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Guide kjeldahl A Guide To Kjeldahl Nitrogen Determination Methods and Apparatus An Industry Service Publication CForward This booklet has been developed to serve as a technical companion in the selection and use of Kjeldahl nitrogen determination methods

A Guide To Kjeldahl Nitrogen Determination Methods and Apparatus An Industry Service Publication CForward This booklet has been developed to serve as a technical companion in the selection and use of Kjeldahl nitrogen determination methods and apparatus This material has been prepared with the help of Kjeldahl chemists consultants and Labconco engineers It will not teach you to perform the Kjeldahl procedure but will help you understand steps in the process This generic presentation is designed to help educate persons unfamiliar with Kjeldahl methodology and answer frequently asked questions raised by Kjeldahl users CHistory Nitrogen determination has a long history in the area of analytical chemistry Johan Kjeldahl ?rst introduced the Kjeldahl nitrogen method in at a meeting of the Danish Chemical Society As chairman of the chemistry department of the Carlsberg Laboratorium near Copenhagen Kjeldahl was assigned to scienti ?cally observe the processes involved in beer making While studying proteins during malt production he developed a method of determining nitrogen content that was faster and more accurate than any method available at the time His method used simple equipment and could be performed by an inexperienced technician Applications Since the Kjeldahl method has gained wide acceptance and is now used for a variety of applications Kjeldahl nitrogen determinations are performed on food and beverages meat feed grain waste water soil and many other samples The method has been re ?ned and tested for a wide variety of substances and approved by various scienti ?c associations including AOAC International formerly the Association of O ?cial Analytical Chemists Association of American Cereal Chemists American Oil Chemists Society Environmental Protection Agency International Standards Organization United States Department of Agriculture What is the Kjeldahl method The Kjeldahl method is a means of determining the nitrogen content of organic and inorganic substances Although the technique and apparatus have been altered considerably over the past years the basic principles introduced by Johan Kjeldahl endure today The Kjeldahl method may be broken down into three main steps Digestion - the decomposition of nitrogen in organic samples utilizing a concentrated acid solution This is accomplished by boiling a homogeneous sample in concentrated sulfuric acid The end result is an ammonium sulfate solution Distillation - adding excess base to the acid digestion mixture to convert NH to NH followed by boiling and condensation of the NH gas in a receiving solution Titration - to quantify the amount of ammonia in the receiving solution The amount of nitrogen in a sample can be calculated from the quanti ?ed amount of ammonia ions in the receiving solution The Digestion Process A general equation for the digestion of an organic sample is shown below as one basic example Organic N H SO ? NH SO H O CO other sample matrix by-products A number of interrelated digestion conditions determine the rate of reaction and the completeness of the breakdown of nitrogen to ammonium sulfate Among these are heat input to the acid digestion mixture amount of inorganic salt added to elevate