Kjeldahl: Blower or Water Ejector?

By Bob Applequist, Senior Application Specialist

On April 25, 2011 in Articles

In the late 1880's, Danish chemist Johan Kjeldahl developed an analytical chemistry method that measures the amount of nitrogen within a substance. The Kjeldahl Method has been used for over 100 years and has dozens of variations. The original method is still widely used and calls for large sample sizes, which in-turn, requires large vessels for boiling samples in acid at very high temperature.

Labconco's very first product was a Kjeldahl Nitrogen Determination Apparatus used by milling companies to test grain for protein content. We are still the sole provider of Macro Kjeldahl Digestion/Distillation Systems.

The first part of the method requires boiling samples in 800 ml vessels at 395° C. Each vessel contains approximately 15-20 ml of pure sulfuric acid. This creates a lot of extremely corrosive acid fumes which must be removed from the laboratory environment.

Labconco offer two types of fume removal devices in our Macro Kjeldahl products: The first type is our Blower Exhaust System. By using a highly corrosion-resistant integral blower that is connected to a fume removal digestion manifold, acid fumes are drawn off the digestion vessels and then pushed out the building through PVC ductwork. Once outside the building, the acid fumes are quickly diluted to safe concentrations by prevailing winds.

The second type of acid removal system is the Water Ejector Removal System. This device relies on large volumes of fast moving water flowing past the digestion manifold to create a vacuum. This vacuum aspiration effect draws the acid fumes out of the manifold where they and dissolve in the water, which drains into the sanitary system.

The acid dissolved in the water does not normally pose a problem for most municipal waster water systems. For proper operation the Water Ejector Removal System requires at least 60 psig pressure and a 6 to 8 gallon per minute flow rate to create a proper vacuum.

The Water Ejector Systems are more costly and less environmentally friendly than blower systems; however, many laboratories are located within buildings that will not allow for venting blower systems.

Additionally, in crowded urban settings, venting even dilute corrosive or smelly fumes can become problematic. Laboratory location is the primary reason why customers select a Macro Kjeldahl System with a Water Ejector Acid Removal System.

See literature to find out more about Labconco's Kjeldahl Systems or read our Guide to Kjeldahl Nitrogen Determination Methods and Apparatus.