Technology

Steam Distillation

Steam distillation procedure

Steam distillation is a separation process used to isolate compounds for quantification, such as ammonia originating from proteins. The main advantage of steam distillation over conventional distillation is that the steam distillation procedure is carried out at lower temperatures and components can be separated from a mixture below their decomposition point.

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Steam distillation vs simple distillation

Simple distillation is used in chemistry to separate two liquids with boiling points that differ by at least 25°C or to separate a liquid from a nonvolatile compound that has a higher viscosity. In the latter case, heat is added to the mixture to reach the boiling point of the more volatile compound, the resulting vapor is collected and immediately condensed back into liquid form. However, the distillate may be only partially pure.

The steam distillation technique is one of the distilling processes that is suitable for the distillation of heat-sensitive compounds. The steam distillation procedure involves bubbling hot steam through the mixture to be distilled, lowering the boiling points of the compounds. The condensate is collected, and the resulting aqueous solution can be used in combination with titration techniques for quantification of the analyte. Steam distillation is heavily used in separation of aromatic compounds, oils from natural products, as well as fragrance production and Kjeldahl nitrogen determination.

The following analytes can be separated by the steam distillation technique and quantified accurately.

Table 1: Table of analytes suitable for steam-distillation extraction.
AnalyteMatrix

Quantification Method

Related Norms

Protein (nitrogen), TKN, TVBN

Food, beverages, pharmaceuticals, feed, waste water

Potentiometric / Colorimetric Titration

AOAC 2001.11
AOAC 920.87
ISO 937
ISO 3188

Ammonium, nitrite, nitrate (Devarda), urea

Fertilizer, soil, cosmetics, hair dye

Potentiometric / Colorimetric Titration

AOAC 892.01
AOAC 955.04
83/514/EEC
Alcohol

Wine, beer, spirits

Densitymeter

EC 2870/2000

Volatile acids

Wine, juice

Potentiometric Titration

OIV-MA-AS313-02

Sulfite, Sulfur dioxide

Wine, beer, dried fruits, seafood

Potentiometric Titration

AOAC 962.16

Cyanide, Amygdalin

Food, feed, waste water

Complexometric Titration

ISO 2164-1975,
AOAC 915.03

VDKs

Beer

UV-Vis Spectrometry

 
Phenol

Soil, waste water

UV-Vis Spectrometry

ISO 6439:1990
DIN 38409-H16-3

Formaldehyde

Textiles, maple sirup

UV-Vis Spectrometry

ISO 14184-1
AOAC 964.21

Limonene (essential oils)

Juice, fragrances, hops

Redox Titration

 

 

Nitrogen / Protein Determination

Proteins are some of the most important nutritional components and are present in almost all food and animal feed products, where they serve as a reliable quality feature. For food products, the protein content must be declared on the product nutritional information for consumers. This declaration is statutory in national and international laws for food producers. By determining the Total Kjeldahl Nitrogen (TKN), the protein content is calculated directly from the nitrogen present in the sample. TKN analysis also determines the content of both organic and inorganic forms of nitrogen in the respective samples. In food analysis, total volatile basic nitrogen (TVBN) is used to determine the freshness of fish and seafood products.

Steam_Distillation_01_Figure.jpg
Fig.1 The three major steps in Kjeldahl nitrogen determinations include digestion, steam distillation and titration.
Step 1: Digestion

The analysis starts with the acid digestion of the sample by using a Digester, converting organic nitrogen to ammonia. The sample needs to be boiled in concentrated sulfuric acid and Kjeldahl Tablets containing potassium sulfate and copper catalyst to convert the organic nitrogen to ammonia (Fig. 2). The Digester is coupled to a Scrubber to remove corrosive fumes to achieve highest safety in the lab.

 

Steam_Distillation_02_Figure.jpg
Fig. 2 The digestion process via block heating.
Step 2: Steam Distillation Procedure and Titration

The second part of the method involves steam distillation extraction with a suitable Distillation Unit. The pH of the digestate must be raised to 9.5 by adding concentrated sodium hydroxide in this alkalization step. At this pH, ammonia gas forms. The ammonia gas is then transferred through steam distillation into the acidic absorbing solution, namely diluted Boric Acid, and converted to ammonium (Fig. 3). Nitrogen concentrations within the receiving solution can then be determined using classical potentiometric or colorimetric electrode determination methods.

Steam_Distillation_03_Figure.jpg
Fig. 3 Steam Distillation Process. ① Steam is inducted into the sample tube ② Steam passes through the sample ③ Analyte passes through the splash protector by means of steam distillation ④ Volatile components are condensed and collected in the receiver.

Steam-volatile analytes

 

Alcohol

Alcohol content must be determined in food and beverages due to legal and taxation purposes. After the steam distillation technique is performed in a suitable Distillation Unit, the alcohol content is determined via a densitymeter, typically a pycnometer or an oscillating U-tube.

SO2

Sulfite is a commonly used preserving agent used in food such as dried fruits and seafood, as well as in beverages such as wine and beer. Since a minor fraction of people experience allergic reactions to this compound, the SO2 content must be monitored for compliance with statutory maximal limits. As part of the labelling requirements, the SO2 content must be declared as well. For SO2 determination, we recommend the usage of the optimized Monier-Williams method with a Potentiometric Titration in diluted H2O2 solution.

Volatile Acids

The fraction of volatile acids is an important parameter for the taste of wine. If wine is exposed for too long to air, alcohol is converted to acetic acid and adds an unpleasant, sour taste to the wine. By degassing carbon dioxide and using tartaric acid before Steam Distillation, the volatile acidity can be determined.

Vicinal Diketones

Vicinal diketones (VDKs) are a group of flavor components in beer. They are formed during beer fermentation and determine also the taste of beer. Excessive or unexpected VDK levels can be a sign of either bacterial infection or improper fermentation. Monitoring and controlling VDK levels can play an important role in flavor formation in beer production.

Ammonium, phenol, cyanide

In environmental analysis, multiple parameters can be determined in soil and water samples such as the ammonium content, the phenol index and the cyanide content. Also, in almond-based food samples, the amount of toxic cyanide plays an important role.

Formaldehyde

Textiles are monitored continuously regarding the level of formaldehyde as contaminants and low levels are prerequisite for obtaining certain certifications. In the glue industry, the formaldehyde content determines the effectiveness of the aminoplastic adhesive and can be determined via the steam distillation procedure. Furthermore, the formaldehyde content in wood materials is used for classification in accordance with the mandatory emission limits.

Steam distillation of essential oils

Extraction of essential oils by steam distillation is one of the most common methods used to obtain high purity products. Essential oils are used in aromatherapy, flood flavoring, cosmetics, fragrances and others. Legislation for specific product uses, such as food flavouring, cosmetics and additives in animal feed, also relates to essential oils. These ingredients must be carefully assessed and labelled to guarantee consumer safety.