CN110068632B - Method for measuring amino content of chitosan derivative based on headspace gas chromatography - Google Patents
Method for measuring amino content of chitosan derivative based on headspace gas chromatography Download PDFInfo
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- CN110068632B CN110068632B CN201910430319.0A CN201910430319A CN110068632B CN 110068632 B CN110068632 B CN 110068632B CN 201910430319 A CN201910430319 A CN 201910430319A CN 110068632 B CN110068632 B CN 110068632B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
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Abstract
The invention discloses a method for measuring the amino content of a chitosan derivative based on headspace gas chromatography, which comprises the steps of reacting excessive ninhydrin with an amino-containing standard substance, then reacting sodium bicarbonate with the rest ninhydrin to generate carbon dioxide, adding no standard substance into a control group, measuring the peak area of the carbon dioxide through the headspace gas chromatography, wherein the relative reduction amount of the carbon dioxide is in a linear relation with the mass of the standard substance, establishing a standard curve, replacing the standard substance with the chitosan derivative with the amino content to be measured, detecting the peak area of the carbon dioxide, obtaining the mass of the corresponding standard substance according to the standard curve, and calculating to obtain the amino content at the moment. Compared with the traditional conductivity titration method, the method of the invention has the advantages that the relative error is not more than 13.03 percent, and the maximum relative standard deviation of the detection of the same sample is 4.83 percent, so the result is objective and accurate, and the speed is higher compared with the traditional determination method.
Description
Technical Field
The invention relates to the technical field of chitosan derivative amino content determination, in particular to a method for measuring the amino content of a chitosan derivative based on headspace gas chromatography.
Background
Headspace gas chromatography, also known as on-liquid gas chromatography. The headspace gas chromatography utilizes the principle that the ratio of volatile components in gas phase and liquid (solid) phase is constant after the volatile components in the liquid (solid) body are balanced in a closed constant temperature system, and carries out gas chromatography analysis on the vapor at the upper part of the liquid (solid) after the balance. It can also carry out a targeted chemical reaction during the sample equilibration process, and convert the components (non-volatile) that could not be measured by the original gas chromatography into volatile components, thereby realizing the indirect measurement of the non-volatile components by the gas chromatography. It adopts gas to sample, and has the advantages of simple sample treatment, high analysis speed, less interference and the like, so that the method is widely concerned and some methods are listed as standard methods.
Chitin is the second largest natural polysaccharide and renewable resource with the next to cellulose content on earth, and is the only natural alkaline polysaccharide existing in large quantities, and the yield reaches hundreds of billions of tons on earth every year. Chitosan dissolved in an acid solution can be prepared by performing deacetylation reaction on the acetamido group at the C-2 position of the chitin saccharide unit using a highly concentrated base. Therefore, a series of derivatization reactions, such as carboxymethylation, hydroxypropylation, acylation, graft modification, and the like, have been developed based on chitosan. The chitosan derivative is widely applied to the high value-added fields such as drug release, wound repair, skin care, pigment and heavy metal adsorption and the like. The content of amino groups (deacetylation degree) not only affects whether the derivatization reaction is successfully realized, but also directly affects the physical and chemical properties of the chitosan derivative, such as solubility, antibacterial property, oxidation resistance, flocculation property, metal chelating capacity and the like. It is clear that accurate determination of the amino group content of chitosan derivatives is highly desirable.
At present, methods commonly used for measuring chitosan derivatives include conductometry, elemental analysis, and nuclear magnetic resonance. The conductivity titration is simple and can be easily accomplished in a small laboratory. However, during the titration of carboxylated chitosan, a large amount of precipitate is generated around the isoelectric point, resulting in incomplete neutralization. Therefore, accuracy is worth considering. In addition, a long experimental time is required. In the elemental analysis method, the repeated structural units of the sample must be known to calculate the deacetylation degree (i.e. the degree of amino substitution) of the chitosan derivative. And the presence of other organic substances or polysaccharides than chitin/chitosan significantly changes the N/C ratio, easily causing a deviation in the measurement results. Nuclear magnetic resonance spectroscopy is the most accurate and allows the determination of the reactive sites of glucosamine units. Although NMR is defined as a standard for the deacetylation degree determination of chitin, and is generally used for calibrating other methods, nuclear magnetic resonance equipment is expensive and requires the operation of a professional technician, making it difficult to popularize.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a method for measuring the amino content of a chitosan derivative based on headspace gas chromatography, which is rapid, accurate and simple and convenient to operate. Overcomes the defects existing in the prior measurement of the amino content of the chitosan derivative.
