A quantitative analysis method

Abstract

The present invention discloses a quantitative analysis method, which belongs to the technical field of instrumental analysis. The analysis method comprises: (1) preparing a standard solution sequence with known concentration; (2) diluting the sample with the standard solution sequence of step (1), and measuring the actual amount of sample added m using an analytical balance; 样 And the actual amount of standard solution added m 标 ; (3) Calculate according to formula 1-3 to obtain the concentration of the element to be tested introduced by the standard solution n 标 and the concentration of the element introduced into the sample n 样 ; (4) Use an analytical instrument to measure dilutions of different sample dilution concentrations w, and obtain the response values ​​i generated by the different dilutions on the analytical instrument used; (5) Use i / w as the horizontal axis and c as the horizontal axis. 标 The slope of the graph is the response coefficient k, and the x-intercept is the content of the element to be measured in the sample c. 样 The present invention greatly improves the sensitivity and accuracy of the existing standard addition method, saves a large amount of reagents, and reduces the analysis cost.

Description

Technical Field

[0001] The invention relates to the technical field of instrumental analysis, and in particular to a quantitative analysis method. Background Art

[0002] The standard addition method is a commonly used quantitative analysis method in analytical chemistry. The preparation process of the diluent for the standard addition method test is: use a pipette / pipette gun to transfer a fixed volume of sample, add standard solutions of different known concentrations, and use a volumetric flask to make up the volume and shake well. The dilution ratio of the sample in the dilution is considered to be a certain value (nominal pipetting volume / nominal volume of the volumetric flask). The actual concentration of the element to be measured in each dilution is the sum of the spiked amount and the sample introduction amount (unknown constant). The measurement and calculation process is: use an instrument (AAS, AES, ICP-MS, etc.) to measure the dilution sequence, obtain the signal measured values ​​corresponding to the dilutions of standard solutions of different concentrations, and plot the signal measured values ​​against the spiked concentration to obtain a standard curve. The intercept of the standard curve on the x-axis / sample dilution ratio is the content of the substance to be measured in the sample, see Figure 1 .

[0003] In practice, there are other operating methods for preparing diluents that are different from the above steps (such as adding different volumes of fixed-concentration standard solution and then fixing the volume, etc.). Their essence is the same as the above steps, that is, using volume measurement to obtain a dilution sequence containing a fixed-concentration sample and different concentrations of the element to be measured.

[0004] The advantages of the standard addition method are that it is simple and easy to use, has a wide range of applications, can be used for various types of samples, and has low requirements for instruments. However, when the existing standard addition method is used to prepare the diluent, the volume measuring instruments such as pipettes and pipettes have relatively large nominal errors (0.5% for pipettes and 2% for pipettes), which affects the accuracy of the measurement; and when the analysts are not well trained, significant operating errors (up to 10% or more) are likely to occur. In addition, when using instruments such as AAS and AES for analysis, the instrument only needs samples below 1mL, but due to the large errors caused by pipetting, it is usually necessary to use a large amount of preparation to reduce the impact of operating errors. Therefore, in actual operation, 50mL, 100mL or even larger volumetric flasks are used for constant volume, resulting in a great waste of standard substances, especially when measuring rare elements such as precious metals, the analysis cost is higher.

[0005] The accuracy of analytical balance is much higher than that of volumetric measuring instruments such as pipettes. In the prior art, if accurate dilution ratio data is needed, an analytical balance is generally used to weigh the actual mass of the sample before and after dilution. However, since the sample and the standard solution in the standard addition method contain the same element to be measured, when the sample dilution ratio is not a certain value, the amount of the element to be measured introduced into the sample and the amount of the element to be measured introduced into the standard solution will change at the same time. The actual concentration of the element to be measured in each dilution solution is the sum of the spiked amount and the amount introduced into the sample (unknown variable). There is no linear relationship between the actual measured signal value and the spiked concentration, and no meaningful results can be obtained. Figure 2 , so it cannot be used in the method of standard addition. Summary of the invention

[0006] The purpose of the present invention is to provide a quantitative analysis method, in which an analytical balance is used to measure the sample dilution ratio of each standard point in the standard addition method, and the interference error caused by the different dilution ratios of each point is eliminated through a specific calculation method, which greatly improves the sensitivity and accuracy of the existing standard addition method, saves a large amount of reagents, and reduces the analysis cost.

