Element Measurement Method Based on Improved Multi-Energy Correction

Abstract

This invention discloses an element measurement method based on an improved multi-energy correction method. Specifically, the plasma temperature of the two calibration solutions is obtained from the spectral image according to the Boltzmann diagram or Saha-Boltzmann diagram. The partition function of the element to be measured is calculated, and the intensity of the corrected spectral line is calculated according to the formula. Finally, the concentration of the element to be measured in the sample is calculated using the multi-energy correction method, thereby reducing the quantitative error caused by changes in the temperature of the light source.

Description

Technical Field

[0001] This invention belongs to the field of analytical technology, including atomic spectroscopy, mass spectrometry, and flame atomic absorption spectroscopy, and relates to a method for elemental measurement. Specifically, it relates to a method for quantitative analysis of elemental content using spectral line intensity information corresponding to multiple wavelengths or multiple energies of the element to be measured. Background Technology

[0002] For techniques such as optical emission spectroscopy / mass spectrometry and flame atomic absorption spectrometry, calibration is a crucial step in quantitative analysis. Inappropriate calibration methods can degrade quantitative results. In common applications, calibration is performed by measuring the analytical signals of multiple standard reference solutions and establishing a calibration curve equation between the instrument response and the analyte concentration. Ideally, the physicochemical environment of the analyte should be identical to that of the standard reference solution and the sample. However, in practice, achieving perfect matrix matching between the reference solution and the sample is difficult, thus posing challenges to quantitative determination. To address the problems caused by matrix effects, commonly used calibration strategies include single-wavelength calibration methods such as external standard methods, internal standard methods, and standard addition methods, as well as the recently proposed multi-energy calibration method.

[0003] Traditional external standard methods are effective for simple matrix determinations. They assume that the reference solution and sample have the same or similar matrix, or that differences in matrix composition have negligible impact on the analytical signal.

[0004] The internal standard method involves adding an internal standard of the same concentration to blank, standard, and sample solutions. A standard curve is established by using the relationship between the ratio of the analytical line intensity to the internal standard intensity and the concentration. Since the selected internal standard has similar physicochemical properties to the analyte and is affected by the same nebulization, transmission, atomization, excitation, and ionization, it can correct signal fluctuations caused by instrument conditions, sampling errors, and some matrix effects.

[0005] The standard addition method is the most commonly used method for complex matrix analysis. This method involves adding equal volumes of sample to a blank and a standard solution of known concentration, and then calculating the concentration of the analyte in the sample using a standard curve. Since the calibration solution and the sample are prepared in the same matrix, matrix effects can be minimized.

[0006] Multi-energy calibration, proposed by Alex Virgilio et al., is a novel calibration method that utilizes multiple wavelengths of the analyte for calibration. Different wavelengths correspond to different excitation energies, hence the names Multi-energy Calibration Method (Analytica Chimica Acta 2017, 982, 31-36), Multi-wavelength Calibration Method (Microchemical journal 2019, 146, 381-386), and Multi-isotope Calibration Method (Analytical and Bioanalytical Chemistry 2018, 410, 1157-1162). This method requires only two calibration solutions, has high throughput, and the calibration solutions contain the same sample concentration, thus exhibiting matrix matching capabilities similar to the standard addition method. Furthermore, it easily identifies potential spectral interferences on specific analytical lines based on outliers observed on the calibration curve for different wavelengths.

[0007] The external standard method is inaccurate when the sample matrix is ​​complex, resulting in significant deviations.

[0008] The standard addition method is a time-consuming and sample-intensive method. For the determination of each sample, 4 to 5 standard solutions must be prepared to establish a standard curve. At the same time, it is difficult to effectively correct for spectral interference.

[0009] The difficulty of the internal standard method lies in the selection of the internal standard. It requires that the internal standard be absent in the sample, ideally have a concentration range consistent with the analyte, and possess physicochemical properties (ionization energy) consistent with the analyte. In practice, the selection of the internal standard is determined by indicators such as recovery rate. Furthermore, the internal standard method still cannot address severe matrix effects.

