CN115047126A - Method for simultaneously and rapidly measuring nitrogen and sulfur contents in aquatic products - Google Patents
Method for simultaneously and rapidly measuring nitrogen and sulfur contents in aquatic products Download PDFInfo
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 title claims abstract description 104
- 229910052757 nitrogen Inorganic materials 0.000 title claims abstract description 54
- 229910052717 sulfur Inorganic materials 0.000 title claims abstract description 45
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 title claims abstract description 42
- 239000011593 sulfur Substances 0.000 title claims abstract description 42
- 238000000034 method Methods 0.000 title claims abstract description 20
- 239000007789 gas Substances 0.000 claims abstract description 34
- 239000001307 helium Substances 0.000 claims abstract description 23
- 229910052734 helium Inorganic materials 0.000 claims abstract description 23
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 claims abstract description 23
- 238000001514 detection method Methods 0.000 claims abstract description 22
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 claims abstract description 19
- 238000001179 sorption measurement Methods 0.000 claims abstract description 19
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 13
- 239000007787 solid Substances 0.000 claims abstract description 13
- 238000012360 testing method Methods 0.000 claims abstract description 12
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 10
- 238000002485 combustion reaction Methods 0.000 claims abstract description 10
- 239000001301 oxygen Substances 0.000 claims abstract description 10
- 238000002360 preparation method Methods 0.000 claims abstract description 9
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical group [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims abstract description 8
- 238000011068 loading method Methods 0.000 claims abstract description 8
- 238000002474 experimental method Methods 0.000 claims abstract description 7
- 238000010438 heat treatment Methods 0.000 claims abstract description 6
- 239000012159 carrier gas Substances 0.000 claims abstract description 5
- 238000000746 purification Methods 0.000 claims abstract description 5
- 238000010926 purge Methods 0.000 claims description 21
- 239000000126 substance Substances 0.000 claims description 16
- 239000010453 quartz Substances 0.000 claims description 15
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 15
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 claims description 14
- 229910018487 Ni—Cr Inorganic materials 0.000 claims description 12
- VNNRSPGTAMTISX-UHFFFAOYSA-N chromium nickel Chemical compound [Cr].[Ni] VNNRSPGTAMTISX-UHFFFAOYSA-N 0.000 claims description 12
- 238000005259 measurement Methods 0.000 claims description 11
- 238000011049 filling Methods 0.000 claims description 7
- 238000002347 injection Methods 0.000 claims description 6
- 239000007924 injection Substances 0.000 claims description 6
- 238000000197 pyrolysis Methods 0.000 claims description 6
- 238000005303 weighing Methods 0.000 claims description 6
- PFRUBEOIWWEFOL-UHFFFAOYSA-N [N].[S] Chemical compound [N].[S] PFRUBEOIWWEFOL-UHFFFAOYSA-N 0.000 claims description 5
- 241000206607 Porphyra umbilicalis Species 0.000 claims description 4
- 229910052802 copper Inorganic materials 0.000 claims description 4
- 239000010949 copper Substances 0.000 claims description 4
- WHBHBVVOGNECLV-OBQKJFGGSA-N 11-deoxycortisol Chemical compound O=C1CC[C@]2(C)[C@H]3CC[C@](C)([C@@](CC4)(O)C(=O)CO)[C@@H]4[C@@H]3CCC2=C1 WHBHBVVOGNECLV-OBQKJFGGSA-N 0.000 claims description 3
- 229920000742 Cotton Polymers 0.000 claims description 3
- 230000003321 amplification Effects 0.000 claims description 3
- 229910002091 carbon monoxide Inorganic materials 0.000 claims description 3
- 239000003795 chemical substances by application Substances 0.000 claims description 3
- 238000010812 external standard method Methods 0.000 claims description 3
- 238000002156 mixing Methods 0.000 claims description 3
- 238000003199 nucleic acid amplification method Methods 0.000 claims description 3
- 238000012545 processing Methods 0.000 claims description 3
- 239000000203 mixture Substances 0.000 claims description 2
- 238000012856 packing Methods 0.000 claims description 2
- RAHZWNYVWXNFOC-UHFFFAOYSA-N Sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 abstract description 26
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 abstract description 6
