The calcium content in the feed is an important indicator of feed quality. According to the growth needs of different livestock and poultry, the feed standard has specified various calcium content indicators for livestock and poultry feed. Excessive calcium will reduce the digestibility of the diet; if the calcium is insufficient, it will easily cause the diseased animals to suffer from rickets and rickets.
At present, the determination of calcium in feed is mainly carried out by potassium permanganate redox titration, EDTA complex titration and atomic absorption spectrophotometry. However, the performance of potassium permanganate is unstable, and the operation is cumbersome and time consuming; while the measurement results of the EDTA method are relatively large; the atomic absorption spectrophotometry is also difficult to popularize due to the expensive instrument. We studied the color reaction and conditions of tribromoarsenazo (abbreviated TBA) and calcium. The results show that it can be used for the determination of trace calcium in feed, which is simple, rapid, and accurate.
1 Main instruments and reagents to obtain
1.1 Instrument
High temperature electric furnace: controllable temperature 550 ± 20 °C; analytical balance: sensitivity 0.0001g; 722 spectrophotometer; PHS-25 acidity agent.
1.2 Reagent calcium standard solution
Weigh 0.2498g of reference calcium carbonate dried to constant weight at 105 ~ 110 °C, dissolve in a mixture of 1mL hydrochloric acid and 10mL water, then transfer it to a 100mL volumetric flask, dilute with water to the mark, and dilute to 10 μg when used. mL.
1.3 NH 3 -NH 4 Cl Buffer
Weigh 27g of NH 4 Cl and dissolve it in an appropriate amount of water. Add 650mL of concentrated ammonia water and dilute to 1L to prepare a buffer with a pH of about 10.7. If PH < 10.5, it can be adjusted with an acidity agent.
1.4 Tribromoarsenazo solution (TBA solution)
0.25 g of tribromoarsenazo was weighed and dissolved in 500 mL of water to prepare a 0.05% aqueous solution.
2 Operation method
2.1 Ordinary spectrophotometry
Accurately transfer a certain amount (5 ~ 60 μg) of calcium standard solution (or treated sample solution) into a 50mL colorimetric tube (or volumetric flask), and then add 6mL 0.05% TBA solution, 10mL NH 3 -NH 4 Cl buffer, dilute to the mark with water, shake well, use the reagent blank at 605nm as the reference to measure the absorbance of the mixed color solution, and make the working curve.
2.2 Tribromoarsenazo method (dual wavelength spectrophotometry)
Based on the 2.1 method of operation, the absorbance of the mixed test solution as the reference test solution blank at 490 nm is added, and the absorbance values ​​measured under different wavelengths and reference conditions are added together, ie, A. Double = A490 + A605, using A double value instead of A605 for calculation, the calculation method is the same as ordinary spectrophotometry.
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