[0010] The multi-energy correction method is susceptible to systematic errors caused by solution preparation. Inaccurate results will occur if the concentration of the reference standard added to solution 1 is incorrect. It is only applicable to analytes that can generate multiple analytical lines, with at least three analytical lines for each element. Similar to the standard addition method, it cannot adequately correct for additive interferences. Furthermore, a calibration curve needs to be established for each sample and each element. It cannot identify errors introduced by variations in light source parameters, which are difficult to determine simply by the R² value of the linear regression coefficient of the calibration curve. Summary of the Invention

[0011] To address the inability of multi-energy correction methods to effectively identify interference caused by changes in light source temperature, an element measurement method based on an improved multi-energy correction approach is proposed, which effectively identifies quantitative errors caused by changes in light source temperature.

[0012] First, let me explain the working principle of this invention:

[0013] Under conditions of optical thinness and thermodynamic / local thermodynamic equilibrium, the relationship between the instrument response or emission intensity of the analyte at a specified characteristic wavelength and the concentration and excitation energy of the analyte is as follows:

[0014]

[0015] Where the subscripts j and i represent the upper and lower energy levels of the element being measured, respectively; I is the intensity of the characteristic spectral line of the element received by the detector; F represents the instrument parameters, which are constants for given experimental conditions; C is the concentration of the element to be measured; λ k A, g, and U(T) represent the characteristic wavelength (k = 1, 2, 3, ..., n), transition probability, statistical weight of excited state, and partition function, respectively, and E, k B T represents the element excitation energy, Boltzmann constant, and plasma temperature, respectively.

[0016] In the calibration process, two calibration solutions are prepared for each sample.

[0017] Calibration solution 1 contains the sample and a calibration solution of an element with a known concentration; calibration solution 2 contains the sample and a blank. For example, calibration solution 1 contains a 50% v / v sample and a 50% v / v calibration solution of an element with a known concentration, while calibration solution 2 contains a 50% v / v sample and a 50% v / v blank sample. Other mixing ratios are also acceptable as long as both solutions contain equal amounts of sample. The following derivation process only applies to the case of a 1:1 dilution ratio.

[0018] By acquiring the spectral information of the two solutions using a spectrometer, the following relationship exists between the two solutions:

[0019] For solution 1:

[0020] For solution 2:

[0021] Where I(λ) k ) Sam+Std With I(λ) k ) Sam These are solutions 1 and 2 at a specific wavelength λ. k The instrument response at position, T1 and T2 are the plasma temperatures of solution 1 and solution 2, respectively, in C. Sam With C StdThese represent the element concentrations in the sample and the spiking concentrations in solution 1, respectively. m1 and m2 are the instrument response constants for the corresponding elements. Since the temperatures in the two solutions may differ, m1 and m2 may not be the same. Therefore, the above formula is rewritten as follows:

[0022] For solution 1:

[0023] For solution 2:

[0024] in, To correct the spectral line intensity, under the condition that the spectrometer's spectral response is corrected, the spectrum obtained for any solution can be analyzed by examining the elements at different wavelengths (λ1, λ2, λ3, ..., λ). n The intensity of atomic or ionic lines and their relationship to excitation energy are used to construct a Boltzmann plot using the following formula.

[0025]

[0026] Plasma temperature information can be obtained from the slope through linear regression, and then the spectral correction intensity I'(λ) can be obtained. k The plasma temperature information, including the value of the atomic and ion lines and the partition function U(T), can also be obtained from the Saha-Boltzmann diagram or multi-element Saha-Boltzmann diagram. These methods are existing technologies in the industry and will not be elaborated further. The partition function can be obtained in advance from the NIST spectral library information through polynomial fitting, yielding the relevant relationship U = f(T).

[0027] Using I'(λ) k ) Sam With I'(λ) k ) Sam+Std Combining formulas 4 and 5, we can obtain:

[0028]

[0029] Using the spectral correction intensity of solution 1 as the dependent variable and the spectral correction intensity of solution 2 as the independent variable, the slope obtained by linear regression is:

[0030]

[0031] Due to the spiking concentration C of the target element Std Given that the concentration of the analyte in the sample is known, it can be calculated using the following formula:

[0032]

[0033] This invention can be achieved through the following technical solutions:

[0034] An element measurement method based on an improved multi-energy correction method, comprising the following steps:

[0035] 1) Prepare two calibration solutions for each sample. Calibration solution 1 contains the sample and a calibration solution of the element to be measured at a known concentration; calibration solution 2 contains the sample and a blank. Both solutions contain equal amounts of sample, and the total volume of sample added to solutions 1 and 2 is V. Sam The volume of calibration solution containing the element of known concentration added is V. Std ;

[0036] 2) Obtain the emission / absorption spectra of the two calibration solutions, and calculate the intensity I(λ) of the characteristic spectral lines of the atoms and ions of the analyte. k ) Sam+Std With I(λ) k ) Sam The intensity of a spectral line can be either the peak area or the peak height.

