Crystal violet-iodine

This classification is based on various criteria, including shape of the bacterium (rod, cocci) and the ability of the bacteria to be stained with a crystal violet-iodine complex in the presence of alcohol (Gram staining). This classification system also contains rickettsiae and chlamydiae both of these tend to be at the interface with viruses in that they are intracellular bacteria. 

Bacteria are classified into two groups on the basis of a staining reaction discovered by Gram in 1884. In this reaction, the cells do or do not retain a crystal violet-iodine dye complex after an alcohol wash. Cells that retain the stain are gram-positive those that do not are gramnegative. This empirical classification divides bacteria into two classes that differ in cell wall structure. 

Discovered by Christian Gram, Danish bacteriologist, in 1884. Gram-positive bacteria are those which, exposed in turn to crystal violet, iodine, and ethanol, are stained purple. 

Gram stain A differential stain that uses crystal violet, iodine, alcohol, and safranin to differentiate bacteria. Gram-positive bacteria stain dark purple Gram-negative ones stain pink/red. 

In practice a few iodine crystals are usually placed on the bottom of a dry, closed trough chamber. After the chamber has become saturated with violet iodine vapor the solvent-free plates are placed in the chamber for 30 s to a few minutes. The iodine vapor condenses on the TLC layers and is enriched in the chromatogram zones. Iodine vapor is a universal detector, there are examples of its application for all types of substances, e.g. amino acids, indoles, alkaloids, steroids, psychoactive substances, lipids (a tabular compilation would be too voluminous to include in this section). 

Rinse the crystal violet from the slide with Gram iodine solution. 

Gram Stain A staining procedure used in classifying bacteria. A bacterial smear on a slide is stained with a purple basic triphenyl methane dye, usually crystal violet, in the presence of iodine/potassium iodide. The cells are then rinsed with alcohol or other solvent, and then counter-stained, usually with safranin. The bacteria then appear purple or red according to their ability to keep the purple stain when rinsed with alcohol. This property is related to the composition of the bacterial cell wall. 

All forms of iodine including the elemental iodine, hypoiodous acid (HOI), hypoiodite anion (OI ), free iodide anion (I-), and triiodide anion (I3 ) in water also may be measured by the Leuco crystal violet method. The sample is treated with potassium peroxymonosulfate to oxidize all iodide species in the sample. It then is treated with leukocrystal violet reagent for color development. Interference from free chlorine may be eliminated by addition of an ammonium salt. 

Elemental composition K 23.55%, I 76.45%. Potassium may be measured by various instrumental methods (see Potassium). Iodide ion in an aqueous solution can be measured by ion chromatography or leuco crystal violet colorimetric method (see Iodine). 

Cover the smear with Gram s iodine solution and let stand for 1 minute. Crystal violet will form a complex with iodine within cells. All cells will remain violet. 

A sample (0.5-1 ml) of the test solution is added to an equal volume of 4,4 -bis(dimethylamino)benzophenone (Michler s ketone) in dry toluene. A few drops of water are added, and the mixture is shaken." A few drops of a 0.2% solution of iodine in glacial acetic acid are added, resulting in the formation of a blue or green colour. A recent variation employs tris(4-dimethylaminophenyl)methane (leuco crystal violet, LCV), followed by aerial oxidation [1]. 

Colour Test. Heat a few crystals with 1 ml of sulphuric acid— violet iodine vapour. 

Gram-negative bacteria—Bacteria with a surface stain using crystal violet, or gentian violet treated with iodine that can be removed by flooding with alcohol, acetone, or aniline. 

Another method of determining chlorine in air ias been based on the liberation of an equivalent amount of iodine, which as I3 forms an extractable ion associate with Crystal Violet [67]. 

Iodide ions (as F or I3 ) can be extracted as ion-pairs with basic dyes such as Crystal Violet [8,9], Brilliant Green [10,11], Rhodamine B (in toluene) [12], or Butylrhodamine (in benzene) [13]. After oxidation of iodide to iodine, the iodine is extracted into CCI4 and then stripped into the aqueous phase (as F) by shaking with thiosulphate. Finally, the F ions associated with Methylene Blue, are extracted into 1,2-dichloroethane [14]. 

The bleaching of Methylene Blue by 8203 affords a sensitive method for determination of thiosulphate [70]. It is possible to determine thiosulphate after extraction of its ion-associates with some basic dyes, e.g., Rhodamine B, Rhodamine 6G, or Crystal Violet [71]. Thiosulphate present in concentrations of the order of 10 M have been determined after the oxidation with iodine by measuring the absorbance due to I3 [72]. Thiosulphate can also be determined in an indirect reaction, in which 8203 reacts with Hg(II) thiocyanate to release SCN which gives a colour reaction with Fe(III) [73]. A method for simultaneous determination of thiosulphate, sulphite, and sulphide has been proposed [74]. 

Jb) Drop a crystal of iodine into a dry test tube, and heat gently the bottom of the tube until a violet vapor arises and a black deposit appears in the upper part of the tube. Observe the crystals of which this black deposit is composed and then heat them by holding the upper part of the test tube in the fiame. (1) Are the crystals iodine (2) Give reasons for your conclusion. (3) Are the size and shape of the crystals the same as those of the original iodine (4) What class of properties underwent change in the transformation of the iodine to... 

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