CN110954640B - Method for detecting trace urea in melamine - Google Patents
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Abstract
The invention discloses a method for detecting trace urea in melamine, and relates to the technical field of chemical detection. The detection method comprises the following steps: detecting peak areas of different urea standard solutions by adopting a high performance liquid chromatography, wherein the chromatographic column is a C18 liquid chromatographic column, drawing a standard curve according to the peak areas of the different urea standard solutions and the concentration of the urea standard solution, detecting the peak area of a sample to be detected by adopting the high performance liquid chromatography under the same condition, and substituting the peak area of the sample to be detected into the standard curve to calculate the content of urea in the sample to be detected. The detection method has the following advantages compared with the prior art: simple operation, short detection time and high accuracy. The method can accurately and quickly detect the content of the trace urea in the melamine and provides data basis for monitoring the content of the urea in the melamine production.
Description
Technical Field
The invention relates to the technical field of chemical detection, in particular to a method for detecting trace urea in melamine.
Background
Urea is the main raw material in the production process of melamine, and the quality of the melamine product is directly influenced by the content of urea in the melamine product. The uncertainty of the content of urea causes that downstream customers cannot stably use melamine for chemical synthesis and other practical applications. At present, the method for measuring urea is mainly a spectrophotometry, and the method has the disadvantages of complex operation, more interference factors and unstable measuring result.
In view of this, the invention is particularly proposed.
Disclosure of Invention
The invention aims to provide a method for detecting trace urea in melamine so as to solve the technical problem.
The invention is realized by the following steps:
a method for detecting trace urea in melamine comprises the following steps: detecting the peak areas of different urea standard solutions by adopting a high performance liquid chromatography, wherein the chromatographic column is a C18 liquid chromatographic column, drawing a standard curve according to the peak areas of the different urea standard solutions and the concentration of the urea standard solution, detecting the peak area of a sample to be detected by adopting the high performance liquid chromatography under the same condition, and substituting the peak area of the sample to be detected into the standard curve to calculate the content of urea in the sample to be detected.
The method for detecting the trace urea in the melamine by adopting the high performance liquid chromatography has the following advantages that: the method is simple to operate, short in detection time and high in accuracy. The method can accurately and rapidly detect the content of the trace urea in the melamine and provides data basis for monitoring the content of the urea in the melamine production.
In a preferred embodiment of the present invention, the chromatographic conditions of the high performance liquid chromatography are as follows: the mobile phase A is methanol, the mobile phase B is aqueous solution, and the volume ratio of the mobile phase A to the mobile phase B is 0-15: 85-100; the detection wavelength is 190-210 nm.
The methanol and the water are used as mobile phases, and the method has the advantages of low cost, small pollution and small toxicity. Within the above volume ratio range of the mobile phase A and the mobile phase B, the chromatographic column is not damaged, and the separation degree is optimal.
In a preferred embodiment of the present invention, the mobile phase is water.
In the preferred embodiment of the present invention, the flow rate of the mobile phase is 0.8-1.2 ml/min. Within the flow velocity range, the urea content in the sample is detected with the best precision, and the recovery rate is the highest.
In a preferred embodiment of the present invention, the elution process comprises: isocratic elution was carried out at a flow rate of 1 mL/min.
In the preferred embodiment of the present invention, the C18 liquid chromatography column is an ODS-SP C18 column.
In the preferred embodiment of the present invention, the C18 liquid chromatography column has a size of 250mm × 4.6mm × 5 μm.
In the preferred embodiment of the present invention, the temperature of the liquid chromatography column is 30-35 deg.C, and the sample amount is 2-5 μ l. Through a plurality of experiments of the inventor, the inventor finds that the quick and accurate determination of the urea content is favorably realized when the chromatographic column is controlled to have the specification. Too large a sample amount will result in a decrease in separation degree, and too small a sample amount will result in a decrease in separation efficiency.
In an embodiment of the invention, the detection method further includes preparing a sample solution to be detected, and the preparing the sample solution to be detected includes dissolving melamine to be detected in water.
