Cerimetry, Iodimetry, Iodometry, Bromometry, Dichrometry and Titration with Potassium-iodate : Pharmaceutical Guidelines -->

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Cerimetry, Iodimetry, Iodometry, Bromometry, Dichrometry and Titration with Potassium-iodate

Originally developed by Ion Atanasio, cerimetry or cerimetry titration is a volumetric chemical analysis technique.

Cerimetry

Originally developed by Ion Atanasio, cerimetry or cerimetry titration is a volumetric chemical analysis technique. This titration is a redox reaction where a change in the color of the Fe-1,10-phenanthroline complex (ferroin) indicates the endpoint. By titrating ferroin with a Ce solution, ferroin can be reversibly discolored in an oxidized state. It was first proposed in the middle of the 19th century to use cerium(IV) salts as volumetric reagents, however, systematic studies did not begin for about 70 years. The standard solutions can be prepared with different Ce salts, but in most cases, cerium sulfate is used.

Iodometry

The appearance or disappearance of elementary iodine, a measure of endpoint, is what is measured by iodometry, a volumetric analytical method. As a titrant, sodium thiosulfate is typically used, and starch as an indicator, along with an iodine compound (either iodate or iodide), depending on the reaction desired.

It consists of the reduction of iodine by thiosulfate into iodide:

I2 + 2 S2O32−S4O62− + 2 I

It is commonly used for measuring the concentration of chlorine in water as an example of what it can be used for. Iodide is oxidized by chlorine when the pH is below 8. A large amount of potassium iodide is added to a known sample amount in an acidic environment (pH is 4. More alkaline pH does not allow the reaction to complete). Iodine is liberated from the starch, which forms a blue clathrate complex. To remove the blue color, thiosulfate must be added to the blue solution.

The iodometric titration results can be influenced by two sources of error. There are two types of oxidation of acid-iodide from the air: one is air oxidation, and the other is air volatility. By adding too much sodium carbonate to the reaction vessel, it is possible to eliminate the first one. During this process, carbon dioxide (which is heavier than air) is formed and oxygen is removed from the vessel. In addition, an excess of iodine solution can be used to counteract the other error by forming triiodide ions, I3-, as liberated iodine is captured.

Iodimetry

A volumetric analysis involves sampling either a standardized solution of iodine or a solution of starch which is titrated with a standardized solution of iodine, allowing the concentration to be determined by titration. Hence, the method is used to combine substances that oxidize potassium iodide to release free iodine, or substances that oxidize potassium iodide to release free iodine. Reaction reactions involve:

I2 +2Na2 S2 O3 → 2NaI+Na2 S4 O6.

Bromometry

Bromometry is a process used to determine how much potassium bromate to add. Including carbazone (C7H9AsN2O4) in the qualitative evaluation of substances & Organo arsenicals using this oxidizing agent is a great use it.

Principle

In an actual solution of HCl with an actual strength greater than IBr, titration depends upon the formation of Iodine monobromide [IBr].

Theory

By adding potassium iodide (KI) to dilute HCl and potassium bromide (KBrO3), potassium bromide (KBrO3) can be assayed as shown below.

KBr03 + HI→ HIO3 + KBr

IO3+ 5I+ 6H+ → 3I2+ 3H2O


Dichrometry

A dichromatic titration is one in which potassium dichromate is used as an oxidizing agent. When potassium dichromate is used in acidic aqueous media it is kept at a pH of 4.0 through the use of dilutions of sulfuric acid. Iodides and ferrous salts can be estimated with sodium dichromate solution.

Cr2O72 + 14H+ + 6e → 2Cr3+ + 7H2O

In the dichromate system, there is a half-reaction

Cr2O72 + 14H+ + 6e → 2Cr3+ + 7H2O

Half reaction relevant to this situation in

Fe2+ → Fe3+ + e

Reaction as a whole is,

Cr02-7 + 6Fe2+ + 14H+ →2Cr3+ + 6Fe3+ + 7H2O

In addition to being a stable double salt with an active constituent, ferrous ammonium sulfate (Mohr's salt) is also a stable compound. In Mohr's salt solution that contains dilute H2SO4 when heated at ordinary room temperature, the acidic potassium dichromate solution is a strong oxidizer and rapidly reduces to green chromic acid when ferrous ions are added. This reaction transforms ferrous sulfate into ferric sulfate, instead of reacting with ammonia sulfate. Indicators that use N-phenyl anthranilic acid are used in manufacturing. When iron ion concentrations are present in a solution, N-phenyl anthranilic acid is not oxidized.

Titration with potassium iodate

KIO3 (potassium iodate) is considered to be a very strong oxidizing agent that can be used in the assay of a wide variety of pharmaceutical substances, including benzalkonium chlorides and potassium iodides.

A quantitative reaction between iodate and iodides (I-) and iodine (I2) occurs. Besides saturated organic acids, alcohols, and proteins, titrations can also depend on several other organic substances.

The molecular formula would be: KIO
3
The molecular weight would be: 214

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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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