CN111208225B - Method for determining EDTA content in liquid detergent - Google Patents
Method for determining EDTA content in liquid detergent Download PDFInfo
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Abstract
The invention provides a method for determining the content of EDTA in a liquid detergent, which comprises the following steps: s1, preparing an EDTA standard stock solution; s2, preparing an EDTA standard working solution; s3, carrying out esterification and derivatization reaction on a liquid detergent sample to be detected to obtain a sample solution to be detected; s4, simultaneously carrying out esterification and derivatization reaction on the EDTA standard working solution obtained in the step S2 according to the step S3 to obtain a standard working solution to be detected; and S5, analyzing and detecting the standard working solution to be detected obtained in the step S4 and the sample solution to be detected obtained in the step S3 by using a gas chromatography-mass spectrometer, and determining the content of EDTA in the detergent sample. The invention can realize accurate quantification of the EDTA content in the liquid detergent, and has the advantages of low quantitative detection limit, and good quantitative accuracy and repeatability.
Description
Technical Field
The invention relates to a method for determining the content of EDTA in a liquid detergent.
Background
EDTA, commonly referred to as ethylenediaminetetraacetic acid or its sodium salt, is an important artificial organic polyacid chelating agent, and is useful as a stabilizer, a dyeing assistant, a fiber-treating assistant, a coagulant, a water-treating agent, a water softener, and the like. It can form stable complex with most metal ions to prevent metal-induced deterioration and oxidation loss, and can be widely used in pharmaceutical industry, chemical industry, food industry, agriculture and pharmaceutical industry, etc. Chelating agents are commonly used in washing products, and although the addition amount is small, the chelating agents play a very important role in improving the quality of products. At the same time, chelating agents can also cause minor negative harm to human health and the natural environment if not handled properly.
The traditional chelating agents include NTA, EDTA, DTPA, STPP and other varieties. Such as EDTA, which is highly likely to be complexed with heavy metals, pollutes soil, has poor biodegradability, remains in the environment for a long time, forms deposits, causes blockage of water pipes, and is finally biodegradable after a long time, but inevitably endangers the ecological environment, and the like.
Along with the improvement of living standard of people, the development of daily chemical products is rapid, the detergent highly permeates into the life of people, and EDTA or sodium salt thereof is added into a plurality of detergent products circulating in the market at present, thus causing serious potential harm to the environment. Therefore, people urgently need to research a good and applicable detection method for detecting the content of the EDTA in the liquid detergent, but no corresponding detection method aiming at the content of the EDTA in the liquid detergent and relevant literature reports exist at present. A standard method for detecting chelating agent (EDTA) in detergent, namely a complexometric titration method, exists in China, the complexometric titration method has certain limitations, the detection result is sometimes unsatisfactory, and EDTA in a sample with low concentration content is sometimes not detected or the accuracy of the detected content is low.
The Chinese invention with the application number of CN201410537619.6 discloses a method for detecting EDTA in laundry detergent, which comprises the following steps: (1) preparing a potassium bicarbonate aqueous solution; (2) adding the laundry detergent to be measured into a potassium bicarbonate water solution, stirring for 10-20 minutes at the temperature of 45-50 ℃, filtering while hot, and naturally cooling to room temperature to obtain a pretreatment solution; (3) adding ionic liquid into the pretreatment liquid, oscillating and extracting, then centrifuging, and removing a water phase to obtain an ionic liquid phase; (4) adding trivalent ferric salt into the ionic liquid phase, fully and uniformly mixing, performing column chromatography separation on gel column chromatography Superose12, firstly washing with n-hexane, then performing gradient elution by taking a petroleum ether-n-propanol mixed solvent as an eluent, and collecting the eluent; (5) evaporating the solvent of the eluent to be nearly dry, dissolving to a constant volume, and filtering by an organic membrane to obtain a detection sample; (6) and (4) carrying out liquid chromatography separation on the detection sample to determine the content. The problem with this patent is that ionic liquids are inevitably used, which can cause contamination of the liquid chromatography column and the liquid chromatography instrumentation system.
Disclosure of Invention
The invention aims to provide a method for measuring the content of EDTA in a liquid detergent, which can realize accurate quantification of the content of EDTA in the liquid detergent, and has the advantages of low quantitative detection limit, and good quantitative accuracy and repeatability.