[0037] 3) Based on the calibration solution spectrum, obtain the atomic parameters of the analyte, including wavelength λ and excitation energy E, from the NIST spectral library. j Statistical weight g j ;

[0038] 4) Calculate the corresponding plasma temperatures T1 and T2;

[0039] 5) Obtain the partition function of the atoms and / or ions of the element to be tested within the specified plasma temperature range based on the NIST spectral library and obtain the approximate relation U = f(T) through polynomial fitting; and calculate the partition function values ​​U(T1) and U(T2) of the elements atoms and / or ions corresponding to the plasma temperature in the previous step.

[0040] 6) Calculate the intensity of the corrected spectral lines at different wavelengths using the following formula;

[0041]

[0042] Where I(λ) k ) represents the spectral line intensity obtained in the second step, k B E is the Boltzmann constant. j U(T) is the energy of the upper energy level, and U(T) is the partition function of the specified ionization state (atom or ion) of the element to be measured.

[0043] 7) Using the spectral correction intensity of solution 1 as the dependent variable and the spectral correction intensity of solution 2 as the independent variable, the slope obtained by linear regression is:

[0044]

[0045] 8) Predict the concentration of the element to be measured in the sample using the following formula:

[0046]

[0047] The present invention also proposes the following technical solutions:

[0048] An element measurement method based on an improved multi-energy correction method, comprising the following steps:

[0049] 1) Prepare two calibration solutions for each sample. Calibration solution 1 contains the sample and a calibration solution of the element to be measured at a known concentration. Calibration solution 2 contains the sample and a blank. Both solutions contain equal volumes of sample. The total volume of sample added to standard solution 1 and standard solution 2 is V. Sam The volume of calibration solution containing the element of known concentration added is V. Std ;

[0050] 2) Obtain the emission / absorption spectra of the two calibration solutions, and calculate the intensity I(λ) of the characteristic spectral lines of the atoms and ions of the analyte. k ) Sam+Std With I(λ) k ) Sam The intensity of a spectral line can be either the peak area or the peak height.

[0051] 3) Based on the calibration solution spectrum, obtain the atomic parameters of the analyte, including wavelength λ and excitation energy E, from the NIST spectral library. j Statistical weight g j ;

[0052] 4) Calculate the corresponding plasma temperatures T1 and T2;

[0053] 5) Calculate the intensity of the corrected spectral lines at different wavelengths using the following formula;

[0054]

[0055] Where I(λ) k ) represents the spectral line intensity obtained in the second step, k B E is the Boltzmann constant. j This refers to higher energy levels.

[0056] 6) Using the spectral correction intensity of standard solution 1 as the dependent variable and the spectral correction intensity of standard solution 2 as the independent variable, the slope obtained by linear regression is:

[0057]

[0058] 7) Predict the concentration of the element to be measured in the sample using the following formula:

[0059]

[0060] Beneficial effects

[0061] This method requires only two calibration solutions, has high throughput, and contains the same sample content, thus possessing simple matrix matching capability. It can easily identify potential spectral interferences on specific analytical lines based on outliers of different wavelength spectral lines on the calibration curve. At the same time, by using corrected spectral line intensity instead of spectral line intensity, it can reduce quantitative errors caused by changes in light source temperature and improve measurement accuracy. Attached Figure Description

[0062] Figure 1 A schematic diagram of the process flow for performing the measurement method of the present invention;

[0063] Figure 2 The above are Boltzmann diagrams of Cr atoms in solutions 1 and 2 of this invention.

