Comparative experiment of glutinous rice moisture detector and national standard oven method
Abstract: Two times of drying, the moisture content of corn is greater than 15% or less than 9%. The first drying: Weigh about 100g of the sample with more than 15% water, and put it into a constant weight vessel to level it. Adjust corn moisture to 9% to 15% in an oven at 60-80 ° C. The adjusted sample is taken out of the oven and placed in the laboratory atmosphere for at least 2 h to reduce the sample to laboratory temperature.
National standard test method for moisture content of glutinous rice (oven method)
1. Subject content and scope of application
This standard specifies the instruments, operating procedures and results calculations used to determine the moisture content of crushed corn and whole corn. This standard applies to the determination of moisture content of crushed corn and whole corn.
2, the definition
The quality of corn smashed by drying at 130-133 ° C for 4 h and whole corn drying for 38 h is the moisture of corn.
3, the principle
The quality of corn drying loss was measured under normal pressure.
4, the instrument
4.1 balance: the sensitivity of 0.01g and 0.001g;
4.2 Crusher: honey seal, easy to clean, no heat when crushing;
4.3 metal dish or glass dish: no cover, can make a single layer of 100g corn kernels distributed at the bottom of the dish;
4.4 aluminum box or glass dish: with a sealed cover, diameter 5.5 ~ 6.0cm, height 3.5 ~ 4.0cm;
4.5 constant temperature oven: there is a blast device, the temperature is maintained at 60 ~ 80 ° C;
4.6 constant temperature oven: the temperature is maintained at 130 ~ 133 ° C;
4.7 Dryer: Contains an effective desiccant.
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5, the operation steps
5.1 Samples that do not require pulverization
The sample of 1.7 mm>particle size>1 mm does not exceed 10%, and the sample of particle size <0.5 mm exceeds 50%.
5.2 Samples to be crushed
5.2.1 Direct crushing
Directly pulverize the moisture content of corn at 9% to 15%. First, clean the pulverizer with a small amount of sample, discard the pulverized material, and then quickly pulverize about 30g of the sample, mix it evenly, and put it into a closed container for use. The second drying method in the secondary drying method.
5.2.2 drying twice
Two times of drying, the moisture content of corn is greater than 15% or less than 9%. The first drying: Weigh about 100g of the sample with more than 15% water, and put it into a constant weight vessel to level it. The corn moisture was adjusted to 9% to 15% in an oven at 60-80 ° C. The adjusted sample was taken out of the oven and placed in the laboratory atmosphere for at least 2 h to reduce the sample to laboratory temperature. Weigh the adjusted sample, then quickly pulverize about 39g, mix well, and put it in a closed container for later use. If the moisture is below 9%, weigh about 100 g of the sample and place it in the laboratory atmosphere until 9% to 15% of moisture is obtained. The second drying: Weigh about 8g of the sample with an aluminum box baked to constant weight, and put it into the bottom of the box to flatten. The aluminum cover is placed on the bottom of the box, placed in the baking net around the thermometer in the oven, and baked at 130-133 ° C for 4 h, then the aluminum box is taken out, capped, and placed in a desiccator to cool to room temperature and weighed.
5.3 whole sample
Using an aluminum box baked to constant weight, quickly weigh 25 to 40 g of the whole sample from 2 kg of the original sample, immediately cover the weighing, and then open the aluminum box containing the sample, and put it into the 130-133 ° C with the lid. In the oven, after drying for 38±2 hours, the aluminum box was taken out, placed in a desiccator, and cooled for 30 to 45 minutes.
6, the result of calculation
6.1 Direct pulverization, the moisture content of the whole sample is calculated according to formula (1):
M0-m1
Moisture (%)=─────×100---------------(1)
M0-m
Where: m--aluminum box quality, g;
M0--quality of sample and aluminum box before baking, g;
M1--quality of sample and aluminum box after baking, g;
6.2 The water content of the two drying samples is calculated according to formula (2):
M1×m3
Moisture (%) = (1 - ─ ─ -) × 100 ------------ (2)
M0×m2
Where: m0--the mass of the sample before the second bake, g;
M1--the mass of the sample after the second baking, g;
M2--the mass of the sample before the first bake, g;
M3--the mass of the sample after the first bake, g.