The purpose of the invention is realized by at least one of the following technical solutions.
The method for measuring the amino content of the chitosan derivative based on the headspace gas chromatography comprises the following steps:
(1) preparation of standard substances: firstly, adding more than three standard substances with different masses into different headspace bottles, adding no standard substance into the headspace bottles of a control group, then adding an equal amount of ninhydrin aqueous solution into each headspace bottle, then placing a glass tube containing an equal amount of sodium bicarbonate solution into each headspace bottle, covering a headspace cap, heating in a water bath for color development reaction, shaking the headspace bottle to uniformly mix the sodium bicarbonate in the glass tube with the remaining ninhydrin solution in the headspace bottle, and heating in the water bath for neutralization reaction;
(2) establishing a standard curve: placing each headspace bottle after neutralization reaction in the step (1) into a headspace sample injector, balancing, performing headspace extraction, and detecting by gas chromatography to obtain CO2A peak area, obtaining a standard curve according to the corresponding relation between the reduction of the peak area of the carbon dioxide containing the standard substance relative to the reference group and the corresponding quality of the standard substance, wherein y is ax + b, the abscissa of the standard curve is the quality of the standard substance, and the corresponding ordinate is the corresponding ordinateA is the slope of the standard curve and b is the intercept of the standard curve for the reduced peak area of carbon dioxide;
(3) sample detection: taking a chitosan derivative with amino content to be detected as a sample to be detected, replacing the standard substance in the step (1) with the sample to be detected, adding the sample to be detected into a headspace bottle, adding the same amount of ninhydrin aqueous solution into each headspace bottle without adding the sample to be detected in a control group, then adding a glass tube containing the same amount of sodium bicarbonate solution into each headspace bottle, covering a headspace cap, and performing color development and neutralization reaction according to the reaction conditions in the step (1); then placing the headspace bottle containing the sample to be detected and the headspace bottle of the control group into a headspace sample injector, and after balancing, recording the peak area of carbon dioxide through extraction detection;
(4) and (4) calculating a result: and (3) corresponding the reduction amount of the peak area of the carbon dioxide containing the sample to be detected in the step (3) relative to the reference group to the standard curve obtained in the step (2), and calculating to obtain the amino content of the chitosan derivative.
Further, the standard substance in step (1) is selected under the condition that it has a similar molecular structure to the chitosan derivative and has a free amino group per repeating unit, such as glucosamine salt, specifically selected from glucosamine hydrochloride or glucosamine sulfate.
Further, the ratio of the amount of ninhydrin substance to the amount of amino group substance of the standard substance in the steps (1) and (3) is more than 2.
Further, the ratio of the amount of the substance of sodium bicarbonate in the headspace bottle of the step (2) to the amount of the substance of amino group of the standard substance is more than 4.
Further, the color reaction condition in the step (1) is that the reaction is carried out for 15-30min at the temperature of 80-95 ℃.
Further, the neutralization reaction condition in the step (1) is that the reaction is carried out for 60-90min at 50-70 ℃.
Further, the headspace sampler conditions of steps (2) and (4) are as follows: the balance temperature is 50-70 deg.C, and the balance time is 5-15 min.
