Mercury vapor release in TKN method

Andrew D. Eaton
Montgomery Labs Inc., Pasadena, Calif.

Chemical & Engineering News (15 Feb 1993) Vol. 71, No. 7, pp. 2.

As chairman of the Joint Editorial Board of Standard Methods for the Examination of Water & Wastewater, I wanted to follow up on several letters that appeared in the August and September issues of C&EN regarding the hazards associated with the use of mercury as a catalyst in the total Kjeldahl nitrogen (TKN) method (Aug. 10, 1992, page 2; Sept. 14, 1992, page 2). Although the 17th and 18th editions of "Standard Methods" discuss the dangers of using mercury as a catalyst (4500 Norg: section A. Introduction, 4. Use of a Catalyst), it is our goal wherever possible to eliminate the use of mercury in our methods.

The Standard Methods Joint Task Group for Organic Nitrogen is currently evaluating the use of copper salts to replace mercuric sulfate as a catalyst in the procedure. The modified method is expected to be published in the 19th edition of "Standard Methods" after the joint task group has verified the effectiveness of the new catalyst via laboratory testing.

In the meantime, it is recommended that any analyst using the macro-Kjeldahl method from "Standard Methods" take special precautions regarding the use of mercuric sulfate as a catalyst, including reviewing the material safety data sheet and conducting distillation in a properly vented hood. Special care should also be taken if metallic mercury is observed to form in the digestion apparatus.

It should be noted that EPA is also actively pursuing the replacement of mercury as a catalyst in the TKN method with other catalysts.

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