[0007] The technical solution adopted by the present invention is:

[0008] A quantitative analysis method comprises the following steps:

[0009] (1) Prepare a series of standard solutions with known concentrations;

[0010] (2) Dilute the sample with the standard solution sequence of step (1) and use an analytical balance to measure the actual amount of sample added m 样 The actual amount of standard solution with known concentration m 标 ;

[0011] (3) Calculate according to the following formula to obtain the concentration of the element to be tested introduced by the standard solution: 标 and the concentration of the element introduced into the sample n 样 ;

[0012] w= m 样 / (m 样 +m 标 ) (1);

[0013] n 标 = c 标 ×(1- w) (2);

[0014] n 样 = c 样 ×w (3);

[0015] Where:

[0016] w-actual dilution concentration of sample, %;

[0017] m 样 - Sample mass, g;

[0018] m 标 -Mass of standard solution, g;

[0019] n 标 -Concentration of the element to be measured introduced by the standard solution, ppm;

[0020] c 标 - The content of the element to be measured in the standard solution, ppm; determined according to step (1);

[0021] n 样 - Concentration of the element to be measured introduced into the sample, ppm;

[0022] c 样 -The content of the element to be tested in the sample, ppm;

[0023] (4) using an analytical instrument to measure dilutions of different sample dilution concentrations w, and obtaining response values ​​i generated by the different dilutions on the analytical instrument used;

[0024] (5) is the horizontal axis, The slope is the response coefficient k, and the x-axis intercept is the content of the element to be measured in the sample c. 样 .

[0025] Further, step (2) comprises:

[0026] 2.1 Place the container on the analytical balance and reset the balance to zero;

[0027] 2.2 Add an appropriate amount of sample to be tested into the container and record the sample mass m after the reading stabilizes. 样 ;

[0028] 2.3 Add a standard solution of known concentration into the container and record the total mass (m 样 +m 标 ).

[0029] Furthermore, the analyzer used in step (4) is one of AAS, AES and ICP-MS.

[0030] The data processing method used in the present invention is as follows:

[0031] According to the Lambert-Beer law, within the measuring range of the analytical instrument, the response value i generated by the diluent on the analytical instrument is proportional to the concentration n of the element to be measured in the diluent. 样 is proportional, that is:

[0032] i=k(n 标+n 样 )(4)

[0033] In the prior art standard addition method, due to k and n 样 is a fixed value, with i to n 标 The result can be obtained by linear fitting. However, when the actual amount added is weighed using an analytical balance, the dilution has a non-fixed dilution factor, n 样 With n 标 All of them are variables, and it is impossible to draw a graph using the existing method. The present invention solves this problem by using the following method:

[0034] According to the above preparation method, there is

[0035] n 标 = c 标 ×(1- w) (2);

[0036] n 样 = c 样 × w (3);

[0037] Substituting equation (2) and equation (3) into equation (4), we can get

[0038] i=k(c 标 ×(1-w)+c 样 ×w)

[0039] With a little change

[0040]

[0041] The above formula shows that in the preparation method of the present invention, as long as the content of the element to be measured in the sample is a certain value, That is A linear function of is the horizontal axis, The slope is the response coefficient k, and the x-axis intercept is the content of the element to be measured in the sample c. 样 .

[0042] Beneficial effects of the present invention:

[0043] 1. By using the analytical balance weighing method to prepare the diluent, accurate measurement of the standard solution and the diluted sample can be achieved. The absolute error of the measurement process can be reduced to about 1 / 500 times of the existing volume method, that is, the existing volume error of 0.05mL can be reduced to 0.1mg, thereby greatly improving the sensitivity and accuracy of the standard addition method and avoiding significant operational errors caused by the pipetting process.

[0044] 2. The method of the present invention is not limited by the specifications and performance of the volume measuring vessel. The diluent can be prepared according to the actual amount required by the analyzer. The sample amount required for a single measurement can be reduced from 5 to 50 g to less than 1 g, and the amount of standard solution can be reduced from 500 mL to less than 10 mL, thereby saving a large amount of analytical reagents and significantly reducing the analysis cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is the standard curve of the standard addition method.

