Reaction-Rate Method for Determining Protein Nitrogen in Grains and Feeds

Abstract In a new automated reaction-rate method for the quantitative determination of protein nitrogen in grains and feeds, the ammonia-sodium phenate-hypochlorite reaction is used for the reaction-rate determination. After samples are digested by the official AOAC block digestion procedure, automated instrumentation is used to precisely and rapidly combine the reactants and transfer the mixed solution to an automated spectrophotometer. The rate of formation of the indophenol during 15 sec at 635 nm is automatically determined and compared with rates obtained for nitrogen standards to determine the protein nitrogen content in the sample. Relative standard deviations of about 0.6% are obtained. Results for grain and feed samples are comparable to those obtained by the official AOAC method.

Download Full-text

Automated Determination of Crude Protein, Phosphorus, Calcium, Iron, and Magnesium in Feeds by Using Stopped-Flow Analyzer

Journal of AOAC INTERNATIONAL ◽

10.1093/jaoac/66.1.188 ◽

1983 ◽

Vol 66 (1) ◽

pp. 188-196

Author(s):

Michael A Koupparis ◽

Eleftherios P Diamandis ◽

Howard V Malmstadt

Keyword(s):

Crude Protein ◽

Reaction Rate ◽

Stopped Flow ◽

Relative Standard ◽

Rate Method ◽

Blue Reaction ◽

Calcium Iron ◽

Phosphomolybdenum Blue ◽

Feed Samples

Abstract Methods are described for determination of crude protein, phosphorus, calcium, iron, and magnesium in feeds, using an automated microprocessor-based stopped-flow analyzer. Crude protein is determined by a reaction-rate procedure based on the ammonia- sodium phenate-hypochloride Berthelot reaction. Phosphorus determination is based on a phosphomolybdenum blue reaction-rate method. o-Cresolphthalein complexone, ferrozine, and calmagite are used as colorimetric reagents for calcium, iron, and magnesium, respectively. The methods are precise with relative standard deviations less than 1%, rapid with analysis rates of 110-266 samples per hour, sensitive, and require less than 1 mL sample and reagent volumes. Results for feed samples are comparable with those obtained by official AOAC methods.

Download Full-text

Total Protein Nitrogen: Evaluation and Comparison of Four Different Methods

Journal of AOAC INTERNATIONAL ◽

10.1093/jaoac/58.4.811 ◽

1975 ◽

Vol 58 (4) ◽

pp. 811-817 ◽

Cited By ~ 1

Author(s):

Larry L Wall ◽

Charles W Gehrke ◽

Terry E Neuner ◽

Robert D Cathey ◽

Paul R Rexroad

Keyword(s):

American Association ◽

Ammonium Salts ◽

Protein Nitrogen ◽

Accuracy And Precision ◽

Feed Control ◽

Relative Standard ◽

Close Range ◽

Kjeldahl Method ◽

Aoac Method ◽

Feed Samples

Abstract This laboratory has evaluated 2 automated nitrogen methods, the Kjel-Foss and the Missouri-Technicon with block digestor. A modified Kjeldahl method using a low level (40 mg) of CuS04 as a catalyst was also studied. These 3 methods were compared with the official AOAC Kjeldahl method. The experimental set numbered 22 samples, consisting of amino acids, ammonium salts, meals, grains, forages, and American Association of Feed Control Officials check feed samples. This set was analyzed in duplicate 3 independent times by each method. The accuracy and precision values for the 4 methods were excellent, within a very close range, and were equal or superior to the AOAC method. All 4 methods gave average relative standard deviations of <1 %. The 4 methods were compared for rapidity and timeliness of analysis, applicability, cost per sample, and labor and physical requirements to provide those who are responsible for protein nitrogen analysis with a basis for choosing a nitrogen method that would be most suitable for their needs.

Download Full-text

Microcomputer Controlled Titration for Determination of Protein Nitrogen in Feeds and Wheat

Journal of AOAC INTERNATIONAL ◽

10.1093/jaoac/62.5.969 ◽

1979 ◽

Vol 62 (5) ◽

pp. 969-975

Author(s):

Alan H B Wu ◽

Taddeo Rotunno ◽

Howard V Malmstadt

Keyword(s):

Standard Deviation ◽

Copper Catalysts ◽

Protein Nitrogen ◽

Sample Number ◽

Testing Program ◽

Direct Titration ◽

Relative Standard ◽

Automatic Titrator ◽

Feed Samples

Abstract The determination of protein nitrogen in feeds and wheat by microcomputer controlled titration is described. The method involves direct titration of ammonia with standard hypochlorite titrant in the presence of bromide. The titrant is delivered by an automatic buret, and the microcomputer controlled, automatically computed potentiometric end points are precise to 0.1% over a 5-fold concentration range of nitrogen. Digestions performed with both mercury and copper catalysts show comparable results. Samples are weighed before digestion by an electronic balance interfaced to the computer which records sample number and weight. An automatic pipet aliquots, dilutes, and buffers samples directly from the digestion tubes; the samples can be immediately titrated with the automatic titrator. The results for protein in NBS standards and check feed samples from an official testing program compare closely with average values reported for these standards. Results show that feed and wheat samples contained 10- 100% protein. Precision for successive aliquots of the same digests is 0.1-0.4% relative standard deviation; precision for multiple digestions of the same sample is 0.1-0.8%.