In a preferred embodiment of the present invention, the melamine to be measured is placed in water and subjected to ultrasonic oscillation. Ultrasonic oscillation is used to promote the melamine to dissolve completely in the water.
In the preferred embodiment of the present invention, the time of the ultrasonic oscillation is 30-60 min. Within the above-mentioned oscillation time range, the melamine dispersion can be rapidly achieved.
In a preferred embodiment of the application of the present invention, the preparing of the sample solution to be tested further includes filtering the sample solution to be tested after the oscillating dissolution.
In the preferred embodiment of the present invention, the above-mentioned filtration is performed by using a 0.25-0.45 μm filter membrane. Impurities such as insoluble substances in the test solution are removed by filtration.
In a preferred embodiment of the present invention, the sample to be tested is a melamine sample produced from urea. The detection method provided by the invention is suitable for the production of melamine by taking urea as a raw material.
The invention has the following beneficial effects:
the invention provides a method for detecting trace urea in melamine, which adopts high performance liquid chromatography to detect the concentration of urea in a urea standard solution, draws a standard curve according to the peak area of the urea standard solution and the concentration of the urea standard solution, and can calculate the content of urea in a sample to be detected according to the standard curve. The method is simple to operate, short in detection time and high in accuracy. The method provided by the invention can be used for accurately and rapidly detecting the content of trace urea in the melamine and providing data basis for monitoring the content of urea in the melamine production.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is a chromatogram of a 0.5mg/L urea standard solution in example 1;
FIG. 2 is a chromatogram of a 1mg/L urea standard solution in example 1;
FIG. 3 is a chromatogram of a 2mg/L urea standard solution in example 1;
FIG. 4 is a chromatogram of a 5mg/L urea standard solution in example 1;
FIG. 5 is a chromatogram of a 10mg/L urea standard solution in example 1;
FIG. 6 is a chromatogram of a 20mg/L urea standard solution in example 1;
FIG. 7 is a chromatogram of a 30mg/L urea standard solution in example 1;
FIG. 8 is a standard curve chart drawn from the chromatogram of the urea standard solution in example 1;
FIG. 9 is a chromatogram and a partial enlarged view of a sample in example 1;
FIG. 10 is a chromatogram of example 3 at wavelengths of 190nm and 195 nm;
FIG. 11 is a chromatogram of example 3 at wavelengths of 200nm, 205nm and 210 nm;
FIG. 12 is a chromatogram of a 0.5mg/L urea standard solution in example 4;
FIG. 13 is a chromatogram of a 1mg/L urea standard solution in example 4;
FIG. 14 is a chromatogram of a 2mg/L urea standard solution in example 4;
FIG. 15 is a chromatogram of a standard solution of 5mg/L urea in example 4;
FIG. 16 is a chromatogram of a 10mg/L urea standard solution in example 4;
FIG. 17 is a chromatogram of a 20mg/L urea standard solution in example 4;
FIG. 18 is a chromatogram of a 30mg/L urea standard solution in example 4;
FIG. 19 is a standard curve chart drawn from the chromatogram of the urea standard solution in example 4;
FIG. 20 is a chromatogram of the sample of example 4;
FIG. 21 is a chromatogram of a 0.5mg/L urea standard solution in a comparative example;
FIG. 22 is a chromatogram of a 1mg/L urea standard solution in a comparative example;
FIG. 23 is a chromatogram of a standard solution of 2mg/L urea in a comparative example;
FIG. 24 is a chromatogram of a 5mg/L urea standard solution in a comparative example;
FIG. 25 is a chromatogram of a standard solution of 10mg/L urea in a comparative example;
FIG. 26 is a chromatogram of a 20mg/L urea standard solution in a comparative example;
FIG. 27 is a chromatogram of a 30mg/L urea standard solution in a comparative example;
FIG. 28 is a graph in which a standard curve is plotted from the chromatogram of the urea standard solution in the comparative example.
