A rapid analysis method for major and trace elements in geological samples

Abstract

The present invention provides a rapid analysis method for major and trace elements in geological samples, comprising the following steps: 1) Weigh 50 mg of geological sample, 100 mg of lithium metaborate and 10 mg of phosphate in a high-purity pyrolytic graphite crucible according to the mass ratio. 2) Gently stir and mix them evenly with a glass rod, cover with a graphite lid, and place in a self-made melting furnace for melting at 950 °C for 5 minutes. 3) Install the obtained glass beads in resin, attach labels, and polish to obtain a sample target. 4) Load the sample target into an ablation cell, ablate the glass with a laser beam to obtain an aerosol, and transfer it to ICP-MS for detection through a carrier gas. 5) Correct the data results by using the multi-external standard - no internal standard method, and the results of major and trace elements can be obtained. The present invention overcomes the problem of loss of volatile elements such as Pb and Zn commonly existing in the traditional molten glass method. The molten glass method is simple, rapid, efficient, and relatively environmentally friendly, and has strong application prospects in the analysis of whole-rock silicate elements.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical analysis, and particularly relates to a rapid analysis method for major and trace elements in geological samples. A fused glass is prepared with a phosphate-borate mixed flux and used in combination with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to rapidly determine the major and trace elements in geological samples. Background Art

[0002] The chemical composition of geological samples is the basis for understanding their petrographic characteristics, revealing the sources of ore-forming fluids and ore-forming processes, providing important information on rock genesis and crust-mantle exchange, and restricting other geochemical processes. Accurately determining the whole-rock element content in geological samples is crucial for promoting the development of earth sciences. Traditionally, wet chemical digestion is often used to convert geological samples into a homogeneous and stable solution, and then the element content is analyzed by instruments such as ICP-MS or ICP-OES. However, this method is not only relatively cumbersome and time-consuming. For example, the standard method for analyzing elements in geological samples - high-pressure closed digestion method requires long and time-consuming sample digestion (48 h), steps such as evaporation to dryness, redissolution (overnight), and dilution. Moreover, it requires a large amount of reagents such as acids, and emits a large amount of harmful substances such as waste gas and waste acid, resulting in environmental pollution and affecting the health of operators. In contrast, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) allows direct solid sampling without digesting the sample powder into a stable solution, avoiding the cumbersome and time-consuming wet chemical digestion steps and the consumption of a large amount of acids, and is highly favored in the multi-element analysis of geological samples. However, due to the complexity and heterogeneity of geological samples, and the micro-sampling characteristics of the laser (the amount of ablated sample is usually <1 μg each time), the amount of ablated sample is too small to be representative, resulting in poor accuracy and precision. Therefore, preparing a homogeneous and mechanically resistant solid target is a prerequisite for representative whole-rock analysis of geological samples by LA-ICP-MS.

[0003] Common solid sample preparation methods mainly include powder pressing method and fused glass method. The powder pressing method is a simple method, but due to dilution and sample heterogeneity, the accuracy is only 10-20%. Ultrafine powder prepared by wet grinding can obtain accuracy comparable to that of fused glass, but there are problems of nugget effect and elemental contamination of possible zircon and sulfide. The fused glass method includes fluxless fusion method and flux fusion method, which can eliminate mineral grain size and structural effects and effectively improve the analysis accuracy. The fluxless fusion method uses refractory metal belts (Ir belt, Mo belt, W belt), Pt capsules, boron nitride crucibles, high-energy infrared lasers, etc. to directly prepare rock powder into glass at 1300-1800 °C. This method is suitable for the fusion of low SiO2 (<55%) and fine-grained rocks, while it is difficult to obtain homogeneous glass for high SiO2 (>55%) and coarse-grained rocks, such as incomplete dissolution of refractory mineral zircon. In contrast, the flux fusion method can completely dissolve refractory minerals such as zircon, and this method has great advantages for the digestion of geological samples rich in refractory minerals such as zircon, rutile, and ilmenite. The fused glass method is beneficial to the preservation and long-term stability of samples, but its significant disadvantage is the loss problem of volatile elements such as Pb and Zn during the high-temperature melting process, which greatly hinders the use of the Ce / Pb ratio to limit the magmatic process of specific geological units. It is investigated that using a sealed hexagonal boron nitride (h-BN) crucible to prepare fused glass can effectively inhibit the loss of volatile elements such as Pb, but there are possible losses of Cr, Cu, and Ni and abnormal Zn test results. In addition, using a sealed Mo-graphite component can also effectively inhibit the loss of volatile elements such as Pb, but this method has the problem of incomplete dissolution of refractory mineral zircon, and this method is troublesome to operate and has low efficiency, and only one sample can be analyzed at a time.

