阅读说明：本技术 用于激光剥蚀电感耦合等离子体质谱分析的固体参考物质及定量分析方法 (Solid reference substance for laser ablation inductively coupled plasma mass spectrometry and quantitative analysis method ) 是由 张国霞 汪正 李青 陈奕睿 郭琳倩 于 2020-05-15 设计创作，主要内容包括：本发明公开用于激光剥蚀电感耦合等离子体质谱分析的固体参考物质及定量分析方法。采用待测金属元素为靶材,通过真空离子镀膜法在平整光滑的固体基材表面镀膜以形成待测元素均匀分布的固体参考物质镀膜。与现有激光剥蚀感耦合等离子体质谱分析的固体参考物质及定量分析方法相比,本发明不仅适合于任何基体样品中任何金属元素的检测,而且操作简单,耗时短,最终采用精准计算方法进行定值,数据准确度更高。(The invention discloses a solid reference substance for laser ablation inductively coupled plasma mass spectrometry and a quantitative analysis method. The metal element to be measured is used as a target material, and a film is coated on the surface of a flat and smooth solid base material by a vacuum ion coating method to form a solid reference material coating film with the uniformly distributed element to be measured. Compared with the existing solid reference substance and quantitative analysis method for laser ablation inductively coupled plasma mass spectrometry, the method provided by the invention is not only suitable for detecting any metal element in any matrix sample, but also simple to operate, short in time consumption, higher in data accuracy and finally adopts an accurate calculation method to carry out fixed value.)

1. The solid reference substance for the laser ablation inductively coupled plasma mass spectrometry is characterized in that a metal element to be detected is used as a target material, and a film is coated on the surface of a flat and smooth solid substrate by a vacuum ion coating method to form a solid reference substance coating film in which the element to be detected is uniformly distributed.

2. The solid reference mass according to claim 1, wherein the solid substrate does not contain the element to be measured or the content of the element to be measured is less than the detection limit of the method.

3. The solid reference substance according to claim 1 or 2, wherein the plating film has a thickness of 0.02 to 2 μm.

4. The solid reference substance according to any one of claims 1 to 3, wherein the solid reference substance coating film of different thickness or concentration gradient is obtained by controlling the coating speed and/or the coating reaction time; preferably, the coating speed is 20-100 nm/min, and the coating reaction time is 1-20 min.

5. The method for the quantitative analysis of a solid reference substance for laser ablation inductively coupled plasma mass spectrometry according to any of claims 1 to 4, comprising the steps of:

(1) the method comprises the steps of adopting the same laser ablation parameters to ablate the prepared solid reference substances with different concentration gradients, collecting inductively coupled plasma mass spectrum data, drawing a standard curve by taking the concentration of an element to be measured in an ablated area as a horizontal coordinate and taking a mass spectrum response signal as a vertical coordinate, wherein the concentration of the element to be measured in the ablated area is obtained through calculation;

(2) randomly selecting a sample to be detected which contains an element to be detected and is close to a solid base material, carrying out ablation on the sample to be detected by adopting the same ablation parameters as the solid reference material subjected to laser ablation in the step (1), and collecting a corresponding mass spectrum signal;

(3) and (3) combining the standard curve obtained in the step (1) with the mass spectrum signal obtained in the step (2) to obtain the content of the element to be detected in the sample to be detected.

6. The quantitative analysis method according to claim 5, wherein the concentration of the element to be measured in the denuded zone is calculated by the following formula: the concentration of the element to be measured in the denuded area = the mass of the element to be measured in the denuded area/the total mass of the sample in the denuded area; mass of the element to be measured in the denudated area = area of the denudated area × density of the element to be measured × speed of vacuum ion plating × reaction time; area of ablated region = size of ablation aperture × ablation rate × ablation time.

7. The quantitative analysis method according to claim 5 or 6, wherein the laser ablation is line scanning or area scanning.

8. The quantitative analysis method according to any one of claims 5 to 7, wherein the ablation rate is 10 to 50 μm/s, and the ablation time is 60 to 300 s; preferably, the laser wavelength is 193nm or 213nm, the laser energy is 20-80%, the laser frequency is 10-20 Hz, and the ablation aperture is 50-100 μm.

9. The quantitative analysis method according to any one of claims 5 to 8, wherein a carrier gas atmosphere of the inductively coupled plasma mass spectrometry is argon gas, and a carrier gas atmosphere of the laser ablation is helium gas; preferably, the ratio of helium to argon is 1:1 to 1: 2; more preferably, the flow rate of the helium gas is 0.6-0.8L/min, and the flow rate of the argon gas is 0.6-0.8L/min.

