Method for measuring water activity by using vapor pressure and device thereof

A moisture and activity technology, applied to the analysis of materials, instruments, etc., can solve the problems of long measurement time, difficult to popularize, expensive measuring instruments, etc., and achieve the effect of easy production and clear device structure

Inactive Publication Date: 2010-12-01
黄鸿兵 +1
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  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0006] At present, the methods for measuring water activity at home and abroad mainly include double heat balance method, graphical incision method, freezing point depression method, pressure measurement method, humidity measurement method, dew point measurement method, etc. to determine the water activity of materials, and the market has also appeared direct Instruments for measuring water activity, but the price of these measuring instruments is relatively expensive, and the price of some imported instruments reaches tens of thousands of RMB
Among the many methods for measuring water activity in the laboratory, the graphical incision method is often used. This method is used in the determination of the water activity of meat products issued by my country. The disadvantage of the graphical incision method is that the measurement time is very long. It takes two hours or even longer to reach the equilibrium of moisture absorption and dehumidification under certain conditions
There are also some foreign articles that use the water vapor pressure of materials to calculate the water activity, and the accuracy and precision are good. However, the devices used in these experiments need liquid nitrogen cooling, precise temperature control at each point and other measures. The calculation equation Involving too many impact factors, it is difficult to promote

Method used

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  • Method for measuring water activity by using vapor pressure and device thereof
  • Method for measuring water activity by using vapor pressure and device thereof
  • Method for measuring water activity by using vapor pressure and device thereof

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0035] Embodiment 1: material preparation

[0036] Using pure water (18.2MΩ, water activity 1.000) as solvent, respectively prepare analytically pure saturated inorganic salt solutions, the water activities of saturated solutions of potassium nitrate, sodium chloride, potassium carbonate and sodium hydroxide under various temperature conditions are known. The degree is shown in Table 1, which has been recognized by domestic and foreign literature. Fill the saturated solution into a brown bottle and keep it away from light. The U-shaped tube of the vapor pressure measuring device is filled with high-vacuum silicone oil, connected to a vacuum pump, and vacuumed to drive away the air in the vacuum silicone oil.

Embodiment 2

[0037] Embodiment 2: Method linear range and correlation:

[0038] Measure the vapor pressure height difference of the standard inorganic salt solution by a vapor pressure device, take the oil column height difference (mm) as the abscissa, and take the water activity as the ordinate to draw a standard curve ( figure 2 ), linear regression analysis was carried out according to the obtained curve, and the linear regression equation and correlation coefficient (Table 2) under the conditions of 15°C, 20°C, and 25°C were obtained. The results showed that the linear relationship of water activity ranged from 0.070 to 1.000 was good.

[0039] Table 1 Aw values ​​of standard water active substances at 15°C, 20°C, and 25°C

[0040]

[0041] Table 2 Regression equation and correlation coefficient (n=5) of standard water-active substances at 15°C, 20°C, and 25°C

[0042]

Embodiment 3

[0043] Example 3: Repeatability

[0044] As shown in Table 3, the corresponding vapor pressure oil column height difference (mm) was measured for each standard water activity substance at 15°C, 20°C, and 25°C, and each sample was measured 5 times. Each substance showed good repeatability, and the relative standard deviations were all below 10%.

[0045] Table 3 Precision Table of Oil Column Height Difference of Standard Water Activity Substances at 15°C, 20°C, and 25°C

[0046]

[0047] Note: RSD is relative standard deviation (standard deviation )

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Abstract

The invention relates to a method for calculating corresponding water activity by using water vapor pressure of a measured material. The invention designs a set of vapor pressure measuring device. The device is mainly characterized in that: a sample bottle, a U-shaped tube and a vacuum pump are connected outside a closed glass tube. The device has clear structure and easy manufacture. The water activity calculating method is simple and convenient, quick in measurement, sensitive and accurate; and the measuring time of a single sample is about 20 minutes. The method provides guarantee for widely measuring the water activity in a working process.

Description

technical field [0001] The invention relates to a method and the design of a device for measuring the water activity of materials by using vapor pressure. Background technique [0002] Moisture in food, wood and other materials exists in different states such as free water and bound water. Water in different states can be divided into two categories: the water connected by hydrogen bonding is called bound water; the water connected by capillary force is called free water. Among them, free water is the water that is easily used by microorganisms, biological enzymes and other biologically active substances, and is related to the properties directly related to the quality of materials such as preservation and texture. Therefore, the level of water content in food does not directly reflect the amount of water that can be used by microorganisms. In order to quantitatively explain the water state in materials, the concept of water activity (Water Activity, Aw) is introduced. The ...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01N7/14
Inventor 黄鸿兵吴光红
Owner 黄鸿兵
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