Solid turbidity standard substance and preparation method thereof

Abstract

The invention relates to a solid turbidity standard substance. The solid turbidity standard substance comprises gellan gum, metal salt and deionized water, the content of the gellan gum is 0.03-1.0 wt%, and the content of the metal cations is 1-100 mM; preferably, the content of the gellan gum is 0.05-0.5 wt%, and the content of the metal salt is 5-60 mM. The solid turbidity standard substance has excellent standing stability, can be stored under conventional conditions, can be repeatedly used without being prepared on site, reduces the influence of human factors in the using process, reduces the economic cost, is green and safe, avoids environmental and health risks, and can meet the requirements of turbidity measurement in various measuring ranges.

Description

Technical Field

[0001] The present invention relates to a turbidity reference material and a preparation method thereof, belonging to the technical field of reference material preparation. Background Art

[0002] Turbidity represents the clarity or turbidity of a transparent medium. In industries such as water quality monitoring, medicine and health, and food, there are quantitative limits on insoluble suspended particulate matter in water, and the main technical parameter characterizing this quantity is turbidity. A turbidimeter is a specialized instrument for measuring the magnitude of turbidity. Before leaving the factory, calibration, verification, etc. of a turbidimeter all require a turbidity reference material as a measurement standard.

[0003] Currently, the internationally recognized and commonly used turbidity reference material is the Formazine standard solution prepared according to the international standard "ISO 7072 Water quality - Turbidity measurement method" promulgated by the International Organization for Standardization. The primary turbidity reference material (GBW12001) in China is a Formazine turbidity reference material developed by the National Institute of Metrology with a standard value of 400 NTU (relative uncertainty 3%, k =2).

[0004] The Formazine turbidity standard solution is a milky white suspension formed by the reaction of hydrazine sulfate and hexamethylenetetramine under certain temperature conditions. Because it is made of pure chemical reagents, it has stable optical properties, good reproducibility and repeatability, and has become a relatively ideal turbidity reference material. However, the Formazine turbidity standard solution has problems such as harsh storage and use conditions, such as requiring refrigeration at 4°C - 8°C in the dark; the suspended particles are prone to sedimentation; it needs to be shaken well before each use, and it is difficult to avoid the influence of bubbles; it needs to be prepared immediately before use and has a short shelf life; the raw material hydrazine sulfate is a highly toxic substance, and hexamethylenetetramine has carcinogenicity; it needs to be treated as hazardous waste after use, posing risks to life, health, and environmental safety; it is for single use only, resulting in high economic costs, etc.

[0005] To overcome the disadvantage of poor stability of the Formazine turbidity reference material, the National Institute of Metrology uses nano-sized latex particles to prepare a polymer suspension turbidity standard solution (NIM-RM2048), which is specifically used for the stability and repeatability detection of turbidimeters. It needs to be sealed and stored in a refrigerated environment at 4°C - 8°C, with a validity period of 6 months.

[0006] CN105571914A uses nano-sized titanium dioxide particles as the reference substance of the turbidity standard solution, supplemented with potassium hydrogen phthalate as a regulator, and is diluted with deionized water to prepare an inorganic turbidity standard solution. This standard turbidity solution does not need to be stored in the dark, has no degradation changes, but has insufficient stability, is prone to sedimentation, can only be stored at room temperature for 30 days, and still needs to be prepared immediately before use, etc.

[0007] CN108458992A discloses a polymer suspension turbidity reference material and its preparation method. By introducing high-density positive or negative charges on the surface of nanoscale cross-linked polystyrene latex particles to improve the system stability, and then dispersing it in deionized water to make a polymer suspension. This standard turbidity solution needs to be prepared immediately before use, and its turbidity value is inevitably affected by human factors. It is difficult to avoid the influence of microbubbles during shaking, and the suspension contains highly toxic substances such as sodium azide. Summary of the Invention

[0008] In order to overcome the deficiencies of existing turbidity standard solutions and improvement schemes, the present invention provides a solid turbidity reference material and its preparation method. Using gellan gum as a raw material, a series of solid gel turbidity reference materials with different turbidity values are made by forming a uniform cross-linked three-dimensional network structure with its solution in the presence of electrolytes at different concentrations. This standard turbidity material is solid, stored under normal conditions, stable when standing, without the problems of suspension flocculation and sedimentation, convenient to use without the need to be prepared immediately before use, has a long storage period, can be reused at low cost, is green and safe, avoiding environmental and health risks, and can meet the needs of turbidity measurement in various ranges.

[0009] In order to achieve the above object, the present invention discloses a solid turbidity reference material, which comprises gellan gum, metal salt and deionized water; the content of gellan gum is 0.03 - 1.0 wt%, and the metal cation concentration is 1 - 100 (mmol / L); preferably, the content of gellan gum is 0.05 - 0.5 wt%, and the metal cation concentration is 5 - 60 (mmol / L).

