CN115290742A - Method for rapidly determining Mg isotope composition in carbonate mineral - Google Patents
Method for rapidly determining Mg isotope composition in carbonate mineral Download PDFInfo
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Abstract
The invention discloses a method for rapidly determining Mg isotope composition in carbonate minerals, which comprises the following steps: placing a standard sample and a sample to be detected into an ablation pool, and connecting a water vapor introducing device in front of the ablation pool; adopting a laser system to denudate the standard sample and the sample to be detected to obtain aerosol; introducing the aerosol into an MC-ICP-MS system through the water vapor introducing device to obtain an Mg isotope initial ratio; calculating the composition of the Mg isotope in the sample to be detected according to a formula I by taking the standard sample as a reference; according to the invention, by introducing water vapor, the deep fractionation effect of the Mg isotope in the carbonate sample is weakened, so that the matrix effect among samples with different chemical compositions and crystal structures is weakened, and the technical problem of poor Mg isotope analysis precision and accuracy is solved.
Description
Technical Field
The invention relates to the technical field of chemical analysis, in particular to the technical field of magnesium isotopes, and particularly relates to a method for rapidly determining Mg isotope composition in carbonate minerals.
Background
Magnesium is a major element and is widely distributed in silicate earth, water circles and biospheres. The abundance of magnesium in the silicate earth makes it a major constituent of minerals in igneous, metamorphic and sedimentary rocks. Carbonate minerals (magnesite, dolomite and siderite) generally have higher Mg content, the Mg isotope composition of the carbonate minerals is one of important tracing means for researching carbon and oxygen recycling, is also an important means for tracing the source of the formed minerals and the evolution of mineral deposits, and is also widely applied to the research of the ancient environment and the ancient climate evolution, and the geochemical research of the Mg isotope of the carbonate minerals has important geological significance.
Typically, the Mg isotope of most geological or biological samples is measured based on solution methods. After the sample is crushed and dissolved, a cation exchange column is used for removing all other impurities in the solution, and then the Mg isotope of the solution after the purification is measured by multi-receiving inductively coupled plasma mass spectrometry (MC-ICPMS), wherein the analysis precision can reach 0.1 per thousand (2 SD) or less (Glay et al, 2001). These methods are highly accurate, but the pre-treatment process is complex and time consuming, since removing the matrix ions is a complex and challenging task. Likewise, another limitation of the solution method is that the analysis requires a relatively large sample volume, which results in the analysis being an overall average of the sample, obscuring the Mg isotope variations in the micrometer scale of the object to be measured.
The laser multi-receiving inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) is one of important means for in-situ isotope analysis in mineral micro-areas, has the advantages of high spatial resolution, small sample consumption, low pollution risk, high speed, economy and the like, and can obtain isotope information on the scale of the mineral micro-areas. However, so far, only about 7% o of Mg isotope fractionation has been observed in geological samples, and therefore, the analytical precision and accuracy of the experimental data of Mg isotopes are extremely high. Because laser analysis is in-situ micro-area sampling, a chemical purification step is lacked, and a matrix is very complex, so that the spectral interference and the matrix effect are serious, and the precision and the accuracy of the Mg isotope obtained by the laser in-situ micro-area analysis are greatly different from those of a solution method.
The main technical difficulties of laser in-situ micro-area analysis of Mg isotope ratio are mass spectrum interference and matrix effect. In general 48 Ca 2+ Is a pair to be considered 24 Mg + Because Ca is one of the main constituent elements of carbonate minerals (Young et al, 2002, deng et al, 2021). To eliminate the interference, the simplest method is to analyze with medium or high mass resolution, which exacerbates the effects of the matrix and greatly reduces the sensitivity. In addition, since it is almost impossible to make the Mg content and matrix elements of the standard sample and the sample to be measured completely the same in laser analysis, the matrix effect is inevitable (Norman et al, 2006, sadekov et al, 2020). Sadekov et al (2020) research shows that when the content of Fe and Mn in calcite is higher (1%), the deviation of Mg isotope analysis can reach 3 per thousand. The chemical composition of carbonate minerals varies greatly in nature, for example the dolomite solid solution series (dolomite (CaMg (CO) 3 ) 2 ) Iron dolomite (Ca (Mg, fe) (CO) 3 ) 2 ) Therefore, the matrix effect is one of the main reasons to be considered. The mass spectrum interference and the matrix effect directly restrict the application of the laser in-situ micro-area carbonate mineral Mg isotope rapid and accurate analysis.
In conclusion, new rapid analytical methods were investigated for effective inhibition of carbonate mineral samples 48 Ca 2+ For is to 24 Mg + The mass spectrum interference and the matrix effect caused by the diversity of chemical components are still the urgent tasks of carrying out laser in-situ micro-area analysis on the Mg isotope composition of carbonate minerals.