Technical Field

The invention belongs to the field of analytical chemistry, and particularly relates to a solid reference substance for laser ablation inductively coupled plasma mass spectrometry and a quantitative analysis method using the solid reference substance.

Background

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a method for direct solid sample injection and micro-area analysis. The method has the advantages of good spatial resolution, high sensitivity, wide dynamic linear range and capability of simultaneously measuring multiple elements. Because the solid direct sample introduction is adopted, the problems of complex sample pretreatment and element pollution to be detected in wet analysis are effectively avoided, and the mass spectrum interference is greatly reduced, so that the method is widely applied to element content and distribution analysis in the fields of geology, metals, biology and the like. However, quantitative analysis is always one of the biggest challenges faced by LA-ICP-MS, mainly because the accuracy and precision of the analysis result are affected by the high matrix effect and the element fractionation effect brought by the direct solid injection analysis, and thus the matrix-matched solid reference substance is crucial to quantitative analysis.

Most of the existing solid reference substance preparation methods and quantitative analysis methods developed aiming at laser ablation inductively coupled plasma mass spectrometry are researched aiming at a certain specific substrate, cannot be applied to any substrate, and how to accurately determine the value of the prepared solid reference substance is also the premise of accurate quantitative analysis. For example, the prior art mentions that a uniform and dense Cr film is coated on the surface of a ZnS substrate material by a magnetic filtration ion plating method; and diffusing the ZnS matrix material plated with the Cr film in a quartz tube sealed in vacuum (<10-1Pa) at 950 ℃ for more than 14 days, and grinding and polishing after the diffusion is finished to obtain the solid standard substance. The method is characterized in that the prepared solid reference substance is digested into solution, and fixed value is carried out by adopting inductively coupled plasma emission spectroscopy, the process is complex to operate and consumes long time, uniform diffusion cannot be ensured (a coating intermediate layer is usually thin relative to a surface layer), and the obtained fixed value data is an average value of Cr element. In addition, doping elements of the solid standard reference substance prepared by the method cannot be uniformly diffused into the base material after high-temperature diffusion, so that the quantitative accuracy cannot be guaranteed. Besides, the method is limited by the diffusibility of the element to be measured in the matrix, and is only suitable for quantitative analysis of Cr element in ZnS matrix material.

Disclosure of Invention

In order to overcome the problem of the lack of the solid standard reference substance in the existing LA-ICP-MS analysis, the invention develops a solid reference substance suitable for LA-ICP-MS analysis and a quantitative analysis method thereof. Compared with the existing solid reference substance and quantitative analysis method for laser ablation inductively coupled plasma mass spectrometry, the method provided by the invention is not only suitable for detecting any metal element in any matrix sample, but also simple to operate, short in time consumption (high-temperature treatment is not needed for the coated solid material), and higher in data accuracy because the value is finally determined by adopting an accurate calculation method.

In a first aspect, the invention provides a solid reference substance for laser ablation inductively coupled plasma mass spectrometry, which is characterized in that a metal element to be detected is used as a target material, and a film is coated on the surface of a flat and smooth solid substrate by a vacuum ion coating method to form a solid reference substance coating film in which the element to be detected is uniformly distributed. In some embodiments, a simple substance of the metal element to be detected is used as the target.

The solid standard reference substance can realize the matrix matching of a sample to be detected and the solid reference substance, solves the matrix effect and the element fractionation effect caused by different matrixes in the LA-ICP-MS analysis, and adopts a vacuum ion plating method to prepare the solid reference substance suitable for laser ablation of elements in the direct solid sample injection analysis. In addition, the solid reference substance does not need to carry out high-temperature and polishing and grinding treatment on the coated sample, the coating layer on the surface of the sample is reserved, the operation is simpler, the uniformity of the laser action surface can be ensured, the deviation between a fixed value and an actual value caused by uneven element distribution is greatly reduced, the concentration of the element to be measured in the sample in the denudation area is obtained by adopting accurate calculation, and the treatment steps of ICP-OES measurement and the like after digestion are not needed. In conclusion, the solid standard reference substance prepared by the method is simple to operate, and can well ensure the uniformity of the element to be detected in the sample, so that the accuracy of quantitative analysis is improved.