[0004] Therefore, how to effectively solve the loss problem of volatile elements such as Pb and Zn commonly existing in the fused glass method is an urgent problem to be solved in the field of geochemical analysis at present. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: to provide a rapid analysis method for major and trace elements in geological samples, using a phosphate-borate mixed flux to make fused glass and rapidly determining major and trace elements in geological samples by LA-ICP-MS. This method overcomes the loss problem of volatile elements such as Pb and Zn in the fused glass method, realizes the complete dissolution of refractory minerals such as zircon, improves the analysis efficiency of geological samples, and embodies the concept of environmental protection.

[0006] The present invention provides the following solutions to solve the above technical problems:

[0007] A rapid analysis method for major and trace elements in geological samples, comprising the following steps:

[0008] S1. Weigh the geological sample, lithium metaborate, and phosphate at a mass ratio of 50 mg:100 mg:10 mg in a high-purity pyrolytic graphite crucible.

[0009] S2. Gently stir and mix them evenly with a glass rod, cover with a graphite lid, and place them in a melting furnace to melt at 950 °C for 5 minutes.

[0010] S3. Install the glass beads obtained after cooling in the resin, attach labels, and polish to obtain a sample target.

[0011] S4. Load the sample target into the ablation cell, use a laser beam to ablate the glass to obtain an aerosol, and transfer it to ICP-MS for detection through a carrier gas.

[0012] S5. Use the multi-external standard - no internal standard method to correct the data results, that is, obtain the results of major and trace elements.

[0013] Furthermore, the geological sample described in S1 needs to be physically pulverized in advance and passed through a 200-mesh sieve to obtain sample powder.

[0014] Furthermore, the geological sample is a rock.

[0015] Furthermore, the rock includes granodiorite, andesite, and basalt.

[0016] Preferably, the lithium metaborate and phosphate described in S1 need to be ground in an agate mortar in advance before use.

[0017] Furthermore, the bottom of the high-purity pyrolytic graphite crucible is designed in a pot-bottom shape, and it needs to be cleaned with ultrapure water (MQ water) before use and dried at 100 °C.

[0018] Furthermore, the melting furnace described in S2 includes a heating system of an intermediate frequency induction furnace, a water cooling system, a graphite material anti-oxidation protection system, a multi-stage intelligent program temperature control system, a multi-stage intelligent program vibration system, and a furnace platform structure combination system.

[0019] Furthermore, the beam spot diameter of the laser beam described in S4 is 60 μm, the ablation frequency is 3 Hz, and the energy density is 3 J / cm -2 , and the carrier gas is helium.

[0020] Furthermore, in the multi-external standard - no internal standard method of S5, Si element is selected as the normalization element, and the multi-external standards are glass samples BCR-2G, BHVO-2G, and BIR-1G, and the data processing is completed using the software ICPMSDataCal.

[0021] The principle of the present invention is as follows: By using the reagent phosphate of the present invention, the loss of volatile elements Pb and Zn can be effectively inhibited. Mixing phosphate with lithium metaborate to melt silicate samples can prepare homogeneous glass for the analysis of major and trace elements by LA-ICP-MS. The addition of phosphate converts Pb and Zn into less volatile lead phosphate and zinc phosphate, thus inhibiting the volatilization of Pb and Zn.

[0022] The present invention discloses a rapid analysis method for major and trace elements in geological samples. Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0023] (1) Compared with the previously reported fused glass method, the present invention can completely dissolve refractory minerals such as zircon, and effectively inhibits the loss of volatile elements Pb and Zn, solving the bottleneck problem in the fused glass method.

[0024] (2) By using the multi-external standard - no internal standard method without measuring Li, B, and P, accurate results of major and trace elements can be directly obtained, which is conducive to the direct analysis of unknown samples without pre-determining the internal standard.

[0025] (3) The present invention does not consume acid. Only solid reagents phosphate and lithium metaborate are used to prepare homogeneous glass from geological samples, which is conducive to the long-term preservation of samples. This process has the characteristics of simplicity, rapidity, and relative environmental friendliness, and can meet the needs of daily analysis of silicate whole rock elements by LA-ICP-MS. Description of the Drawings

[0026] Figure 1 is the flow chart of the present invention; Detailed Embodiments

[0027] The following further describes the rapid analysis method for major and trace elements in geological samples provided by the present invention in combination with embodiments. Of course, the following embodiments should not be construed as limiting the present invention.

