Fabric purity

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The purity of a substance describes the proportion of a desired substance in the total substance mixture .

Separation processes are used in chemical and physical process engineering to clean mixtures of substances . They are not to be confused with cleaning in manufacturing technology .

Basics

In the ideal case, the purity would be 1 (corresponds to 100%) if it does not contain any impurities. The content of foreign substances (impurities, minerals, trace elements) is given in percent (%, hundredths), per thousand (‰, thousandths), ppm ( parts per million , millionths) or ppb ( parts per billion , billionths) depending on the amount . However, it must be noted whether it is a volume concentration or a mass ratio or a relative amount of substance .

Purity classes

Chemical substances are usually traded in different purity classes. The exact specification depends on the manufacturer and fabric. The following additives are used in the substance designation (sorted according to increasing purity):

  • raw (also crudum , crd. ) - uncleaned quality
  • technical - substance is used for general technical purposes, is usually manufactured on an industrial scale and can have a foreign odor and color.
  • for synthesis - substance contains small amounts of impurities, which mostly do not interfere with syntheses, since a purification takes place during the manufacture of the synthesis product.
  • pure ( purum ) - chemically pure quality with a substance content of 97%, unless otherwise stated. In terms of color and characteristic data, it largely corresponds to the relevant literature. Suitable for synthesis and laboratory purposes. Sensitive products are filled under protective gas.
  • pure ( purissimum , puriss. ) - particularly pure quality with a substance content of at least 99%, often with a certificate of analysis. No foreign substances can be detected with common analytical methods. Appearance and characteristic data correspond to the relevant literature. Sensitive products are filled under protective gas.
  • for analysis (also pure, e.g. , pa = pro analysi or analysenrein ) - can be used for analytical procedures, as the content of foreign substances is given.
  • ultra-pure - for specific applications, with a detailed guarantee certificate and information on the maximum levels of relevant impurities

These terms and their order have a long tradition in chemistry and pharmacology , even if they have not yet been standardized and the associated purity is determined by the respective manufacturer according to the intended use. Manufacturers have met the increased demands of modern trace analysis with new degrees of purity such as Traceselect (Fluka) or Suprapur (Merck).

Apothecary jar with Latin abbreviations

Usual additional information

These details and abbreviations are used to describe the purity of chemicals more precisely:

  • Section. ( absolute ) - cleaned
  • anhydr. ( anhydricus ) - anhydrous
  • redist. - double distilled
  • conc. ( concentratus ) - concentrated
  • cryst. (also crist. , cystallisatum ) - crystallized
  • dep. (also depur. , depuratum ) - purified
  • least. ( distillatum ) - distilled
  • dil. ( dilutus ) - diluted
  • GC -information determined by gas chromatography
  • Weight % - weight percent
  • glass distilled - high-purity solvents that only come into contact with glassware during processing
  • Krist. - crystallized
  • praec. (praecipitatum) - pleases
  • talk. - Double distilled, deviating from this: distilled from solvent waste, i.e., as expected, with impurities of unknown type and proportion
  • resubl. - twice sublimated
  • sicc. ( siccatum ) - dried, anhydrous
  • sine H 2 O - without water
  • sol. (also solut. , solutus ) - solved
  • Rod. - stabilized
  • subl. ( sublimatum ) - sublimated
  • subt. ( subtilis ) - fine
  • tot. ( totus ) - as a whole, not divided

Specifications and technical data sheets

  • Manufacturers and - mostly commercial - consumers of chemicals often regulate the purity requirements (including tolerance values) contractually and therefore bindingly with one another in specifications stating test methods .
  • The purity specifications given by manufacturers in “technical data sheets” are often only “typical values” and often only describe a guaranteed quality to the detriment of the customer in a vague and imprecise manner.

Medicinal substances

Special regulations can result in information tailored to the intended use, e.g. B. for drugs (active ingredients in drugs). If a drug name (INN) is supplemented by a reference to a recognized pharmacopoeia - e.g. B. Acetylsalicylic acid , European Pharmacopoeia - this describes a precisely defined purity for this substance according to the European Pharmacopoeia ( Pharmacopoea Europaea , Ph. Eur., Referred to in Switzerland as the European Pharmacopoeia ). In the European Pharmacopoeia [as in other pharmacopoeias , such as the United States Pharmacopeia (USP-NF)], the analysis methods ( test procedures ) for determining purity are also precisely specified. The purity requirements and the analytical methods can differ from one another in the various pharmacopoeias.

Indication of the purity of gases

For industrial gases , the purity is expressed using two-digit abbreviations. The first digit denotes the number of nines, the second digit is the first decimal place other than “nine”.

Examples
  • Hydrogen 6.0 → hydrogen with a purity of ≥ 99.99990 vol .-%
  • Nitrogen 3.8 → nitrogen with a purity of ≥ 99.98% by volume
  • Acetylene 2.4 → acetylene with a purity of ≥ 99.4% by volume

Specification of the purity for metals

For metals, the purity is indicated by a number followed by N. Similar to the system used to specify the purity of gases, the number indicates the number of nines. The purity 6N accordingly means 99.9999%, e.g. B. in silicon .

Impurity (contamination)

In various technical, industrial, scientific and medical fields, one speaks of contamination (also contamination ) when there is contamination of substances, goods, medicines, foodstuffs, organisms and the like. a. by undesirable, usually harmful substances of various kinds. Limits (maximum values) are often given in specifications for contaminants, e. B. for residual solvents in pharmaceuticals , pharmaceutical excipients and medicinal products in the pharmacopoeias .

In food law, such undesirable substances are referred to as food contaminants .

See also

literature

  • Felix Goldbach: Analysis of the supply chain structures in the photovoltaic industry. GRIN Verlag, 2011.

Individual evidence

  1. ↑ a b Quality designations , University of Duisburg-Essen, 2014.
  2. ^ Meyendorf, Keune; Chemische Schulexperimente, Volume 1, 1985, Verlag Volk und Wissen.
  3. ↑ See also guideline CPMP / ICH / 283/95 of the International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use ; as well as the European Pharmacopoeia. 6th edition. Deutscher Apotheker Verlag, Stuttgart 2008, ISBN 978-3-7692-3962-1 , pp. 869-879.