Preferably, the thickness of the plating film is 0.02 to 2 μm. If the plating layer is too thin, the attachment amount of the element to be detected is too small, and the response signal is too low, so that the standard curve is not favorably drawn; if the plating layer is too thick: the coating cannot be completely degraded by laser, so that the deviation between the acquired data and the calculated data exists, and the quantification is inaccurate; in addition, the excessively thick coating easily causes the proportion of elements to be measured in the laser ablation particles to be excessively high, so that the matrix effect is increased again.

The invention can obtain the coating of the solid reference substance with different concentration gradients by controlling the coating speed and/or the coating reaction time. Preferably, the coating speed is 20-100 nm/min, and the coating reaction time is 1-20 min.

In order to avoid that the base sample contains the element to be detected, so that the calculated quality of the element to be detected in the coating layer has deviation from the actual quality of the element to be detected, and the accuracy of quantitative analysis is influenced, preferably, the base material does not contain the element to be detected or the content of the element to be detected is less than the detection limit of the method.

Preferably, the vacuum degree of the vacuum ion plating method is 0.1 to 0.5 MPa.

In a second aspect, the present invention further provides a method for quantitatively analyzing the solid reference substance for laser ablation inductively coupled plasma mass spectrometry, including the following steps:

(1) the method comprises the steps of adopting the same laser ablation parameters to ablate the prepared solid reference substances with different concentration gradients, collecting inductively coupled plasma mass spectrum data, drawing a standard curve by taking the concentration of an element to be measured in an ablated area as a horizontal coordinate and taking a mass spectrum response signal as a vertical coordinate, wherein the concentration of the element to be measured in the ablated area is obtained by accurate calculation without a complicated constant value process;

(2) randomly selecting a sample to be detected which contains an element to be detected and is close to a solid base material, carrying out ablation on the sample to be detected by adopting the same ablation parameters as the solid reference material subjected to laser ablation in the step (1), and collecting a corresponding mass spectrum signal;

(3) and (3) combining the standard curve obtained in the step (1) with the mass spectrum signal obtained in the step (2) to obtain the content of the element to be detected in the sample to be detected.

Preferably, the concentration of the element to be measured in the denuded zone is calculated as follows: the concentration of the element to be measured in the denudated area is equal to the mass of the element to be measured in the denudated area/the total mass of the sample in the denudated area; the mass of the element to be measured in the denudated area is equal to the area of the denudated area, the density of the element to be measured, the vacuum ion plating speed and the reaction time; the area of the denuded zone is the size of the denuded aperture x denuded rate x denuded time.

Because the concentration of the element to be measured in the denuded zone is obtained by calculation, the element to be measured in the coating in the denuded zone is guaranteed to be completely denuded. Preferably, the element to be measured in the coating in the denuded area is denuded for one time to the extent of more than 90%. In some embodiments, the quantitative analysis result can be more accurate by optimizing the laser ablation parameters such that the signal response intensity of the second repeated ablation is less than 10% of the corresponding intensity of the first signal.

Preferably, the laser ablation manner is line scanning or surface scanning, and preferably line scanning.

Preferably, the ablation rate (also referred to as "scanning rate") is 10-50 μm/s, and the ablation time is 60-300 s.

Preferably, the laser wavelength is 193nm or 213nm, the laser energy is 20-80%, the laser frequency is 10-20 Hz, and the ablation aperture is 50-100 μm.

Preferably, the carrier gas atmosphere of the inductively coupled plasma mass spectrometry is argon; and the carrier gas atmosphere of the laser ablation is helium.

Preferably, the ratio of helium to argon is 1:1-1: 2; preferably, the flow rate of the helium gas is 0.6-0.8L/min, and the flow rate of the argon gas is 0.6-0.8L/min.

The invention has the following advantages:

(1) the method is suitable for solid matrixes made of any materials;

(2) forming a layer of uniformly distributed thin film of the element to be detected on the surface of the solid matrix in a vacuum ion plating mode;

(3) the target material element is used as the element to be detected, and the target material can be any metal element;

(4) the content of the elements to be detected with different concentration gradients can be obtained by controlling the reaction time of the sample and the target material;

(5) according to the method, the concentration of the element to be measured in the denuded area can be accurately calculated by controlling the thickness of the coating film, so that a standard curve can be drawn as an abscissa.

Drawings

FIG. 1 is a diagram of an aluminum alloy substrate and a solid reference material prepared by a vacuum ion plating method, which sequentially comprises, from left to right, the aluminum alloy substrate, the solid reference material prepared by reaction for 1min, the solid reference material prepared by reaction for 2min, the solid reference material prepared by reaction for 5min, and the solid reference material prepared by reaction for 10 min;

FIG. 2 is a micro-area distribution diagram of Ni element of a solid reference substance under laser ablation, and it can be seen that a coating layer of the Ni element is uniformly distributed;

FIG. 3 is a standard curve for quantitative analysis of Ni element in aluminum-based samples by laser ablation inductively coupled plasma mass spectrometry.