[0064] Figure 3 The relationship between Cr atomic partition function and temperature;

[0065] Figure 4 Multi-energy correction curves based on the intensity of 10 Cr correction spectral lines;

[0066] Figure 5 Multi-energy correction curves based on the intensity of 10 Cr spectral lines. Detailed Implementation

[0067] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0068] like Figure 1 The diagram shown illustrates the process flow for implementing the measurement method of this invention. This invention provides an element measurement method based on an improved multi-energy correction method, comprising the following steps:

[0069] 1) Prepare two calibration solutions for each sample. Calibration solution 1 contains the sample and a calibration solution of the analyte at a known concentration; calibration solution 2 contains the sample and a blank. Both solutions contain equal volumes of sample, and the total volume of sample added to solutions 1 and 2 is V. Sam The volume of calibration solution containing the element of known concentration added is V. Std ;

[0070] 2) Obtain the emission / absorption spectra of the two calibration solutions, and calculate the intensity I(λ) of the characteristic spectral lines of the atoms and ions of the analyte. k ) Sam+Std With I(λ) k ) Sam The intensity of a spectral line can be either the peak area or the peak height.

[0071] 3) Based on the calibration solution spectrum, obtain the atomic parameters of the analyte, including wavelength λ and excitation energy E, from the NIST spectral library. j Statistical weight g j ;

[0072] 4) Calculate the corresponding plasma temperatures T1 and T2 using any of the following methods: Boltzmann double-line method, Boltzmann diagram, Saha-Boltzmann diagram, or multi-element Saha-Boltzmann diagram.

[0073] 5) Obtain the partition function of the atoms and / or ions of the element to be tested within the specified plasma temperature range based on the NIST spectral library and obtain the approximate relation U = f(T) through polynomial fitting; and calculate the partition function values ​​U(T1) and U(T2) of the elements atoms and / or ions corresponding to the plasma temperature in the previous step.

[0074] 6) Calculate the intensity of the corrected spectral lines at different wavelengths using the following formula;

[0075]

[0076] Where I(λ) k ) represents the spectral line intensity obtained in the second step, k B E is the Boltzmann constant. j U(T) is the energy of the upper energy level, and U(T) is the partition function of the specified ionization state (atom or ion) of the element to be measured.

[0077] 7) Using the spectral correction intensity of solution 1 as the dependent variable and the spectral correction intensity of solution 2 as the independent variable, the slope obtained by linear regression is:

[0078]

[0079] 8) Predict the concentration of the element to be measured in the sample using the following formula:

[0080]

[0081] Example

[0082] The following is a specific conceptual example to illustrate the execution process and effects of this invention:

[0083] The sample contains C Sam A solution of Cr element with a concentration of 0.50 μg / L;

[0084] Solution 1 was prepared using 5.00 mL of C Std It was prepared using a Cr standard of 10.0 μg / L and a 5.00 mL sample.

[0085] Solution 2 was prepared by mixing 5.00 mL of the same sample with 5.00 mL of blank.

[0086] Assume that a 10.0 μg / L Cr solution will produce 1000 Cr free atoms. Therefore, solutions 1 and 2 will produce 525 and 25 free atoms, respectively. However, due to the change in the temperature of the light source, the spectral line intensities at different wavelengths will change. Table 1 shows the spectral line intensities of 10 atoms of Cr for the two solutions, including atomic parameter information.

[0087] Table 1. Intensity data of 10 atomic spectral lines of Cr corresponding to the two calibration solutions.

[0088]

[0089]

[0090] The plasma temperatures corresponding to solution 1 and solution 2 were calculated using the Boltzmann plot method, and the corresponding Boltzmann plots are shown below. Figure 2 As shown, the calculation results are T1 = 5000K and T2 = 5500K;

[0091] The partition function of Cr in the specified plasma temperature range (3500–5800 K) was obtained from the NIST spectral library and approximate by polynomial fitting, yielding the formula U = f(T). The fitted relationship is as follows: Figure 3 As shown.

[0092] The calculated values ​​are U(T1) = 10.4 and U(T2) = 11.44.

[0093] according to The intensity of the corrected spectral lines at different wavelengths is calculated, as shown in the table below:

[0094]

[0095] Using the spectral correction intensity of solution 1 as the dependent variable and the spectral correction intensity of solution 2 as the independent variable, a linear regression curve was constructed, as follows: Figure 4 As shown.