According to the invention, the reduced ninhydrin and imine group are obtained by using the reaction of excessive ninhydrin and primary amino group of chitosan derivative, and the imine group is unstable to generate ammonia gas. Ninhydrin, hydrindantin and ammonia gas generate purple complex, as formula (1), and the ninhydrin which is added in excess is consumed quantitatively, while ninhydrin has similar phenolic hydroxyl molecular structure and shows weak acidity, and carbon dioxide generated by reaction with sodium bicarbonate, as formula (2), is detected quantitatively by headspace gas chromatography. And (3) the carbon dioxide exists in a gas-liquid two-phase equilibrium in the aqueous solution system of the chitosan or the derivative thereof in the headspace bottle. Therefore, the partition coefficient of carbon dioxide in the headspace bottle complies with henry's law, i.e. equation (3):
in the formula: cG，CLExpressed as the concentration of carbon dioxide in the gas phase and in the liquid phase, respectively.
After the ninhydrin reacts with primary amino groups of the chitosan derivatives for color development, as the ninhydrin is quantitatively consumed, carbon dioxide generated by the reaction of the ninhydrin with sodium bicarbonate is reduced, which is shown in that the area of the carbon dioxide peak detected by headspace gas chromatography is reduced, and the reduction value (y) is in a linear relationship with the mass (x) of the sample to be detected, namely a standard curve. The abscissa in the standard curve can also be converted into the amino content (X), and at this time, the amino content (X) and the carbon dioxide reduction amount (Y) are in a linear relationship, as shown in formula (4);
Y＝Ax+B (4)
in the formula: a is the slope a multiplied by 1/(m multiplied by 215.5) in the standard curve, B is the intercept B in the standard curve, 215.5 is the relative molecular weight of glucosamine hydrochloride, and m is the quality of the sample to be detected. And (4) substituting the formula (4) according to the reduction amount of the carbon dioxide obtained in the step (3) to directly obtain the amino content of the sample to be detected.
If the amino content of the chitosan derivative is different, the ninhydrin which is excessively added in the color reaction is quantitatively consumed, ninhydrin with different mass is remained in the headspace bottle system, the ninhydrin reacts with sodium bicarbonate to generate carbon dioxide with different molar numbers, the release rate of the carbon dioxide to the headspace of the headspace bottle is different, and the peak areas of the detected carbon dioxide are different.
Based on the principle, adding different masses of aqueous solution of glucosamine hydrochloride into the headspace bottle, performing color reaction with excessive ninhydrin, then reacting the residual ninhydrin with sodium bicarbonate to generate carbon dioxide, and establishing a mathematical model between the gas phase signal value of the carbon dioxide reduced in the reaction system added with the glucosamine hydrochloride and the amino content of the standard glucosamine hydrochloride in the corresponding headspace bottle by comparing the peak areas of the carbon dioxide in the reaction system added with the glucosamine hydrochloride and the peak areas of the carbon dioxide in the reaction system not added with the glucosamine hydrochloride. Then, an unknown chitosan derivative sample is subjected to a color reaction with ninhydrin with the same mass, then the reaction of the remaining ninhydrin with sodium bicarbonate is measured by headspace gas chromatography, the obtained reduced carbon dioxide signal value is compared with a standard curve, and the amino content of the unknown sample is obtained by calculating according to formula (4).
Compared with the prior art, the invention has the following advantages and effects:
(1) when the method is used for measuring the chitosan derivative, too many samples do not need to be prepared, and the sample consumption is small;
(2) the color reaction and the neutralization reaction are carried out in a headspace bottle, the amino content is converted into a reduced carbon dioxide signal value by utilizing a chemical reaction, headspace gas chromatography analysis is carried out, and then the chromatographic signal value is brought into a pre-established mathematical model (a standard curve and/or a formula 4) to obtain the amino content of the chitosan derivative.
Therefore, the method for measuring the amino content of the chitosan derivative not only can simplify the operation process, but also greatly shortens the testing time and enables the testing result to be given immediately, and compared with the traditional conductivity titration method, the method provided by the invention has the advantages that the relative error is not more than 13.03%, and the maximum relative standard deviation is 4.83% for the detection of the same sample, so the result is objective and accurate.
In conclusion, the method for determining the amino content of the chitosan derivative has the advantages of high determination speed, high result accuracy and simple operation, and can be used for determining the amino content of the chitosan derivative. The method is particularly suitable for analyzing large-batch samples in a laboratory to optimize synthesis conditions.
