Method for testing formaldehyde content in concrete admixture
阅读说明：本技术 一种混凝土外加剂中甲醛含量的测试方法 (Method for testing formaldehyde content in concrete admixture ) 是由 李格丽 方云辉 钟丽娜 郭元强 林添兴 于 2018-06-22 设计创作，主要内容包括：本发明公开了一种混凝土外加剂中甲醛含量的测试方法,包括如下步骤：(1)混凝土外加剂样品预处理；(2)标准工作曲线的绘制；(3)甲醛浓度计算。本发明采用离子液体顶空单滴液相微萃取联合使用的方法对混凝土外加剂进行预处理,使混凝土外加剂中的残留甲醛分离出来,而不经过蒸馏的步骤,避免蒸馏过程中目标物的溢出,减少测量误差,操作步骤简单,省时,使用仪器方便,可操作性强。(The invention discloses a method for testing formaldehyde content in a concrete admixture, which comprises the following steps: (1) pretreating a concrete additive sample; (2) drawing a standard working curve; (3) and (4) calculating the concentration of formaldehyde. The method adopts the ionic liquid headspace single-drop liquid phase microextraction combined use method to pretreat the concrete admixture, so that the residual formaldehyde in the concrete admixture is separated without a distillation step, the overflow of a target object in the distillation process is avoided, the measurement error is reduced, the operation steps are simple, the time is saved, the use of instruments is convenient, and the operability is strong.)
1. The method for testing the formaldehyde content in the concrete admixture is characterized by comprising the following steps:
(1) pretreating a concrete additive sample: treating a concrete admixture sample by adopting ionic liquid headspace single-drop liquid-phase microextraction to obtain an extracted sample solution, adding a first treatment solution and a second treatment solution into the extracted sample solution to extract for 30-60 min, and standing after extraction is finished to obtain a working solution of a sample to be detected for later use; wherein the first treatment liquid is a strong alkali solution with the concentration of 0.1-0.5 wt%, and the second treatment liquid is a strong oxidant solution with the concentration of 0.1-0.5 wt%;
(2) drawing a standard working curve: accurately transferring 0.00-10.00 mL of formic acid from a 100mg/L formic acid standard solution into a 100mL volumetric flask, diluting with ultrapure water, fixing the volume to a scale, shaking up, placing on an ion chromatograph for testing to obtain a peak area of a formic acid standard working curve, and drawing a standard working curve of concentration-peak area to obtain a formic acid standard curve equation;
(3) calculating the concentration of formaldehyde: putting the working solution of the sample to be tested prepared in the step (1) into an ion chromatograph after passing through a 0.2-0.3 mu m microporous filter membrane for testing, performing parallel testing for a plurality of times, taking an average value, substituting the average value into the standard curve obtained in the step (2) to obtain the concentration of formic acid in the concrete admixture sample, and then obtaining the concentration of formic acid in the concrete admixture sample according to a formula
the ionic liquid headspace single-drop liquid phase microextraction step comprises the following steps: accurately weighing a proper amount of concrete admixture sample into a headspace bottle, adding 1-2 mL of surfactant, sealing and soaking for 10-20 min, then extracting 2.5-3.5 mu L of extract liquor, inserting the extract liquor into the headspace of a sample to be detected in the headspace bottle, performing headspace extraction for 5-10 min, drawing the obtained liquid drop back to a micro-syringe, and repeating the operation until the extraction is finished to obtain the extracted sample solution; the extract liquid is hexafluorophosphate ionic liquid, tetrafluoroborate ionic liquid or bis (trifluoromethyl alkylsulfonyl) imide ionic liquid;
the ion chromatograph adopts an IonPac AS18 anion analysis column, a 4 × 250mm, an IonPac AG18 protection column, a 4 × 50mm and an AERS5004mm anion suppressor, the current of the suppressor is 50mA, an electric conductivity detector is arranged, the temperature of the chromatographic column is 30-50 ℃, the sample injection amount is 10-30 muL, the flow rate is 0.5-1.0 mL/min, the leacheate contains 15mmol/L of sodium hydroxide, 3mmol/L of sodium tetraborate and 1.2mmol/L of sodium gluconate, and the solvent of the leacheate is water.
2. The test method of claim 1, wherein: the surfactant is Tween20 (Tween20), polyoxyethylene octyl phenol ether-10 (OP-10), disodium cocomonoethanolamide sulfosuccinate monoester (DMSS) or potassium monododecyl phosphate (MAPK).
3. The test method of claim 1: the method is characterized in that: the extract liquid is 1-hexyl-2, 3-dimethyl imidazole hexafluorophosphate ionic liquid, 1-dodecyl-3-methyl imidazole hexafluorophosphate ionic liquid, 1-butyl-2, 3-dimethyl imidazole tetrafluoroborate ionic liquid or 1-octyl-3-methyl imidazole bis (trifluoromethyl sulfonyl) imide ionic liquid.
4. The test method of claim 1, wherein: the strong base in the strong base solution is one of choline, guanidine, quaternary ammonium base, sodium methoxide, sodium ethoxide, potassium ethoxide and sodium tert-butoxide.