Disclosure of Invention
The invention mainly aims to provide a method for rapidly determining Mg isotope composition in carbonate minerals, and aims to solve the problems of troublesome method, serious mass spectrum interference and inaccurate test result of the existing method for detecting Mg isotope composition.
In order to achieve the purpose, the invention provides a method for rapidly determining the Mg isotope composition in carbonate minerals, which is characterized by comprising the following steps:
placing a standard sample and a sample to be detected into an ablation pool, and connecting a water vapor introducing device in front of the ablation pool;
adopting a laser system to denudate the standard sample and the sample to be detected to obtain aerosol;
introducing the aerosol into an MC-ICP-MS system through the water vapor introducing device to obtain an Mg isotope initial ratio;
calculating the composition of the Mg isotope in the sample to be detected according to a formula I by taking the standard sample as a reference, wherein the formula I is as follows: delta. For the preparation of a coating 2x Mg＝{[( 2x Mg/ 24 Mg) Sample to be tested /( 2x Mg/ 24 Mg) Standard sample ]-1 }. Times.1000, wherein, 2x mg is 25 Mg + And 26 Mg + the signal intensity of, 24 Mg is 24 Mg + Signal strength of, delta 2x And Mg is the Mg isotope composition in the sample to be detected.
Optionally, the aerosol is introduced into the MC-ICP-MS system through the water vapor introduction device to obtain the initial ratio of the Mg isotope,
the water vapor introduced into the device comprises ultrapure water vapor.
Optionally, in the step of introducing the aerosol into the MC-ICP-MS system through the water vapor introducing device to obtain the initial ratio of the Mg isotope,
the flow rate of the steam introducing device is 5.3-8.0 mg/min.
Optionally, the aerosol is introduced into the MC-ICP-MS system by the water vapor introduction device, and the step of obtaining the initial ratio of Mg isotope comprises:
introducing water vapor into a compensation argon gas path, uniformly mixing the water vapor with argon gas, then introducing the water vapor into a helium gas path, and uniformly mixing the water vapor with helium gas to obtain carrier gas rich in water vapor;
and introducing the aerosol in the denudation pool into an MC-ICP-MS system through the carrier gas rich in the water vapor to obtain the initial ratio of the Mg isotope.
Optionally, the flow rate of the argon is 0.8 to 1.05L/min.
Optionally, in the step of obtaining the aerosol by using a laser system to degrade the standard sample and the sample to be tested,
the laser system comprises a 193nm excimer nanosecond laser system.
Optionally, the standard sample and the sample to be tested are put into an ablation pool, in the step of connecting a water vapor introducing device in front of the ablation pool,
the sample to be detected comprises any one of magnesite, dolomite and siderite.
Optionally, in the sample to be detected, the ratio of calcium element to magnesium element is 0.01-6.79; and/or the presence of a gas in the gas,
in the sample to be detected, the ratio of the iron element to the magnesium element is 0-17.40; and/or the presence of a gas in the gas,
in the sample to be detected, the ratio of manganese element to magnesium element is 0-2.10.
Optionally, the standard sample and the sample to be tested are put into an ablation pool, in the step of connecting a water vapor introducing device in front of the ablation pool,
the standard sample comprises any one of MGS-3 magnesite, DOL-8 dolomite and SD-5 siderite.
Optionally, the step of placing the standard sample and the sample to be tested into an ablation pool, and connecting a water vapor introducing device in front of the ablation pool comprises:
embedding two parts of carbonate minerals into epoxy resin to prepare a sample target, determining a standard sample and a sample to be detected according to the sample target, putting the standard sample and the sample to be detected into an erosion pool, and connecting a water vapor introducing device in front of the erosion pool.
The analysis method provided by the invention is simple and efficient; the complex sample pretreatment process is avoided, and the sample can be rapidly put into use; meanwhile, the method fills the blank of analyzing the Mg isotope composition of magnesite, dolomite and siderite in a laser in-situ micro-area,providing a sharp tool for the development of geology related disciplines; in the technical scheme of the invention, the deep fractionation effect of the Mg isotope in the carbonate sample is weakened by introducing water vapor into the laser ablation system, so that the matrix effect among samples with different chemical compositions and crystal structures is weakened, and the technical problem of poor Mg isotope analysis precision and accuracy is solved. Meanwhile, aerosol is introduced into the MC-ICP-MS system through the water vapor introducing device, so that the aerosol can be effectively inhibited from being contained in a sample to be detected 48 Ca 2+ To pair 24 Mg + The mass spectrum interference solves the technical problem that the low mass resolution ratio can not be used for accurately measuring the Mg isotope of the carbonate mineral with the high Ca/Mg ratio due to the mass spectrum interference in the laser ablation sample injection analysis method in the laser system.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.