In order to solve the technical problems, the technical scheme of the invention is as follows:
a method for measuring the content of EDTA in a liquid detergent comprises the following steps:
s1, preparing EDTA standard stock solution, precisely weighing 0.1g of ethylenediamine tetraacetic acid standard substance to 0.0001g, placing the ethylenediamine tetraacetic acid standard substance into a 100mL volumetric flask, adding ultrapure water to scale and fix the volume to obtain the EDTA standard stock solution with the mass concentration of 1000 mg/L;
s2, preparing an EDTA standard working solution, respectively taking 1mL, 0.5mL, 0.2mL, 0.1mL and 0.01mL of EDTA standard stock solutions in a 100mL volumetric flask, diluting with ultrapure water to a scale constant volume, shaking up, and performing ultrasonic treatment for 10 minutes to obtain the EDTA standard working solution;
s3, weighing a to-be-detected detergent sample in a test tube with a plug scale, adding ultrapure water to completely dissolve the detergent sample to obtain a detergent sample solution, opening an infrared radiation heater to heat to 300 ℃, placing the detergent sample solution under the infrared radiation heater, moving out after 1min, cooling to room temperature, adjusting the pH value of the to-be-detected detergent sample solution to 2.0-5.5 with an acid reagent, adding an esterification reagent, shaking uniformly, carrying out esterification reaction at a constant temperature of 60-120 ℃ for 0.5-4h, taking out and shaking every 5-30 min during the reaction, cooling to room temperature after the esterification reaction is completed to obtain a reaction sample solution, transferring the reaction sample solution, washing the test tube with the plug scale with a sodium carbonate solution in batches to obtain a washing solution, mixing the reaction sample solution with the washing solution, adding isooctane or n-heptane and a sodium salt, shaking uniformly, centrifuging for 3-15 min, taking a supernatant, and filtering a filter membrane with the diameter of 0.45 mu m to obtain the to-be-detected sample solution;
s4, performing esterification reaction on the EDTA standard working solution obtained in the step S2 according to the step S3 to obtain a standard working solution to be detected;
and S5, analyzing and detecting the standard working solution to be detected obtained in the step S4 and the sample solution to be detected obtained in the step S3 by using a gas chromatography-mass spectrometer, and determining the content of EDTA in the detergent sample.
Further, in the step S3, the mass of the detergent sample is 0.2-1.5 g, and the volume of water for dissolving the detergent sample is 5-25 mL; the distance between the liquid detergent sample and the infrared radiation heater was 20 cm.
Further, in step S3 of the present invention, the acid reagent is glacial acetic acid, hydrochloric acid or sulfuric acid.
Furthermore, in step S3, the volume of the esterification reagent is 3-15 mL, and the esterification reagent is a 10% volume fraction of a methanol sulfate solution, an ethanol sulfate solution, or an acetyl chloride methanol solution.
Further, in step S3 of the present invention, the temperature of the esterification reaction is 60 ℃, 80 ℃, 100 ℃ or 120 ℃, and the time of the esterification reaction is 0.5h, 1h, 2h, 3h or 4 h.
Further, in the step S3, the mass fraction of the sodium carbonate solution is 2-15%, the volume of the sodium carbonate solution is 5-20 mL, and the number of times of cleaning is 2-5. Preferably, the mass fraction of the sodium carbonate solution is 8%.
In step S3, the volume of isooctane or n-heptane is 1 to 5mL, the sodium salt is anhydrous sodium sulfate, sodium bisulfate or sodium chloride, and the weight of the sodium salt is 0.5 to 3 g.
Further, in step S3 of the present invention, the rotation speed of the centrifuge during centrifugation is 3000, 5000, 8000, 10000 or 12000 rpm.
Further, in step S5 of the present invention, the conditions of the gas chromatography-mass spectrometer are as follows: the gas-phase capillary column is a DB-5MS column with the thickness of 30m multiplied by 0.25 mu m multiplied by 0.32mm, the injection inlet temperature is 250 ℃, the flow rate is 1.0mL/min, the injection volume is 1 mu L, the carrier gas is helium, the ion source temperature is 230 ℃, the quadrupole temperature is 150 ℃, and the solvent delay time is 3 min; the temperature programming process comprises the following steps: maintaining at 100 deg.C for 1min, heating to 220 deg.C at 40 deg.C/min, maintaining for 5min, heating to 300 deg.C at 50 deg.C/min, and maintaining for 10 min.
