Disclosure of Invention
In view of the above, it is necessary to provide a method for establishing a mathematical model of the spectral interference coefficient of iron in cadmium measurement by ICP-OES method and an application method thereof, so as to solve the above problems.
The invention provides a method for establishing a mathematical model of a spectral interference coefficient of iron in cadmium determination by an ICP-OES method, which comprises the following steps: preparing a plurality of mixed standard solutions containing cadmium and iron, wherein the preparation concentration of cadmium is 0.001-0.1 mg/L, and the preparation concentration of iron is 1-1000 mg/L; measuring the apparent concentration of cadmium in the mixed standard solution by an ICP-OES method, wherein the detection wavelength of the cadmium is 214.439 nm; dividing the apparent concentration of cadmium by the prepared concentration to be used as an interference coefficient; and fitting the relationship among the interference coefficient, the cadmium preparation concentration and the iron preparation concentration, establishing a nonlinear surface fitting equation and drawing a three-dimensional fitting surface graph.
Preferably, in the step of preparing a plurality of mixed standard solutions containing cadmium and iron, 70 mixed standard solutions of 1% nitric acid and 1% hydrochloric acid systems of different concentrations are prepared in a permutation combination, each of the mixed standard solutions having a cadmium concentration selected from one of 0.001mg/L, 0.002mg/L, 0.005mg/L, 0.01mg/L, 0.02mg/L, 0.05mg/L and 0.1mg/L and an iron concentration selected from one of 1mg/L, 2mg/L, 5mg/L, 10mg/L, 20mg/L, 50mg/L, 100mg/L, 200mg/L, 500mg/L and 1000 mg/L.
Preferably, when the ICP-OES method is used for measuring the apparent concentration of the cadmium, the working parameters are as follows: the RF power was 1.2kW, the argon flow rate was 15L/min, and the pump speed was 6 rps.
Preferably, a Power2D model is selected to fit the relationship between the interference coefficient and the formulated concentration of cadmium and iron according to an iterative optimization algorithm.
Preferably, the surface fitting equation is: xi is z0+ B × power (x, C) + D × power (y, E) + F × power (x, C) × power (y, E), where xi is the interference coefficient, x is the formulated concentration of cadmium and y is the formulated concentration of iron.
The invention also provides an application method of the mathematical model for measuring the spectral interference coefficient of iron in cadmium by the ICP-OES method, which comprises the following steps: detecting the mixed standard solution containing cadmium and iron by using an ICP-OES method, drawing a calibration curve of the cadmium and the iron, and determining the apparent concentration of the cadmium and the concentration of the iron, wherein the detection wavelength of the cadmium is 214.439nm, and the detection wavelength of the iron is 238.204 nm; calculating an interference coefficient according to the curved surface fitting equation; and correcting the apparent concentration of the cadmium by using the interference coefficient.
The invention also provides an application method of the mathematical model for measuring the spectral interference coefficient of iron in cadmium by the ICP-OES method, which comprises the following steps: weighing 0.15-0.25 g of a sample of a water system sediment component analysis standard substance in a microwave digestion tank, adding water for wetting, and then adding 8-10 ml of nitric acid and 2-4 ml of hydrochloric acid; digesting the sample by a microwave digestion method, cooling, taking out, dispelling acid to 1-2 mL, cooling, transferring to a 50mL volumetric flask, and adding water to fix the volume to a scale; detecting the sample by an ICP-OES method to determine the apparent concentration of cadmium and the concentration of iron, wherein the detection wavelength of cadmium is 214.439nm, and the detection wavelength of iron is 238.204 nm; converting according to the curved surface fitting equation to obtain a power equation of an interference coefficient; and calculating an interference coefficient, correcting the apparent concentration of the cadmium by using the interference coefficient, and calculating the content of the cadmium in the sample.
The method for establishing the mathematical model of the spectral interference coefficient of the iron during the cadmium determination by the ICP-OES method can establish the nonlinear surface fitting equation so as to correct the apparent concentration of the cadmium in the mixed standard solution containing the cadmium and the iron by using the surface fitting equation during application, thereby obtaining an accurate determination result. Meanwhile, the nonlinear surface fitting equation can also be applied to the determination of cadmium in the component analysis standard substance GBW07305a (GSD-5a) of the actual sample water system sediment so as to calculate the content of cadmium in the sample.