Download Full-text

A kinetic method for the determination of phenol

Journal of the Serbian Chemical Society ◽

10.2298/jsc0210661m ◽

2002 ◽

Vol 67 (10) ◽

pp. 661-667 ◽

Cited By ~ 9

Author(s):

Snezana Mitic ◽

Valentina Zivanovic

Keyword(s):

Standard Deviation ◽

River Water ◽

Reaction Rate ◽

Kinetic Method ◽

Potassium Periodate ◽

Experimental Conditions ◽

Inhibiting Effect ◽

Relative Standard ◽

Kinetic Expression

Akinetic method for the determination of phenol is proposed. The method is based on the inhibiting effect of phenol on the Mn(II) catalysis of the oxidation of malachite green with potassium periodate. The reaction rate was followed spectrophotometrically at 615 nm. Kinetic expression for the reaction in the presence and absence of phenol are postulated. The optimal experimental conditions for the determination of phenol were established and phenol was determined in concentrations from 30.0 to 188.0 ng/cm3 with a relative standard deviation of 5.5%. The lower detecton limit is 7.8 ng/cm3. The effects of certain foreign ions upon the reaction rate were determined for the assessment of the selectivity of the method. The method was applied for the determination of phenol in tap and river water.

Download Full-text

A Simplified Modification of the AOAC Official Method for Determination of Total Dietary Fiber Using Newly Developed Enzymes: Preliminary Interlaboratory Study

Journal of AOAC International ◽

10.1093/jaoac/90.1.225 ◽

2007 ◽

Vol 90 (1) ◽

pp. 225-237 ◽

Cited By ~ 6

Author(s):

Kenichiro Kanaya ◽

Shusaku Tada ◽

Bunpei Mori ◽

Rie Takahashi ◽

Sachie Ikegami ◽

...

Keyword(s):

Dietary Fiber ◽

Enzymatic Digestion ◽

Interlaboratory Study ◽

Total Dietary Fiber ◽

Stabilizing Agents ◽

Modified Method ◽

Relative Standard ◽

Aoac Method ◽

Standard Deviations

Abstract A preliminary interlaboratory study was conducted to evaluate the validity of the modified AOAC method for determination of total dietary fiber by Tada and Innami, in which the 3-step enzymatic digestion process in AOAC Method 991.43 is modified to a 2-step process without pH adjustment. Total dietary fiber contents in 8 representative foodstuffs were measured using both the original AOAC Method 991.43 and the modified method in 6 research facilities in Japan. Repeatability relative standard deviations, reproducibility relative standard deviations, and Horwitz ratio values from the modified method were equivalent to those from AOAC Method 991.43, except in the rice sample. However, this exceptional case shown in the modified method was entirely dissolved by the addition of α-amylase stabilizing agents. The modified method, which shortens the process of enzymatic digestion from 3 to 2 steps and in which only reaction temperature is adjusted under the same pH, was found not only to give accurate values comparable to the original method, but also to substantially reduce the labor required by the laboratory staff in the process of routine analysis. This study revealed that the validity of the modified method was further ensured by adding α-amylase stabilizing agents to the reaction system.

Download Full-text

Determination of Protein Nitrogen in Plants

Journal of AOAC INTERNATIONAL ◽

10.1093/jaoac/60.3.590 ◽

1977 ◽

Vol 60 (3) ◽

pp. 590-593 ◽

Cited By ~ 1

Author(s):

T Powell Gaines

Keyword(s):

Acetic Acid ◽

Plant Tissue ◽

Nonprotein Nitrogen ◽

Protein Nitrogen ◽

Aoac Method ◽

The Mean

Abstract A method is described for determining protein nitrogen (PN) in plants. Plant tissue extracted with 0.5% acetic acid to remove nonprotein nitrogen (NPN) prior to Kjeldahl analysis gave results very close to true PN, whereas AOAC crude PN method 2.049 gave results much too high. True PN was determined as the mean of 3 independently derived values and was used as the basis for comparing the proposed PN method with AOAC method 2.049. Failure of the AOAC method to differentiate between NPN and/or inorganic ammoniacal N and actual PN causes values derived from this method to be too high when it was used to determine PN in plants.

Download Full-text

Optimization of an Aqueous Two-Phase System for the Determination of Trace Ethyl Carbamate in Red Wine

Journal of Food Protection ◽

10.4315/0362-028x.jfp-18-594 ◽

2019 ◽

Vol 82 (8) ◽

pp. 1377-1383 ◽

Cited By ~ 1

Author(s):

LIJUAN MA ◽

WENZHE TONG ◽

LIPING DU ◽

SHIYONG HUANG ◽

JINYAN WEI ◽

...

Keyword(s):

Quantitative Determination ◽

Red Wine ◽

Ethyl Carbamate ◽

Phase System ◽

Extraction Temperature ◽

Two Phase ◽

Aqueous Two Phase System ◽

Relative Standard ◽

Standard Deviations

ABSTRACT In this study, a novel method using gas chromatography–mass spectrometry coupled with ethanol and K2HPO4 aqueous two-phase system (ATPS) was established for the quantitative determination of trace ethyl carbamate (EC) in red wine. The parameters that influence EC extraction in an aqueous two-phase system, including extraction temperature, time, pH, and ethanol concentration, were optimized. Method validation results indicated that the regression coefficient of the proposed method was 0.9979 in the linear range of 10 to 100 μg/L, and the limits of detection and quantification were 2.8 and 9.2 μg/L, respectively. Four red wine samples made from different grape varieties were processed by the proposed method for the repeatability verification, and EC concentrations were between 15.8 and 37.3 μg/L, with the relative standard deviations ranging from 3.5 to 6.6%. Results of the precision assay showed the average recovery of EC in red wine at 95.4 to 107.1%, with the relative standard deviations ranging from 1.4 to 6.2%. This method proved to be simple and reliable for quantitative determination of trace EC in red wine and would give guidance for quality monitoring of various red wines in the production process.

Download Full-text