- AKEJUJNQAAGONA-UHFFFAOYSA-N sulfur trioxide Chemical compound O=S(=O)=O AKEJUJNQAAGONA-UHFFFAOYSA-N 0.000 abstract description 6
- 239000001569 carbon dioxide Substances 0.000 abstract description 3
- 229910002092 carbon dioxide Inorganic materials 0.000 abstract description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 abstract description 3
- 229910001868 water Inorganic materials 0.000 abstract description 3
- 238000011084 recovery Methods 0.000 description 20
- 241000238557 Decapoda Species 0.000 description 10
- DLYUQMMRRRQYAE-UHFFFAOYSA-N tetraphosphorus decaoxide Chemical compound O1P(O2)(=O)OP3(=O)OP1(=O)OP2(=O)O3 DLYUQMMRRRQYAE-UHFFFAOYSA-N 0.000 description 10
- 241000237509 Patinopecten sp. Species 0.000 description 8
- 235000020637 scallop Nutrition 0.000 description 8
- 241000251468 Actinopterygii Species 0.000 description 6
- 230000000694 effects Effects 0.000 description 5
- 235000013372 meat Nutrition 0.000 description 5
- QAOWNCQODCNURD-UHFFFAOYSA-N sulfuric acid Substances OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 5
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 4
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 4
- 235000013305 food Nutrition 0.000 description 4
- 102000004169 proteins and genes Human genes 0.000 description 4
- 108090000623 proteins and genes Proteins 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- MPCRDALPQLDDFX-UHFFFAOYSA-L Magnesium perchlorate Chemical compound [Mg+2].[O-]Cl(=O)(=O)=O.[O-]Cl(=O)(=O)=O MPCRDALPQLDDFX-UHFFFAOYSA-L 0.000 description 3
- 239000003513 alkali Substances 0.000 description 3
- 239000010425 asbestos Substances 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 239000000567 combustion gas Substances 0.000 description 3
- 230000029087 digestion Effects 0.000 description 3
- 239000002808 molecular sieve Substances 0.000 description 3
- 229960003753 nitric oxide Drugs 0.000 description 3
- 235000019391 nitrogen oxide Nutrition 0.000 description 3
- 229910052895 riebeckite Inorganic materials 0.000 description 3
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- ZCYVEMRRCGMTRW-UHFFFAOYSA-N 7553-56-2 Chemical compound [I] ZCYVEMRRCGMTRW-UHFFFAOYSA-N 0.000 description 2
- 239000002253 acid Substances 0.000 description 2
- 229910021529 ammonia Inorganic materials 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 239000000945 filler Substances 0.000 description 2
- 229910052740 iodine Inorganic materials 0.000 description 2
- 239000011630 iodine Substances 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- 239000004570 mortar (masonry) Substances 0.000 description 2
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 238000010561 standard procedure Methods 0.000 description 2
- 239000012086 standard solution Substances 0.000 description 2
- 241000282414 Homo sapiens Species 0.000 description 1
- 239000003463 adsorbent Substances 0.000 description 1
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 description 1
- 229910052921 ammonium sulfate Inorganic materials 0.000 description 1
- 235000011130 ammonium sulphate Nutrition 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- KGBXLFKZBHKPEV-UHFFFAOYSA-N boric acid Chemical compound OB(O)O KGBXLFKZBHKPEV-UHFFFAOYSA-N 0.000 description 1
- 239000004327 boric acid Substances 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000002596 correlated effect Effects 0.000 description 1
- 230000000875 corresponding effect Effects 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000004821 distillation Methods 0.000 description 1
- 229940046892 lead acetate Drugs 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- JCXJVPUVTGWSNB-UHFFFAOYSA-N nitrogen dioxide Inorganic materials O=[N]=O JCXJVPUVTGWSNB-UHFFFAOYSA-N 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000004448 titration Methods 0.000 description 1
- 238000012795 verification Methods 0.000 description 1
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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
- G01N30/02—Column chromatography
- G01N30/62—Detectors specially adapted therefor
- G01N30/64—Electrical detectors
- G01N30/66—Thermal conductivity detectors
-
- 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
- G01N30/02—Column chromatography
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
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- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analyzing Non-Biological Materials By The Use Of Chemical Means (AREA)
Abstract