Detailed Description
In order that the above objects, features and advantages of the present invention may be more clearly understood, a detailed description of the present invention is given below in conjunction with specific embodiments. It should be noted that the embodiments and features of the embodiments of the present application may be combined with each other without conflict.
In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention, and the described embodiments are merely a subset of the embodiments of the present invention, rather than a complete embodiment. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
The invention provides a method for establishing a mathematical model of a spectral interference coefficient of iron in cadmium determination by an ICP-OES method, which comprises the following steps.
(1) Preparing a plurality of mixed standard solutions containing cadmium and iron, wherein the preparation concentration of cadmium is 0.001-0.1 mg/L, and the preparation concentration of iron is 1-1000 mg/L.
In one embodiment, 70 mixed standard solutions of 1% nitric acid and 1% hydrochloric acid systems of different concentrations are prepared in a combined manner, wherein the cadmium concentration in each mixed standard solution is selected from one of 0.001mg/L, 0.002mg/L, 0.005mg/L, 0.01mg/L, 0.02mg/L, 0.05mg/L and 0.1mg/L, and the iron concentration is selected from 1mg/L, 2mg/L, 5mg/L, 10mg/L, 20mg/L, 50mg/L, 100mg/L, 200mg/L, 500mg/L andone of 1000mg/L, the number of the mixed standard solution is x i y j (i=1,2,3……, 7;j=1,2,3……,10)。
(2) And measuring the apparent concentration of cadmium in the mixed standard solution by using an ICP-OES method, wherein the detection wavelength of the cadmium is 214.439 nm.
Spectral interference of Fe214.445nm with Cd214.439nm as determined by ICP-OES method, as shown in FIG. 1, mainly results in partial overlap interference.
In one embodiment, the ICP-OES instrument has operating parameters as shown in Table 1 below when measuring the apparent concentration of Cd214.439nm by the ICP-OES method.
TABLE 1 Instrument operating parameters
Item
|
Parameter(s)
|
RF power (kW)
|
1.2
|
Argon flow rate (L/min)
|
15
|
Pump speed (rps)
|
6
|
Reading time(s)
|
3
|
Number of readings
|
3
|
Detection wavelength (nm)
|
Cd(214.439),Fe(238.204) |
(3) The apparent concentration of cadmium divided by the formulated concentration was taken as the interference factor.
Specifically, the interference coefficient of iron to cadmium in each mixed standard solution is calculated respectively. Fig. 2 shows the calculation result of the interference coefficient ξ.
(4) And fitting the relationship among the interference coefficient, the cadmium preparation concentration and the iron preparation concentration, establishing a nonlinear surface fitting equation and drawing a three-dimensional fitting surface graph.
In one embodiment, a relation between a Power2D model fitting interference coefficient xi and a preparation concentration x (mg/L) of Cd and a preparation concentration y (mg/L) of Fe is selected according to an iterative algorithm Levenberg-Marquardt optimization algorithm, a nonlinear surface fitting equation is established, and a three-dimensional fitting surface graph is drawn. Referring to fig. 3, fig. 3 is a three-dimensional fitting surface diagram. It will be appreciated that other models may be selected for fitting.
Specifically, the nonlinear surface fitting equation is ξ ═ z0+ B × power (x, C) + D × power (y, E) + F × power (x, C) × power (y, E).
See table 2 for the results of the nonlinear surface fit.
TABLE 2 results of fitting of nonlinear surfaces
In one embodiment, the application method of the mathematical model of the spectral interference coefficient of iron in the determination of cadmium by the ICP-OES method is to apply the curve fitting equation to the determination of cadmium in the iron-cadmium mixed standard solution, wherein the concentration of cadmium is 0.001-0.1 mg/L, and the concentration of iron is 1-1000 mg/L. The application method specifically comprises the following steps.
Firstly, a mixed standard solution containing cadmium and iron is detected by an ICP-OES method, a cadmium and iron calibration curve is drawn, and the apparent concentration of cadmium and the concentration of iron are measured, wherein the detection wavelength of cadmium is 214.439nm, and the detection wavelength of iron is 238.204 nm. Working parameters of the ICP-OES instrument are set according to the table 1, calibration curves of cadmium and iron are drawn, and the correlation of the calibration curves of all elements is better than 0.999. And (4) measuring the mixed standard solution under the same condition, and calculating the content of the element to be measured.