Detailed Description

The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.

The following shows a solid reference material for laser ablation inductively coupled plasma mass spectrometry according to the present invention.

First, a suitable substrate and target material are selected.

With respect to the selection of the substrate (which may also be referred to as a "base material"), any solid substrate may be selected for the present invention. The substrate preferably contains no element to be measured or the content of the element to be measured is less than the detection limit of the method. The substrate surface should be as flat and smooth as possible. The substrate surface can be cleaned of contaminants by ultrasonic cleaning. The ultrasonic cleaning time may be, for example, 1 to 10 minutes. The size of the substrate material is ensured to be placed in a sample tank and a laser ablation tank of a coating machine. The specific size can be determined according to the model of the instrument and the model of the sample pool in the experiment.

Regarding the selection of the metal target, the invention selects the metal element to be detected as the target. The element to be measured includes, but is not limited to, a nickel target (Ni target), a titanium target (Ti target), a zinc target (Zn target), a chromium target (Cr target), a magnesium target (Mg target), a niobium target (Nb target), a tin target (Sn target), an aluminum target (Al target), an indium target (In target), an iron target (Fe target), a zirconium target (Zr target), a silicon target (Si target), a copper target (Cu target), a tantalum target (Ta target), a germanium target (Ge target), a silver target (Ag target), a cobalt target (Co target), a gold target (Au target), a gadolinium target (Gd target), a lanthanum target (La target), an yttrium target (Y target), a cerium target (Ce target), a hafnium target (Hf target), a molybdenum target (Mo target), a vanadium target (V target), a tungsten target (W target), and the like. The purity of the target material is preferably greater than or equal to 99.99%.

Subsequently, the preparation of the solid reference substance was carried out by vacuum ion plating. In some embodiments, the substrate dried after ultrasonic cleaning is placed in a coating machine, and the reaction time is controlled to obtain solid reference substances containing different concentrations of the elements to be measured. The method does not need to carry out high-temperature and polishing and grinding treatment on the coated sample, retains the coating layer on the surface of the sample, is simpler to operate, can also ensure the uniformity of the laser action surface, and greatly reduces the deviation of a fixed value and an actual value caused by uneven element distribution. In addition, the concentration of the element to be measured in the sample of the denudation area is obtained by accurate calculation, and processing steps such as ICP-OES measurement after digestion and the like are not needed. In conclusion, the solid standard reference substance prepared by the method is simple to operate, and can well ensure the uniformity of the element to be detected in the sample, so that the accuracy of quantitative analysis is improved.

The thickness of the coating film is preferably 0.02-2 mu m. Therefore, the phenomenon that the coating is too thin, so that the attachment amount of the element to be detected is too small, and the response signal is too low, which is not beneficial to drawing a standard curve can be avoided; the method can also avoid the phenomenon that the cladding layer is too thick to be completely degraded by the laser, so that the deviation exists between the collected data and the calculated data, the quantification is inaccurate, and the proportion of elements to be measured in the laser-degraded particles is too high due to the too thick cladding layer, so that the matrix effect is increased again.

Because the concentration of the element to be measured in the denudation area is obtained by adopting a calculation method through the solid reference substance provided by the invention, the thickness of the coating film needs to be strictly controlled in order to ensure that the film is broken down by laser denudation. Therefore, the plating speed is preferably 20nm/min to 100nm/min, and the plating reaction time is preferably 1 to 20 min. If the coating speed is lower than 20nm/min and the reaction time is lower than 1min, or if the coating speed is higher than 100nm/min and the reaction time is higher than 20min, the laser ablation can not be guaranteed to break down the coating in sequence, so that the prepared film is not suitable for the invention.

The invention obtains the total mass of the elements to be measured attached to the surface of the solid base material (namely, the total mass of the sample of the denuded area) through calculation. The calculation formula is as follows:

m ═ V ρ wherein: m is the total mass of the elements to be detected; v is the total volume; rho is the density of the element to be measured. Formula (1)

V — sxl wherein: s is the surface area of the substrate; and L is the thickness of the element coating to be measured. Formula (2)

L ═ v × t wherein: v speed of vacuum ion plating; t is: and (4) reaction time. Formula (3)

The invention also discloses a performance investigation method of the solid reference substance, which comprises the step of carrying out uniformity, stability and quantitative accuracy investigation on the prepared solid reference substance by adopting an LA-ICP-MS instrument.

