CN106442776A - Method for measuring acetyl content - Google Patents

Abstract

The invention discloses a method for measuring the content of acetyl groups, in particular to a method for measuring the content of acetyl groups by using chemical transformation combined with full-volatility headspace gas chromatography. The steps are: (1) prepare standard solution; (2) establish standard curve; (3) sample processing; (4) analyze and detect by headspace-gas chromatography; (5) calculate the result. The beneficial effect of the method is that the determination of the acetyl group content by the above-mentioned method has the advantages of convenience, quickness, high accuracy, etc., and is suitable for batch detection of samples.

Description

A method for measuring acetyl content

technical field

The invention belongs to the field of analysis and detection, and in particular relates to a method for measuring acetyl group content.

Background technique

The acetyl group is an acyl functional group composed of a methyl group and a carbonyl group, and is an important functional group. It exists in a variety of substances, such as plant fiber raw materials, modified starch and chitosan, etc. Acetyl groups contained in plant fiber raw materials will form organic acids during pulping and prehydrolysis, which will affect the consumption of alkali during pulping and the utilization of subsequent prehydrolyzate. The amount of acetyl group in modified starch, chitosan and other substances also has an important impact on the properties of the substance. The properties of acetate-modified starch are mainly affected by the content of acetyl groups. As the content of acetyl groups increases, the viscosity decreases, the transparency increases, the gelatinization temperature decreases, and the dehydration and retrogradation properties decrease. Therefore, according to the amount of acetyl group, the most suitable acetate modified starch for the food produced can be selected in order to achieve the best application effect. Therefore, accurate determination of acetic acid group content is of great significance for substance utilization or substance quality control.

At present, the methods for determining the content of acetyl groups mainly include biological enzymatic method and titration method, among which the titration method is widely used. The titration method is to hydrolyze the acetyl group to form acetic acid, and then distill the acetic acid to measure the content by neutralization titration, so as to obtain the content of the acetyl group. The determination result of this method is relatively accurate, but distillation is required, and the operation is cumbersome and time-consuming. Therefore, it is particularly necessary to establish a simple, rapid and accurate method for determining the content of acetyl groups.

Contents of the invention

The object of the present invention is to overcome the disadvantages of the current method for measuring acetyl group content and provide a method for measuring acetyl group content. The measuring principle of the present invention is that under the action of p-toluenesulfonic acid ethanol solution, the acetyl group is converted into ethyl acetate, and then the amount of ethyl acetate produced by the full-volatility headspace-gas chromatography is used to calculate the amount of acetyl acetate in the sample. base content. According to the method, rapid determination can be realized, the operation is simple and easy to master, the analysis result has high accuracy, has certain practicability, and is suitable for batch detection.

The present invention is achieved through the following technical solutions.

A method for determining the content of acetyl groups, the method utilizes chemical conversion technology in combination with full-volatility headspace-gas chromatography to measure the content of acetyl groups, specifically comprising the following steps:

(1) Prepare ethyl acetate standard solution: accurately measure an appropriate amount of ethyl acetate in a volumetric flask, add absolute ethanol to be constant to the scale of the volumetric flask to obtain ethyl acetate standard solution;

(2) Establish a standard curve: using a headspace sampler, add different volumes of ethyl acetate standard solutions to multiple headspace sample vials, seal the vials, place them on the sample stage, and perform top Air-gas chromatographic detection, a standard curve can be obtained between the gained ethyl acetate signal peak area and the ethyl acetate add-on;

(3) Sample treatment: put the sample to be tested in a reaction bottle, and add an appropriate amount of p-toluenesulfonic acid and absolute ethanol into the bottle, then seal it, place it in a water bath for processing, and cool it in an ice bath after the reaction Afterwards, dilute to volume with absolute ethanol, to be determined;

(4) Analysis and detection: Accurately measure an appropriate amount of the treated solution to be tested, add it into the headspace sample vial with a headspace sampler, seal the headspace sample vial, place it on the sample stage, and then carry out Headspace-gas chromatographic detection, record the ethyl acetate chromatographic peak area of the sample;

(5) Result calculation: compare the peak area obtained in step (4) with the standard curve in step (2), and obtain the content of acetyl groups in the sample by calculation.

Further optimized, the concentration of the ethyl acetate standard solution in step (1) is 0.1-20.0 g/L.

Further optimized, the volume of ethyl acetate standard solution added in step (2) is 0-45 μL.

Further optimized, the mass ratio of the sample to be tested, p-toluenesulfonic acid and absolute ethanol added in step (3) is 1:10:30-1:100:300.

Further optimized, the temperature of the oil bath where the reaction bottle is placed in step (3) is 60-120° C., and the reaction time is 5-120 min.

Further optimized, the operating conditions of the headspace sampler in steps (2) and (4) are: the temperature of the sampler heating furnace is 60-115° C.; the equilibration time of the headspace bottle in the oven is 0.5-8.0 min.