FIG. 1 is a graph showing the change of the ratio of 26Mg/24Mg in MGS-3 magnesite according to the invention in example 1 and comparative example 1 with the depth of denudation, and the comparison of the delta 26MgDHF values (the upper curve is for comparative example 1, and the lower curve is for example 1);
FIG. 2 is a graph comparing the 44Ca2+/24I ratio in example 2 of the present invention and comparative example 2;
FIG. 3 is a graphical representation of the effect of different laser ablation frequencies on the results of DOL-8 dolomite Mg isotope analysis in example 3;
FIG. 4 is a graphical representation of the effect of beam spot size on the results of DOL-8 dolomite Mg isotope analysis in example 4;
FIG. 5 is a graphical representation of the results of a delta 26Mg analysis of DOL-4 dolomite in example 6 and comparative example 6;
FIG. 6 is a graphical representation of the results of a delta 25Mg analysis of DOL-4 dolomite in comparative example 6 and comparative example 6;
FIG. 7 is a graph showing the results of the δ 26Mg isotope analysis of SD-1 siderite in example 7 and comparative example 7;
FIG. 8 is a graph showing the results of the delta 25Mg isotope analysis of SD-1 siderite in comparative example 7 and comparative example 7;
fig. 9 is a schematic flowchart of an embodiment of the method for rapidly determining the Mg isotope composition in carbonate minerals according to the present invention.
The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially. In addition, the meaning of "and/or" appearing throughout includes three juxtapositions, exemplified by "A and/or B", including either A or B or both A and B. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The main technical difficulties of laser in-situ micro-area analysis of Mg isotope ratio are mass spectrum interference and matrix effect. In general 48 Ca 2+ Is a pair to be considered 24 Mg + Because Ca is one of the main constituent elements of carbonate minerals (Young et al, 2002. To eliminate interference, the simplest method is to analyze with medium or high mass resolution, but medium or high mass resolutionResolution exacerbates the effects of the matrix and can significantly reduce sensitivity. In addition, since it is almost impossible to make the Mg content and matrix elements of the standard sample and the sample to be measured completely the same in laser analysis, the matrix effect is inevitable (Norman et al, 2006, sadekov et al, 2020). Sadekov et al (2020) research shows that when the content of Fe and Mn in calcite is higher (1%), the deviation of Mg isotope analysis can reach 3 per thousand. The chemical composition of carbonate minerals varies greatly in nature, for example the dolomite solid solution series (dolomite (CaMg (CO) 3 ) 2 ) -iron dolomite (Ca (Mg, fe) (CO) 3 ) 2 ) Therefore, the matrix effect is one of the main reasons to be considered. The mass spectrum interference and the matrix effect directly restrict the application of the laser in-situ micro-area carbonate mineral Mg isotope rapid and accurate analysis.
In view of the above, the invention provides a method for rapidly determining the Mg isotope composition in carbonate minerals, which effectively inhibits the Mg isotope composition in carbonate minerals by introducing a small amount of water vapor before a laser ablation pool 48 Ca 2+ To pair 24 Mg + The mass spectrum interference of the method also weakens the deep fractionation effect of the Mg isotope so as to improve the matrix effect, thereby obtaining the Mg isotope composition in the carbonate mineral to be detected; in combination with the schematic flow chart of an embodiment of the method for rapidly determining the Mg isotope composition in the carbonate mineral shown in fig. 9, the method for rapidly determining the Mg isotope composition in the carbonate mineral includes the following steps:
and S10, placing the standard sample and the sample to be detected into an ablation pool, and connecting a water vapor introducing device in front of the ablation pool.
Inductively coupled plasma mass spectrometry distinguishes different ions by the mass-to-charge ratio (mass/charge) of the elements, since, during detection, the ions are separated by the mass-to-charge ratio (mass/charge) of the elements 48 Ca 2+ And 24 Mg + because the mass-to-charge ratios are the same and the instrument cannot distinguish, the received signal with mass number 24 includes 48 Ca 2+ And 24 Mg + is difficult to realize 24 Mg + The accurate detection of.