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 conventional products which are not indicated by manufacturers and are commercially available.
The features and properties of the present invention are described in further detail below with reference to examples.
Example 1
The embodiment provides a method for detecting trace urea in melamine. The method specifically comprises the following steps:
(1) preparation of 0.1mg/mL urea standard solution: accurately weighing superior urea 1.000g in a beaker, adding a small amount of water in an ultrasonic cleaner, and carrying out ultrasonic frequency: and (4) performing ultrasonic treatment for 10min at 40KHz to completely dissolve the urea. And transferring the dissolved solution into a 1000mL volumetric flask, diluting the solution to a scale mark by using water, and carrying out constant volume to obtain a 1mg/mL urea standard solution.
Transferring 10mL of 1mg/mL urea standard solution into a 100mL volumetric flask by using a pipette, and adding 90mL of water to prepare 0.1mg/mL urea standard solution.
(2) Diluting the sample: according to the volume of the urea standard solution in the following table 1, 0ml, 0.5ml, 1ml, 2ml, 5ml, 10ml, 20ml and 30ml of 0.1mg/ml urea standard solution are respectively added into 8 100ml volumetric flasks and the volume is increased to 100ml by water. Filtered through a 0.45 μm syringe filter and ready for use.
TABLE 1 plotting Standard Curve dilution gradient for each sample
| volume/mL of urea standard solution | 0.00 | 0.50 | 1.00 | 2.00 | 5.00 | 10.00 | 20.00 | 30.00 |
| Corresponding urea content/mg | 0.00 | 0.05 | 0.10 | 0.20 | 0.50 | 1.00 | 2.00 | 3.00 |
(3) Preparation of sample solution: accurately weighing 2.0g of a sample into a 100mL beaker, adding about 60mL of water, carrying out ultrasonic treatment by an ultrasonic cleaner for 20min, transferring the sample into a 100mL volumetric flask, diluting the sample to a scale by using water, shaking the sample evenly, standing the sample, and filtering the sample by using a 0.45 mu m needle filter to obtain a sample solution.
(4) High performance liquid chromatography conditions:
a chromatographic column: selecting a chromatographic column resistant to pure water phase, having C18 packing (particle size of 5 μm), column length of 250 μm and inner diameter of 4.6 mm; pure water is adopted as a mobile phase, and the flow rate is as follows: 1.0mL/min, isocratic elution; the sample injection amount is 5 uL; the detection wavelength is 190 nm; the column temperature was 35 ℃.
Through multiple experiments of the inventor, under the chromatographic condition, the urea peak time is about 3.16min, the melamine peak time is about 5.85min, and the separation effect is good.
(5) The liquid chromatography was adjusted to optimal conditions according to the instrument operating conditions. And respectively injecting 10uL of sample, and determining the urea standard solution. And drawing a standard curve according to the measured peak height or peak area respectively corresponding to the mass (mg) of the urea.
The chromatogram of the 0.5mg/L urea standard solution is shown in FIG. 1, the chromatogram of the 1.0mg/L urea standard solution is shown in FIG. 2, the chromatogram of the 2.0mg/L urea standard solution is shown in FIG. 3, the chromatogram of the 5.0mg/L urea standard solution is shown in FIG. 4, the chromatogram of the 10.0mg/L urea standard solution is shown in FIG. 5, the chromatogram of the 20.0mg/L urea standard solution is shown in FIG. 6, and the chromatogram of the 30.0mg/L urea standard solution is shown in FIG. 7. A standard curve is drawn from the chromatogram of the urea standard solution, and is shown in FIG. 8. Y59660 x + 656.24.
(6) The peak height or peak area of the sample solution was measured under the same conditions as the measurement standard curve, and the chromatogram of the sample was obtained by substituting the chromatogram shown in FIG. 9 into the regression equation to obtain the urea mass (mg) in the sample solution.
After the measurement is completed, the instrument is firstly washed by water for 30min, then washed by methanol for 30min, and finally closed according to the operating rules of the instrument.
