CN113049511A - Pretreatment method of pectin and determination method of nitrate content in pectin - Google Patents
Pretreatment method of pectin and determination method of nitrate content in pectin Download PDFInfo
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- 235000010987 pectin Nutrition 0.000 title claims abstract description 80
- 229920001277 pectin Polymers 0.000 title claims abstract description 80
- 239000001814 pectin Substances 0.000 title claims abstract description 80
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 title claims abstract description 49
- 229910002651 NO3 Inorganic materials 0.000 title claims abstract description 45
- 238000000034 method Methods 0.000 title claims abstract description 22
- 238000002203 pretreatment Methods 0.000 title claims abstract description 16
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims abstract description 66
- YPJKMVATUPSWOH-UHFFFAOYSA-N nitrooxidanyl Chemical compound [O][N+]([O-])=O YPJKMVATUPSWOH-UHFFFAOYSA-N 0.000 claims abstract description 24
- 238000002798 spectrophotometry method Methods 0.000 claims abstract description 11
- 238000002835 absorbance Methods 0.000 claims description 55
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 30
- 239000000706 filtrate Substances 0.000 claims description 26
- 238000003756 stirring Methods 0.000 claims description 17
- 238000002156 mixing Methods 0.000 claims description 15
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 15
- GEHMBYLTCISYNY-UHFFFAOYSA-N Ammonium sulfamate Chemical compound [NH4+].NS([O-])(=O)=O GEHMBYLTCISYNY-UHFFFAOYSA-N 0.000 claims description 14
- 238000001914 filtration Methods 0.000 claims description 13
- 238000007865 diluting Methods 0.000 claims description 6
- 239000012528 membrane Substances 0.000 claims description 6
- 239000007788 liquid Substances 0.000 claims description 5
- 238000001471 micro-filtration Methods 0.000 claims description 4
- 239000011541 reaction mixture Substances 0.000 claims description 4
- 239000011148 porous material Substances 0.000 claims description 3
- 238000001514 detection method Methods 0.000 abstract description 17
- 238000011084 recovery Methods 0.000 abstract description 7
- 238000002474 experimental method Methods 0.000 abstract description 3
- 239000000126 substance Substances 0.000 abstract description 3
- 239000000243 solution Substances 0.000 description 48
- 238000005259 measurement Methods 0.000 description 8
- 238000012360 testing method Methods 0.000 description 8
- 239000012086 standard solution Substances 0.000 description 6
- 238000000605 extraction Methods 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 239000003153 chemical reaction reagent Substances 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- 235000013305 food Nutrition 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 238000010521 absorption reaction Methods 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- 239000003795 chemical substances by application Substances 0.000 description 3
- 239000010453 quartz Substances 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- IOVCWXUNBOPUCH-UHFFFAOYSA-M Nitrite anion Chemical compound [O-]N=O IOVCWXUNBOPUCH-UHFFFAOYSA-M 0.000 description 2
- 238000005034 decoration Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- MMDJDBSEMBIJBB-UHFFFAOYSA-N [O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[NH6+3] Chemical compound [O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[NH6+3] MMDJDBSEMBIJBB-UHFFFAOYSA-N 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 229910021538 borax Inorganic materials 0.000 description 1
- 239000007853 buffer solution Substances 0.000 description 1
- 229910052793 cadmium Inorganic materials 0.000 description 1
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 0.000 description 1
- 230000002596 correlated effect Effects 0.000 description 1
- 230000000875 corresponding effect Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000004328 sodium tetraborate Substances 0.000 description 1
- 235000010339 sodium tetraborate Nutrition 0.000 description 1
- 238000012421 spiking Methods 0.000 description 1
- 235000013311 vegetables Nutrition 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/38—Diluting, dispersing or mixing samples
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Abstract
The invention provides a pectin pretreatment method and a method for measuring nitrate content in pectin, and belongs to the technical field of chemical detection. According to the method, the nitrate radical in the pectin is extracted by adopting the ethanol solution with the volume concentration of 50-85%, the problems that the pectin is held and is not easy to dissolve are solved, the nitrate radical in the pectin can be fully extracted, and the accuracy of the obtained result is high when the nitrate radical content is measured by using an ultraviolet spectrophotometry. The method is simple to operate and has extremely low cost. The result of the embodiment shows that the detection precision of the detection method provided by the invention is 5.4%, the recovery rate of the standard addition recovery experiment is 91.1-106.6%, and the detection limit is 50 mg/kg.