Compared with the prior art, the invention has the following beneficial effects:
1) because the raw material of the liquid detergent possibly contains a small amount of heavy metal, and EDTA can exist in different complex forms in the liquid detergent, the pH value of the liquid detergent sample is adjusted, the complex is converted into EDTA, then esterification reaction derivatization is carried out by using an esterifying agent to treat the EDTA in the liquid detergent sample, an analysis method for detecting the EDTA by using a gas chromatography-mass spectrometer is established, and specific gas chromatography-mass spectrometry conditions are selected, so that the accurate quantification of the EDTA content in the liquid detergent is realized, and the high performance liquid chromatography which can cause the pollution of instruments and chromatographic columns can be replaced.
2) The detergent has more raw materials, and can interfere with the esterification and detection of EDTA to influence the detection accuracy and detection limit, so that the invention also carries out infrared irradiation treatment on a detergent sample, reduces the interference generated by other raw materials in the detergent by using instantaneous temperature rise, improves the esterification degree of the EDTA, further improves the detection accuracy and reduces the detection limit.
3) The detection method for EDTA in the prior art has the problems of high detection limit, and poor quantitative accuracy and repeatability, and the invention has better quantitative accuracy and repeatability and lower quantitative detection limit through verification, thereby being worthy of popularization.
Detailed Description
The present invention will be described in detail with reference to specific embodiments, and the exemplary embodiments and descriptions thereof herein are provided to explain the present invention but not to limit the present invention.
Example 1
The method for measuring the content of EDTA in the liquid detergent comprises the following steps:
s1, preparing EDTA standard stock solution, precisely weighing 0.1g of ethylenediamine tetraacetic acid standard substance to 0.0001g, placing the ethylenediamine tetraacetic acid standard substance into a 100mL volumetric flask, adding ultrapure water to scale and fix the volume to obtain the EDTA standard stock solution with the mass concentration of 1000 mg/L;
s2, preparing an EDTA standard working solution, respectively taking 1mL, 0.5mL, 0.2mL, 0.1mL and 0.01mL of EDTA standard stock solutions in a 100mL volumetric flask, diluting with ultrapure water to a scale constant volume, shaking up, and performing ultrasonic treatment for 10 minutes to obtain the EDTA standard working solution;
s3, weighing 0.2g of a to-be-detected liquid detergent sample into a test tube with a plug scale, adding 5mL of ultrapure water to completely dissolve the liquid detergent sample to obtain a liquid detergent sample solution, opening an infrared radiation heater to heat to 300 ℃, placing the liquid detergent sample solution at a position 30cm below the infrared radiation heater, moving out after 1min, cooling to room temperature, adjusting the pH value of the liquid detergent sample solution to be detected to 2.5 with glacial acetic acid, adding 8mL of a 10% volume fraction methanol sulfate solution, shaking uniformly, carrying out an esterification reaction at a constant temperature of 80 ℃ for 2h, taking out the liquid detergent and shaking every 20min during the reaction, cooling to room temperature after the esterification reaction is finished to obtain a reaction sample solution, transferring the reaction sample solution, cleaning the test tube with the plug scale 2 times with 10mL of 8% mass fraction sodium carbonate solution to obtain a cleaning solution, mixing the cleaning solution with the reaction sample solution, adding 1mL of isooctane and 1g of anhydrous sodium sulfate, shaking and mixing uniformly, centrifuging for 3min at the rotating speed of 10000 rpm, taking supernate and filtering with a 0.45 mu m filter membrane to obtain a sample solution to be detected;
s4, performing esterification reaction on the EDTA standard working solution obtained in the step S2 according to the step S3 to obtain a standard working solution to be detected;
s5, analyzing and detecting the standard working solution to be detected obtained in the step S4 and the sample solution to be detected obtained in the step S3 by using a gas chromatography-mass spectrometer, and determining the content of EDTA in the detergent sample, wherein the conditions of the gas chromatography-mass spectrometer are as follows: the gas-phase capillary column is a DB-5MS column with the thickness of 30m multiplied by 0.25 mu m multiplied by 0.32mm, the injection inlet temperature is 250 ℃, the flow rate is 1.0mL/min, the injection volume is 1 mu L, the carrier gas is helium, the ion source temperature is 230 ℃, the quadrupole temperature is 150 ℃, and the solvent delay time is 3 min; the temperature programming process comprises the following steps: maintaining at 100 deg.C for 1min, heating to 220 deg.C at 40 deg.C/min, maintaining for 5min, heating to 300 deg.C at 50 deg.C/min, and maintaining for 10 min.