The sampling mode of the laser ablation system is in-situ micro-area ablationAnd aerosol particles generated after the sample is degraded are conveyed to the inductively coupled plasma through the carrier gas to be ionized. In the denudation process, the sample is influenced by the thermal effect of laser energy, and the proportion of volatilization and aerosol formation of each isotope of Mg is different along with the increment of denudation depth, so that the test value (depth fractionation effect) of the Mg isotope is influenced. Due to the difference of chemical composition and crystal structure, the deep fractionation effect generated by different samples is inconsistent, so that the accurate determination of the Mg isotope is difficult to realize. In the embodiment, the water vapor introducing device is connected in front of the denudation pool, and the sample to be detected is introduced into the LA-MC-ICP-MS system through the water vapor introducing device, so that the situation that the sample to be detected is effectively inhibited 48 Ca 2+ For is to 24 Mg + The mass spectrum interference reduces the Mg isotope deep fractionation effect so as to improve the matrix effect, and the influence of the denudation behavior on Mg isotope analysis is reduced by optimizing various parameters of a nanosecond laser denudation system, so that the Mg isotope composition in carbonate minerals is rapidly and accurately determined, and the laser in-situ micro-area carbonate mineral Mg isotope analysis technology is more effectively applied to geological research; therefore, the problem can be solved by connecting the water vapor introducing device 48 Ca 2+ For is to 24 Mg + The method is simple and efficient, and can be rapidly put into use.
Before the step S10, a carbonate mineral sample is required to be screened, and a standard sample and a sample to be detected are determined; during actual selection, the standard sample and the sample to be detected need to be ensured to be the same type of mineral, and during actual operation, screening can be performed according to the following method: selecting two parts of carbonate mineral particles with good crystal forms, embedding the two parts of carbonate mineral particles into epoxy resin to prepare a sample target, specifically, uniformly distributing points on the selected carbonate mineral sample, analyzing by a laser inductively coupled plasma mass spectrometer (LA-ICP-MS), determining the component uniformity of the two carbonate mineral samples, analyzing by LA-MC-ICP-MS, determining the isotope ratio uniformity of the two carbonate mineral samples, and determining a standard sample and a sample to be detected according to the uniformity.
Further, in this embodiment, the mass spectrometer resolution used for analysis is selected to be low mass resolution.
Further, the sample to be detected comprises one of magnesite, dolomite and siderite. The standard sample comprises one of MGS-3 magnesite, DOL-8 dolomite and SD-5 siderite; in practical application, the principle of unity needs to be considered, that is, a standard sample and a sample to be detected are carbonate minerals of the same type, and in one embodiment, when the sample to be detected is magnesite, the standard sample is MGS-3 magnesite; in another embodiment, the sample to be detected is dolomite, and the standard sample is DOL-8 dolomite; in another embodiment, the sample to be tested is siderite, and the standard sample is SD-5 siderite.
Furthermore, in order to ensure the accuracy of the test result, in some embodiments, the ratio of various elements in the sample to be tested needs to be controlled, specifically, the ratio of calcium element to magnesium element in the sample to be tested is 0.01 to 6.79; the ratio of the iron element to the magnesium element is 0-17.40; the ratio of manganese element to magnesium element is 0-2.10. The inventor has proved through a great deal of experimental tests that the flow of the introduced water vapor can be effectively inhibited within the element ratio range 48 Ca 2+ To pair 24 Mg + The mass spectrum interference of the Mg isotope is reduced, and meanwhile, the deep fractionation effect of the Mg isotope is weakened. It should be noted that the above range is a preferable range, but does not mean that the above range is not applicable within the range of the element ratio or within the range of the water vapor flow rate, and theoretically, the Mg isotope composition of the carbonate mineral can be determined by selecting an appropriate water vapor flow rate according to the method provided by the present invention according to the experimental requirements.
Specifically, when step S10 is performed, it may be performed by: embedding two parts of carbonate minerals into epoxy resin to prepare a sample target, determining a standard sample and a sample to be detected according to the sample target, putting the standard sample and the sample to be detected into an ablation pool, and connecting a water vapor introduction device in front of the ablation pool.
In the present invention, the reason is that 48 Ca 2+ And 24 Mg + signals overlap and it is not possible to measure either one aloneIsotopic intensity, therefore, in this example, 48 Ca 2+ signal intensity by measurement 44 Ca 2+ To calculate; the isotope of Mg includes 24 Mg、 25 Mg and 26 Mg。
the water vapor introducing device can be arranged according to the conventional arrangement in the field, and the details are not repeated.
And S20, denudating the standard sample and the sample to be detected by adopting a laser system to obtain aerosol.
It should be noted that, in the actual test process, optimization of laser system parameters is also crucial to improving accuracy of Mg isotope composition in the lateral roof carbonate minerals, and repeated research and test by the inventor have shown that changing laser ablation frequency, beam spot size and energy density all have obvious influence on laser ablation frequency on Mg isotope analysis, specifically, in some embodiments, the laser system ablation frequency is 2-6 Hz; the beam spot size of the laser system is 33-75 μm; the energy density of the laser system is 2-6J/cm 2 The result measured in the test range of the laser system is more accurate; it should be noted that the above ranges are preferred ranges, but do not mean that the above ranges are not applicable, and theoretically, the Mg isotopic composition of the carbonate mineral can be determined by selecting appropriate conditions according to the method provided by the present invention based on experimental requirements.