The invention discloses a method for simultaneously and rapidly measuring the nitrogen and sulfur content in aquatic products, belonging to the technical field of aquatic product detection, and the method comprises the following steps: 1) selected instruments and equipment, 2) preparation of a standard curve, 3) a testing step, 4) instrument conditions used in an experiment, and 5) calculation and expression of results; the method of the invention utilizes aquatic products to be burnt and decomposed into gas at 900 ℃ in oxygen-enriched atmosphere, the gas enters a reduction copper part at the lower part of a combustion tube under the driving of high-purity helium as carrier gas, sulfur trioxide is converted into sulfur dioxide, nitrogen oxide is converted into nitrogen, water and carbon dioxide in the mixed gas are respectively absorbed through 2 purification columns, the adsorption columns adsorb the sulfur dioxide, and the rest nitrogen directly enters a thermal conductivity detector to detect the content of the nitrogen. Heating the sulfur dioxide adsorption column, and loading the analyzed sulfur dioxide into a thermal conductivity detector by helium to detect the content of the sulfur dioxide; the method meets the detection requirements that nitrogen and sulfur in the aquatic products are not needed to be digested, a solid sample can be directly injected and simultaneously measured, and the timeliness is strong.
Description
Technical Field
The invention belongs to the technical field of aquatic product detection, and particularly relates to a method for simultaneously and rapidly determining the nitrogen and sulfur content in an aquatic product.
Background
Aquatic products are important sources for obtaining high-quality proteins by human beings, and the current detection method corresponding to the content of the proteins in the food is the national standard GB 5009.5-2016 determination of the proteins in food safety national standard, and the method needs to add concentrated sulfuric acid for high-temperature decomposition at 420 ℃ under the condition of catalytic heating, so that the generated ammonia is combined with the sulfuric acid to generate ammonium sulfate; alkalifying and distilling to free ammonia, absorbing with boric acid, titrating with sulfuric acid or hydrochloric acid standard titration solution, calculating nitrogen content according to acid consumption, and multiplying by conversion coefficient to obtain protein content. The method is far away from the requirement of real-time monitoring of product quality; in addition: the detection principle in the national food safety standard GB 5009.34-2016 of the people's republic of China is that a sample is acidified and distilled in a closed container, the distillate is absorbed by lead acetate solution, the absorbed solution is acidified by hydrochloric acid and titrated by iodine standard solution, and the sulfur dioxide content in the sample is calculated according to the consumed iodine standard solution (the standard is only used for dry food). At present, two existing detection methods are complex in detection steps, multiple in factors influencing data accuracy and long in time consumption.
Disclosure of Invention
The technical scheme to be solved by the invention is to provide a method for simultaneously and rapidly measuring the nitrogen and sulfur content in aquatic products. The method utilizes aquatic products to generate nitrogen oxide gases such as carbon dioxide, water, nitric oxide and the like and gases such as sulfur dioxide, sulfur trioxide and the like by combustion decomposition at 900 ℃ in an oxygen-rich atmosphere, under the drive of high-purity helium as carrier gas, the high-purity helium enters the reduction copper at the lower part of the combustion tube, redundant oxygen is absorbed, sulfur trioxide is converted into sulfur dioxide, nitric oxide is converted into nitrogen, then magnesium perchlorate and phosphorus pentoxide are adopted to absorb water in the mixed gas, alkali asbestos is adopted to absorb carbon dioxide in the mixed gas, the rest gas is nitrogen and sulfur dioxide, a carbon molecular sieve is adopted to absorb the sulfur dioxide in the rest gas, the rest nitrogen directly enters a thermal conductivity detector to detect the content of the nitrogen, after the nitrogen detection is finished, heating the sulfur dioxide adsorption column, resolving sulfur dioxide from the adsorbent, and loading helium into a thermal conductivity detector to detect the content of the sulfur dioxide; the detection requirements that nitrogen and sulfur in the aquatic products are not digested, a solid sample can be directly injected and simultaneously detected, and the timeliness is strong are met.