Next, the corresponding interference coefficient ξ value is calculated from the fitting equation ξ ═ z0+ B × power (x, C) + D × power (y, E) + F × power (x, C) × power (y, E).
Then, the measured concentration X of cadmium was corrected by using the interference coefficient ξ value, and the relative error δ between the correction result and the preparation concentration of cadmium was calculated, and fig. 4 is a table showing the calculation result of the correction of cadmium in a mixed standard solution containing cadmium and iron. As shown in FIG. 4, the relative error delta between the corrected cadmium concentration and the prepared concentration is in the range of-17.8% -22.0%.
In another embodiment, the application method of the mathematical model of the spectral interference coefficient of iron in the measurement of cadmium by the ICP-OES method is to apply the surface fitting equation to the measurement of cadmium in the water-based sediment component analysis standard substance GBW07305a (GSD-5 a). The application method specifically comprises the following steps.
Firstly, referring to EPA3051A-2007 microwave digestion method, weighing 0.15g-0.25g of a sample of a water system sediment component analysis standard substance GBW07305a (GSD-5a) in a microwave digestion tank, adding a small amount of water for wetting, adding 8-10 ml of nitric acid and 2-4 ml of hydrochloric acid, and setting the following microwave conditions: (1)100 ℃, 5atm, 2 min; (2)120 ℃, 8atm for 3 min; (3)150 ℃, 10atm for 3 min; (4)180 ℃, 20atm, 3 min; (5)210 ℃, 40atm, 15 min. Digesting the sample by a microwave digestion method, cooling, taking out, dispelling acid to 1-2 mL, cooling, transferring to a 50mL volumetric flask, and adding water to a constant volume to reach a scale. Preferably, 9ml of nitric acid and 3ml of hydrochloric acid are added.
And secondly, detecting the sample by using an ICP-OES method to respectively determine the apparent concentration of cadmium and the concentration of iron in the sample, wherein the detection wavelength of cadmium is 214.439nm, and the detection wavelength of iron is 238.204 nm.
Then, the above surface fitting equation is converted into ξ - [ B + F × power (y, E) ] × power (X, C) × power (ξ, -C) - [ z0+ D × power (y, E) ] ═ 0, let a ═ B + F × power (y, E) ], B ═ power (X, C), C ═ B + F × power (y, E) ] × power (X, C), D ═ z0+ D × power (y, E), and then the known values are substituted into the equation to obtain the power equation ξ -0.18231 × power (ξ,1.241) -1.04160 ═ 0, ξ -0.18697 × power (ξ,1.241) -1.04297 ═ 0, and ξ -0.17163 × power (ξ,1.241) -1.04549.
Calculating the interference coefficient xi value, and utilizing the interference coefficient xi value to measure the apparent concentration X of cadmium Cd Correction is carried out to obtain the actual concentration x Cd And then calculating the content of cadmium in the sample.
In this embodiment, three samples are taken together, and referring to fig. 5, the calibration results of cadmium in the three samples are 1.42mg/kg, 1.36mg/kg, and 1.45mg/kg, respectively, which are all within the range of the standard value of 1.37 ± 0.10mg/kg given by the standard substance certificate, which indicates that the accurate result can be obtained by the calibration of cadmium measurement of the actual sample by the fitting result.
The method for establishing the mathematical model of the spectral interference coefficient of iron during cadmium determination by using the ICP-OES method can establish a nonlinear surface fitting equation so as to correct the apparent concentration of cadmium in a mixed standard solution containing cadmium and iron by using the surface fitting equation during application, thereby obtaining an accurate determination result. Meanwhile, the nonlinear surface fitting equation can be applied to the determination of cadmium in the component analysis standard substance GBW07305a (GSD-5a) of the actual sample water system sediment so as to calculate the content of cadmium in the sample. The mathematical model is not applicable to other spectral interferences except for Fe214.445nm in Cd214.439nm, and other measurement wavelengths of Fe can be considered to be selected to measure the Fe content if interference exists at Fe238.204nm.
While the preferred embodiments of the invention have been illustrated and described, it will be appreciated by those skilled in the art that various changes and modifications may be made without departing from the true scope of the invention. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.