[0010] The metal cation comes from a divalent metal salt, and the divalent metal salt is preferably a soluble salt of calcium, magnesium, zinc or barium. The salt is one of sulfate, nitrate and halide, and the halide is preferably chloride or bromide.

[0011] The gellan gum is preferably low-acyl gellan gum, in which the acetyl content is less than 2.0 wt%, the glyceroyl content is less than 1.0 wt%, and the total ash content is ≤15 wt%.

[0012] Preferably, the solid turbidity reference material can be formed by standing at 0℃ - 30℃, and preferably by refrigerating and cooling at 2℃ - 10℃ and standing for molding.

[0013] A preparation method for preparing a solid turbidity reference material includes the following steps: (1) Add gellan gum powder to deionized water and heat it to stir until it dissolves to obtain a gellan gum dispersion; (2) Filter the gellan gum dispersion through a microporous membrane while it is hot to remove insoluble impurities; (3) Add a metal salt under stirring and heating conditions to obtain a mixed solution; (4) Sterilize the mixed solution to obtain the sterilized liquid; (5) Aliquot the sterilized liquid into sterilized transparent colorimetric flasks, let it stand still to cool down, and obtain the gel turbidity standard substance indicating different turbidity values.

[0014] Preferably, in step (1), the stirring temperature is 80°C - 90°C, and the stirring and dissolving time is 1 - 10 h, more preferably 2 - 4 h.

[0015] Preferably, the microporous membrane in step (2) preferably has a micropore diameter ≤ 0.45 μm.

[0016] Preferably, during the stirring and heating process in step (3), keep the filtrate temperature > 60°C, and the stirring time is 1 - 12 h.

[0017] Preferably, in step (4), use moist heat sterilization at a temperature of 121°C for 15 - 30 min.

[0018] Preferably, the gel turbidity standard substance in step (5) needs to stand and form at 2°C - 30°C, preferably 2°C - 10°C, and the forming and curing time > 5 h.

[0019] Compared with the prior art, the solid turbidity standard substance prepared by the present invention has excellent static stability, can be stored under conventional conditions, can be reused without the need to prepare it immediately before use, reduces the influence of human factors during the use process, reduces the economic cost, is green and safe, avoids environmental and health risks, and can meet the needs of turbidity measurement for various ranges. Specific Embodiments

[0020] The following describes the present invention based on embodiments, but the present invention is not limited to these embodiments only.

[0021] The turbidity of the turbidity standard substance described in the present invention is measured using a turbidimeter (model WZB - 170, Leici).

[0022] Example 1 Preparation of 10.0 NTU Turbidity Standard Substance A solid turbidity reference material, and its preparation method includes the following steps: Place the reactor in a constant temperature water bath, add 100 ml of deionized water, then add 0.060 g of low-acyl gellan gum, turn on the reflux condenser, heat up to 80 °C, and stir to fully dissolve the raw materials for 2 h. Filter the above solution while it is hot through a 0.45-μm polytetrafluoroethylene (PTFE) microporous membrane while keeping the temperature (keep the filtrate temperature at 60 °C) to remove insoluble impurities. Pour the filtrate into a three-necked flask, continue heating, keep the temperature at 90 °C, then add 0.057 g of anhydrous calcium chloride thereto, and stir to dissolve and mix evenly. Then transfer the above solution to an autoclave, set the conditions: 121 °C, 15 minutes, and perform moist heat sterilization. Subsequently, quickly dispense the above hot solution (keep the temperature at 60 °C) into sterilized transparent colorimetric flasks, and let it stand and cool in a freezer to form (temperature 8 °C, forming and aging time 10 h) to obtain a solid gel turbidity reference material. After comparing and calibrating with a primary reference material, a turbidity reference material with a standard value of 10.0 NTU is obtained.

[0023] Example 2 Preparation of 50.0 NTU Turbidity Reference Material A solid turbidity reference material, and its preparation method includes the following steps: Place the reactor in a constant temperature water bath, add 100 ml of deionized water, then add 0.10 g of low-acyl gellan gum, turn on the reflux condenser, heat up to 85 °C, and stir to fully dissolve the raw materials for 2 h. Filter the above solution while it is hot through a 0.45-μm polytetrafluoroethylene (PTFE) microporous membrane while keeping the temperature (keep the filtrate temperature at 60 °C) to remove insoluble impurities. Pour the filtrate into a three-necked flask, continue heating, keep the temperature at 80 °C, then add 0.305 g of anhydrous magnesium chloride thereto, and stir to dissolve and mix evenly. Then transfer the above solution to an autoclave, set the conditions: 121 °C, 15 minutes, and perform moist heat sterilization. Subsequently, quickly dispense the above hot solution (keep the temperature at 60 °C) into sterilized transparent colorimetric flasks, and let it stand and cool at 10 °C in a refrigerator to form (aging time 8 h) to obtain a solid gel turbidity reference material. After comparing and calibrating with a primary reference material, a turbidity reference material with a standard value of 50.0 NTU is obtained.

