Sample Numbers .sup.60Ni/.sup.58Ni SE NBS986 1000 ng 1 0.385267 0.000005 NBS986 1000 ng 2 0.385257 0.000005 NBS986 1000 ng 3 0.385278 0.000006 NBS986 1000 ng 4 0.385267 0.000006 NBS986 1000 ng 5 0.385259 0.000005 NBS986 1000 ng 6 0.385275 0.000004 NBS986 1000 ng 7 0.385283 0.000004 NBS986 1000 ng 8 0.385259 0.000005 Mean SD 0.385268 0.000010

TABLE-US-00003 TABLE 3 Analysis results of 800 ng international standard NIST 986 in Example 2 Sample Numbers .sup.60Ni/.sup.58Ni SE NBS986 800 ng 1 0.385247 0.000005 NBS986 800 ng 2 0.385251 0.000006 NBS986 800 ng 3 0.385275 0.000004 NBS986 800 ng 4 0.385282 0.000005 NBS986 800 ng 5 0.385271 0.000004 NBS986 800 ng 6 0.385277 0.000004 NBS986 800 ng 7 0.385252 0.000005 NBS986 800 ng 8 0.385255 0.000005 Mean SD 0.385264 0.000014

TABLE-US-00004 TABLE 4 Analysis results of 500 ng international standard NIST 986 in Example 3 Sample Numbers .sup.60Ni/.sup.58Ni SE NBS986 500 ng 1 0.385247 0.000006 NBS986 500 ng 2 0.385251 0.000005 NBS986 500 ng 3 0.385278 0.000006 NBS986 500 ng 4 0.385261 0.000004 NBS986 500 ng 5 0.385240 0.000006 NBS986 500 ng 6 0.385261 0.000006 NBS986 500 ng 7 0.385254 0.000006 NBS986 500 ng 8 0.385234 0.000005 Mean SD 0.385253 0.000014

TABLE-US-00005 TABLE 5 Analysis results of 400 ng international standard NIST 986 in Example 4 Sample Numbers .sup.60Ni/.sup.58Ni SE NBS986 400 ng 1 0.385255 0.000006 NBS986 400 ng 2 0.385247 0.000006 NBS986 400 ng 3 0.385235 0.000006 NBS986 400 ng 4 0.385252 0.000006 NBS986 400 ng 5 0.385282 0.000008 NBS986 400 ng 6 0.385221 0.000006 NBS986 400 ng 7 0.385274 0.000006 NBS986 400 ng 8 0.385250 0.000006 Mean SD 0.385252 0.000020

TABLE-US-00006 TABLE 6 Analysis results of the 200 ng international standard NIST 986 in Example 5 Sample Numbers .sup.60Ni/.sup.58Ni SE NBS986 200 ng 1 0.385288 0.000008 NBS986 200 ng 2 0.385244 0.000007 NBS986 200 ng 3 0.385257 0.000008 NBS986 200 ng 4 0.385278 0.000007 NBS986 200 ng 5 0.385226 0.000008 NBS986 200 ng 6 0.385286 0.000006 NBS986 200 ng 7 0.385268 0.000008 NBS986 200 ng 8 0.385251 0.000008 Mean SD 0.385262 0.000022

TABLE-US-00007 TABLE 7 Signal intensity and emission duration of zirconium phosphate for different sample amounts of nickel Sample Transmission amount (ng) .sup.58Ni(mV) time (minutes) 1000 1100~2300 >25 800 900~1900 >25 500 650~1400 >22 400 500~1100 >20 200 400~550 >18

[0075] Tables 2 to 6 list the results of analyses of different sample sizes (1000 ng, 800 ng, 500 ng, 400 ng, 200 ng) of the international standard NIST 986 with 30 g of zirconium phosphate suspension. The analytical results show that the internal precision of the .sup.60Ni/.sup.58Ni ratio for all samples of 4001000 ng is better than 0.000006 (1SE), which is within error from the reference value of NBS986 (.sup.60Ni/.sup.58Ni=0.3851990.000108, 1SD) reported by Gramlich et al (1989) It is consistent within the analytical error, and the external precision of repeated analyses is better than 0.000020 (1SD). Even for a sample size of 200 ng, the internal precision of the .sup.60Ni/.sup.58Ni ratio of all samples is better than 0.000009 (1SE), and the external precision of repeated analyses is better than 0.000022. The external precision of different sample sizes in this work is 5-fold improvement than that of the existing TIMS technology (Gramlich et al Journal of Research of the National Institute of Standards and Technology, 1989, 94, 347-356). The sample size is significantly reduced from 5 g reported by Gramlich et al.(1989) to 0.2 g in this work.

[0076] It is obviously in Table 6 that a good external precision of (0.000022) of .sup.60Ni/.sup.58Ni ratio is obtained even for a 200 ng trace sample using zirconium hydrogen phosphate emitter, which demonstrates that the zirconium hydrogen phosphate emitter has extremely high sensitivity and high accuracy for Ni isotope analysis.

[0077] To further verify the ionization effect of the emitter provided by the present invention on the trace Ni sample, Table 7 lists the emission duration and emission intensity of different sample sizes. .sup.58Ni has the highest isotope abundance in the Ni isotope system, hence, the emission intensity of .sup.58Ni is used as a direct scale for sensitivity evaluation. Table 7 shows that the analytical method provided by the present invention, even for a 200 ng nickel sample, the intensity of .sup.58Ni can reach 400-550 mV, and the .sup.58Ni signal in this range can be stably emitted for more than 18 minutes, and the actual sample collection only requires 16 minutes (4 s integration, 200 cycles of data acquisition) and can obtain good internal precision better than 0.002% (RSE). This also shows that the emitter provided by the present invention has extremely high sensitivity and high accuracy for Ni isotope analysis.

[0078] One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting.

[0079] It will thus be seen that the objects of the present invention have been fully and effectively accomplished. Its embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.