Search: dodecyl sulfate

Many basic dyes (e.g. methylene blue) behave in a similar way to cation-active substances. Methylene blue forms a complex with dodecyl sulfate (anion-active surfactant), for example, which is soluble in organic solvents such as dichloromethane with blue colour. By adding quaternary ammonium compounds (QAV), this complex is decomposed and the methylene blue migrates from the dichloromethane into the aqueous phase. When titrating quaternary ammonium compounds with dodecyl sulfate, this process takes place in the opposite direction, i.e. the methylene blue migrates from the aqueous to the dichloromethane phase. The end point of the titration is reached when the aqueous and dichloromethane phases have the same colour depth.

Or to put it in other words:

Methylene blue (water-soluble dye in cationic form) forms a complex with dodecyl sulfate (anionic surfactant), which is soluble in organic solvents, e.g. dichloromethane, with blue colour. On the other hand, QAV also forms a complex with dodecyl sulfate, so that the indicator migrates into the organic phase once the equivalence point has been exceeded.

Visible pre-germination is evident at the rootlet and is therefore grounds for rejecting a barley lot. However, after the barley is cleaned and the rootlets are removed, the so-called “hidden pre-germination” can be made visible using the staining methods described below.

Kernels suspected of having pre-germinated are boiled for ½−1 min in a 20 % solution of copper sulfate, allowed to remain for 30 min in the hot solution and are subsequently rinsed with water. The acrospire is stained green, making it clearly visible.

Sulfate ions are precipitated with barium ions in the form of barium sulfate and determined gravimetrically. 

Barium chloride sulfate is precipitated as coarse crystalline barium sulfate. The precipitate is determined gravimetrically:

SO₄^2- + Ba²⁺ → BaSO₄
 

A water sample is run through an ion exchanger in which all of the cations are replaced with hydrogen ions. The sulfate is determined through titration in the presence of a previously prepared barium chloride solution, of which a known amount in excess of that required is added in advance. The quantity is measured by complexometric titration. The difference between the initial concentration of barium chloride and the amount determined by back titration corresponds to the sulfate content.

In many cases, particularly at higher contents, an alternative and sufficiently accurate measurement is possible, called the “negative m value” or the “total mineral acid value” (without carbonic acid). This is achieved through titration. Subsequently, the mval values for the anions (Cl^-, NO₃^-, NO₂^-, PO₄^3-) are subtracted from the result.

In the presence of barium chloride, sulfate ions form barium sulfate, which is only slightly soluble in water. The turbidity produced by doing so is determined with a photometer.