Description
Technical Field
The invention relates to the technical field of chemical detection, in particular to a pectin pretreatment method and a method for measuring nitrate content in pectin.
Background
Pectin is widely applied in food, medicine and other industries, and has great market demand. Due to the particularity of the solubility of pectin, the pectin is difficult to completely dissolve in water and is very easy to agglomerate. Both the national standard (for example, GB5009.33-2016 national food safety Standard determination of nitrite and nitrate) (the first method of extraction with water, the second method of extraction with saturated borax solution +70 deg.C water, or the third method of extraction with ammonia buffer solution + water) and the traditional detection method of nitrate ion (for example, SN/T4589-2016 improved cadmium reduction analysis method for rapid determination of nitrate in export vegetables) require pectin to be dissolved in water, and due to the particularity of the solubility of pectin, nitrate ion in the pectin sample cannot be sufficiently leached out during the pretreatment of the sample, which results in loss of nitrate ion and inaccurate detection result.
Disclosure of Invention
In view of the above, the present invention provides a pretreatment method for pectin, which can avoid the problem of pectin clumping and accurately detect the nitrate content in pectin, and a method for measuring the nitrate content in pectin.
In order to achieve the purpose of the invention, the invention provides the following technical scheme:
the invention provides a pretreatment method for determining nitrate content in pectin, which comprises the following steps:
(1) stirring and mixing the ethanol solution and the pectin sample, and sequentially standing and microfiltering to obtain pectin filtrate; the volume concentration of the ethanol solution is 50-85%;
(2) mixing the pectin filtrate with hydrochloric acid and ammonium sulfamate, and diluting to desired volume with water to obtain solution to be tested.
Preferably, the mass ratio of the volume of the ethanol solution to the pectin sample in the step (1) is 100mL: 1-5 g.
Preferably, the stirring and mixing temperature in the step (1) is 15-30 ℃.
Preferably, the stirring and mixing speed in the step (1) is 500-600 rpm, and the time is 10-40 min.
Preferably, the standing time in the step (1) is 5-10 min.
Preferably, the microfiltration in the step (1) is needle filter filtration, and the pore diameter of the microfiltration membrane is 0.45-0.80 μm.
Preferably, the mass ratio of the volume of the pectin filtrate to the amount of the hydrochloric acid and the ammonium sulfamate in the step (2) is 1-5 mL:1mmol: 30-100 mg;
the volume-to-volume ratio of the pectin solution is 1-5 mL: 100 mL.
The invention provides a method for measuring nitrate content in pectin, which comprises the following steps:
(a) detecting the absorbance A of the solution to be detected obtained by the pretreatment method of any one of claims 1 to 7 at a wavelength of 210nm by using an ultraviolet spectrophotometry210And an absorbance A at a wavelength of 275nm275Calculating the corrected absorbance of nitrate according to formula 1
In the formula 1, the reaction mixture is,
corrected absorbance for nitrate;
A210the absorbance of the solution to be detected at the wavelength of 210 nm;
A275the absorbance of the solution to be detected at the wavelength of 275 nm;
(b) according to the standard curve and the corrected absorbance of the nitrate radical in the liquid to be detected obtained in the step (a)
Obtaining the mass concentration of nitrate radical in pectin; the standard curve is the mass of nitrate and the corrected absorption of nitrateLinear dependence of luminosity.
According to the invention, 50-85% ethanol solution is adopted to extract nitrate radicals in pectin, so that the problems of cluster holding and difficult dissolution of the pectin are avoided, the nitrate radicals in the pectin can be fully extracted, and when an ultraviolet spectrophotometry method is used for measuring the content of the nitrate radicals, the accuracy of the obtained result is high. The method is simple to operate and has extremely low cost. The result of the embodiment shows that the detection precision of the detection method provided by the invention is 5.4%, the recovery rate of the standard addition recovery experiment is 91.1-106.6%, and the detection limit is 50 mg/kg.