The invention is completed according to the following operation method:
a method for simultaneously and rapidly measuring the nitrogen and sulfur content in aquatic products comprises the following steps: 1) selected instruments and equipment, 2) preparation of a standard curve, 3) a testing step, 4) instrument conditions used in an experiment, and 5) calculation and expression of results;
1) instruments and equipment:
(1) the direct sample introduction nitrogen and sulfur tester comprises a solid sample introduction system, a two-stage purging device, 2 purification packing columns, 1 adsorption column, a nickel-chromium wire resistance furnace, a quartz tube, 2 gas path control systems and a tin foil cup; the solid sample introduction system is sequentially connected with 2 purifying packed columns and 1 adsorption column, the quartz tube is positioned in the nickel-chromium wire resistance furnace, and 2 gas path control systems respectively control high-purity helium and oxygen;
(2) the thermal conductivity cell detector comprises a Mass Flow Controller (MFC), a gas circuit control system, a reference gas flow controller and a detector;
(3) high purity helium and oxygen;
2) preparation of a standard curve: are respectively provided withWeighing a sample of standard substance laver, placing in a tinfoil cup, placing in a nickel-chromium wire resistance furnace, performing pyrolysis, and allowing the generated mixed gas to pass through 2 purifying and filling columns in sequence to respectively adsorb H 2 O and CO 2 The nitrogen oxides are reduced into N by copper in a nickel-chromium wire resistance furnace 2 ，N 2 Loading high-purity helium gas into a thermal conductivity detector for measurement; heating the adsorption column, SO 2 Analyzing from the adsorption column agent, loading helium into a thermal conductivity detector to detect the content of the helium, and drawing a standard curve by using the nitrogen-sulfur concentration and the fluorescence area of a thermal conductivity cell;
3) the testing steps are as follows:
uniformly mixing the crushed (or homogenized fresh) samples, putting the mixture into a tin foil cup, and measuring the nitrogen and sulfur value by using the instrument and equipment in the step 1), wherein the detection method is the same as the preparation of the standard curve in the step 2);
4) conditions of the apparatus used for the experiment:
(1) conditions of the solid sample injection system: the purging time is 20 s; the pyrolysis temperature is 900 ℃, and the time is 100 s; the first purifying packed column filler is magnesium perchlorate and phosphorus pentoxide for adsorbing H 2 O; the second purifying packed column has alkali asbestos and phosphorus pentoxide as stuffing for adsorbing CO 2 (ii) a The adsorption column is filled with carbon molecular sieve for adsorbing SO 2 ；
(2) Thermal conductivity cell detector conditions: the thermistor is 8K omega, the amplification circuit is 7 times, the carrier gas flow rate is 250mL/min, the reference gas flow rate is 50mL/min, and the reading time is 6(s);
5) and calculating and expressing the result:
drawing a standard working curve by using an external standard method in data processing software, storing the standard working curve, analyzing and processing the peak area of a sample, correcting by using an external standard to obtain the concentration of nitrogen and sulfur in the sample to be detected, and calculating according to the following formulas (1) and (2) to obtain the content of the substance to be detected in the sample:
X 1 ＝C/m/100.............. (1)
in the formula:
X 1 -the content of test substance N in the sample, g/100 g;
c, the concentration of N in the sample to be detected, mg;
m represents the sample weight and mg;
X 2 ＝C/m/100.............. (2)
in the formula:
X 2 -the content of the test substance S in the sample, g/100 g;
c, the concentration of S in the sample to be detected, mg;
m represents the sample amount, mg.
Furthermore, the sample is combusted at the front section of the quartz tube, the copper wire is arranged at the rear section of the quartz tube to reduce the combusted gas, and high-temperature-resistant cotton is arranged between the combustion section and the reduction section in the quartz tube to separate the combustion section from the reduction section. The invention integrates the oxidation pipe and the reduction pipe, simplifies the system, shortens the flow of the combustion gas and saves the detection time.
