Proportioning

In analytical Chemistry, the proportioning is the action which consists in determining the quantity of a substance specifies (the Analyte) present in another or in a mixture (the matrix).

There exists a great number of assay techniques, here are some:

Gravimetric proportionings

A gravimetric analysis consists in determining the quantity of analyte by weighing.

Examples:

  • Proportioning of water by weight loss to the dessication
  • Proportioning of ashes after calcination
  • Proportionings by precipitation:
    • Proportioning of copper according to Rivot
    • Proportioning of the money in the form of cerargyrite

Titrimetric proportionings

See also: Titration

A proportioning titrimetric consists in determining the quantity of reagent (titrating it) necessary to the quantitative transformation of the component to be proportioned (the analyte). For example, proportioning of hydrochloric acid using a solution of sodium hydroxide of known concentration.

Examples:

  • Proportioning by volumetric titration
  • Proportioning by gravimetric titration
  • Proportioning by coulometric titration

Colorimetric proportioning or proportioning by colorimetry

See also: Dosage_colorimétrique, colorimetric Proportioning

To proportion or titrate a chemical Species in solution, it is to determine its molar Concentration. For that, one makes react a known volume of the solution containing the Réactif to proportion with a species, known as titrating reagent introduced in known Quantité. The Reaction concerned, of known equation, is called reaction of proportioning or titration.

Photometric proportionings or spectrophotometric

Determination of the quantity of analyte per measurement of the absorption of the light to a wavelength given by this one (in UV, the visible one or IR).

Other techniques

  • Detection coupled to a chromatograph in gas phase:
    • Catharomètre (detecting by thermal conductibility): Measure variation of the thermal conductibility of the carrier gas.
    • FID: Detector with ionization of flame. After separation by the GC, the substances arrive at one in a flame of hydrogen/Oxygène (air). While burning, they are transformed into Ion S which, while passing between two polarized electrodes, creates an electric current. The measurement of this current makes it possible to proportion the substance.
    • ECD: Detector with capture of electron. After separation by the GC, the substances arrive at one in the detector where is an ionizing source (rays β). The formed ions are captured by electrodes and, the current thus formed, measured.

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