[0024] Example 3 Preparation of 100.0 NTU Turbidity Reference Material A solid turbidity reference material, and its preparation method includes the following steps: Place the reactor in a constant temperature water bath, add 100 ml of deionized water, then add 0.30 g of low-acyl gellan gum, turn on the reflux condenser, heat up to 85 °C, and stir to fully dissolve the raw materials for 3 hours. Filter the above solution through a 0.45 μm polytetrafluoroethylene (PTFE) microporous membrane while keeping it warm (maintain the filtrate temperature at 60 °C) to remove insoluble impurities. Pour the filtrate into a three-necked flask, continue heating, keep the temperature at 80 °C, then add 0.196 g of zinc sulfate thereto, and stir to dissolve and mix evenly. Then transfer the above solution to an autoclave, set the conditions: 121 °C, 18 minutes, and perform moist heat sterilization. Subsequently, quickly dispense the above hot solution (maintain the temperature at 70 °C) into sterilized transparent colorimetric flasks, and let it stand and cool down to form in a refrigerator at 10 °C (aging time: 6 hours) to obtain a solid gel turbidity reference material. After comparing and calibrating with a primary reference material, a turbidity reference material with a standard value of 100.0 NTU is obtained.

[0025] Example 4 Preparation of 200.0 NTU Turbidity Reference Material A solid turbidity reference material, and its preparation method includes the following steps: Place the reactor in a constant temperature water bath, add 100 ml of deionized water, then add 0.30 g of low-acyl gellan gum, turn on the reflux condenser, heat up to 80 °C, and stir to fully dissolve the raw materials for 4 hours. Filter the above solution through a 0.45 μm polytetrafluoroethylene (PTFE) microporous membrane while keeping it warm (maintain the filtrate temperature at 60 °C) to remove insoluble impurities. Pour the filtrate into a three-necked flask, continue heating, keep the temperature at 80 °C, then add 0.457 g of anhydrous magnesium sulfate thereto, and stir to dissolve and mix evenly. Then transfer the above solution to an autoclave, set the conditions: 121 °C, 20 minutes, and perform moist heat sterilization. Subsequently, quickly dispense the above hot solution (maintain the temperature at 70 °C) into sterilized transparent colorimetric flasks, and let it stand and cool down to form in a refrigerator at 10 °C (aging time: 5 hours) to obtain a solid gel turbidity reference material. After comparing and calibrating with a primary reference material, a turbidity reference material with a standard value of 200.0 NTU is obtained.

Claims

1. A solid turbidity standard substance, comprising gellan gum, a metal salt and deionized water; the gellan gum content is 0.03-1.0wt%, and the metal cation concentration is 1-100 (mmol / L); preferably, the gellan gum content is 0.05-0.5wt%, and the metal cation concentration is 5-60 (mmol / L).

2. The standard substance according to claim 1, characterized in that The metal salt is a divalent metal salt, and the divalent metal salt is preferably a soluble salt of calcium, magnesium, zinc, or barium. The salt is one of sulfate, nitrate, and halide, and the halide is preferably chloride or bromide.

3. The standard substance according to claim 1, characterized in that The gellan gum is preferably low-acyl gellan gum, with an acetyl content of less than 2.0 wt %, a glycerol acyl content of less than 1.0 wt %, and a total ash content of ≤15 wt %.

4. The standard substance according to claim 1, characterized in that The solid turbidity standard substance can be formed by standing still at 2°C-30°C, preferably refrigerated at 2°C-10°C.

5. A method for preparing the solid turbidity standard substance according to any one of claims 1 to 4, comprising the following steps: (1) adding gellan gum powder to deionized water and heating it to dissolve it while stirring to obtain a gellan gum dispersion; (2) filtering the gellan gum dispersion through a microporous filter membrane while hot to remove insoluble impurities; (3) adding a metal salt under stirring and heating conditions to obtain a mixed solution; (4) sterilizing the mixed solution to obtain a sterilized liquid; (5) The sterilized liquid is dispensed into sterile transparent colorimetric bottles and allowed to stand to cool and form into gel turbidity standard substances indicating different turbidity values.

6. The method according to claim 5, characterized in that The stirring temperature in step (1) is 80°C-90°C, and the stirring and dissolving time is 1-12h, more preferably 2-4h.

7. The method according to claim 5, characterized in that The microporous filter membrane in step (2) preferably has a pore size of ≤0.45 μm.

8. The method according to claim 5, characterized in that During the stirring and heating process in step (3), the filtrate temperature is maintained at >60°C and the stirring time is 1-12 hours.

9. The method according to claim 5, characterized in that In step (4), moist heat sterilization is performed at a temperature of 121°C for 15-30 min.

10. The method according to claim 5, characterized in that The gel turbidity standard substance in step (5) needs to be at 0°C-30°C, preferably 2°C-10°C, and the molding and aging time should be greater than 5h.