The two-stage purging is to perform first-stage purging when a sample enters a sample falling hole of the ball cup, and after the ball cup rotates and is isolated from the outside air, the sample falling hole is opposite to the air inlet pipe, and then, second-stage purging is performed. The invention adds the first-stage purging, only the first-stage purging of the second-stage purging is adopted in the prior art, and the first-stage purging can maximally remove N in the container 2 The residue is reduced to 1%, the invention creatively adds the first-stage purging, after the two-stage purging, the nitrogen residue can be reduced to about 1% of the sample accommodating cavity by 1% to 0.01%, and the problem of excessive nitrogen residue is solved, namely the residual N in the sample is reduced 2 。
Compared with the prior art, the invention has the beneficial effects that:
1. the experimental conditions are reasonably selected, the detection data is accurate and reliable, the nitrogen and sulfur in the aquatic products can be directly subjected to solid sample injection and simultaneously measured without digestion, and the pollution caused by digestion with strong acid is avoided;
2. the method has the characteristics of high detection speed of the nitrogen and sulfur content in the aquatic products and strong timeliness of quality supervision. Meanwhile, the defects of detection data distortion and long detection result period caused by incomplete digestion or distillation in the traditional national standard method are overcome.
3. The configuration conditions of the direct sample introduction nitrogen and sulfur tester can simultaneously measure the nitrogen and sulfur in the sample, and the analysis time is shortened from hours of the traditional national standard method to only 6 minutes, thereby meeting the requirement of implementing supervision on the effectiveness of measuring the nitrogen and sulfur content in the aquatic products.
Drawings
FIG. 1 is a schematic structural view of a combustion section and a reduction section in a quartz tube;
FIG. 2 is a plot of a nitrogen standard curve fit spectrum;
FIG. 3 is a sulfur standard curve fit spectrum;
FIG. 4 is a chart of a nitrogen sulfur standard curve; as can be seen from the figures 2, 3 and 4, the linear relation of nitrogen and sulfur is well correlated, and instruments and conditions selected by the invention can completely meet the requirement of the rapid detection of nitrogen and sulfur in aquatic products.
Fig. 5 is a flow chart of sample combustion gases.
Detailed Description
The technical contents of the present invention will be described in detail below by way of examples with reference to the accompanying drawings, but the scope of the present invention is not limited in any way by the examples.
The aquatic products have various types and varieties, and representative laver, scallop, prawn and grilled fish fillet in the aquatic products are selected as verification examples.
Example 1: measurement of Nitrogen (N) Sulfur (S) in scallop:
a method for simultaneously and rapidly measuring the nitrogen and sulfur content in aquatic products is shown in a whole flow chart of figure 5, and comprises the following steps: 1) selected instruments and equipment, 2) preparation of a standard curve, 3) a testing step, 4) instrument conditions used in an experiment, and 5) calculation and expression of results;
1) instruments and equipment: a direct sample introduction nitrogen and sulfur tester, a thermal conductivity cell detector and high-purity helium and oxygen; the direct sample introduction nitrogen and sulfur tester is developed for solving the technical problem of the invention;
(1) direct sample introduction nitrogen and sulfur tester: the device is provided with a solid sample introduction system, a two-stage purging device, two purifying and filling columns, 1 adsorption column, a nickel-chromium wire resistance furnace, a quartz tube, 2 gas path control systems and a tinfoil cup; the solid sample introduction system is sequentially connected with 2 purifying and filling columns and 1 adsorption column, the quartz tube is positioned in the nickel-chromium wire resistance furnace, as shown in figure 1, the front section of the quartz tube burns a sample, the rear section is provided with a copper wire for reducing the burnt gas, and high-temperature-resistant cotton is arranged between the combustion section and the reduction section in the quartz tube to separate the combustion section from the reduction section. The invention integrates the oxidation pipe and the reduction pipe, simplifies the system, shortens the flow of the combustion gas and saves the detection time.