Example 2
The method for measuring the content of EDTA in the liquid detergent comprises the following steps:
s1, preparing EDTA standard stock solution, precisely weighing 0.1g of ethylenediamine tetraacetic acid standard substance to 0.0001g, placing the ethylenediamine tetraacetic acid standard substance into a 100mL volumetric flask, adding ultrapure water to scale and fix the volume to obtain the EDTA standard stock solution with the mass concentration of 1000 mg/L;
s2, preparing an EDTA standard working solution, respectively taking 1mL, 0.5mL, 0.2mL, 0.1mL and 0.01mL of EDTA standard stock solutions in a 100mL volumetric flask, diluting with ultrapure water to a scale constant volume, shaking up, and performing ultrasonic treatment for 10 minutes to obtain the EDTA standard working solution;
s3, weighing 1.5g of a to-be-measured liquid detergent sample into a test tube with a plug scale, adding 25mL of ultrapure water to completely dissolve the liquid detergent sample to obtain a liquid detergent sample solution, opening an infrared radiation heater to heat to 300 ℃, placing the liquid detergent sample solution at a position 30cm below the infrared radiation heater, moving out after 1min, cooling to room temperature, adjusting the pH value of the liquid detergent sample solution to be measured to 2 with hydrochloric acid, adding 15mL of a sulfuric acid ethanol solution with a volume fraction of 10%, shaking uniformly, carrying out an esterification reaction at a constant temperature of 60 ℃ for 4h, taking out the liquid detergent and shaking once every 30min during the reaction, cooling to room temperature after the esterification reaction is finished to obtain a reaction sample liquid, transferring the reaction sample liquid, washing the test tube with the plug scale 2 times with 5mL of a sodium carbonate solution with a mass fraction of 15% to obtain a washing liquid, mixing the washing liquid with the reaction sample liquid, adding 2mL of n-heptane and 0.5g of sodium bisulfate, shaking and mixing uniformly, centrifuging for 15min at the rotating speed of 3000 r/min, and filtering supernate with a 0.45-micron filter membrane to obtain a sample solution to be detected;
s4, performing esterification reaction on the EDTA standard working solution obtained in the step S2 according to the step S3 to obtain a standard working solution to be detected;
s5, analyzing and detecting the standard working solution to be detected obtained in the step S4 and the sample solution to be detected obtained in the step S3 by using a gas chromatography-mass spectrometer, and determining the content of EDTA in the detergent sample, wherein the conditions of the gas chromatography-mass spectrometer are as follows: the gas-phase capillary column is a DB-5MS column with the thickness of 30m multiplied by 0.25 mu m multiplied by 0.32mm, the injection inlet temperature is 250 ℃, the flow rate is 1.0mL/min, the injection volume is 1 mu L, the carrier gas is helium, the ion source temperature is 230 ℃, the quadrupole temperature is 150 ℃, and the solvent delay time is 3 min; the temperature programming process comprises the following steps: maintaining at 100 deg.C for 1min, heating to 220 deg.C at 40 deg.C/min, maintaining for 5min, heating to 300 deg.C at 50 deg.C/min, and maintaining for 10 min.