Further, in the present embodiment, the laser system is selected to be a 193nm excimer nanosecond laser system.
And S30, introducing the aerosol into an MC-ICP-MS system through the water vapor introducing device to obtain an initial ratio of the Mg isotope.
In performing step S30, it may be performed by: and introducing the aerosol into the water vapor introducing device, and introducing the aerosol into an MC-ICP-MS system in a mode of compensating argon gas to convey water vapor to obtain the initial ratio of the Mg isotope.
The introduced water vapor is ultrapure water, and the ultrapure water is continuously pumped into a water vapor introducing device through a peristaltic pump and then is brought into the LA-MC-ICP-MS system through the supplemented argon; controlling the amount of introduced water vapor by adjusting the pump speed and the argon flow; compared with the method for directly measuring the Mg isotope composition of the carbonate mineral without introducing water vapor, the analysis precision and accuracy of the Mg isotope of the carbonate mineral after introducing the water vapor are obviously improved.
Specifically, in some embodiments, the water vapor is generated by a Milli-Q ultrapure water system (millipore, billerica, MA, USA), and the peristaltic pump is a peristaltic pump installed on a Sammer fly inductively coupled plasma, specifically, the peristaltic pump has a pump speed of 25-40rpm during actual operation.
Further, in order to ensure the accuracy of the measurement structure and avoid the influence of other unnecessary factors, in some embodiments, the water vapor introduced into the water vapor introduction device comprises ultra-pure water vapor.
Furthermore, the flow rate of the steam introducing device is 5.3-8.0 mg/min, and the flow rate of the argon is 0.8-1.05L/min.
It should be noted that in the actual testing process, calibration of instrument quality fractionation is also required in combination with the standard-sample cross-over method (SSB).
Step S40, calculating the composition of the Mg isotope in the sample to be detected according to a formula I by taking the standard sample as a reference, wherein the formula I is as follows: delta 2x Mg＝{[( 2x Mg/ 24 Mg) Sample to be tested /( 2x Mg/ 24 Mg) Standard sample ]-1 }. Times.1000, wherein, 2x mg is 25 Mg + And 26 Mg + the signal intensity of, 24 Mg is 24 Mg + Signal strength of, delta 2x And Mg is the Mg isotope composition in the sample to be detected.
The technical solutions of the present invention are further described in detail below with reference to specific examples and drawings, it should be understood that the following examples are merely illustrative of the present invention and are not intended to limit the present invention.
Example 1
(1) Putting MGS-3 magnesite in a denudation pool;
(2) Connecting a water vapor introducing device, adopting 193nm excimer nanosecond laser to degrade an MGS-3 magnesite sample, and introducing aerosol generated by degradation into MC-ICP-MS for determination through water vapor; deriving the obtained original data, and calculating the Mg isotope fractionation among different denudation depths by using a formula II, wherein the formula II is as follows:
δ 26 Mg DHF ＝[( 26 Mg/ 24 Mg) last 10 sec. /( 26 Mg/ 24 Mg) first 10 sec. -1]×1000
wherein, delta 26 Mg DHF Is an isotopic composition of Mg: ( 26 Mg/ 24 Mg) last 10 sec And (a) 26 Mg/ 24 Mg) first 10 sec Ten seconds after denudation respectively 26 Mg and 24 average value of Mg Signal intensity ratio and ten seconds before etching 26 Mg and 24 average of Mg signal intensity ratio. Delta 26 Mg DHF Closer to 0 indicates less deep fractionation effect.
Comparative example 1
1) Putting MGS-3 magnesite in a denudation pool;
(2) Not connecting a water vapor introducing device, adopting 193nm excimer nanosecond laser to degrade an MGS-3 magnesite sample, and directly introducing aerosol generated by degradation into MC-ICP-MS for determination; the obtained raw data is derived, and Mg isotope fractionation between different ablation depths is calculated by using a formula II.
Example 1 and comparative example 1 demonstrate that the introduction of water vapor serves to attenuate the Mg isotope deep fractionation effect by comparing the size of Mg isotope fractionation with the depth of denudation in the absence of water vapor and in the presence of water vapor; fig. 1 shows one of the calculation results.
From fig. 1, it can be seen that: delta of MGS-3 magnesite without adding water vapor 26 Mg DHF A value of-1.46% o and delta after introduction of water vapour 26 Mg DHF The value is-1.05 ‰. It can be seen that the deep fractionation effect can be weakened by adding water vapor, thereby improving the analysis accuracy of the Mg isotope composition.
Example 2
In the present embodiment, it is preferred that, 24 i represents the signal strength of 24 mass numbers, which comprises 48 Ca 2+ And 24 Mg + the signal strength of (c).