2 gas circuit control systems respectively control high-purity helium and oxygen;
the two-stage purging is to perform first-stage purging when a sample enters a sample falling hole of the ball cup, the purged gas is helium, after the ball cup rotates and is isolated from the outside air, the sample falling hole faces the helium inlet pipe, and then, second-stage purging is performed.
(2) Thermal conductivity cell detector part: the device is provided with a Mass Flow Controller (MFC), a gas circuit control system, a reference gas flow controller and a detector;
(3) high purity helium and oxygen;
2) preparation of a standard curve: respectively weighing 2.24, 4.25, 5.71, 10.81, 16.51, 21.78, 25.40 and 31.61mg of samples with nitrogen content (5.0 +/-0.3%) of laver GBW10023 (GSB-14), placing the samples in tin foil, placing the tin foil in a nickel-chromium wire resistance furnace for pyrolysis, and respectively adsorbing H by generated mixed gas through 2 purification columns 2 O and CO 2 The nitrogen oxides are reduced into N by copper in a nickel-chromium wire resistance furnace 2 ，N 2 Loading high-purity helium gas into a thermal conductivity detector for measurement; heating SO 2 Adsorption column, SO 2 Analyzing from the adsorption column agent, loading high-purity helium into a thermal conductivity detector to detect the content of the helium, and drawing a standard curve by using the nitrogen-sulfur concentration and the fluorescence area of a thermal conductivity cell;
3) the testing steps are as follows:
weighing about 15.0mg of scallop standard substance GBW10024(N is 12.8 +/-0.8%; S is 1.5 +/-0.1%) in a tin foil cup, and measuring the nitrogen and sulfur value by using a direct sample injection nitrogen and sulfur tester;
4) conditions of the apparatus used for the experiment:
(1) conditions of a solid sample injection device: the purging time is 20 s; the pyrolysis temperature is 900 ℃, and the time is 100 s; first of allThe filler for purifying packed column is magnesium perchlorate and phosphorus pentoxide for adsorbing H 2 O; the second purifying and filling adsorption column has alkali asbestos and phosphorus pentoxide as stuffing for adsorbing CO 2 (ii) a The adsorption column is filled with carbon molecular sieve for adsorbing SO 2 ；
(2) Conditions of the thermal conductivity cell instrument: the thermistor is 8K omega, the amplification circuit is 7 times, the carrier gas flow rate is 250mL/min, the reference gas flow rate is 50mL/min, and the reading time is 6(s);
5) and calculating and expressing the result:
drawing a standard working curve by using an external standard method in data processing software, storing the standard working curve, analyzing and processing the peak area of a sample, correcting by using an external standard to obtain the concentration of nitrogen and sulfur in the sample to be detected, and calculating according to the following formulas (1) and (2) to obtain the content of the substance to be detected in the sample:
X 1 ＝C/m/100.............. (1)
in the formula:
X 1 the content of the substance N to be detected in the sample is g/100 g;
c, the concentration of N in the sample to be detected, mg;
m represents the sample weight and mg;
X 2 ＝C/m/100.............. (2)
in the formula:
X 2 -the content of the test substance S in the sample, g/100 g;
c, the concentration of S in the sample to be detected, mg;
m represents the sample weight and mg; the content of the substance to be measured in the sample can be obtained by the following calculation formula (1):
X＝C/m/10.............. (1)
6. results and discussion:
TABLE 1 analytical Properties of the instruments
| Linear Range (mg) | Coefficient of correlation (R) | Detection limit (μ g/g) | RSD(％) |
| 2.0-100 | ﹥0.9999 | 0.66 | 3.79％ |
As can be seen from table 1 and fig. 2: the analysis performance of the instrument completely meets the requirement of measuring the nitrogen content;
TABLE 2 analytical Properties of the instruments
| Linear Range (mg) | Coefficient of correlation (R) | Detection limit (μ g/g) | RSD(％) |
| 2.0-100 | ﹥0.9998 | 2.29 | 5.44 |
As can be seen from table 2 and fig. 3: the analytical performance of the instrument completely meets the requirement of measuring the sulfur content; as can be seen from FIG. 4, the nitrogen and sulfur elements in the sample can be simultaneously detected.