Compared with the existing acidified ethanol extracting agent, the acidified ethanol extracting agent uses the ethanol solution as the extracting agent, and can reduce the interference of impurities in the acidified ethanol, thereby improving the detection accuracy.
Drawings
FIG. 1 is a calibration absorbance standard curve of nitrate concentration versus nitrate in example 1.
Detailed Description
The invention provides a pretreatment method for determining nitrate content in pectin, which comprises the following steps:
(1) stirring and mixing the ethanol solution and the pectin sample, and standing and filtering the mixture in sequence to obtain pectin filtrate; the volume concentration of the ethanol solution is 50-85%;
(2) sampling the pectin filtrate, mixing the sampled pectin filtrate with hydrochloric acid and ammonium sulfamate, and diluting to constant volume with water to obtain a solution to be detected;
the method comprises the steps of stirring and mixing an ethanol solution and a pectin sample, and standing and filtering the mixture in sequence to obtain pectin filtrate. The invention has no special requirements on the type of the pectin sample, and the pectin sample known to those skilled in the art can be used for determining the nitrate content by using the method provided by the invention. In the invention, the volume concentration of the ethanol solution is 50-85%, preferably 60-75%. In the invention, the mass ratio of the volume of the ethanol solution to the pectin is preferably 100mL: 1-5 g, and more preferably 100mL: 2-4 g.
In the invention, the stirring and mixing temperature is preferably 15-30 ℃, and more preferably 20-25 ℃. The invention is stirred at the temperature, which can ensure the good dispersion stability of the pectin, and when the temperature is too high, the pectin is dissolved, so that the mixed solution is viscous and can not be filtered.
In the invention, the stirring and mixing speed is preferably 500-600 rpm, and more preferably 550 rpm; the time is preferably 10 to 40min, and more preferably 20 to 30 min.
In the invention, the standing time is preferably less than or equal to 10min, and more preferably 5-8 min.
In the present invention, the filtration is preferably a needle filter filtration, and the pore size of the filtration membrane for filtration is preferably 0.45 to 0.80 μm, and more preferably 0.5 to 0.6 μm.
After the pectin filtrate is obtained, the pectin filtrate is sampled, the sampled pectin filtrate is mixed with hydrochloric acid and ammonium sulfamate, and the volume is determined by water to obtain the liquid to be detected. In the invention, the mass ratio of the volume of the pectin filtrate to the molar weight of the hydrochloric acid to the mass of the ammonium sulfamate is preferably 1-5 mL:1mmol: 30-100 mg, and more preferably 2-4 mL:1mmol: 50-70 mg. In the invention, the hydrochloric acid is preferably added in the form of a hydrochloric acid aqueous solution, and the molar concentration of the hydrochloric acid aqueous solution is preferably 1-3 mol/L; in the invention, the hydrochloric acid has the function of adjusting the pH value of the filtrate and eliminating the interference of carbonate with alkalinity.
In the invention, the ammonium sulfamate is preferably added in the form of an aqueous solution, and the concentration of the ammonium sulfamate solution is preferably 10-50 g/L. In the invention, the ammonium sulfamate has the functions of reducing the interference of organic matters in pectin filtrate and improving the recovery rate and precision of detection.
The present invention does not require any particular mixing means, and mixing means known to those skilled in the art may be used. In the invention, the ratio of the volume of the pectin solution to the constant volume is preferably 1-5 mL: 100mL, more preferably 2-4 mL: 100 mL.
The invention provides a method for measuring nitrate content in pectin, which comprises the following steps:
(a) obtaining the absorbance A of the solution to be detected at 210nm by ultraviolet spectrophotometry210Absorbance A at a wavelength of 275nm275Calculating the corrected absorbance of nitrate according to formula 1
In the formula 1, the reaction mixture is,
corrected absorbance for nitrate;
A210the absorbance of the solution to be detected at the wavelength of 210 nm;
A275the absorbance of the solution to be detected at the wavelength of 275 nm;
(b) correcting the absorbance of the nitrate radical according to the standard curve and the nitrate radical obtained in step (a)
Obtaining the mass concentration of nitrate radical in pectin; the standard curve is a linear relationship curve of the mass of nitrate and the corrected absorbance of nitrate.