[0046] Figure 2 This is a standard curve diagram made using the existing standard addition method at different dilution ratios.

[0047] Figure 3 This is a standard curve diagram prepared using the existing method in Example 1.

[0048] Figure 4 This is a standard curve diagram prepared using the method of the present invention in Example 1.

[0049] Figure 5 This is the standard curve diagram of Comparative Example 1. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solution and advantages of the present invention more clear, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and a preferred implementation manner.

[0051] The present invention provides a quantitative analysis method, comprising the following steps:

[0052] (1) Prepare a series of standard solutions with known concentrations;

[0053] (2) Place the container on an analytical balance and reset the balance to zero;

[0054] (3) Add an appropriate amount of the sample to be tested into the container and record the sample mass m after the reading stabilizes. 样 ;

[0055] (4) Add a standard solution of known concentration into the container and record the total mass (m) of the sample and the standard solution after the reading stabilizes. 样 +m 标 );

[0056] The concentration of the element to be measured introduced by the standard solution is calculated by the following formula: 标 and the concentration of the element introduced into the sample n 样 ;

[0057] w= m 样 / (m 样 +m 标 ) (1);

[0058] n 标 = c 标 (1- w) (2);

[0059] n 样 = c 样 w (3);

[0060] Where:

[0061] w-actual dilution concentration of sample, %;

[0062] m 样 - Sample mass, g;

[0063] m 标 -Mass of standard solution, g;

[0064] n 标 -Concentration of the element to be measured introduced by the standard solution, ppm;

[0065] c 标 - The content of the element to be measured in the standard solution, ppm; determined according to step (1);

[0066] n 样 - Concentration of the element to be measured introduced into the sample, ppm;

[0067] c 样 -The content of the element to be tested in the sample, ppm;

[0068] (5) using an analytical instrument to measure dilutions of different sample dilution concentrations w to obtain response values ​​i generated by the different dilutions on the analytical instrument used; the analyzer is one of AAS, AES and ICP-MS;

[0069] (6) According to the drawing principle of the standard addition method, substitute equations (2) and (3) into equation (4) to obtain equation (5);

[0070] i = k(n 标 +n 样 ) (4);

[0071]

[0072] by is the horizontal axis, The slope is the response coefficient k, and the x-axis intercept is the content of the element to be measured in the sample c. 样 .

[0073] Example 1

[0074] The analysis method of the present invention is used to measure the sodium content in the sample to be tested using an atomic absorption spectrometer:

[0075] (1) Use a series of standard solutions with known sodium concentrations as standard solutions. The sodium content in the standard solutions is c 标 They are 0.0078ppm, 0.0284ppm, 0.0576ppm, 0.1084ppm, 0.2064ppm and 0.3074ppm respectively.

[0076] (2) The sample dilution solution is obtained by the preparation method of the present invention, and the calculated sample dilution concentration w and the concentration of the element to be measured introduced by the standard solution n are 标 , as shown in Table 1 below.

[0077] Table 1

[0078]

[0079] (3) The diluted solutions were tested using an atomic absorption spectrometer (AAS) to obtain the signal intensity (acetylene-air flame atomization, 589.0 nm absorbance) corresponding to each diluted solution, as shown in Table 2.

[0080] Table 2

[0081]

[0082] Using the existing standard addition method, n 标 The results are shown in Table 1. Figure 3 ;from Figure 3 It can be seen that accurate results cannot be obtained by using the existing standard addition method for drawing.

[0083] (4) According to the method of the present invention, the i / w value and the c(1-w) / w value are calculated, as shown in Table 3 below;

[0084] Table 3

[0085]

[0086] by is the horizontal axis, Plot as the vertical axis, and see the result Figure 4 ;

[0087] from Figure 4 It can be seen that the regression equation is y = 0.52043x + 0.5615, and the determination coefficient R 2 =0.99996, the sodium concentration in the sample to be tested n 样 That is, the absolute value of the intercept of the fitting curve on the x-axis is 1.0788 (ppm).

[0088] The analysis process consumed 0.8672 g of sample and 9.0083 g of standard solution.