6.3 Number of measurements and allowable difference
The difference between the two test results is not more than 0.15%, and the average is obtained, which is the measurement result. The measurement result takes the second place after the decimal point.
Appendix A Absolute Method (Reference)
A1 application range
This method is only used to check and improve the method of moisture determination in corn, and is not used for arbitration analysis.
A2 instrument
A2.1 balance: Sensitivity 0.01g and 0.001g;
A2.2 vacuum pump: step down to 1.3 ~ 2.6kPa (equivalent to 1.3 ~ 2.6 mbar = 10 ~ 20mmHg);
A2.3 depressurization dryer: the volume allows storage of vessels containing 100g of corn kernels;
A2.4 glass cup: for storing phosphorus pentoxide;
A2.5 glass drying tube: divided into two parts, one part is placed on the sample tray, and the other part is placed in a cup containing phosphorus pentoxide to be connected with the vacuum pump;
A2.6 metal or glassware sample tray;
A2.7 constant temperature oven: with air blowing device, the temperature is maintained at 45 ~ 50 ° C, and the temperature is maintained at 130 ~ 133 ° C;
A2.8 Air Drying Curtain: A gas cylinder containing sulfuric acid (P20 ≥ 1.83 g/ml) was connected to a tube containing phosphorus pentoxide coated on glass fibers.
A3 reagent
The reagents used in this standard are of analytical grade. Dioxane (GB2305-80). Sulfuric acid (GB625-77).
A4 operation steps
A4.1 Samples that do not require pulverization
The sample of 1.7 mm>particle size>1 mm does not exceed 10%, and the sample of particle size <0.5 mm exceeds 50%.
A4.2 Samples to be pulverized
A4.2.1 direct smash
The moisture content of corn is 9% to 15%, which is directly pulverized. First, the pulverizer is cleaned with a small amount of sample, the pulverized material is discarded, and then about 30 g of the sample is quickly pulverized, uniformly mixed, and placed in a closed container for use. The following step is performed by the second drying operation in the twice drying method.
A4.2.2 drying twice
Two times of drying, the moisture content of corn is greater than 15% or less than 9%. The first drying: weigh about 100g of the sample with more than 15% water, put it into the constant weight of the vessel and flatten it, then put the vessel into the dryer, put a few 1cm thick in the dryer. When the cup of phosphorus pentoxide is depressurized to 1.3 to 2.6 kPa (corresponding to 10 to 20 mmHg) by a vacuum pump, the vacuum pump is turned off, the vacuum is maintained, and the sample is stored in a desiccator for about 2 to 4 days to adjust the moisture to 9%. ～15%, the air slowly enters the dryer through the drying curtain to restore atmospheric pressure, the sample is kept in the laboratory atmosphere for at least 24h, the temperature is reduced to the laboratory temperature, and then weighed, then quickly pulverized by about 30g, and evenly mixed. Put it in a closed container for use. If the moisture is below 9%, weigh about 100 g of the sample and place it in the laboratory atmosphere until 9% to 15% of moisture is obtained. The second drying: Weigh about 3g of the sample with a vessel that is baked to constant weight, and spread it to the bottom of the dish. Open the vessel containing the sample (the lid is left in the dryer) and place it on the closed end of the drying tube. Place the cup containing about 1 cm thick of phosphorus pentoxide near the sample vessel, fix the two parts of the drying tube, and open the vacuum pump. When pressing to 1.3~2.6kPa, close the vacuum pump, put the matching drying tube with sample into the oven with temperature control at 45~50°C, take out the tube from the oven after about 10h, cool to room temperature, connect the tube In the vacuum pump, the air is passed through the drying curtain into the drying tube, allowing it to return to atmospheric pressure, and the sample vessel is quickly taken out and covered with a weighing. The above operation is repeated until the sample mass is constant (for example, until the interval of 24 h, the difference between two consecutive weighings is less than 0.0006 g).
A5 result calculation
A6.1 Direct pulverization, the water content of the whole sample is calculated according to formula (A1):
M0-m1
Moisture (%) = ─────-×100---------------(A1)
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