Example 3
The method for measuring the content of EDTA in the liquid detergent comprises the following steps:
s1, preparing EDTA standard stock solution, precisely weighing 0.1g of ethylenediamine tetraacetic acid standard substance to 0.0001g, placing the ethylenediamine tetraacetic acid standard substance into a 100mL volumetric flask, adding ultrapure water to scale and fix the volume to obtain the EDTA standard stock solution with the mass concentration of 1000 mg/L;
s2, preparing an EDTA standard working solution, respectively taking 1mL, 0.5mL, 0.2mL, 0.1mL and 0.01mL of EDTA standard stock solutions in a 100mL volumetric flask, diluting with ultrapure water to a scale constant volume, shaking up, and performing ultrasonic treatment for 10 minutes to obtain the EDTA standard working solution;
s3, weighing 0.5g of a to-be-detected liquid detergent sample into a test tube with a plug scale, adding 10mL of ultrapure water to completely dissolve the liquid detergent sample to obtain a liquid detergent sample solution, opening an infrared radiation heater to heat to 300 ℃, placing the liquid detergent sample solution at a position 30cm below the infrared radiation heater, moving out after 1min, cooling to room temperature, adjusting the pH value of the liquid detergent sample solution to be detected to 3 with sulfuric acid, adding 15mL of an acetyl chloride methanol solution with a volume fraction of 10%, shaking uniformly, carrying out an esterification reaction at a constant temperature of 90 ℃ for 3h, taking out the liquid detergent and shaking once every 10min during the reaction, cooling to room temperature after the esterification reaction is finished to obtain a reaction sample solution, transferring the reaction sample solution, cleaning the test tube with the plug scale with 3 times by using 15mL of a sodium carbonate solution with a mass fraction of 6% to obtain a cleaning solution, mixing the cleaning solution with the reaction sample solution, adding 3mL of isooctane and 1.5g of sodium chloride, shaking and mixing uniformly, centrifuging for 6min at the rotating speed of 5000 r/min, and filtering the supernate with a 0.45-micron filter membrane to obtain a sample solution to be detected;
s4, performing esterification reaction on the EDTA standard working solution obtained in the step S2 according to the step S3 to obtain a standard working solution to be detected;
s5, analyzing and detecting the standard working solution to be detected obtained in the step S4 and the sample solution to be detected obtained in the step S3 by using a gas chromatography-mass spectrometer, and determining the content of EDTA in the detergent sample, wherein the conditions of the gas chromatography-mass spectrometer are as follows: the gas-phase capillary column is a DB-5MS column with the thickness of 30m multiplied by 0.25 mu m multiplied by 0.32mm, the injection inlet temperature is 250 ℃, the flow rate is 1.0mL/min, the injection volume is 1 mu L, the carrier gas is helium, the ion source temperature is 230 ℃, the quadrupole temperature is 150 ℃, and the solvent delay time is 3 min; the temperature programming process comprises the following steps: maintaining at 100 deg.C for 1min, heating to 220 deg.C at 40 deg.C/min, maintaining for 5min, heating to 300 deg.C at 50 deg.C/min, and maintaining for 10 min.
Example 4
S1, preparing EDTA standard stock solution, precisely weighing 0.1g of ethylenediamine tetraacetic acid standard substance to 0.0001g, placing the ethylenediamine tetraacetic acid standard substance into a 100mL volumetric flask, adding ultrapure water to scale and fix the volume to obtain the EDTA standard stock solution with the mass concentration of 1000 mg/L;
s2, preparing an EDTA standard working solution, respectively taking 1mL, 0.5mL, 0.2mL, 0.1mL and 0.01mL of EDTA standard stock solutions in a 100mL volumetric flask, diluting with ultrapure water to a scale constant volume, shaking up, and performing ultrasonic treatment for 10 minutes to obtain the EDTA standard working solution;
s3, weighing 0.8g of a to-be-detected liquid detergent sample into a test tube with a plug scale, adding 15mL of ultrapure water to completely dissolve the liquid detergent sample to obtain a liquid detergent sample solution, opening an infrared radiation heater to heat to 300 ℃, placing the liquid detergent sample solution at a position 30cm below the infrared radiation heater, moving out after 1min, cooling to room temperature, adjusting the pH value of the liquid detergent sample solution to be detected to 4 with glacial acetic acid, adding 10mL of a 10% volume fraction methanol sulfate solution, shaking uniformly, carrying out esterification reaction at a constant temperature of 100 ℃ for 1h, taking out the liquid detergent and shaking at intervals of 15min during the reaction, cooling to room temperature after the esterification reaction is finished to obtain a reaction sample solution, transferring the reaction sample solution, cleaning the test tube with the plug scale with 16mL of a 5% mass fraction sodium carbonate solution for 4 times to obtain a cleaning solution, mixing the cleaning solution with the reaction sample solution, adding 4mL of n-heptane and 2g of anhydrous sodium sulfate, shaking and mixing uniformly, centrifuging for 4min at the rotating speed of 8000 rpm, and filtering the supernate with a 0.45-micron filter membrane to obtain a sample solution to be detected;
s4, performing esterification reaction on the EDTA standard working solution obtained in the step S2 according to the step S3 to obtain a standard working solution to be detected;
s5, analyzing and detecting the standard working solution to be detected obtained in the step S4 and the sample solution to be detected obtained in the step S3 by using a gas chromatography-mass spectrometer, and determining the content of EDTA in the detergent sample, wherein the conditions of the gas chromatography-mass spectrometer are as follows: the gas-phase capillary column is a DB-5MS column with the thickness of 30m multiplied by 0.25 mu m multiplied by 0.32mm, the injection inlet temperature is 250 ℃, the flow rate is 1.0mL/min, the injection volume is 1 mu L, the carrier gas is helium, the ion source temperature is 230 ℃, the quadrupole temperature is 150 ℃, and the solvent delay time is 3 min; the temperature programming process comprises the following steps: maintaining at 100 deg.C for 1min, heating to 220 deg.C at 40 deg.C/min, maintaining for 5min, heating to 300 deg.C at 50 deg.C/min, and maintaining for 10 min.