Drawings
FIG. 1 is a graph of reduced carbon dioxide peak area signal (y) against a mass (x) standard of glucosamine hydrochloride.
Detailed Description
The present invention will be described in further detail with reference to specific examples.
The instrument used in the invention: HP-7694 type automatic headspace sampler, Agilent A7890 type gas chromatograph (thermal conductivity detector, DB-5 type capillary chromatographic column), headspace bottle (21.6ml), and bottle cap with blue polytetrafluoroethylene spacer.
Reagents used in the present invention: chitosan derivatives (solid content 80-90%), ninhydrin (analytically pure), sodium bicarbonate (analytically pure), glucosamine hydrochloride with a purity of 99.99%.
Examples
(1) Preparation of a standard sample: accurately weighing five glucosamine hydrochloride samples (0.0100g, 0.0150g, 0.0200g, 0.0250g and 0.0300g), respectively placing into a 20mL headspace sample injection bottle, adding 7mL of 0.01g/mL ninhydrin solution into the headspace bottle to uniformly disperse the samples, gently placing into a glass vial, carefully adding 0.9mL of sodium bicarbonate solution (with the concentration of 1.2mol/L) by using a pipette gun, and sealing by using a bottle cap; placing the whole headspace bottle in a water bath at 90 ℃ for reaction for 15min, manually shaking the headspace sample injection bottle to uniformly mix sodium bicarbonate in a glass vial with a ninhydrin solution containing a chitosan derivative, and placing the mixture in a water bath at 60 ℃ for reaction for 60 min; control blank vials (containing no glucosamine hydrochloride) were also prepared, and the rest was exactly as above. After the reaction is finished, the fact that the purple substances are generated due to the reaction of the amino and the ninhydrin in the headspace bottles of the experimental group can be obviously found, and the purple substances are not generated in the control group.
(2) Establishing a standard curve: placing a headspace bottle containing glucosamine hydrochloride and a blank ninhydrin solution in a headspace sample injector, setting the balance temperature at 60 ℃, the sample balance time at 5min, the gas-carried balance time in the headspace sample bottle at 12s, the pipeline inflation time at 12s, the pipeline balance time at 3s, the loop balance time at 12s, and the gas chromatograph operating conditions: the chromatographic column temperature is 105 ℃, nitrogen (flow rate is 3.1ml/min) is used as carrier gas, the detector temperature is 250 ℃, then extraction is carried out, the carbon dioxide peak area is recorded, a standard curve is obtained according to the corresponding relation between the reduction of the carbon dioxide signal value detected by the sample bottle and the blank bottle and the corresponding glucosamine hydrochloride quality, as shown in figure 1, a good linear relation between the glucosamine hydrochloride quality and the carbon dioxide reduction value can be found, the correlation is 0.988, and then a good linear relation between the amino content and the carbon dioxide reduction value can be shown by a formula 4.
(3) Sample detection: and (3) preparing a chitosan derivative sample (0.0200g) with the amino content to be detected in the step (1), placing the headspace bottle containing the sample to be detected in a headspace sample injector, performing headspace gas chromatography analysis by adopting the same headspace sample injector operating conditions and gas chromatograph operating conditions as those in the step (2), recording a chromatographic peak area signal value of the sample, comparing the chromatographic peak area signal value with a carbon dioxide peak area corresponding to a control group, and calculating a difference value.
(4) And (4) calculating a result: and (3) corresponding the chromatographic peak area signal value difference obtained in the step (3) with the standard curve obtained in the step (2), and calculating according to a formula (4) to obtain the amino content of the chitosan derivative of the sample to be detected.
The amino group content was measured by the method of the present invention and the conventional conductometry method, respectively, for 6 unknown samples measured according to the method described in application example 1, and the relative error was not more than 13.03%, as shown in table 1. Therefore, the method can be considered to have better accuracy for measuring the amino content of the chitosan derivative.