[0096] The slope obtained from linear regression is: Slope = 0.0476;

[0097] Given C std =10.0 μg / L, V Sam =V Std =5.00mL, according to Predict the concentration of the element to be measured in the solution from the sample: C Sam =0.5μg / L, which is consistent with the actual concentration;

[0098] In contrast, below Figure 5 The calibration curves prepared using the traditional multi-energy correction method are presented.

[0099] Based on the linear regression slope Slope = 0.0878 and R² = 0.9922, according to Predict the concentration of the element to be measured in the solution from the sample: C Sam =0.96μg / L, quantitative deviation 92.5%, indicating that plasma temperature seriously affects the quantitative accuracy of traditional multi-energy correction methods, while the method proposed in this invention can effectively suppress the influence of this factor.

[0100] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An element measurement method based on an improved multi-energy correction method, characterized in that, The method includes the following steps: 1) Prepare two calibration solutions for each sample. The first calibration solution contains the sample and a calibration solution of the element to be measured at a known concentration. The second calibration solution contains the sample and a blank. Both solutions contain equal volumes of sample. The total volume of sample added to the first and second standard solutions is V. Sam The volume of calibration solution containing the element of known concentration added is V. Std ; 2) Obtain the emission or absorption spectra of the two calibration solutions, and calculate the intensity I(λ) of the characteristic spectral lines of the atoms and ions of the analyte. k ) Sam+Std With I(λ) k ) Sam Spectral line intensity is either peak area or peak height; 3) Based on the calibration solution spectrum, obtain the atomic parameters of the analyte, including wavelength λ and excitation energy E, from the NIST spectral library. j Statistical weight g j ; 4) Calculate the corresponding plasma temperatures T1 and T2; 5) Obtain the partition function of the element atom or ion to be tested within the specified plasma temperature range based on the NIST spectral library and obtain the approximate relation U = f(T) through polynomial fitting; and calculate the partition function values ​​U(T1) and U(T2) of the element atom or ion corresponding to the plasma temperature in the previous step. 6) Calculate the intensity of the corrected spectral lines at different wavelengths using the following formula; Where I(λ) k ) represents the spectral line intensity obtained in the second step, k B E is the Boltzmann constant. j U(T) is the energy of the upper energy level, and U(T) is the partition function of the atom or ion of the element to be measured in a specified ionization state. 7) Using the spectral correction intensity of the first standard solution as the dependent variable and the spectral correction intensity of the second standard solution as the independent variable, the slope obtained by linear regression is: 8) Predict the concentration of the element to be measured in the sample using the following formula:

2. An element measurement method based on an improved multi-energy correction method, characterized in that, The method includes the following steps: 1) Prepare two calibration solutions for each sample. The first calibration solution contains the sample and a calibration solution of the element to be measured at a known concentration. The second calibration solution contains the sample and a blank. Both solutions contain equal volumes of sample. The total volume of sample added to the first and second standard solutions is V. Sam The volume of calibration solution containing the element of known concentration added is V. Std ; 2) Obtain the emission or absorption spectra of the two calibration solutions, and calculate the intensity I(λ) of the characteristic spectral lines of the atoms and ions of the analyte. k ) Sam+Std With I(λ) k ) Sam Spectral line intensity is either peak area or peak height; 3) Based on the calibration solution spectrum, obtain the atomic parameters of the analyte, including wavelength λ and excitation energy E, from the NIST spectral library. j Statistical weight g j ; 4) Calculate the corresponding plasma temperatures T1 and T2; 5) Calculate the intensity of the corrected spectral lines at different wavelengths using the following formula; Where I(λ) k ) represents the spectral line intensity obtained in the second step, k B E is the Boltzmann constant. j This refers to higher energy levels. 6) Using the spectral correction intensity of the first standard solution as the dependent variable and the spectral correction intensity of the second standard solution as the independent variable, the slope is obtained by linear regression: 7) Predict the concentration of the element to be measured in the sample using the following formula:

3. The element measurement method based on an improved multi-energy correction method according to claim 1 or 2, characterized in that: The method for calculating the corresponding plasma temperatures T1 and T2 in step 4) can be any one of the following: Boltzmann double-line method, Boltzmann diagram, Saha-Boltzmann diagram, or multi-element Saha-Boltzmann diagram.

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