(1) Placing DOL-4 dolomite (the ratio of Ca/Mg is 6.79) into an ablation pool;
(2) Connecting with a water vapor introducing device, adopting 193nm excimer nanosecond laser to ablate DOL-4 dolomite sample, introducing the aerosol generated by ablation into MC-ICP-MS via water vapor, measuring with low mass resolution, adjusting sample injection amount by changing the size of laser ablation beam spot during measurement, and recording 44 Ca 2+ And 24 i signal value.
Comparative example 2
(1) Placing DOL-4 dolomite (the ratio of Ca/Mg is 6.79) into an ablation pool;
(2) Without connecting with vapor introducing device, adopting 193nm excimer nanosecond laser to ablate DOL-4 dolomite sample, directly introducing aerosol generated by ablation into MC-ICP-MS for determination with low mass resolution, changing size of laser ablation beam spot during determination process to adjust sample injection amount, and recording 44 Ca 2+ And 24 i signal value.
Example 1 and comparative example 1 were generated by comparing samples without and with added water vapor 44 Ca 2 + / 24 I ratio difference to prove that the introduction of water vapor plays a role in inhibiting 48 Ca 2+ The effect of yield, the test results are shown in fig. 2.
From fig. 2, it can be seen that: when no water vapor is added, with the increase of the denudation beam spots, 44 Ca 2+ / 24 the ratio of I is increased, and when the beam spot size is not less than 90 μm, 44 Ca 2+ / 24 the I ratio is kept unchanged; 44 Ca 2+ / 24 when the ratio of I to I is the highest, 48 Ca 2+ the influence on the Mg isotope composition is up to 0.76 per thousand; after the introduction of water vapor, even under extreme spot size conditions, 44 Ca 2+ / 24 the ratio of I is also within 0.001, 48 Ca 2+ the influence on the Mg isotope composition is less than 0.09 per thousand, and the influence can be ignored. Indicating that in the case of introducing steam, even for carbon having a high Ca/Mg ratio (6.79)Acid salt sample thereof 48 Ca 2+ Interference influence can be not considered, and no deduction can be realized under the condition of low mass resolution 48 Ca 2+ The Mg isotope composition of the carbonate sample can be determined by interference.
Example 3
(1) Placing DOL-8 dolomite in an ablation pool;
(2) Connecting a water vapor introducing device, adopting 193nm excimer nanosecond laser to denude DOL-4 dolomite samples, introducing aerosol generated by denudation into MC-ICP-MS through water vapor, and determining with low mass resolution; wherein, in the actual operation process, other parameters are kept unchanged (namely the size of the ablation beam spot is 75 μm, the energy density is 3J/cm < 2 >), DOL-8 dolomite which is ablated at the ablation frequency of 2Hz is used as a standard sample, and the DOL-8 dolomite which is ablated at different laser ablation frequencies (2 Hz, 4Hz, 6Hz, 8Hz and 10 Hz) is corrected; the test results are shown in fig. 3.
Example 4
(1) Placing DOL-8 dolomite in an ablation pool;
(2) Connecting a water vapor introducing device, adopting 193nm excimer nanosecond laser to denude DOL-4 dolomite samples, introducing aerosol generated by denudation into MC-ICP-MS through water vapor, and determining with low mass resolution; wherein, in the actual operation process, keeping other parameters unchanged (namely the ablation frequency is 2Hz, the energy density is 3J/cm < 2 >), using DOL-8 dolomite with an ablation beam spot of 75 mu m as a standard sample, and correcting the DOL-8 dolomite ablated under different laser ablation beam spots (33 mu m, 40 mu m, mu m50, 75 mu m, 90 mu m and 108 mu m); the test results are shown in fig. 4.
Examples 3 and 4 determine the effect of the parameters of the laser system on the Mg isotope test by changing the parameters of the laser system, and only changing a certain parameter value while fixing other parameters in the test process.
From fig. 3, it can be seen that: the higher the frequency, delta 26 The greater the deviation of Mg value, the poorer the precision, and at 10Hz, delta 26 The Mg deviation is as high as 0.60 per mill.
From fig. 4, it can be derived that: within the above range of variation of the beam spot size, delta 26 Deviation of Mg valueThe difference is only 0.23 per thousand, so the beam spot size has little influence on the analysis of the Mg isotope composition.
Example 5
(1) Placing MGS-3 magnesite and MGS-1 magnesite in a denudation pool;
(2) Adopting 193nm excimer nanosecond laser to denude MGS-3 magnesite and MGS-1 magnesite to obtain aerosol;
(3) Connecting a water vapor introducing device, introducing the aerosol into MC-ICP-MS through the water vapor introducing device for determination, and obtaining an initial ratio of Mg isotope;
(4) And calculating the Mg isotope composition of the MGS-1 magnesite by using the formula I on the basis of the MGS-3 magnesite.