5. The test method of claim 1, wherein: the strong oxidant is one of hydrogen peroxide, sodium peroxide and potassium peroxide.
6. The test method of claim 1, wherein: the extraction mode in the step (1) is ultrasonic, oscillation, constant temperature water bath or cold soaking.
7. The test method of claim 6, wherein: the temperature of the constant-temperature water bath is 40-60 ℃, and the temperature of the cold soaking is 0-10 ℃.
8. The test method of claim 1, wherein: the temperature of the chromatographic column is 40 ℃, the sample injection amount is 25 mu L, and the flow rate is 0.8 mL/min.
Technical Field
The invention belongs to the technical field of building material detection, and particularly relates to a method for testing the formaldehyde content in a concrete admixture.
Background
Formaldehyde is a colorless, strongly pungent gas at room temperature and is readily soluble in water, alcohols and ethers. Formaldehyde has high toxicity to human and animals, has been determined by the world health organization to be a carcinogenic and teratogenic substance, and is also one of the potential strong mutagenic substances. But because of easy preparation, wide application and low price, formaldehyde is widely applied to the production of resin, plastic, rubber, interior wall coating, concrete admixture, plywood and adhesive. Concrete admixtures have been widely used in construction in recent years for improving the workability of concrete. Along with the wide use of the admixture, some substances harmful to human bodies in the admixture are also released, and formaldehyde is one of the substances. The formaldehyde in the concrete admixture is mainly released from polycyclic aromatic sulfonate, water-soluble resin sulfonate, aliphatic water reducing agent and the like. In the process of producing the water reducing agent, in order to ensure that the dispersing performance of the water reducing agent is better, the using amount of formaldehyde is increased, so that free formaldehyde contained in the admixture and formaldehyde generated in degradation can be released in use, and formaldehyde pollution of buildings can be caused. The nation imposes a mandatory limit on the limit of harmful substances for indoor decoration and also limits the limit of formaldehyde in concrete admixtures.
Formaldehyde is chemically very reactive and therefore, many methods can be used for the quantitative analysis of formaldehyde, such as titrimetric methods, spectrophotometry, chromatography, electrochemical analysis, instrumental detection, etc. However, the electrochemical analysis method has the problems of much interference, poor stability and the like in the experimental process, and the use frequency is low. The titration analysis method is suitable for being used when the content concentration of the free formaldehyde is high, and the spectrophotometry, the chromatography and the instrument detection method are suitable for being used when the content of the free formaldehyde is low. The most common method in chromatography is gas chromatography, which is generally carried out by derivatization through a derivatization reagent, but the separation problem of derivative isomers is difficult to solve, so that the application of the derivative isomers is limited; the instrument detection method is convenient to carry, visual in reading and rapid in measurement, but has serious interference in instrument detection and higher price, so that the instrument detection method is generally usedIs subject to restrictions; the spectrophotometric method is commonly used, and examples thereof include acetylacetone spectrophotometric method, phenol reagent method, 4-amino-3-hydrazine-5-thio-1, 2, 4-triazocene spectrophotometric method (AHMT method), chromic acid method, and fuschin sulfite method. The limit of the residual formaldehyde in the concrete admixture in the national standard is determined by acetylacetone spectrophotometry. Distilling out residual formaldehyde in a sample by distillation, reacting with acetylacetone under a heating condition under the condition of a buffer solution with a pH value of 6 to generate a yellow complex, and testing by using an ultraviolet spectrophotometer to calculate the content of the residual formaldehyde. The test is not interfered by acetaldehyde, and has the advantages of simple method, good selectivity and reproducibility and small error, but the test method also has certain defects, such as distillation is needed, ice blocks are needed to cool a fraction outlet in order to prevent the distilled formaldehyde from volatilizing at high temperature, the operation is complicated and time-consuming, and great inconvenience is brought to an operator; the complex formation needs to be carried out at a constant temperature of 60 ℃ for 30min, such as at room temperature, takes longer time, cannot realize rapid determination, and is in the presence of SO2The test in the environment of (2) also has a certain influence on the measurement result.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a method for testing the formaldehyde content in a concrete admixture.