After the liquid to be detected is obtained, the invention obtains the absorbance A of the liquid to be detected at the wavelength of 210nm by using an ultraviolet spectrophotometry210Absorbance A at a wavelength of 275nm275Calculating the corrected absorbance of nitrate according to formula 1
In the formula 1, the reaction mixture is,
is nitrate radical calibrationA positive absorbance;
A210the absorbance of the solution to be detected at the wavelength of 210 nm;
A275the absorbance of the solution to be detected at 275nm wavelength is shown.
The method for testing the absorbance of the solution to be tested by the ultraviolet spectrophotometry has no special requirement, and the ultraviolet spectrophotometry which is well known by the technical personnel in the field can be used. The invention preferably uses an ultraviolet spectrophotometer to test the absorbance, and when testing, a 1cm quartz absorption cell is preferably used as the absorption cell.
Corrected absorbance of nitrate radical was obtained
Then, the present invention corrects the absorbance according to the standard curve and the obtained nitrate radical
Obtaining the mass concentration of nitrate radical in pectin; the standard curve is a linear relationship curve of the mass of nitrate and the corrected absorbance of nitrate. In the present invention, the method for obtaining the standard curve preferably includes the steps of:
(1) accurately divide 0, 10, 20, 50, 100, 200, 400, 600, 800 and 1000. mu.g of nitrate (nitrate is a commercially available 1000. mu.g/mL nitrate standard solution with a standard substance certificate (NO)3 -Metering) 50mL of pure water, 1mL of hydrochloric acid solution with the concentration of 1mol/L and 5mL of ammonium sulfamate solution with the concentration of 50g/L are added into a 100mL volumetric flask, diluted to scales by pure water and shaken up to obtain a series of nitrate radical standard solutions;
(2) obtaining the absorbance A of the solution to be detected at the wavelength of 210nm by using an ultraviolet spectrophotometry210Absorbance A at a wavelength of 275nm275Calculating the corrected absorbance of nitrate according to formula 1
And drawing a standard curve by taking the mass of the nitrate radical as an abscissa and the absorbance value as an ordinate. The method for drawing the standard curve is not specialFor example, standard curves can be drawn using methods well known to those skilled in the art. In the present invention, the mass of the nitrate nitrogen is positively correlated with the corrected absorbance.
As a specific embodiment of the present invention, the standard curve is:
y＝0.001296x+0.004114 R2＝0.0999874，x＝0～1000μg/100mL。
after obtaining the mass of the nitrate radical, the invention calculates the mass concentration of the nitrate radical in the pectin sample according to the formula 2:
in formula 2,. rhoNO3ˉThe mass concentration of nitrate radical in the pectin sample is mg/kg;
m is the mass of nitrate radical obtained according to a standard curve, mu g;
m1is the pectin sample mass, g;
V1the sampling volume of the pectin filtrate in the step (2) is mL;
V2volume of ethanol solution, mL.
The method for measuring nitrate content in pectin provided by the present invention is described in detail with reference to the following examples, but they should not be construed as limiting the scope of the present invention.
Example 1
(1) Dispersing 2g pectin in 60 vol% ethanol solution at 25 deg.C, mechanically stirring at 500rpm for 20min, diluting to 100mL with ethanol, standing for 10min, and filtering with 0.45 μm filter membrane to obtain pectin filtrate.
(2) And (3) putting 5mL of filtrate into a 100mL volumetric flask, adding 1mL of 1mol/L hydrochloric acid solution and 5mL of 50g/L ammonium sulfamate solution, fixing the volume to the scale with pure water, and shaking up to obtain the solution to be detected.
