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From Kjeldahl and Micro-Kjeldahl analysis to Alcoholic Strength Determinations and other distillation applications: VELP offers a broad set of test tubes. Discover how to choose the correct one depending on your needs.
Different laboratory applications require various instruments and accessories. Depending on the sample and the analysis, the choice of the right size and shape of a test tube to be used is important. 

To suit different requests, a wide range of glass test tubes for digestion and distillation units is available as regards the:
  • Size/Shape
  • Length 
  • Capacity 
Straight tubes are usually suggested for most digestion and distillation applications. Volumetric tubes, with constriction on the neck, find applications when the digestate has to be diluted to a fixed volume before starting the analysis.

Moreover, optimal sample amounts depend on the expected nitrogen content which in turn affects the choice of titrant concentration, the volume of 96-98% sulfuric acid and the choice of the test tube.

Standard Distillation Test Tubes

Standard Distillation Test Tubes
Applications: Total Kjeldahl Nitrogen determination, ammoniacal nitrogen, nitric nitrogen (Devarda), TVBN, sulphites, phenols, volatile acids and cyanides
Sample weight: 0.1 – 5 g
External Diameter: Ø42 mm
Height: 300 mm
Code: A00000144

Standard Test Tubes are widely used for protein determination on food, feed and beverage following the Kjeldahl method, as well as the distillation of different samples according to other applications and methods.

Samples of heterogeneous material often need to be fairly large to ensure that they are representative. There is no lower limit of sample size in the 250 mL tubes; they simply allow greater flexibility for most types of samples.

Depending on the expected nitrogen content, optimal amounts of sample are usually in the range of 0.1-5 g.


Applications: micro-Kjeldahl analysis on small sample sizes, homogeneous samples with relatively high nitrogen content
Sample weight: 10 – 30 mg
External Diameter: Ø26 mm
Height: 300 mm
Code: A00000146

Designed for Kjeldahl extraction on a micro-scale, Micro Kjeldahl tubes can be used if the material is homogeneous and small samples are fully representative, or if it is specified by an approved method (AOAC method 960.52, Microchemical determination of Nitrogen). Note that the Micro-Kjeldahl method requires smaller volumes of chemical reagents. 

Micro Kjeldahl units are also used to perform the step of nitrogen content determination during the dietary fiber extraction process

Kjeldahl balloon - Alcoholic Strength Determination

Kjeldahl balloon - Alcoholic Strength Determination
Applications: alcoholic strength determination on alcohol samples by steam distillation and volume
Sample volume: 100 – 200mL
External Diameter: Ø100 mm
Height: 300 mm
Code: A00000082

The Kjeldahl balloon is used for the distillation of alcohol samples: 
  • Wine 
  • Beer 
  • Spirits 
  • Other alcoholic beverages
Steam distillation is a method to determine the alcoholic strength of alcoholic beverages: the distillate obtained is an ethanol-water mixture and, using a measurement of density, the alcoholic strength can be calculated.

Jumbo Test Tubes

Jumbo Test Tubes
Applications: Kjeldahl analysis on low nitrogen liquid samples
Sample volume: < 100mL
External Diameter: Ø50 mm
Height: 300 mm
Code: A00000185

Jumbo tubes are perfectly fitting in standard digestion and distillation systems due to the upper diameter of 42 mm, and they are designed for handling larger liquid volumes, typically 50-100 mL.

To determine total nitrogen in low nitrogen liquid samples such as water according to the Kjeldahl method, where it is necessary to sum organic nitrogen (proteins, nucleic acids, urea, synthetic organic chemicals) and ammonia nitrogen, Jumbo test tubes are a convenient accessory.

1-Liter Test Tubes

1-Liter Test Tubes
Applications: separation of hydrocyanic acid from wastewaters
Sample volume: 200 mL
External Diameter: Ø80 mm
Height: 300 mm
Code: A00001083

Heavy metal complexes, sulfides, aromatic amines, oxidants and dyes interfere with cyanides' colorimetric or titrimetric determination.

Hydrocyanic acid has to be separated from the water sample by distillation. As 200 mL of sample are analyzed, a 1-liter test tube has to be used to perform the analysis and obtain reliable and accurate results.
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