Comparative example 5
(1) Placing MGS-3 magnesite and MGS-1 magnesite in a denudation pool;
(2) Adopting 193nm excimer nanosecond laser to degrade MGS-3 magnesite and MGS-1 magnesite to obtain aerosol;
(3) Directly introducing the aerosol into MC-ICP-MS for determination to obtain an initial ratio of Mg isotope;
(4) And calculating the Mg isotope composition of the MGS-1 magnesite by using the formula I on the basis of the MGS-3 magnesite.
From example 5 and comparative example 5 it can be concluded that: delta of MGS-1 magnesite without adding water vapor 25 The analysis precision of the Mg value is 0.12 per mill; and after introducing steam, the delta of MGS-1 magnesite 25 The analysis accuracy of the Mg value was 0.06 ‰, and the analysis accuracy of example 5 was improved by 1 time as compared with that of comparative example 5.
Example 6
(1) Placing DOL-4 dolomite (the ratio of Ca to Mg is 6.79) and DOL-8 dolomite in an ablation pool;
(2) Adopting 193nm excimer nanosecond laser to denude DOL-4 dolomite and DOL-8 dolomite to obtain aerosol;
(3) Connecting a water vapor introducing device, introducing the aerosol into MC-ICP-MS through the water vapor introducing device for determination, and obtaining an initial ratio of Mg isotope;
(4) And calculating the Mg isotope composition of the MGS-1 magnesite by using the formula I and using DOL-8 dolomite as a reference.
Comparative example 6
(1) Placing DOL-4 dolomite (the ratio of Ca to Mg is 6.79) and DOL-8 dolomite in an ablation pool;
(2) Adopting 193nm excimer nanosecond laser to denude DOL-4 dolomite and DOL-8 dolomite to obtain aerosol;
(3) Directly introducing the aerosol into MC-ICP-MS for determination to obtain an initial ratio of Mg isotope;
(4) And calculating the Mg isotope composition of the MGS-1 magnesite by using the formula I and using DOL-8 dolomite as a reference.
The analysis results of example 6 and comparative example 6 are shown in fig. 5 and 6, DOL-8 dolomite is used as a standard sample, and the Mg isotope composition of DOL-4 dolomite sample is corrected; the yellow diamond and blue triangle icons represent the average values of the Mg isotopic composition of the DOL-4 dolomite samples obtained without and with water vapor, respectively.
From fig. 5 and 6, it can be seen that: the Mg isotope composition analysis is carried out on the sample with high Ca/Mg ratio by adopting a mode of adding water vapor, so that the analysis accuracy and precision can be effectively improved.
Example 7
(1) Putting SD-1 siderite and SD-5 siderite in a denudation pool;
(2) Adopting 193nm excimer nanosecond laser to denude SD-1 siderite and SD-5 siderite to obtain aerosol;
(3) Connecting a water vapor introducing device, introducing the aerosol into MC-ICP-MS through the water vapor introducing device for determination, and obtaining an initial ratio of Mg isotope;
(4) And calculating the Mg isotope composition of the SD-1 siderite by using a formula I with the SD-5 siderite as a reference.
Comparative example 7
(1) Putting SD-1 siderite and SD-5 siderite in a denudation pool;
(2) Adopting 193nm excimer nanosecond laser to denude SD-1 siderite and SD-5 siderite to obtain aerosol;
(3) Directly introducing the aerosol into MC-ICP-MS for determination to obtain an initial ratio of Mg isotope;
(4) And calculating the Mg isotope composition of the SD-1 siderite by using a formula I with the SD-5 siderite as a reference.
The analysis results of example 7 and comparative example 7 are shown in fig. 7 and 8, and it can be derived from fig. 7 and 8 that: delta of SD-1 siderite without steam addition 26 Mg and delta 25 The analysis precision of the Mg value is 0.27 per mill and 0.25 per mill respectively (2SD, n = 13); and delta of SD-1 siderite after introduction of steam 26 Mg and delta 25 The analysis accuracy of the Mg value is 0.18% o and 0.10% o (2sd, n = 6), respectively, and the analysis accuracy of example 7 is also significantly improved compared with that of comparative example 7.
In summary, the results of examples 1 and 2 can prove that the deep fractionation effect can be weakened by introducing water vapor before the laser ablation cell, the Mg isotope analysis accuracy can be effectively improved, and meanwhile, the Mg isotope analysis can be effectively inhibited 48 Ca 2+ To pair 24 Mg + The mass spectrum interference can be realized under the condition of low mass resolution without deduction 48 Ca 2+ The Mg isotope composition of the carbonate sample can be determined by interference. Example 3 illustrates that it is important to select the appropriate laser ablation frequency during the test. It can also be demonstrated from example 6 that, even if the chemical composition of the samples differs significantly from the standard after the introduction of the water vapor (Ca/Mg, fe/Mg, mn/Mg ratios of the DoL-4 dolomite samples 6.79, 2.82, 2.10, respectively, ca/Mg, fe/Mg, mn/Mg ratios of the DOL-8 dolomite standards 1.94, 0.00, respectively), the matrix mismatch allows the exact determination of the Mg isotopic composition. The method avoids a complex sample pretreatment process and a pollution risk in a chemical purification process, is simple and efficient, and is suitable for popularization and use.
