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6.
Result calculation
(1) Data logging
(2) Result calculation
Where X——the ash content in the sample, g/100g
m 1 ——the mass of crucible and ash, g
m 2 ——the mass of the crucible, g
m 3 ——the mass of the crucible and the sample, g
The measurement result retains two significant digits (three significant digits are retained when the ash content is greater than or equal to 10g/100g, and two significant digits are retained when the ash content is less than 10g/100g)
.
7.
Tips
(1) This method is applicable to the determination of ash in foods other than starch and its derivatives
.
(2) Pretreatment of different types of samples
① Solid samples with low moisture content (cereals, beans): pulverize, sieving, and weighing → carbonization
.
②Liquid samples (milk, fruit juice): weighing → steaming in a water bath
.
③Samples with high water content (if vegetable): prepare uniform sample→weigh→dry in oven
.
④Fat-rich samples (animal products, cheese, etc.
): weighing→drying→fat-lifting (to prevent expansion or burning during carbonization)
⑤ Samples rich in sugar, protein and starch: add pure vegetable oil or octanol to prevent foaming before carbonization
.
⑥ For food samples such as beans and their products with high phosphorus content, meat and poultry products, egg products, aquatic products, milk and dairy products, the magnesium acetate method is used for ashing (see "Related Links")
.
(3) Purpose of carbonization Carbonization is the process of oxidizing the organic matter in the sample into carbon particles at low temperature
.
Its purpose: ① prevent the sample from flying due to the rapid evaporation of the water in the sample at high temperature during burning; ② prevent the foaming and swelling substances such as sugar, protein , starch, etc.
from foaming and expanding at high temperature and overflowing the crucible; ③ Ashing directly without carbonization, the carbon particles are easy to be encased, and the ashing is incomplete
(4) The main points of operation during the burning and cooling of the sample
①When putting the crucible into the high-temperature furnace or taking it out of the furnace, it should be placed in the furnace mouth for a while to preheat or cool the crucible to prevent the crucible from rupturing due to drastic temperature changes
②Clamp the crucible in the furnace after preheating the crucible tongs to prevent the crucible from cracking due to large temperature differences
③The sintered crucible should be cooled to below 200℃ and then moved into the desiccator.
④The hot crucible will heat the air in the desiccator.
⑤When taking out the cooled crucible field from the desiccator, because the inside is vacuum, air should be allowed to enter slowly when the cover is opened to restore normal pressure to prevent the residual ash from flying
⑥The used crucible should be discarded in time.
(5) See "Related Links" for the selection of ashing conditions
(6) The residue obtained from the determination of total ash can be used for the determination of other ash, and can also be reserved for the analysis of Ca, P, Fe and other components
Related Links: Determination of Total Ash in Flour (1)