Example 5
S1, preparing EDTA standard stock solution, precisely weighing 0.1g of ethylenediamine tetraacetic acid standard substance to 0.0001g, placing the ethylenediamine tetraacetic acid standard substance into a 100mL volumetric flask, adding ultrapure water to scale and fix the volume to obtain the EDTA standard stock solution with the mass concentration of 1000 mg/L;
s2, preparing an EDTA standard working solution, respectively taking 1mL, 0.5mL, 0.2mL, 0.1mL and 0.01mL of EDTA standard stock solutions in a 100mL volumetric flask, diluting with ultrapure water to a scale constant volume, shaking up, and performing ultrasonic treatment for 10 minutes to obtain the EDTA standard working solution;
s3, weighing 1g of a to-be-measured liquid detergent sample into a test tube with a plug scale, adding 20mL of ultrapure water to completely dissolve the liquid detergent sample to obtain a liquid detergent sample solution, opening an infrared radiation heater to heat to 300 ℃, placing the liquid detergent sample solution at a position 30cm below the infrared radiation heater, moving out after 1min, cooling to room temperature, adjusting the pH value of the liquid detergent sample solution to be measured to 5.5 with glacial acetic acid, adding 12mL of a 10% volume fraction methanol sulfate solution, shaking uniformly, carrying out esterification reaction at a constant temperature of 120 ℃ for 0.5h, taking out the liquid detergent and shaking every 10min during the reaction, cooling to room temperature after the esterification reaction is finished to obtain a reaction sample solution, transferring the reaction sample solution, cleaning the test tube with the plug scale 5 times with 20mL of a 2% mass fraction sodium carbonate solution to obtain a cleaning solution, mixing the cleaning solution with the reaction sample solution, adding 5mL of n-heptane and 3g of sodium sulfate, shaking and mixing uniformly, centrifuging for 3min at the rotating speed of 12000 r/min, and filtering supernate with a 0.45-micron filter membrane to obtain a sample solution to be detected;
s4, performing esterification reaction on the EDTA standard working solution obtained in the step S2 according to the step S3 to obtain a standard working solution to be detected;
s5, analyzing and detecting the standard working solution to be detected obtained in the step S4 and the sample solution to be detected obtained in the step S3 by using a gas chromatography-mass spectrometer, and determining the content of EDTA in the detergent sample, wherein the conditions of the gas chromatography-mass spectrometer are as follows: the gas-phase capillary column is a DB-5MS column with the thickness of 30m multiplied by 0.25 mu m multiplied by 0.32mm, the injection inlet temperature is 250 ℃, the flow rate is 1.0mL/min, the injection volume is 1 mu L, the carrier gas is helium, the ion source temperature is 230 ℃, the quadrupole temperature is 150 ℃, and the solvent delay time is 3 min; the temperature programming process comprises the following steps: maintaining at 100 deg.C for 1min, heating to 220 deg.C at 40 deg.C/min, maintaining for 5min, heating to 300 deg.C at 50 deg.C/min, and maintaining for 10 min.
Reference example 1
Unlike example 1, the esterification reaction step is not included in step S3.
Reference example 2
Unlike example 1, step S3 does not include a step of adjusting the pH of the liquid detergent sample solution.
Reference example 3
Unlike example 1, the step of performing infrared irradiation on the liquid detergent sample solution was not included in step S3.
Reference example 4
Unlike example 1, the pH of the liquid detergent sample solution in step S3 was adjusted to 1.9.
