Lasker and Enkelwitz Test for Ketoses

The Lasker and Enkelwitz test utilizes Benedict's solution, although the reaction is carried out at a much lower temperature. The color changes that are seen during this test are the same as with Benedict's solution. Use DILUTE sugar solutions with this test (0.02 M).

Method

Add 1 ml of the solution to be tested to 5 ml of Benedict's solution to a test tube and mix well. The test tube is heated in a 55oC water bath for 10-20 minutes. Ketopentoses demonstrate a positive reaction within 10 minutes, while ketohexoses take about 20 minutes to react. Aldoses do not react positively with this test.