(3) Absorbance (A) was measured using an ultraviolet spectrophotometer at a wavelength of 210nm using a 1cm quartz cuvette with a reagent blank as a reference210) (ii) a Adjusting the wavelength to 275nm, and measuring the absorbance (A) while using the reagent blank as a reference275) Calculating the corrected absorbance of nitrate according to formula 1
(4) Accurately dividing 0, 10, 20, 50, 100, 200, 400, 600, 800 and 1000 mu g of nitrate into 100mL volumetric flasks, adding 50mL of pure water, 1mL of 1mol/L hydrochloric acid solution and 5mL of 50g/L ammonium sulfamate solution, diluting the solutions to a scale with the pure water, and shaking up to obtain a series of nitrate standard solutions; obtaining the absorbance A of the solution to be detected at the wavelength of 210nm by using an ultraviolet spectrophotometry210Absorbance A at a wavelength of 275nm275Calculating the corrected absorbance of nitrate according to formula 1
And drawing a standard curve by taking the mass of the nitrate radical as an abscissa and the absorbance value as an ordinate. Corrected absorbance for series of nitrate standard solutions
As shown in table 1.
TABLE 1 corrected absorbances corresponding to series of nitrate standard solutions
A standard curve was plotted according to the data in Table 1, and the resulting standard curve is shown in FIG. 1.
Determination of detection limit: a sample (2 g) was taken, extracted with 50mL of a 60% ethanol solution, and 5mL of the filtrate was obtained, which was 50mg/kg when the absorbance of the sample on the curve was 10. mu.g at the lowest point. Namely the detection limit.
(5) According to the standard curve and the corrected absorbance of the nitrate radical obtained in the step (3)
And calculating the mass concentration of nitrate radical in the pectin according to the formula 2.
The same sample is tested for precision by repeating the test for ten times by different people according to the method. The results obtained are shown in Table 2.
TABLE 2 results of the precision test
1mL of nitrate radical standard solution with the concentration of 1000 mu g/mL is added into the ethanol solution in the step (1), the rest operations are the same, and the obtained detection result minus the sample result is divided by a theoretical value, namely the recovery rate of adding the standard.
The results of the recovery of the four spiking operations were 91.1%, 106.6%, 97.8%, and 93.9%, respectively.
As can be seen from the above tests, the determination method provided by the invention has good accuracy.
Example 2
(1) Dispersing 2g pectin in 60 vol% ethanol solution at 25 deg.C, mechanically stirring at 500rpm for 20min, diluting to 100mL with ethanol, standing for 10min, and filtering with 0.45 μm filter membrane to obtain pectin filtrate.
(2) And (3) putting 5mL of filtrate into a 100mL volumetric flask, adding 1mL of 1mol/L hydrochloric acid solution and 5mL of 50g/L ammonium sulfamate solution, fixing the volume to the scale with pure water, and shaking up to obtain the solution to be detected.
(3) Absorbance (A) was measured using an ultraviolet spectrophotometer at a wavelength of 210nm using a 1cm quartz cuvette with a reagent blank as a reference210) (ii) a Adjusting the wavelength to 275nm, and measuring the absorbance (A) while using the reagent blank as a reference275) Calculating the corrected absorbance of nitrate according to formula 1
(4) Corrected absorbance of nitrate according to the standard curve obtained in example 1 and the standard curve obtained in step (3)
And calculating the mass concentration of nitrate radical in the pectin according to the formula 2, wherein the two test results are 996mg/kg and 984mg/kg respectively.
The same pectin samples were tested by spectrophotometry according to the second method of GB5009.33-2016 (determination of nitrite and nitrate in national food Standard for food safety), with results of 952mg/kg and 944 mg/kg. Therefore, the method provided by the invention has good accuracy.
Comparative example 1
Weighing 2.0g of pectin sample same as in example 1, adding 50mL of 60% ethanol solution into a 100mL beaker, stirring for 10min, 20min, 30min, 40min, 50min and 60min respectively, filtering, and taking 5mL of filtrate, wherein the subsequent operation is the same as in example 1.
The results of the measurement of the different stirring times of the same sample are shown in Table 3.
TABLE 3 measurement results of different stirring times of the same sample
| Time | 10min | 20min | 30min | 40min | 50min | 60min |
| Results (mg/kg) | 703 | 730 | 700 | 719 | 800 | 930 |
As can be seen from Table 3, as the extraction time of ethanol increased, the detection result was higher when the extraction time was not less than 50 min. This is because the pectin dissolves due to too long stirring time, resulting in a thick and not clear solution, which is not suitable for the later experiments.