The above are only preferred embodiments of the present invention, and do not limit the scope of the present invention, and it is obvious to those skilled in the art that various modifications and variations can be made in the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall be included in the scope of the present invention.
Claims (10)
1. A method for rapidly determining the Mg isotope composition in carbonate minerals is characterized by comprising the following steps:
placing a standard sample and a sample to be detected into an ablation pool, and connecting a water vapor introducing device in front of the ablation pool;
adopting a laser system to denudate the standard sample and the sample to be detected to obtain aerosol;
introducing the aerosol into an MC-ICP-MS system through the water vapor introducing device to obtain an Mg isotope initial ratio;
calculating the composition of the Mg isotope in the sample to be detected according to a formula I by taking the standard sample as a reference, wherein the formula I is as follows: delta 2x Mg＝{[( 2x Mg/ 24 Mg) Sample to be tested /( 2x Mg/ 24 Mg) Standard sample ]-1 }. Times.1000, wherein, 2x mg is 25 Mg + And 26 Mg + the signal intensity of, 24 Mg is 24 Mg + Signal strength of (d), delta 2x And Mg is the Mg isotope composition in the sample to be detected.
2. The method for rapidly determining the Mg isotope composition in carbonate minerals according to claim 1, wherein the aerosol is introduced into the MC-ICP-MS system through the water vapor introduction device to obtain the Mg isotope initial ratio,
the water vapor in the water vapor introduction device comprises ultra-pure water vapor.
3. The method for rapidly determining the Mg isotope composition in carbonate minerals according to claim 1, wherein in the step of introducing the aerosol into the MC-ICP-MS system through the water vapor introducing means to obtain the initial ratio of Mg isotopes,
the flow speed of the steam introduced into the device is 5.3-8.0 mg/min.
4. The method for rapidly determining the Mg isotope composition in carbonate minerals according to claim 1, wherein the step of introducing the aerosol into the MC-ICP-MS system through the water vapor introducing device to obtain the Mg isotope initial ratio comprises the steps of:
introducing water vapor into a compensation argon gas path, uniformly mixing the water vapor with argon, then introducing the water vapor into a helium gas path, and uniformly mixing the water vapor with helium to obtain carrier gas rich in water vapor;
and introducing the aerosol in the denudation pool into an MC-ICP-MS system through the carrier gas rich in the water vapor to obtain the initial ratio of the Mg isotope.
5. The method for rapidly determining the Mg isotope composition in carbonate minerals according to claim 4, wherein the flow rate of argon is 0.8 to 1.05L/min.
6. The method for rapidly determining the Mg isotope composition in carbonate minerals according to claim 1, wherein in the step of obtaining the aerosol by eroding the standard sample and the sample to be tested by a laser system,
the laser system comprises a 193nm excimer nanosecond laser system.
7. The method for rapidly determining the Mg isotope composition in carbonate minerals according to claim 1, wherein in the step of placing the standard sample and the sample to be tested in an ablation tank, connecting a water vapor introduction device in front of the ablation tank,
the sample to be detected comprises any one of magnesite, dolomite and siderite.
8. The method for rapidly determining the Mg isotope composition in carbonate minerals according to claim 7, wherein the ratio of calcium element to magnesium element in the sample to be determined is 0.01 to 6.79; and/or the presence of a gas in the gas,
in the sample to be detected, the ratio of the iron element to the magnesium element is 0-17.40; and/or the presence of a gas in the gas,
in the sample to be detected, the ratio of manganese element to magnesium element is 0-2.10.
9. The method for rapidly determining the Mg isotope composition in carbonate minerals according to claim 1, wherein in the step of placing the standard sample and the sample to be tested in an ablation tank, connecting a water vapor introduction device in front of the ablation tank,
the standard sample comprises any one of MGS-3 magnesite, DOL-8 dolomite and SD-5 siderite.
10. The method for rapidly determining the Mg isotope composition in carbonate minerals according to claim 1, wherein the step of placing the standard sample and the sample to be tested in an ablation tank, and connecting a water vapor introduction device in front of the ablation tank comprises the steps of:
embedding two parts of carbonate minerals into epoxy resin to prepare a sample target, determining a standard sample and a sample to be detected according to the sample target, putting the standard sample and the sample to be detected into an ablation pool, and connecting a water vapor introduction device in front of the ablation pool.
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