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COMMENT CHOISIR LE BON TUBE À ESSAI POUR VOTRE APPLICATION

18/07/2022

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.

COMMENT CHOISIR LE BON TUBE À ESSAI POUR VOTRE APPLICATION

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

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.

Micro-Kjeldahl

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

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

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

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.

Ø48 Test Tubes

Sample weight: 0.1 – 5 g

External Diameter: Ø48 mm

Height: 260 mm

Capacity: 300 mL

A dedicated 6 positions digestion unit, as well as a spacer and an adapter, have been developed by VELP to meet the needs of customers accustomed to working with these test tubes for a wide range of Kjeldahl analyses.

COD Test Tubes

Sample weight: g

External Diameter: Ø42 mm

Height: 200 mm

Capacity: 200 mL

In Chemical Oxygen Demand (COD) analysis are used high optical glass quality for accurate colorimetric analysis to determine the amount of organic compounds in a water source.

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