TABLE 3 measurement results of N recovery in scallop standard substance
TABLE 4 measurement results of S recovery in scallop standard substance
As can be seen from tables 3 and 4, the measured recovery rate of N in the scallop standard substance is 100.2-102.8%, the recovery rate of S is 96.66-103.3%, the recovery effect is ideal, and the recovery effect meets the detection standard.
Example 2: determination of nitrogen (N) and sulfur (S) in fresh and alive prawn meat: the apparatus and equipment used were the same as in example 1.
Homogenizing edible part of fresh prawn, weighing about 50.0mg in a tin foil cup, and measuring nitrogen value with a direct sample introduction nitrogen-sulfur tester; additionally, two 5.00g of the homogenate homogeneous sample are weighed, 0.9330g and 2.294g of prawn GB10050(N is 13.5%; S is 1.0%) which is a national standard substance are respectively added and put into a mortar for even development, and the background content of the prawn GB10050 is equivalent to 0.5 time and 1.0 time of N, 23 times and 32 times of S; respectively weighing about 50.0mg of the test sample in a tin foil cup, and measuring the nitrogen and sulfur values by using the instrument and the equipment in the embodiment 1; the other conditions were the same as those of the scallop in example 1, and the results of the normalized recovery of N and S from the fresh and alive prawn meat were measured (see tables 5 and 6).
TABLE 5 measurement results of N recovery in fresh prawn meat
TABLE 6 measurement results of S recovery in fresh prawn meat
As shown in Table 5 and Table 6, the results of the measurement of the normalized recovery rate of N in the fresh shrimp meat are 97.31-100.2%, the recovery rate of S is 96.93-105.5%, the recovery effect is ideal, and the detection standard is met.
Example 3: determination of nitrogen (N) sulfur (S) in grilled fish fillets:
cutting the baked fillet into pieces, crushing and uniformly mixing the pieces in a crusher, weighing about 20.0mg of the pieces in a tin foil cup, and measuring the nitrogen and sulfur values by using the instrument and equipment in the embodiment 1; in addition, two 1.00g of the evenly crushed samples are weighed, 0.4167g and 1.4280g of national standard substance prawn GB10050(N is 13.5 percent and S is 1.0 percent) are respectively added into the evenly crushed samples, the evenly crushed samples are placed into a mortar for even development, about 20.0mg of the samples are respectively weighed into a tin foil cup according to the base content of N which is 0.5 time and 1.0 time of the added standard, and S which is 7.88 times and 14.76 times of the added standard, and the nitrogen and sulfur values are measured by the instrument and the equipment which are described in the embodiment 1; the other conditions were the same as those of scallop, and the results of the recovery of N, S in the grilled fish fillet were measured (see tables 7 and 8).
TABLE 7 measurement results of recovery of N in grilled fish fillet under the standard
TABLE 8 measurement results of recovery of S from grilled fish fillet
Table 7 and Table 8 show that the recovery rate of the N in the grilled fish fillet is 95.33-101.3%, the recovery rate of the S is 92.26-100.2%, and the recovery effect is ideal.
As described above, it can be seen from tables 1 and 2 that: the analytical performance of the combined instrument completely meets the requirement for measuring the content of nitrogen (N) and sulfur (S) in the dry and fresh aquatic products, and tables 3, 4, 5, 6, 7 and 8 show that the recovery rate of the standard substances and the standard samples is 92.26-105.5%, and the recovery effect is ideal. The selected instruments and instrument conditions, the gas separation and purification tube filling materials and the pretreatment of the sample are reasonable and in place. The method has the beneficial effects that the protein (N x 6.25) sulfur (S) in the aquatic product can be directly subjected to solid sample injection and simultaneously and rapidly analyzed and measured.
The method can accurately and reliably measure the N, S content in the aquatic product in only 6 minutes, and meets the current requirement on high timeliness of product quality safety monitoring.