Further optimized, the gas chromatography operating conditions in steps (2) and (4) are: column temperature is 25-49°C; carrier gas is helium, and its flow rate is 3.0-5.0mL/min; the detector is flame ionization detection detector (FID), the detector temperature is 200-250°C.

For further optimization, take an appropriate amount of the sample to be tested as described in step (4), the volume of which is 5-40 μL.

Further optimized, the formula for calculating the acetyl group content described in step (5) is:

In the formula, C is the content of ethyl acetate in the processed sample obtained by the standard curve; V is the total volume of the solution after the step (3) sample is processed to constant volume; m is the absolute dry weight of the sample to be measured; 43 is the amount of acetyl Molecular weight; 88 is the molecular weight of ethyl acetate.

Further optimized, the above-mentioned method for determining the acetyl content specifically includes the following steps:

(1) Preparation of ethyl acetate standard solution: accurately measure an appropriate amount of ethyl acetate in a volumetric flask, add absolute ethanol to constant volume to the scale of the volumetric flask to obtain ethyl acetate standard solution.

(2) Establish a standard curve: Add 0-45 μL of ethyl acetate standard solution with a concentration of 0.1-20.0 g/L to a series of headspace sample vials, seal the vials, and place them on the sample stage. Carry out headspace-gas chromatographic detection then, can obtain a calibration curve between the obtained ethyl acetate signal peak area and ethyl acetate addition.

(3) Sample treatment: Add the sample to be tested, p-toluenesulfonic acid and absolute ethanol in the mass ratio of 1:10:30 to 1:100:300 into the reaction bottle successively, then seal it, place it in a water bath, and React at 60-120°C for 5-120 minutes. After the reaction is completed, cool in an ice bath and dilute with absolute ethanol for determination.

(4) Analysis and detection: Accurately measure 5-40 μL of the treated solution to be tested, add it into the headspace sample vial with a micro-sampling needle, seal the sample vial, place it on the sample stage, and then carry out the headspace sample vial. Air-gas chromatographic detection, record the ethyl acetate chromatographic peak area of the sample.

(5) Result calculation: compare the peak area obtained in step (4) with the standard curve in step (2), and obtain the content of acetyl groups in the sample by calculation.

Compared with the prior art, the present invention has the following advantages and technical effects:

(1) The method is easy to operate and has strong specificity;

(2) The method has good accuracy and high sensitivity;

(3) The measurement process takes a short time;

(4) Strong anti-interference ability;

(5) Suitable for batch testing.

detailed description

The present invention is described in further detail below in conjunction with embodiment. The present invention is not limited to the following embodiments. The embodiments are only used to explain the present invention, not to limit the present invention, and all simple changes related to the present invention shall belong to the protection scope of the present invention.

The formula for calculating the acetyl group content in the following examples is:

In the formula, C is the content of ethyl acetate in the processed sample obtained by the standard curve; V is the total volume of the solution after the step (3) sample is processed to constant volume; m is the dry weight of the sample to be measured; 43 is the acetyl group Molecular weight; 88 is the molecular weight of ethyl acetate.

The mensuration of acetyl group content in the plant fiber raw material of embodiment 1

(1) Preparation of ethyl acetate standard solution: Accurately measure 1.000 g of ethyl acetate in a volumetric flask, add absolute ethanol to dilute to 100 mL to obtain ethyl acetate standard solution.

(2) Establish a standard curve: use a headspace sampler, add 0, 5, 10, 15, 20, 25, 30, 40 μL of ethyl acetate standard solution into multiple headspace sample vials, and seal the vials , and then it is placed on the sample stage, and then the headspace-gas chromatography is detected, and a standard curve can be obtained between the peak area of the ethyl acetate signal and the amount of ethyl acetate added.

(3) Sample treatment: 0.200g of the sample to be tested (plant fiber raw material) is placed in a reaction bottle, and 5g of p-toluenesulfonic acid and 20g of absolute ethanol are added to the bottle, then sealed, placed in a water bath, and heated at 100 React at ℃ for 30min, after the reaction is completed, cool in an ice bath and dilute to 50mL with absolute ethanol for determination.

(4) Analysis and detection: Accurately measure 30 μL of the treated solution to be tested, add it into the headspace sample vial with a micro-sampling needle, seal the sample vial, place it on the sample stage, and then carry out headspace- Gas chromatographic detection, record the ethyl acetate chromatographic peak area of the sample. The operating conditions of the above-mentioned headspace sampler are: the temperature of the heating furnace is 85°C; the equilibration time of the headspace sample bottle in the oven is 4.5min; The flow rate is 4.0 mL/min; the detector is a flame ionization detector, and the detector temperature is 225°C.

(5) Determination of results: compare the peak area obtained in step (4) with the standard curve of step (2), and obtain the content of acetyl groups in the sample by calculation. The results of the measurement data are shown in Table 1.

Table 1

The mensuration of acetyl group content in the modified starch of embodiment 2

(1) Preparation of ethyl acetate standard solution: accurately measure 2.000 g of ethyl acetate in a volumetric flask, add absolute ethanol to dilute to 100 mL to obtain ethyl acetate standard solution.

