阅读说明：本技术 水产品中氮硫含量的同时快速测定方法 (Method for simultaneously and rapidly measuring nitrogen and sulfur contents in aquatic products ) 是由 尚德荣 宁劲松 赵艳芳 谷文艳 盛晓风 丁海燕 康绪明 于 2021-09-17 设计创作，主要内容包括：本发明公开了一种水产品中氮硫含量的同时快速测定方法,属于水产品检测技术领域,所述方法包括：1)选用的仪器及设备,2)标准曲线的制备,3)测试步骤,4)实验所用的仪器条件,5)结果计算与表述；本发明方法利用水产品在900℃和富氧气氛下燃烧分解成气体,在高纯氦气为载气的带动下,进入燃烧管下部的还原铜处,三氧化硫转化为二氧化硫,氮氧化物转化为氮气,经过2根净化柱分别吸收混合气体中的水和二氧化碳,吸附柱吸附二氧化硫,余下的氮气直接进入热导检测器检测氮气含量。加热二氧化硫吸附柱,解析出来的二氧化硫由氦气载入热导检测器检测其含量；满足了水产品中氮硫不用消化、固体样品可以直接进样同时测定、时效性强的检测需求。(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.)

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 purifying and filling 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 H₂O and CO₂The nitrogen oxides are reduced into N by copper in a nickel-chromium wire resistance furnace₂，N₂Loading high-purity helium gas into a thermal conductivity detector for measurement; heating the adsorption column, SO₂Analyzing 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 H₂O; the second purifying packed column is used for adsorbing CO₂(ii) a The adsorption column is used for adsorbing SO₂；

(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:

X₁＝C/m/100..............(1)

in the formula:

X₁-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;

X₂＝C/m/100..............(2)

in the formula:

X₂-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.

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 acquiring high-quality proteins by human beings, and the detection method corresponding to the content of the proteins in the current food is the national standard GB 5009.5-2016 determination of the proteins in food in national standard for food safety, and the method needs to add concentrated sulfuric acid for high-temperature decomposition at 420 ℃ under the condition of catalytic heating, and 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 national food safety standard GB 5009.34-2016 is to acidify and distill the sample in a closed container, the distillate is absorbed by lead acetate solution, the absorbed solution is acidified by hydrochloric acid, the iodine standard solution is titrated, and the sulfur dioxide content in the sample is calculated according to the consumed iodine standard solution (the standard is only used for drying 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 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.

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 purifying and filling 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 (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 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 H₂O and CO₂The nitrogen oxides are reduced into N by copper in a nickel-chromium wire resistance furnace₂，N₂Loading high-purity helium gas into a thermal conductivity detector for measurement; heating the adsorption column, SO₂Analyzing 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 H₂O; the second purifying packed column has alkali asbestos and phosphorus pentoxide as stuffing for adsorbing CO₂(ii) a The adsorption column is filled with carbon molecular sieve for adsorbing SO₂；

(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:

X₁＝C/m/100..............(1)

in the formula:

X₁-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;

X₂＝C/m/100..............(2)

in the formula:

X₂-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.

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 product 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: fitting a spectrogram by using a nitrogen standard curve;

FIG. 2: fitting a spectrogram of a sulfur standard curve;

FIG. 3: the linear relation of the nitrogen and sulfur is well related as can be seen from figure 1, figure 2 and figure 3 of the spectrograms of the nitrogen and sulfur standard curves, and instruments and conditions selected by the invention can completely meet the requirement of simultaneously and rapidly detecting the nitrogen and sulfur in aquatic products.

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: determination of nitrogen (N) and sulfur (S) in scallop:

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: 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 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) 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 columns₂O and CO₂The nitrogen oxides are reduced into N by copper in a nickel-chromium wire resistance furnace₂，N₂Loading high-purity helium gas into a thermal conductivity detector for measurement; heating SO₂Adsorption column, SO₂Analyzing 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; the first purifying packed column filler is magnesium perchlorate and phosphorus pentoxide for adsorbing H₂O; the second purifying and filling adsorption column has alkali asbestos and phosphorus pentoxide as stuffing for adsorbing CO₂(ii) a The adsorption column is filled with carbon molecular sieve for adsorbing SO₂；

(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:

X₁＝C/m/100..............(1)

in the formula:

X₁-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;

X₂＝C/m/100..............(2)

in the formula:

X₂-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. 1: 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. 2: the analytical performance of the instrument completely meets the requirement of measuring the sulfur content; as can be seen from FIG. 3, the nitrogen and sulfur elements in the sample can be detected simultaneously.

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 the edible part of fresh prawn, weighing about 50.0mg in a tin foil cup, and measuring the nitrogen value by using 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 equipment described 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 uniformly crushed samples are weighed, 0.4167g and 1.4280g of the national standard substance prawn GB10050(N is 13.5 percent and S is 1.0 percent) are respectively added into the uniformly crushed samples to be uniformly crushed in a mortar, about 20.0mg of the samples are respectively weighed into tin foil cups according to the background content of the uniformly crushed samples which is 0.5 times and 1.0 times of N, 7.88 times and 14.76 times of S, 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

As shown in Table 7 and Table 8, the recovery rate of N in the grilled fish fillet measured by the inventor is 95.33-101.3%, the recovery rate of 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.