[0089] The preparation process uses a common analytical balance with a minimum division value of 0.1 mg and a nominal accuracy of 0.1 mg for quantitative analysis, and the standard uncertainty of a single weighing is 0.05 mg. According to the weighing sampling amount in the above table, the relative uncertainties of the six dilutions are 0.0696%, 0.0677%, 0.0696%, 0.0697%, 0.0711%, and 0.0695%, respectively, and the average relative uncertainty of the dilution concentration is 0.0695%.

[0090] Comparative Example 1

[0091] The sodium element in the sample was measured by atomic absorption spectrometer using the conventional standard addition method:

[0092] (1) A series of standard solutions with known sodium concentrations were used as standard solutions. The sodium contents in the standard solutions were 0.0078 ppm, 0.0284 ppm, 0.0576 ppm, 0.1084 ppm, 0.2064 ppm, and 0.3074 ppm, respectively.

[0093] (2) Use a pipette to transfer 5.00 mL of sample into a 50 mL volumetric flask, dilute to the mark with the standard solution of known concentration, and shake well to obtain the sample dilution solution;

[0094] (3) The above dilutions were tested using a flame atomic absorption spectrometer to obtain the signal intensity (absorbance at 589.0 nm) corresponding to each dilution, see Table 4.

[0095] Table 4

[0096]

[0097] (4) n 标 The results are shown in Table 1. Figure 5 ;from Figure 5 It can be seen that the regression equation is y = 0.52404x + 0.05555, and the determination coefficient R 2 = 0.99986. Sodium content in the sample = intercept of the standard curve on the x-axis / sample dilution ratio: 1.0600 (ppm).

[0098] The analysis process of Comparative Example 1 consumed 30.00 mL of sample and 300.00 mL of standard solution. The sample and standard solution were aqueous solutions, with a density of 1.00 g / mL. Compared with the method in Example 1, the existing standard addition method consumed 34.6 times more sample and 33.3 times more standard solution.

[0099] The preparation process of Comparative Example 1 uses a pipette with a nominal value of 10mL±0.50% and a Class A volumetric flask with a nominal value of 50mL±0.10%. Calculated by rectangular distribution, the standard uncertainty of the pipette is 0.0433mL, the standard uncertainty of the volumetric flask is 0.0866mL, and the combined relative uncertainty of the diluent concentration is 0.883%, which is 13.4 times higher than the relative uncertainty of the diluent concentration of 0.0659% in Example 1. It can be seen that the preparation process of the present invention is still significantly better than the existing standard addition method in terms of precision under the premise of greatly reducing the amount of samples and reagents.

[0100] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications are also within the protection scope of the present invention.

Claims

1. A quantitative analysis method, characterized in that: The following steps are involved: (1) Prepare a series of standard solutions with known concentrations; (2) Dilute the sample with the standard solution sequence of step (1) and use an analytical balance to measure the actual amount of sample added m 样 And the actual amount of standard solution added m 标 ; (3) Calculate according to the following formula to obtain the concentration of the element to be measured introduced by the standard solution: 标 and the concentration of the element introduced into the sample n 样 ; w= m 样 / (m 样 +m 标 ) (1); n 标 = c 标 ×(1- w) (2); n 样 = c 样 ×w (3); Where: w-actual dilution concentration of sample, %; m 样 - Sample mass, g; m 标 -Mass of standard solution, g; n 标 -Concentration of the element to be measured introduced by the standard solution, ppm; c 标 -The content of the element to be measured in the standard solution, ppm; n 样 - Concentration of the element to be measured introduced into the sample, ppm; c 样 -The content of the element to be tested in the sample, ppm; (4) using an analytical instrument to measure dilutions of different sample dilution concentrations w, and obtaining response values ​​i generated by the different dilutions on the analytical instrument used; (5) is the horizontal axis, The slope is the response coefficient k, and the x-axis intercept is the content of the element to be measured in the sample c. 样 .

2. The quantitative analysis method according to claim 1, characterized in that Step (2) comprises: 2.1 Place the container on the analytical balance and reset the balance to zero; 2.2 Add an appropriate amount of sample to be tested into the container and record the sample mass m after the reading stabilizes. 样 ; 2.3 Add a standard solution of known concentration into the container and record the total mass (m 样 +m 标 ).

3. The quantitative analysis method according to claim 1, characterized in that: The analyzer used in step (3) is one of AAS, AES and ICP-MS.

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