Reference example 5
Unlike example 1, the pH of the liquid detergent sample solution in step S3 was adjusted to 5.6.
Reference example 6
The difference from example 1 was that the time for the esterification reaction in step S3 was 29 min.
Reference example 7
Except for example 1 that the time for the esterification reaction in step S3 was 241 min.
Reference example 8
Except for example 1 that the temperature of the esterification reaction in step S3 was 59 ℃.
Reference example 9
Except for example 1 that the temperature of the esterification reaction in step S3 was 121 ℃.
The first test example: EDTA quantitative accuracy test
The EDTA quantification accuracy of each of examples 1 to 5 and reference examples 1 to 9 was determined, and the results are shown in Table 1:
TABLE 1
As can be seen from Table 1, the EDTA quantification accuracy of examples 1-5 of the present invention is 97.97-98.75%, which is higher, among which the best in example 1. The partial operation of reference examples 1-9 is different from that of example 1, wherein the quantitative accuracy of reference example 1 is reduced to about 30%, and the detection accuracy is basically not achieved, which indicates that the esterification reaction is the key to improve the detection quantitative accuracy; the quantitative accuracy of the reference example 2 is reduced a lot, which shows that the adjustment of the pH value of the liquid detergent sample solution has a great influence on the quantitative accuracy; the quantitative accuracy of reference example 3 is reduced to a certain extent, which shows that the infrared irradiation of the liquid detergent sample solution can improve the quantitative accuracy of detection.
The quantitative accuracy of the reference examples 4 and 5 is reduced a lot, which shows that the quantitative accuracy is reduced when the pH value of the liquid detergent sample solution is beyond the range defined by the invention; the quantitative accuracy rate of reference example 6 is only reduced after that of reference example 2, which shows that the esterification degree is insufficient when the esterification time is shorter than 0.5h, thereby greatly reducing the quantitative accuracy rate, while the quantitative accuracy rate of reference example 7 is reduced only a little, which shows that the quantitative accuracy rate is slightly reduced when the esterification time is longer than 4h, and the invention limits the esterification time range to 0.5-4h in consideration of higher cost when the time is longer; the quantitative accuracy of reference example 8 is reduced a little, which means that the esterification degree is not enough when the esterification temperature is lower than 60 ℃, and the quantitative accuracy is reduced, while the quantitative accuracy of reference example 9 is reduced only a little, which means that the quantitative accuracy is slightly reduced when the esterification temperature is higher than 120 ℃, and the esterification temperature range is limited to 60-120 ℃ in consideration of the higher temperature and higher cost.
Test example two: quantitative detection limit test
The quantitative detection limits of examples 1-5, reference examples 1-3 and comparative examples 1 and 2 were determined respectively, with comparative example 1 being the determination of the content of chelating agent (EDTA) in detergent of GB/T13173-.
The test results are shown in table 2:
TABLE 2
As can be seen from Table 2, the quantitative detection limit of examples 1 to 5 of the present invention was 0.03. mu.g/g, and the quantitative detection limit was low. The partial operations of reference examples 1 to 3 were different from those of example 1 in that the quantitative detection limit of reference example 1 was greatly increased, indicating that the esterification reaction was the key to lowering the quantitative detection limit; the quantitative detection limit of the reference examples 2 and 3 is increased a lot, which shows that the functions of adjusting the pH value of the detergent sample solution and reducing the quantitative detection limit can be achieved by performing infrared irradiation on the detergent sample solution.