(2) Establish a standard curve: use a headspace sampler, add 0, 5, 10, 15, 20, 25, 30, 40 μL of ethyl acetate standard solution into multiple headspace sample vials, and seal the vials , and then it is placed on the sample stage, and then the headspace-gas chromatography is detected, and a standard curve can be obtained between the obtained ethyl acetate signal peak area and the amount of ethyl acetate added.

(3) Sample treatment: put 0.100g of the sample to be tested (modified starch) in a reaction bottle, and add 10g of p-toluenesulfonic acid and 50g of absolute ethanol into the bottle, then seal it, place it in a water bath, and heat it at 100°C The reaction was carried out for 20 minutes. After the reaction was completed, the reaction was cooled in an ice bath and the volume was adjusted to 50 mL with absolute ethanol for determination.

(4) Analysis and detection: Accurately measure 30 μL of the treated solution to be tested, add it to the headspace sample bottle with a sampler, seal the sample bottle, place it on the sample stage, and then carry out headspace-gas phase analysis. For chromatographic detection, record the ethyl acetate chromatographic peak area of the sample. The operating conditions of the above-mentioned headspace sampler are: the temperature of the heating furnace is 115°C; the equilibration time of the headspace sample bottle in the oven is 8.0min; the operating conditions of the gas chromatography are: the column temperature is 49°C; the carrier gas is helium, The flow rate is 5.0 mL/min; the detector is a flame ionization detector, and the detector temperature is 250°C.

Table 2

(5) Determination of results: compare the peak area obtained in step (4) with the standard curve of step (2), and obtain the content of acetyl groups in the sample by calculation. The results of the measurement data are shown in Table 2.

Claims (9)

1. a method for measuring acetyl group content, it is characterized in that, the method utilizes chemical conversion technology in conjunction with full-volatility headspace-gas chromatography to measure the content of acetyl group, specifically comprising the following steps: (1) Prepare ethyl acetate standard solution: Accurately measure ethyl acetate in a volumetric flask, add absolute ethanol to make up to the scale of the volumetric flask to obtain ethyl acetate standard solution; (2) To establish a standard curve: use a headspace sampler, add different volumes of ethyl acetate standard solutions to multiple headspace sample vials, seal the headspace sample vials, place them on the sample stage, and perform top Air-gas chromatographic detection, a standard curve can be obtained between the gained ethyl acetate signal peak area and the ethyl acetate add-on; (3) Sample treatment: put the sample to be tested in a reaction bottle, add p-toluenesulfonic acid and absolute ethanol into the bottle, seal it, place it in a water bath for processing, and cool it in an ice bath after the reaction is over. Dilute to volume with absolute ethanol, to be determined; (4) Analysis and detection: Accurately measure the solution to be tested in step (3), add it into the headspace sample vial with a headspace sampler, seal the headspace sample vial, place it on the sample stage, and then carry out Headspace-gas chromatographic detection, record the ethyl acetate chromatographic peak area of the sample; (5) Result calculation: compare the peak area obtained in step (4) with the standard curve in step (2), and calculate the content of acetyl groups in the sample. 2. A method for measuring acetyl group content according to claim 1, characterized in that: the concentration of the ethyl acetate standard solution in step (1) is 0.1-20.0 g/L. 3. A method for measuring acetyl group content according to claim 1, characterized in that: the volume of ethyl acetate standard solution added in step (2) is 0-45 μL. 4. A method for determining acetyl group content according to claim 1, characterized in that the mass ratio of the sample to be tested, p-toluenesulfonic acid and absolute ethanol in step (3) is 1:10:30 ~1:100:300. 5. A method for measuring acetyl group content according to claim 1, characterized in that: in step (3), the temperature of the water bath where the reaction bottle is placed is 60-120°C, and the reaction time is 5-120min. 6. A method for determining acetyl group content according to claim 1, characterized in that: the operating conditions of the headspace sampler described in step (2) and step (4) are: sampler heating furnace The temperature is 60-115°C; the equilibration time of the headspace vial in the oven is 0.5-8.0 min. 7. A method for determining acetyl group content according to claim 1, characterized in that: the operating conditions of gas chromatography used in step (2) and step (4) are: column temperature is 25-49°C; carrier gas The gas is helium, the flow rate is 3.0~5.0 mL/min; the detector is a flame ionization detector, and the detector temperature is 200~250°C. 8. A method for determining the content of acetyl groups according to claim 1, characterized in that: the formula for calculating the content of acetyl groups in step (5) is: In the formula, C is the content of ethyl acetate in the processed sample obtained from the standard curve; V is the total volume of the solution after the sample is processed to constant volume in step (3); m is the absolute dry weight of the sample to be tested; 43 is the amount of acetyl Molecular weight; 88 is the molecular weight of ethyl acetate. 9. A method for determining acetyl group content according to claim 1, characterized in that: the volume of the solution to be tested in step (4) is 5-40 μL.