Example 2
This example performed accuracy verification on the detection method of example 1. To verify the accuracy of the above detection method, a recovery test was performed.
The method specifically comprises the following steps:
weighing 10g of sample to be measured, dissolving the sample in a 500 mL volumetric flask, shaking up and fixing the volume to obtain 0.02g/mL of sample to be measured, respectively transferring 90mL of the sample to four 100mL volumetric flasks, respectively and accurately adding 0.1mg/mL standard samples of 0.5mL, 1mL and 2mL into the four samples to be measured, wherein the adding amounts of the standard samples are 0.05mg, 0.10mg and 0.20mg respectively, and then calculating m according to a high performance liquid chromatography measuring method Sample + label Urea content of in (m) Sample + label -m Knowing the urea content of the liquid to be tested )/m Sign And calculating the recovery rate. The results are shown in Table 2.
TABLE 2 recovery rate experiment
From table 2, it can be determined that the recovery rate is 97.73%, and that the recovery rate is good, which meets the analysis requirements, and also shows that the method has higher accuracy.
Example 3
In this example, the same sample was measured at different detection wavelengths under the same elution conditions and sample treatment conditions as in example 1. The method specifically comprises the following steps:
preparation of sample solution: accurately weighing 2.0g of a sample into a 100mL beaker, adding about 60mL of water, carrying out ultrasonic treatment with an ultrasonic cleaner at the ultrasonic frequency of 40KHz for 20min, transferring the sample into a 100mL volumetric flask, diluting the sample to a scale with water, shaking up, standing, and filtering the sample by using a 0.45-micron needle filter to obtain a sample solution.
High performance liquid chromatography conditions: selecting a chromatographic column resistant to pure water phase, having C18 packing (particle size of 5 μm), column length of 250 μm and inner diameter of 4.6 mm; pure water is adopted as a mobile phase, and the flow rate is as follows: 1.0mL/min, isocratic elution; the sample injection amount is 5 uL; the column temperature is 35 ℃; measurements were carried out at different wavelengths (190nm, 195nm, 200nm, 205nm, 210 nm).
Under the chromatographic conditions, the urea peak time is about 3.16min, and the melamine peak time is about 5.85min, but the sensitivity decreases with increasing wavelength, and urea cannot be detected after 210 nm. (the chromatogram is shown in FIGS. 10 and 11, and it is clear from FIGS. 10 and 11 that the peak of urea in melamine decreases in sensitivity with increasing wavelength.)
After the measurement is completed, the instrument is firstly washed by water for 30min, then washed by methanol for 30min, and finally closed according to the operating rules of the instrument.
Example 4
The embodiment provides a method for detecting trace urea in melamine. The method specifically comprises the following steps:
(1) preparation of 0.1mg/mL urea standard solution: accurately weighing 1.000g of superior urea in a beaker, adding a small amount of water in an ultrasonic cleaner, and carrying out ultrasonic treatment for 10min at the ultrasonic frequency of 40KHz to completely dissolve the urea. And transferring the dissolved solution into a 1000mL volumetric flask, diluting with water to a scale mark, and performing constant volume to obtain a 1mg/mL urea standard solution.
Transferring 10mL of 1mg/mL urea standard solution into a 100mL volumetric flask by using a pipette, and adding 90mL of water to prepare 0.1mg/mL urea standard solution.
(2) Diluting the sample: according to the volume of the urea standard solution in the following table 1, 0ml, 0.5ml, 1ml, 2ml, 5ml, 10ml, 20ml and 30ml of 0.1mg/ml urea standard solution are respectively added into 8 100ml volumetric flasks and the volume is increased to 100ml by water. Filtered through a 0.45 μm syringe filter and ready for use.
