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GB/T 6437-2018 English PDF (GBT6437-2018)

GB/T 6437-2018 English PDF (GBT6437-2018)

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GB/T 6437-2018: Determination of phosphorus in feeds -- Spectrophotometry

This Standard specifies the spectrophotometry for the determination of total phosphorus content in feeds. This Standard applies to the determination of phosphorus in feed ingredients and feed products. When the sampling volume is 5g and the volume is set to 100mL, the detection limit is 20mg/kg, and the quantification limit is 60mg/kg.
GB/T 6437-2018
GB
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 65.120
B 46
Replacing GB/T 6437-2002
Determination of phosphorus in feeds - Spectrophotometry
ISSUED ON: SEPTEMBER 17, 2018
IMPLEMENTED ON: APRIL 01, 2019
Issued by: State Administration for Market Regulation;
Standardization Administration of the People's Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Principle ... 4
4 Reagents or materials ... 5
5 Instruments and equipment ... 5
6 Specimen preparation ... 6
7 Analysis steps ... 6
8 Test data processing ... 7
9 Precision ... 8
Determination of phosphorus in feeds - Spectrophotometry
1 Scope
This Standard specifies the spectrophotometry for the determination of total phosphorus content in feeds.
This Standard applies to the determination of phosphorus in feed ingredients and feed products.
When the sampling volume is 5g and the volume is set to 100mL, the detection limit is 20mg/kg, and the quantification limit is 60mg/kg.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. GB/T 601, Chemical reagent - Preparations of standard volumetric solutions GB/T 602, Chemical reagent - Preparations of standard solutions for impurity GB/T 603, Chemical reagent - Preparations of reagent solutions for use in test methods
GB/T 6682, Water for analytical laboratory use - Specification and test methods GB/T 14699.1, Feeding stuffs - Sampling
GB/T 20195, Animal feeding stuffs - Preparation of test samples
3 Principle
The total phosphorus in the specimen is digested and formed yellow vanadium molybdenum yellow [(NH4)3PO4NH4VO3??16MoO3] complex with ammonium
vanadium molybdate under acidic conditions. The absorbance value of vanadium molybdenum yellow is proportional to the concentration of total phosphorus. Measure the absorbance value of vanadium molybdenum yellow in the specimen solution at a wavelength of 400nm. Perform quantitative comparison with standard series. 6 Specimen preparation
Take representative feed samples according to GB/T 14699.1. Use the quartering method to reduce to about 200g. Prepare samples according to GB/T 20195. Pass through an analytical sieve with a pore size of 0.42mm after crushing. Mix well. Put it into a grinding bottle for later use.
7 Analysis steps
7.1 Specimen pretreatment
7.1.1 Dry ashing method
Weigh 2g~5g of specimen, accurate to 1mg. Put in a crucible. Carefully conduct carbonization on the electric stove. Put into a high temperature furnace. Burn at 550??C for 3h (or continue to measure the crude ash). Take out and cool. Add 10mL of hydrochloric acid solution (4.3) and a few drops of nitric acid (4.1). Carefully boil about 10min. Transfer to a 100mL volumetric flask after cooling. Add water to dilute to the scale mark. Shake well. It shall be the specimen solution.
7.1.2 Wet digestion method
Weigh 0.5g~5g of specimen, accurate to 1mg. Put it in a Kjeldahl flask. Add 30mL of nitric acid (4.1). Carefully heat and boil until the yellow smoke escapes. Slightly cool. Add 10mL of perchloric acid (4.2). Continue to heat until perchloric acid emits white smoke (do not evaporate to dryness). The solution is basically colorless. Cool. Add 30mL of water. Heat it till it is boiling. After cooling, transfer to a 100mL volumetric flask with water and dilute to the scale mark. Shake well and it shall be the specimen solution.
7.1.3 Hydrochloric acid dissolution method (applicable to trace element premix) Weigh 0.2g~1g of specimen, accurate to 1mg. Place in a 100mL beaker. Slowly add 10mL of hydrochloric acid solution (4.3). Make them all dissolved. Transfer to 100mL volumetric flask after cooling. Add water to dilute to the scale mark. Shake well and it shall be the specimen solution.
7.2 Preparation of phosphorus standard working solution
Accurately pipette 0mL, 1mL, 2mL, 5mL, 10mL, 15mL of phosphorus standard stock solution (4.4) into 50mL volumetric flasks (that is, the phosphorus content is 0??g, 50??g, 100??g, 250??g, 500??g, 750??g). Add 10mL of ammonium vanadium molybdate
developer (4.5) to each volumetric flask. Use water to dilute to the scale mark. Shake well. Place it at room temperature for more than 10min. Take 0mL of phosphorus standard solution as reference. Use 1cm cuvette. Measure the absorbance of each

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