In order to eliminate the element fractionation effect more effectively and ensure that the coating layer is completely degraded by laser, different laser degradation conditions are selected adaptively for samples of different substrates. Preferably, the laser ablation adopts a laser wavelength of 193nm or 213nm, laser energy of 20-80%, laser frequency of 10-20 Hz and ablation aperture of 50-100 μm. In some embodiments, the scanning speed is 10-50 μm/s, and the denudation time is 60-300 s. In addition, laser ablation uses helium as a carrier gas. The flow rate of the helium gas may be 0.6 to 0.8L/min. The laser ablation can be performed on the prepared solid reference substance in a line ablation or surface ablation mode.

In order to better reduce the influence of the matrix effect on the accuracy of the quantitative analysis result, the sample can be any sample to be detected which contains the element to be detected and is close to the matrix of the solid reference substance.

For rough observation of the surface content of the sample, a line denudation mode (short time consumption and good stability) can be selected, and a surface denudation mode (long time consumption) can be selected for fine analysis of the surface of the sample. The better denudation mode for the uniformity inspection of the solid reference substance is surface scanning, and a distribution imaging graph of the element to be detected on the surface of the Al matrix is obtained. The preferred mode of degradation for the data required for quantitative analysis of the sample according to the present invention is line scanning.

The standard sample prepared by the method is excellent in uniformity, good in stability, wide in linear range, good in linear correlation and good in repeatability, and can be used for LA-ICP-MS quantitative analysis of element content in a solid sample. RSD of response signal of any scanning line at different positions of sample is obtained in LA-ICP-MS line scanning mode<10 percent, and adopts LA-ICP-MS to collect solid reference substances with different concentration gradients, and the linear correlation coefficient R of a quantitative curve²Greater than 0.999.

The operation process of the quantitative analysis comprises the steps of adopting the same laser ablation parameter to ablate the prepared solid reference substances with different concentrations, collecting mass spectrum data, arranging the data and drawing a standard curve. And finally, selecting any substrate sample containing the element to be detected, and carrying out denudation on the sample by adopting the denudation parameters same as those of the reference substance to obtain the content of the element in the sample. The quality of sample denudation under different denudation conditions is different, and the denudation quality consistent with that of solid reference substance denudation can be ensured by adopting the denudation parameters of the matrix sample identical to that of the reference substance, so that the matrix effect caused by different matrix qualities is reduced.

And finally digesting the sample into a solution by adopting an aqua regia system, and analyzing by adopting an inductively coupled plasma emission spectrometry. The results obtained by the two methods are compared, and the accuracy of the quantitative analysis is ensured.

Inductively coupled plasma mass spectrometry uses an argon carrier gas. When the ratio of helium to argon is 1:1, the stability of mass spectrum response signals is better. The flow rate of argon gas is preferably 0.6-0.8L/min.

And drawing a standard curve, selecting the concentration of the element to be detected in the denuded area as an abscissa, taking the mass spectrum response signal as an ordinate, and drawing a unary linear regression graph.

The concentration of the element to be measured in the denuded area can be obtained by calculation. The calculation formula is as follows:

the concentration of the element to be measured in the denuded zone is m (mass of the element to be measured in the denuded zone)/m (total mass of the sample in the denuded zone). Formula (4)

m (mass of the element to be measured in the ablated region) is S (area of the ablated region) multiplied by rho multiplied by v multiplied by t, wherein rho is the density of the element to be measured; v speed of vacuum ion plating. t is: and (4) reaction time. Formula (5)

S (area of ablated region) is the size of ablation aperture x ablation rate x ablation time. Formula (6)

The present invention will be described in detail by way of examples. It is to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art in light of the foregoing description are intended to be included within the scope of the invention. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.

The instrument parameters are as follows: the vacuum ion plating instrument adopted by the invention is an EI-5Z type instrument of Japan Efa department company, the laser ablation adopts a 213nm Nd-YAG laser ablation sample injection system of NEW WAVE company, the laser wavelength is 213nm, the energy is 40 percent, the laser frequency is 20Hz, the ablation aperture is 100 mu m, the scanning speed is 10 mu m/s, and the helium flow is 0.7L/min; ICP-MS is a Thermo X series II CCT type four-stage rod, argon is used as carrier gas, and the flow of the argon is 0.7L/min.