Table 1 plots standard curve dilution gradients for each sample.
| volume/mL of urea standard solution | 0.00 | 0.50 | 1.00 | 2.00 | 5.00 | 10.00 | 20.00 | 30.00 |
| Corresponding urea content/mg | 0.00 | 0.05 | 0.10 | 0.20 | 0.50 | 1.00 | 2.00 | 3.00 |
(3) Preparation of sample solution: accurately weighing 2.0g of a sample into a 100mL beaker, adding about 60mL of water, carrying out ultrasonic frequency ultrasonic treatment for 20min by an ultrasonic cleaner, transferring the sample into a 100mL volumetric flask, diluting the sample to a scale by water, shaking up, standing, and filtering the sample by a 0.45-micron needle filter to obtain a sample solution.
(4) High performance liquid chromatography conditions:
a chromatographic column: selecting a column resistant to pure aqueous phase having a C18 packing (particle size 5 μm), a column length of 250 μm and an internal diameter of 4.6 mm; 10% methanol +90 pure water was used as the mobile phase, flow rate: 1.0mL/min, low pressure gradient elution; the sample injection amount is 10 uL; the column temperature is 30 ℃; the detection wavelength was 190 nm.
Under the chromatographic conditions, the urea peak time is about 1.6min, the melamine peak time is about 4.6min, and the separation effect is good.
(5) The liquid chromatography was adjusted to optimal conditions according to the instrument operating conditions. And respectively injecting 10uL of sample, and determining the urea standard solution. And drawing a standard curve or a regression equation according to the measured peak height or peak area respectively corresponding to the mass (mg) of the urea.
The chromatogram of the 0.5mg/L urea standard solution is shown in FIG. 12, the chromatogram of the 1.0mg/L urea standard solution is shown in FIG. 13, the chromatogram of the 2.0mg/L urea standard solution is shown in FIG. 14, the chromatogram of the 5.0mg/L urea standard solution is shown in FIG. 15, the chromatogram of the 10.0mg/L urea standard solution is shown in FIG. 16, the chromatogram of the 20.0mg/L urea standard solution is shown in FIG. 17, and the chromatogram of the 30.0mg/L urea standard solution is shown in FIG. 18. A standard curve is drawn from the chromatogram of the urea standard solution, as shown in FIG. 19. Y4372.1 x + 12486.
(6) The peak height or peak area of the sample solution was measured under the same conditions as the measurement standard curve, and the chromatogram of the sample is shown in FIG. 20. And substituting the mass into a regression equation to obtain the mass (mg) of the urea in the sample solution.
After the measurement is completed, the instrument is firstly washed by water for 30min, then washed by methanol for 30min, and finally closed according to the operating rules of the instrument.
Comparative example
The embodiment provides a method for detecting trace urea in melamine. The method specifically comprises the following steps:
(1) preparation of 0.1mg/mL urea standard solution: accurately weighing 1.000g of superior urea in a beaker, adding a small amount of water in an ultrasonic cleaner, and carrying out ultrasonic treatment for 10min at the ultrasonic frequency of 40KHz to completely dissolve the urea. And transferring the dissolved solution into a 1000mL volumetric flask, diluting with water to a scale mark, and performing constant volume to obtain a 1mg/mL urea standard solution.
10mL of the 1mg/mL urea standard solution is transferred into a 100mL volumetric flask by a pipette, and 90mL of water is added to prepare the 0.1mg/mL urea standard solution.
(2) Diluting the sample: according to the volume of the urea standard solution in the following table 1, 0ml, 0.5ml, 1ml, 2ml, 5ml, 10ml, 20ml and 30ml of 0.1mg/ml urea standard solution were added into 8 100ml volumetric flasks, respectively, and the volume was made up to 100ml with water. Filtered through a 0.45 μm syringe filter and ready for use.
TABLE 1 plotting Standard Curve dilution gradient for each sample
| volume/mL of urea standard solution | 0.00 | 0.50 | 1.00 | 2.00 | 5.00 | 10.00 | 20.00 | 30.00 |
| Corresponding urea content/mg | 0.00 | 0.05 | 0.10 | 0.20 | 0.50 | 1.00 | 2.00 | 3.00 |
(3) Preparation of sample solution: accurately weighing 2.0g of a sample in a 100mL beaker, adding about 60mL of water, ultrasonically cleaning for 20min by an ultrasonic cleaner, transferring the sample into a 100mL volumetric flask, diluting the sample to a scale by water, shaking up, standing, and filtering by a 0.45 mu m needle filter to obtain a sample solution.