Test example three: repeatability test
Repeated tests were performed with 2 different samples of detergent with known EDTA addition, each sample was tested according to example 1, each sample was subjected to 6 parallel experiments, and RSD% of EDTA content was calculated as shown in table 3:
| sample (I) | EDTA content RSD (%) |
| Sample 1 | 0.492 |
| Sample 2 | 0.346 |
TABLE 3
As can be seen from Table 3, the RSD of the detection of different detergent samples is less than 0.5%, which shows that the invention has excellent repeatability and is worthy of popularization.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (6)
1. A method for measuring the content of EDTA in a liquid detergent is characterized by comprising the following steps: the method comprises the following steps:
s1, preparing EDTA standard stock solution, precisely weighing 0.1g of ethylenediamine tetraacetic acid standard substance to 0.0001g, placing the ethylenediamine tetraacetic acid standard substance into a 100mL volumetric flask, adding ultrapure water to scale and fix the volume to obtain the EDTA standard stock solution with the mass concentration of 1000 mg/L;
s2, preparing an EDTA standard working solution, respectively taking 1mL, 0.5mL, 0.2mL, 0.1mL and 0.01mL of EDTA standard stock solutions in a 100mL volumetric flask, diluting with ultrapure water to a scale constant volume, shaking up, and performing ultrasonic treatment for 10 minutes to obtain the EDTA standard working solution;
s3, weighing a to-be-detected liquid detergent sample into a test tube with a plug scale, adding ultrapure water to completely dissolve the liquid detergent sample to obtain a liquid detergent sample solution, opening an infrared radiation heater to heat to 300 ℃, wherein the mass of the liquid detergent sample is 0.2-1.5 g, the volume of water for dissolving the liquid detergent sample is 5-25 mL, the distance between the liquid detergent sample solution and the infrared radiation heater is 20cm, placing the liquid detergent sample solution right below the infrared radiation heater, moving out after 1min, cooling to room temperature, adjusting the pH value of the liquid detergent sample solution to be detected to 2.0-5.5 by using an acid reagent, wherein the acid reagent is glacial acetic acid, hydrochloric acid or sulfuric acid, adding an esterification reagent, the volume of the esterification reagent is 3-15 mL, the esterification reagent is a 10% volume fraction methanol sulfate solution, an ethanol sulfate solution or an acetyl chloride methanol solution, shaking uniformly, and carrying out esterification reaction at a constant temperature of 60-120 ℃ for 0.5-4h, taking out the mixture every 5-30 min during the reaction, shaking the mixture, cooling the mixture to room temperature after the esterification reaction to obtain reaction sample liquid, transferring the reaction sample liquid, washing a test tube with a plug scale by using a sodium carbonate solution in multiple times to obtain washing liquid, mixing the washing liquid with the reaction sample liquid, adding isooctane or n-heptane and sodium salt, shaking the mixture uniformly, centrifuging the mixture for 3-15 min, and filtering the supernatant through a 0.45 mu m filter membrane to obtain a sample solution to be detected;
s4, performing esterification reaction on the EDTA standard working solution obtained in the step S2 according to the step S3 to obtain a standard working solution to be detected;
and S5, analyzing and detecting the standard working solution to be detected obtained in the step S4 and the sample solution to be detected obtained in the step S3 by using a gas chromatography-mass spectrometer, and determining the content of EDTA in the detergent sample.
2. The method for determining the content of EDTA in a detergent according to claim 1, wherein: in the step S3, the temperature of the esterification reaction is 60 ℃, 80 ℃, 100 ℃ or 120 ℃, and the time of the esterification reaction is 0.5h, 1h, 2h, 3h or 4 h.
3. The method for determining the content of EDTA in a detergent according to claim 2, wherein: in the step S3, the mass fraction of the sodium carbonate solution is 2-15%, the volume of the sodium carbonate solution is 5-20 mL, and the number of times of cleaning is 2-5.
4. The method for determining the content of EDTA in a detergent according to claim 3, wherein: in the step S3, the volume of isooctane or n-heptane is 1-5 mL, the sodium salt is anhydrous sodium sulfate, sodium bisulfate or sodium chloride, and the weight of the sodium salt is 0.5-3 g.
5. The method for determining the content of EDTA in a detergent according to claim 4, wherein: in step S3, the rotation speed of the centrifuge during centrifugation is 3000, 5000, 8000, 10000 or 12000 rpm.
6. The method for determining the content of EDTA in a detergent according to claim 5, wherein: in the step S5, the conditions of the gas chromatography-mass spectrometer are as follows: the gas-phase capillary column is a DB-5MS column with the thickness of 30m multiplied by 0.25 mu m multiplied by 0.32mm, the injection inlet temperature is 250 ℃, the flow rate is 1.0mL/min, the injection volume is 1 mu L, the carrier gas is helium, the ion source temperature is 230 ℃, the quadrupole temperature is 150 ℃, and the solvent delay time is 3 min; the temperature programming process comprises the following steps: maintaining at 100 deg.C for 1min, heating to 220 deg.C at 40 deg.C/min, maintaining for 5min, heating to 300 deg.C at 50 deg.C/min, and maintaining for 10 min.
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