The technical scheme of the invention is as follows:
a method for testing the formaldehyde content in a concrete admixture comprises the following steps:
(1) pretreating a concrete additive sample: treating a concrete admixture sample by adopting ionic liquid headspace single-drop liquid-phase microextraction to obtain an extracted sample solution, adding a first treatment solution and a second treatment solution into the extracted sample solution to extract for 30-60 min, and standing after extraction is finished to obtain a working solution of a sample to be detected for later use; wherein the first treatment liquid is a strong alkali solution with the concentration of 0.1-0.5 wt%, and the second treatment liquid is a strong oxidant solution with the concentration of 0.1-0.5 wt%;
(2) drawing a standard working curve: accurately transferring 0.00-10.00 mL of formic acid from a 100mg/L formic acid standard solution into a 100mL volumetric flask, diluting with ultrapure water, fixing the volume to a scale, shaking up, placing on an ion chromatograph for testing to obtain a peak area of a formic acid standard working curve, and drawing a standard working curve of concentration-peak area to obtain a formic acid standard curve equation;
(3) calculating the concentration of formaldehyde: putting the working solution of the sample to be tested prepared in the step (1) into an ion chromatograph after passing through a 0.2-0.3 mu m microporous filter membrane for testing, performing parallel testing for a plurality of times, taking an average value, substituting the average value into the standard curve obtained in the step (2) to obtain the concentration of formic acid in the concrete admixture sample, and then obtaining the concentration of formic acid in the concrete admixture sample according to a formula
the ionic liquid headspace single-drop liquid phase microextraction step comprises the following steps: accurately weighing a proper amount of concrete admixture sample into a headspace bottle, adding 1-2 mL of surfactant, sealing and soaking for 10-20 min, then extracting 2.5-3.5 mu L of extract liquor, inserting the extract liquor into the headspace of a sample to be detected in the headspace bottle, performing headspace extraction for 5-10 min, drawing the obtained liquid drop back to a micro-syringe, and repeating the operation until the extraction is finished to obtain the extracted sample solution; the extract liquid is hexafluorophosphate ionic liquid, tetrafluoroborate ionic liquid or bis (trifluoromethyl alkylsulfonyl) imide ionic liquid;
the ion chromatograph adopts an IonPac AS18 anion analytical column, a 4 × 250mm, an IonPac AG18 protective column, a 4 × 50mm and an AERS5004mm anion suppressor, the current of the suppressor is 50mA, a conductivity detector is arranged, the temperature of the chromatographic column is 30-50 ℃, the sample injection amount is 10-30 muL, the flow rate is 0.5-1.0 mL/min, the leacheate contains 15mmol/L of sodium hydroxide, the method comprises the following steps of (1) adding sodium hydroxide into sodium gluconate-sodium borate leacheate, wherein the sodium tetraborate and the sodium gluconate are respectively 3mmol/L and 1.2mmol/L, the solvent of the leacheate is water (the sodium hydroxide (potassium) leacheate is weak in leaching capacity and needs higher concentration, and the sodium gluconate-sodium borate leacheate is strong in leaching capacity and suitable for measuring weak acid anions.
In a preferred embodiment of the invention, the surfactant is Tween20 (Tween20), polyoxyethylene octylphenol ether-10 (OP-10), disodium cocomonoethanolamide sulfosuccinate (DMSS), or potassium monododecyl phosphate (MAPK).
In a preferred embodiment of the present invention, the extraction liquid is 1-hexyl-2, 3-dimethylimidazolium hexafluorophosphate ionic liquid, 1-dodecyl-3-methylimidazolium hexafluorophosphate ionic liquid, 1-butyl-2, 3-dimethylimidazolium tetrafluoroborate ionic liquid or 1-octyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide ionic liquid.
In a preferred embodiment of the present invention, the strong base in the strong base solution is one of choline, guanidine, quaternary ammonium base, sodium methoxide, sodium ethoxide, potassium ethoxide, and sodium tert-butoxide.
In a preferred embodiment of the present invention, the strong oxidizing agent is one of hydrogen peroxide, sodium peroxide, and potassium peroxide.
In a preferred embodiment of the present invention, the extraction in step (1) is performed by means of ultrasound, shaking, thermostatic water bath or cold soaking.
Further preferably, the temperature of the constant-temperature water bath is 40-60 ℃, and the temperature of the cold soaking is 0-10 ℃. Furthermore, the temperature of the constant-temperature water bath is 50 ℃, and the temperature of the cold soaking is 5 DEG C
In a preferred embodiment of the invention, the column temperature is 40 ℃, the sample size is 25 μ L, and the flow rate is 0.8 mL/min.
The invention has the beneficial effects that:
1. the method adopts the ionic liquid headspace single-drop liquid phase microextraction combined use method to pretreat the concrete admixture, so that the residual formaldehyde in the concrete admixture is separated without a distillation step, the overflow of a target object in the distillation process is avoided, the measurement error is reduced, the operation steps are simple, the time is saved, the use of instruments is convenient, and the operability is strong.
2. The invention adopts the technical scheme that under the alkaline condition, the separated formaldehyde is oxidized into the formic acid by using the oxidant, and then the formic acid is tested by using the ion chromatography, so that the content of the formaldehyde is indirectly tested, the testing sensitivity is high, the testing time is effectively shortened, and the testing efficiency is improved.
3. The mixed leacheate is used for leaching and analyzing the sample, has strong leaching capacity and better separation effect, can effectively separate weak acid anions from other ions, improves the separation degree, and enables the result of quantitative analysis to be more accurate and reliable.
4. The ion chromatography is applied to the test of the formaldehyde content in the concrete admixture, so that the test method of the formaldehyde content in the concrete admixture is widened, and a new test means is provided for the test of the formaldehyde content in the concrete admixture.
Drawings
FIG. 1 is a liquid chromatogram of formic acid.
Fig. 2 is a liquid chromatogram of a working solution of a sample to be measured in embodiment 1 of the present invention.
In the above figure, the solvent peak is at a retention time of about 3.40min, and the formic acid peak is at a retention time of about 8.30min
Detailed Description
The technical solution of the present invention is further illustrated and described by the following detailed description.