[0028] To better elaborate the technical solution of the present invention, the embodiments of the present invention will be described more clearly in combination with the drawings. Please refer to Figure 1 , the present invention provides a rapid analysis method for major and trace elements in geological samples, including the following steps:

[0029] S1, first physically crush the geological sample, pass it through a 200-mesh sieve to obtain sample powder. Pre-grind lithium metaborate and diammonium hydrogen phosphate in an agate mortar. Weigh 50 mg of geological sample, 100 mg of lithium metaborate, and 10 mg of diammonium hydrogen phosphate into a pot-shaped high-purity pyrolytic graphite crucible. The geological sample is rock, including granodiorite, andesite, and basalt. The high-purity pyrolytic graphite crucible is pre-cleaned with MQ water before use and dried at 100 °C.

[0030] In step S2, gently stir and mix evenly with a glass rod, cover it with a graphite lid, and place it in a melting furnace for melting at 950 °C for 5 min. The stirring rod is not limited to a glass rod, and a plastic rod can also be used. The graphite lid is placed on the sample and flux mixture to compress the reaction space of the sample and reagent as much as possible.

[0031] The melting furnace described in step S2 includes a heating system of an intermediate frequency induction furnace, a water cooling system, a graphite material anti-oxidation protection system, a multi-stage intelligent program temperature control system, a multi-stage intelligent program vibration system, and a furnace platform structure combination system.

[0032] Among them, the heating system of the intermediate frequency induction furnace includes a copper coil, and the induced current generated by the copper coil is used to heat the sample.

[0033] The water cooling system is controlled by independent circulating water, and the inside of the copper coil is filled with water to achieve the cooling purpose.

[0034] The graphite material anti-oxidation protection system is controlled by argon, and the melting chamber is flushed with argon to protect the graphite material from oxidation.

[0035] The multi-stage intelligent program temperature control system is controlled by a control panel, and the corresponding heating power and heating time are set as required in different temperature sections.

[0036] The multi-stage intelligent program vibration system is controlled by a control panel. The vibration switch and vibration time are set as required in different temperature sections. The vibration frequency is adjusted to a suitable position through a rotary switch. The vibration device is located below the furnace platform structure combination system and is connected to the bottom of the furnace platform structure combination system through mechanical components.

[0037] The furnace platform structure combination system includes a quartz crucible embedded in the copper coil. The quartz crucible is embedded with a graphite matrix. The graphite matrix is a circular graphite block with a certain thickness. Four holes are opened on the front of the graphite matrix for placing the graphite crucible. A quartz cover plate is provided above the graphite matrix. A thermocouple is provided inside the graphite matrix.

[0038] In step S3, the glass beads obtained after cooling are installed in the resin and labeled. After the resin is air-dried, the sample target is polished with sandpaper (mesh numbers: 1000, 2000, 5000, 7000), and then the surface of the sample is ultrasonically cleaned with ultrapure water, and the sample target is dried with an air gun.

[0039] In step S4, the sample target is loaded into the ablation cell, and the glass is ablated with a laser beam to obtain an aerosol, which is transmitted to ICP-MS for detection through helium gas.

[0040] In step S4, before performing the element test, it is necessary to ablate the international silicate glass standard sample NIST 610 to obtain the best 238 U +Signal intensity while ensuring ThO + / Th + signal ratio is lower than 0.3%, U + / Th + ratio is close to 1. Among them, the spot diameter of the laser beam is 60 μm, the ablation frequency is 3 Hz, and the energy density is 3 J cm -2 .

[0041] S5. The multi-external standard - no internal standard method is used to correct the data results, that is, the results of major and trace elements are obtained. Among them, Si element is selected as the normalization element, and the multi-external standards are glass samples BCR-2G, BHVO-2G, and BIR-1G. The data processing is completed using the software ICPMSDataCal.

[0042] In the following examples, the sources of the raw materials selected are as follows:

[0043] Diammonium hydrogen phosphate of high purity (Shanghai Aladdin Biochemical Technology Co., Ltd., 99.99%)

[0044] Lithium metaborate (Shanghai Macklin Biochemical Co., Ltd., ≥99.99%)

[0045] Ultra-pure water (Millipore-Simplicity personal ultra-pure water system of Merck Millipore Corporation, USA, water outlet resistivity 18.2 MΩ / cm)

[0046] Example 1

[0047] Weigh 50 ± 1 mg of basalt (BHVO-2) sample powder, 100 ± 1 mg of lithium metaborate, and 10 ± 1 mg of diammonium hydrogen phosphate in a high-purity pyrolytic graphite crucible in sequence;

