GB/T 27985-2011 English PDF (GBT27985-2011)

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GB/T 27985-2011: Determination of tannin in feeds -- Spectrophotometry
GB/T 27985-2011
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 65.120
B 46
Determination of tannin in feeds - Spectrophotometry
ISSUED ON: DECEMBER 30, 2011
IMPLEMENTED ON: JUNE 01, 2012
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine;
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 and solutions ... 4
5 Instruments and equipment ... 5
6 Sample preparation ... 6
7 Analysis steps ... 6
8 Calculation and expression of results ... 7
9 Repeatability ... 7
Determination of tannin in feeds - Spectrophotometry
1 Scope
This Standard specifies the spectrophotometry for the determination of tannin in feeds.
This Standard applies to the determination of tannin content in compound feeds and
single feeds.
The detection-limit of this method is 17.5 mg/kg, and the linear range is 0.50 mg/L ~
6.00 mg/L.
2 Normative references
The following referenced documents are indispensable for the application of this
document. For dated references, only the edition cited applies to this document. For
undated references, the latest edition (including any amendment) applies to this
document.
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
Use acetone solution to extract tannin compounds in the feed; after filtration, take the
filtrate, add sodium tungstate-phosphomolybdic acid mixed solution and sodium
carbonate solution; after color development, use the reagent as a blank control; use a
spectrometer to determine the absorbance value at a wavelength of 760 nm; use tannic
acid as a standard curve to determine the tannin content in the feed.
4 Reagents and solutions
Unless otherwise specified, the reagents used in this Standard shall be analytical
reagents, and the water shall comply with the provisions of GB/T 6682 for grade-3
water.
4.1 Sodium tungstate (Na2O4W·2H2O).
4.2 Phosphomolybdic acid (H3Mo12O40P·XH2O).
5.8 Erlenmeyer flask with stopper: 250 mL.
5.9 Medium-speed quantitative filter paper.
6 Sample preparation
Take samples according to GB/T 14699.1; prepare samples according to GB/T 20195.
Grind them; pass them through a 0.45 mm sieve; mix well; put them in airtight
containers; store them at low temperature in the dark for future use.
7 Analysis steps
7.1 Preparation of test solution
Weigh 1 g ~ 2 g of the sample (accurate to 0.000 1 g); put it into a 250 mL Erlenmeyer
flask with stopper (5.8); add 50.00 mL of acetone solution (4.7) accurately; seal it with
a stopper; place it on an oscillator (5.4) and shake for 40 min; let it stand still; use
medium-speed quantitative filter paper (5.9) to filter; discard the initial filtrate, and
continue the filtration for determination.
7.2 Determination
7.2.1 Drawing of the standard curve
Accurately measure 0.00 mL, 0.50 mL, 1.00 mL, 2.00 mL, 3.00 mL, 4.00 mL, 5.00 mL
and 6.00 mL of tannic acid standard solution (4.10); respectively put them into 50 mL
volumetric flasks filled with about 30 mL of water; shake well; add 2.5 mL of sodium
tungstate-phosphomolybdic acid mixed solution (4.3); add 5.0 mL of sodium carbonate
solution (4.5); shake well; use water to dilute to 50 mL respectively; shake well. The
concentration of tannic acid standard solution is 0.00 mg/L, 0.50 mg/L, 1.00 mg/L, 2.00
mg/L, 3.00 mg/L, 4.00 mg/L, 5.00 mg/L and 6.00 mg/L respectively. Let it stand for 30
min; after color development, use 0.00 mg/L of the standard curve as the blank; measure
the absorbance of the standard solution at a wavelength of 760 nm; draw the standard
curve with the concentration of tannin as the abscissa and the absorbance value as the
ordinate.
7.2.2 Determination of sample
Accurately measure 1.00 mL of the test solution (7.1); put it into a 50 mL volumetric
flask filled with about 30 mL of water; shake well; add 2.5 mL of sodium tungstate-
phosphomolybdic acid mixed solution (4.3); add 5.0 mL of sodium carbonate solution
(4.5); shake well; use water to dilute to 50 mL; shake well. Let it stand for 30 min to
develop color; then, use 0.00 mg/L of the standard curve as a blank; measure the
absorbance of the sample solution at a wavelength of 760 nm; obtain the concentration
of tannin in the test solution (7.1) according to the standard curve. If the absorbance