Comparative example 2
2.0g of the same pectin sample as in example 1 was weighed into a 100mL beaker, and ethanol solutions with a volume concentration of 60% at 15 ℃, 30 ℃, 40 ℃, 50 ℃, 60 ℃ and 70 ℃ were added, respectively, and after stirring for 20min, filtration was carried out to obtain 5mL of filtrate, and the subsequent operations were the same as in example 1.
The results of the measurement of the ethanol temperature of the same sample are shown in Table 4.
TABLE 4 measurement results of different ethanol temperatures of the same sample
As can be seen from Table 4, the detection results were higher as the temperature of ethanol was increased (40 ℃); the ethanol temperature is not less than 50 ℃ and the test can not be carried out.
Comparative example 3
2.0g of pectin sample was weighed in a 100mL beaker, 50mL of 60% ethanol solution was added, and the mixture was stirred for 20min and filtered through medium-speed quantitative filter paper and a 0.45 μm filter membrane, and 5mL of the filtrate was obtained, and the subsequent operation was the same as in example 1. Each filter material was tested in triplicate.
The results of the measurements on the different filter materials are shown in Table 5.
TABLE 5 measurement results of different filter materials
Comparative example 4
2.0g of pectin sample was weighed into a 100mL beaker, 50mL of 60% ethanol solution was added, and the mixture was stirred for 20min, vacuum filtered and filtered through a needle filter (0.45 μm filter) to obtain 5mL of filtrate, and the subsequent operation was the same as in example 1. Each filter material was tested in triplicate.
The results of the measurements of the different filtration methods are shown in table 6.
TABLE 6 measurement results of different filter materials
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (8)
1. A pretreatment method for determining nitrate content in pectin comprises the following steps:
(1) stirring and mixing the ethanol solution and the pectin sample, and sequentially standing and microfiltering to obtain pectin filtrate; the volume concentration of the ethanol solution is 50-85%;
(2) mixing the pectin filtrate with hydrochloric acid and ammonium sulfamate, and diluting to desired volume with water to obtain solution to be tested.
2. The pretreatment method according to claim 1, wherein the mass ratio of the volume of the ethanol solution to the pectin sample in the step (1) is 100mL: 1-5 g.
3. The pretreatment method according to claim 1, wherein the temperature for stirring and mixing in the step (1) is 15 to 30 ℃.
4. The pretreatment method according to claim 1, wherein the stirring and mixing in the step (1) are performed at a rate of 500 to 600rpm for 10 to 40 min.
5. The pretreatment method according to claim 1, wherein the standing time in the step (1) is 5 to 10 min.
6. The pretreatment method according to claim 1, wherein the microfiltration in the step (1) is a pin-head filtration, and the pore size of the microfiltration membrane is 0.45 to 0.80 μm.
7. The pretreatment method according to claim 2, wherein the mass ratio of the volume of the pectin filtrate to the amount of the hydrochloric acid and the ammonium sulfamate in the step (2) is 1 to 5mL:1mmol:30 to 100 mg;
the volume-to-volume ratio of the pectin solution is 1-5 mL: 100 mL.
8. A method for measuring nitrate content in pectin comprises the following steps:
(a) detecting the absorbance A of the solution to be detected obtained by the pretreatment method of any one of claims 1 to 7 at a wavelength of 210nm by using an ultraviolet spectrophotometry210And an absorbance A at a wavelength of 275nm275Calculating the corrected absorbance of nitrate according to formula 1
In the formula 1, the reaction mixture is,
corrected absorbance for nitrate;
A210the absorbance of the solution to be detected at the wavelength of 210 nm;
A275the absorbance of the solution to be detected at the wavelength of 275 nm;
(b) according to the standard curve and the corrected absorbance of the nitrate radical in the liquid to be detected obtained in the step (a)
Obtaining the mass concentration of nitrate radical in pectin; the standard curve is a linear relationship curve of the mass of nitrate and the corrected absorbance of nitrate.
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