TABLE 1 comparison of the results of the amino group content of chitosan derivatives determined by headspace gas chromatography with the conductometric titration method
The peak area values of carbon dioxide chromatography in amino group contents of chitosan derivatives measured in 3 parallel samples prepared according to the method described in application example 1 are shown in table 2, and the relative standard deviation is 4.83% at most. Therefore, the method can be considered to have better reproducibility for measuring the amino content of the chitosan derivative.
TABLE 2 chromatographic peak area values of carbon dioxide in amino group content of chitosan derivatives measured by headspace gas chromatography
As described above, the present invention can be preferably realized.
The embodiments of the present invention are not limited to the above-described embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit of the present invention should be construed as equivalents thereof, and they are included in the scope of the present invention.
Claims (5)
1. The method for measuring the amino content of the chitosan derivative based on the headspace gas chromatography is characterized by comprising the following steps of:
(1) preparation of standard substances: firstly, adding more than three standard substances with different masses into different headspace bottles, adding no standard substance into the headspace bottles of a control group, then adding an equal amount of ninhydrin aqueous solution into each headspace bottle, then placing a glass tube containing an equal amount of sodium bicarbonate solution into each headspace bottle, covering a headspace cap, heating in a water bath for color development reaction, shaking the headspace bottle to uniformly mix the sodium bicarbonate in the glass tube with the remaining ninhydrin solution in the headspace bottle, and heating in the water bath for neutralization reaction;
(2) establishing a standard curve: placing each headspace bottle after neutralization reaction in the step (1) into a headspace sample injector, balancing, performing headspace extraction, and detecting by gas chromatography to obtain CO2A peak area, obtaining a standard curve according to the corresponding relation between the reduction of the peak area of the carbon dioxide containing the standard substance relative to the reference group and the corresponding quality of the standard substance, wherein y is ax + b, the abscissa of the standard curve is the quality of the standard substance, the corresponding ordinate is the peak area of the reduced carbon dioxide, a is the slope of the standard curve, and b is the intercept of the standard curve;
(3) sample detection: taking a chitosan derivative with amino content to be detected as a sample to be detected, replacing the standard substance in the step (1) with the sample to be detected, adding the sample to be detected into a headspace bottle, adding the same amount of ninhydrin aqueous solution into each headspace bottle without adding the sample to be detected in a control group, then adding a glass tube containing the same amount of sodium bicarbonate solution into each headspace bottle, covering a headspace cap, and performing color development and neutralization reaction according to the reaction conditions in the step (1); then placing the headspace bottle containing the sample to be detected and the headspace bottle of the control group into a headspace sample injector, and after balancing, recording the peak area of carbon dioxide through extraction detection;
(4) and (4) calculating a result: corresponding the reduction amount of the peak area of the carbon dioxide containing the sample to be detected in the step (3) relative to the reference group to the standard curve obtained in the step (2), and calculating to obtain the amino content of the chitosan derivative;
the standard substance in the step (1) is glucosamine salt;
the ratio of the amount of the ninhydrin substance to the amount of the amino group substance of the standard substance in the steps (1) and (3) is more than 2;
the neutralization reaction condition in the step (1) is that the reaction is carried out for 60-90min at 50-70 ℃.
2. The method according to claim 1, wherein the glucosamine salt is glucosamine hydrochloride or glucosamine sulfate.
3. The method of claim 1, wherein the ratio of the amount of the substance of sodium bicarbonate in the headspace bottle of step (2) to the amount of the substance of amino group of the standard substance is greater than 4.
4. The method according to claim 1, wherein the color-developing reaction condition in the step (1) is 80-95 ℃ for 15-30 min.
5. The method of claim 1, wherein the headspace injector conditions of steps (2) and (4) are as follows: the balance temperature is 50-70 deg.C, and the balance time is 5-15 min.
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| CN114716727A (en) * | 2022-04-18 | 2022-07-08 | 北华大学 | Cellulose-chitosan composite aerogel and preparation method and application thereof |
| CN117092274A (en) * | 2023-07-14 | 2023-11-21 | 国药集团致君（深圳）坪山制药有限公司 | Method for determining sevelamer carbonate content |
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