(4) High performance liquid chromatography conditions:
a chromatographic column: selecting a column resistant to pure aqueous phase having a C18 packing (particle size 5 μm), a column length of 250 μm and an internal diameter of 4.6 mm; flow rate: 1.0 mL/min; the sample injection amount is 5 uL; the detection wavelength is 190 nm; the column temperature was 35 ℃.
The mobile phase A of the chromatogram is acetonitrile, the mobile phase B is aqueous solution, and the volume ratio of the mobile phase A to the mobile phase B is 5: 95.
Under the chromatographic conditions described above, the urea peak time was about 1.6 min.
(5) The liquid chromatography was adjusted to optimal conditions according to the instrument operating conditions. And respectively injecting 10uL of sample, and determining the urea standard solution. And drawing a standard curve according to the measured peak height or peak area respectively corresponding to the mass (mg) of the urea.
The chromatogram of the 0.5mg/L urea standard solution is shown in FIG. 21, the chromatogram of the 1.0mg/L urea standard solution is shown in FIG. 22, the chromatogram of the 2.0mg/L urea standard solution is shown in FIG. 23, the chromatogram of the 5.0mg/L urea standard solution is shown in FIG. 24, the chromatogram of the 10.0mg/L urea standard solution is shown in FIG. 25, the chromatogram of the 20.0mg/L urea standard solution is shown in FIG. 26, and the chromatogram of the 30.0mg/L urea standard solution is shown in FIG. 27. A standard curve is drawn from the chromatogram of the urea standard solution, as shown in FIG. 28. 6111.7x +60860, R 2 0.0166. The spectrum and data in FIG. 28 show that the standard solution curve has no linear relationship by using acetonitrile + water as the mobile phase.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. The method for detecting trace urea in melamine is characterized by comprising the following steps: detecting peak areas of different urea standard solutions by adopting a high performance liquid chromatography, wherein the chromatographic column is a C18 liquid chromatographic column, drawing a standard curve according to the peak areas of the different urea standard solutions and the concentration of the urea standard solution, detecting the peak area of a sample to be detected by adopting the high performance liquid chromatography under the same condition, and substituting the peak area of the sample to be detected into the standard curve to calculate the content of urea in the sample to be detected;
the chromatographic conditions of the high performance liquid chromatography are as follows: the mobile phase is water, and the detection wavelength is 190-210 nm;
the elution procedure included: isocratic elution, wherein the flow rate of the mobile phase is 1 mL/min;
the preparation of the sample solution to be tested comprises dissolving melamine to be tested in water.
2. The detection method according to claim 1, wherein the C18 liquid chromatography column is an ODS-SP C18 column.
3. The method of claim 2, wherein the C18 liquid chromatography column has a specification of 250mm x 4.6mm x 5 μm.
4. The detection method according to claim 3, wherein the column temperature of the liquid chromatography column is 30 to 35 ℃ and the sample amount is 2 to 5. mu.l.
5. The detection method according to claim 1, characterized in that the melamine to be detected is placed in water and subjected to ultrasonic oscillation; the ultrasonic oscillation time is 30-60 min.
6. The method according to claim 1, wherein the preparing the sample solution to be tested further comprises filtering the sample solution to be tested after the shaking dissolution.
7. The detection method according to claim 6, wherein the filtration is performed with a filter of 0.25 to 0.45 μm.
8. The detection method according to claim 1, wherein the sample to be detected is a melamine sample produced from urea.
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| CN116381111A (en) * | 2023-03-21 | 2023-07-04 | 广州质量监督检测研究院 | Method for detecting urea-formaldehyde resin in melamine-formaldehyde material |
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