Claims (3)
1. A method for simultaneously and rapidly measuring the nitrogen and sulfur content in aquatic products is characterized by comprising the following steps: 1) selected instruments and equipment, 2) preparation of a standard curve, 3) a testing step, 4) instrument conditions used in an experiment, and 5) calculation and expression of results;
1) instruments and equipment:
(1) the direct sample introduction nitrogen and sulfur tester comprises a solid sample introduction system, a two-stage purging device, 2 purification packing columns, 1 adsorption column, a nickel-chromium wire resistance furnace, a quartz tube, 2 gas path control systems and a tin foil cup; the solid sample introduction system is sequentially connected with 2 purifying filling columns and 1 adsorption column, the quartz tube is positioned in the nickel-chromium wire resistance furnace, and 2 gas path control systems respectively control high-purity helium and oxygen;
(2) the thermal conductivity cell detector comprises a mass flow controller, a gas path control system, a reference gas flow controller and a detector;
(3) high purity helium and oxygen;
2) preparation of a standard curve: respectively weighing a sample of standard substance laver, placing in a tinfoil cup, placing in a nickel-chromium wire resistance furnace, performing pyrolysis, sequentially passing through 2 purifying and filling columns to respectively adsorb H 2 O and CO 2 The nitrogen oxides are reduced into N by copper in a nickel-chromium wire resistance furnace 2 ，N 2 Loading high-purity helium gas into a thermal conductivity detector for measurement; heating the adsorption column, SO 2 Analyzing from the adsorption column agent, loading helium into a thermal conductivity detector to detect the content of the helium, and drawing a standard curve by using the nitrogen-sulfur concentration and the fluorescence area of a thermal conductivity cell;
3) the testing steps are as follows:
uniformly mixing the crushed samples, placing the mixture in a tin foil cup, and measuring the nitrogen and sulfur value by using the instrument and equipment in the step 1), wherein the detection method is the same as the preparation of the standard curve in the step 2);
4) conditions of the apparatus used for the experiment:
(1) conditions of the solid sample injection system: the purging time is 20 s; the pyrolysis temperature is 900 ℃, and the time is 100 s; the first purifying packed column is used for adsorbing H 2 O; the second purifying packed column is used for adsorbing CO 2 (ii) a The adsorption column is used for adsorbing SO 2 ；
(2) Thermal conductivity cell detector conditions: the thermistor is 8K omega, the amplification circuit is 7 times, the carrier gas flow rate is 250mL/min, the reference gas flow rate is 50mL/min, and the reading time is 6(s);
5) and calculating and expressing the result:
drawing a standard working curve by using an external standard method in data processing software, storing the standard working curve, analyzing and processing the peak area of a sample, correcting by using an external standard to obtain the concentration of nitrogen and sulfur in the sample to be detected, and calculating according to the following formulas (1) and (2) to obtain the content of the substance to be detected in the sample:
X 1 ＝C/m/100.............. (1)
in the formula:
X 1 the content of the substance N to be detected in the sample is g/100 g;
c, the concentration of N in the sample to be detected, mg;
m represents the sample weight and mg;
X 2 ＝C/m/100.............. (2)
in the formula:
X 2 -the content of the test substance S in the sample, g/100 g;
c, the concentration of S in the sample to be detected, mg;
m represents the sample amount, mg.
2. The method for simultaneously and rapidly measuring the nitrogen and sulfur content in the aquatic products according to claim 1, wherein a sample is combusted at the front section of a quartz tube, a copper wire is arranged at the rear section of the quartz tube to reduce the combusted gas, and high temperature resistant cotton is arranged between the combustion section and the reduction section in the quartz tube to separate the combustion section from the reduction section.
3. The method for simultaneously and rapidly measuring the nitrogen and sulfur content in the aquatic products according to claim 1, wherein the two-stage purging is a first-stage purging when the sample enters the sample falling hole of the ball cup, and when the ball cup rotates and is isolated from the outside air, the sample falling hole faces the air inlet pipe, and then a second-stage purging is performed.
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