[0048] Gently stir the sample and reagents evenly with a glass rod, cover the graphite lid, compress the reaction space of the sample and reagents as much as possible, and place it in a melting furnace to melt at 950 °C for 5 min;

[0049] Install the glass beads obtained after cooling in the resin and attach labels. After the resin dries, polish the sample target with sandpaper (mesh numbers: 1000, 2000, 5000, 7000), then ultrasonically clean the sample surface with ultra-pure water, and dry the sample target with an air gun;

[0050] Install the sample target into the ablation cell, ablate the glass with a laser beam to obtain aerosol, and transfer it to ICP-MS for detection through helium gas. Before the sample test, ablate the international silicate glass standard sample NIST 610 to obtain the best 238 U + signal intensity while ensuring ThO + / Th+ The signal ratio is lower than 0.3%, U + / Th + The ratio is close to 1, where the spot diameter of the laser beam used is 60 μm, the ablation frequency is 3 Hz, and the energy density is 3 J cm -2 .

[0051] The multi-external standard - no internal standard method is used to correct the data results. The Si element is selected as the normalization element, and the glass samples BCR-2G, BHVO-2G, and BIR-1G are used as external standards. The data processing is completed using the software ICPMSDataCal. The results are shown in Table 1.

[0052] Example 2

[0053] Example 2 is generally the same as Example 1, except that the geological sample selected in this example is basalt (BCR-2). The results are shown in Table 1.

[0054] Example 3

[0055] Example 3 is generally the same as Example 1, except that the geological sample selected in this example is basalt (GSR-3). The results are shown in Table 1.

[0056] Example 4

[0057] Example 4 is generally the same as Example 1, except that the geological sample selected in this example is andesite (AGV-2). The results are shown in Table 1.

[0058] Example 5

[0059] Example 5 is generally the same as Example 1, except that the geological sample selected in this example is granodiorite (GSP-2). The results are shown in Table 1.

[0060] Table 1 lists the measured values and reference values of 42 major and trace elements in 5 geological reference materials including basalt, andesite, and granodiorite by using the method proposed in the present invention. It can be seen from Table 1 that the measured values of most elements in different types of rocks analyzed are consistent with the reference values within a 10% deviation range, indicating the reliability of the method for rapidly determining major and trace elements in geological samples by using the phosphate-borate mixed flux to prepare fused glass with LA-ICP-MS. It should be noted that the measured values of Pb and Zn elements are consistent with the reference values within a 10% deviation, indicating that the addition of phosphate effectively solves the problem of loss of volatile elements Pb and Zn commonly existing in the fused glass method.

[0061]

[0062]

[0063] It should be noted that any modifications, equivalent replacements, improvements, etc. to the technical solution of the present invention, without departing from the gist and scope of the technical solution of the present invention, shall be included within the protection scope of the present invention.

Claims

1. A rapid analysis method for major and trace elements in geological samples, characterized in that the geological sample is rock, and the geological sample needs to be physically pulverized in advance and screened through a 200-mesh sieve to obtain sample powder; the rapid analysis method includes the following steps: S1. Weigh 50 mg: 100 mg: 10 mg of geological sample, lithium metaborate and phosphate in a high-purity pyrolytic graphite crucible according to the mass ratio; In step S1, the lithium metaborate and phosphate need to be pre-ground in an agate mortar before use. The bottom of the high-purity pyrolytic graphite crucible is designed in a pot-bottom shape, and it needs to be washed with ultrapure water and dried at 100 °C before use; S2. Gently stir and mix with a glass rod, cover with a graphite lid, and place it in a melting furnace to melt at 950 °C for 5 minutes; S3. Install the glass beads obtained after cooling in resin, attach labels, and polish to obtain a sample target; S4. Load the sample target into the ablation cell, use a laser beam to ablate the glass to obtain aerosol, and transfer it to ICP-MS for detection through a carrier gas; In step S4, the spot diameter of the laser beam is 60 μm, the ablation frequency is 3 Hz, and the energy density is 3 J / cm -2 , and the carrier gas is helium; S5. Use the multi-external standard - no internal standard method to correct the data results, that is, obtain the results of major and trace elements.

2. The rapid analysis method for major and trace elements in geological samples according to claim 1, characterized in that, The rock includes granodiorite, andesite, and basalt.

3. A rapid analysis method for major and trace elements in geological samples according to claim 1, characterized in that, In the multi-external standard - no internal standard method in step S5, Si element is selected as the normalization element, and the multi-external standards are glass samples BCR-2G, BHVO-2G, and BIR-1G. The data processing is completed using software ICPMSDataCal.

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