be obtained. ph controlled staining at ph 1.0 it stains only sulfated polysaccharides and at ph 2.5 also stains carboxyl group containing sugars such as sialic acids and uronic acids intensify the stain of hyaluronic acids, which would also stain albeit relatively weakly by their half sulfate esters at ph 1.0. electrolyte controlled staining a staining method where at a fixed ph of about 5.5, different critical salt concentration (classically mgcl2, but nacl, kcl, libr are potential alternatives) can be used where the smaller (faster diffusing) salt cation competes with alcian blue to bind to the anionic sites. target material specific critical electrolyte concentration (cec) is supposed to selectively identify sulphated, carboxylated and phosphated structures for example as the targets. stability according to john a. kiernan—one of the editors of the 10th edition of conn's biological stains" 10th ed 2002 published on behalf of the biological stain commission: alcian blue 8g differs from most other dyes in that it can deteriorate even in the solid state, changing to an insoluble pigment. acidic solutions of alcian blue 8g are often stable for some years. churukian's lab manual gives a recommended shelf life of 6 months. an alcian blue solution with a precipitate should be discarded and replaced, not filtered and used. some dyes sold as alcian blue 8g are unstable in solutions at ph 5.6 and above; they precipitate in less than 24 hours. batches of alcian blue that do not form stable solutions cannot be used in scott's "critical electrolyte concentration" methods for histochemical characterization of different glycosaminoglycans, which require solutions at ph 5.7-5.8 with variable concentrations of mgcl2. the pyridine variant of alcian blue (alcian blue-tetrakis(methylpyridinium) chloride, cas 123439-83-8, cb6503730, pubchem 24860335) is more stable than the original alcian blue dyes and may be just as good as a stain. explanation of staining selectivity nucleic acids are generally basophilic because they have a very high density of negative charge due to the sugar phosphate backbone. however, in contrast to other basic i.e. cationic dyes, alcian blue usually (given the right ph and salt concentrations, and normal temperature and duration in minutes, not hours) preferably stains acidic glycosaminoglycans but not the chromatin and nissel substance, the mechanism of which had been a mystery for a long time and various theories were proposed. though the presumed basis of the staining is its positive charge attracted to negative structures (e.g. acidic sugars), bulkiness (width 2.5–3 nm, compared to toluidine blue ~0.7 x1.1 nm) makes its diffusion very slow in less permeable parts of the tissue and thus prevent it from staining highly negative yet compact structures such as chromatin and nissl substance. however prolonged staining (few days at 25 °c) or dna denaturing conditions may allow alcian blue to also stain the nucleus. the isolation of the positive charge from the aromatic electron cloud by the intervening methylene bridges makes the localized positive charged regions "hard" ions in contrast to soft ions where the charge is delocalized over the whole aromatic pi cloud. when these hard cations encounter the hard anions e.g. in form of sulfate they form salts without regard for the precise chemical nature of the anion. the resulting salts are highly stable but can be slowly exchanged with high concentration of salts. washing with water or alkali treatment after staining causes base catalyzed hydrolysis and removal of the pendant positively charged side chains and the resulting compound is phthalocyanine blue, which forms a blue water-insoluble dye precipitate. the precipitates are so robust that they withstand harsh conditions like pas or other counterstaining and also dehydration and embedding treatments (in contrast toluidine blue is partially extracted away during dehydration). this unleachability is the chemical basis of the ingrain dyeing for which ab (ingrain blue 1) was originally designed by the dye industry. manufacturing and purity the historic alcian blue varied so much batch to batch that only the 8gx (e.g. not even the 8gs) batch produced by ici was later decided to be the biologically useful ones. commercially available batches usually contained about 49% of the actual dye and rest used to be sulfate, boric acid, dextrin and other impurities and by various extraction methods up to 80% pure extracts can be made. actually the dye does not necessary contain all 4 substituents but might contain 2 or 3 of them and have various geometric isomers. but anyhow the manufacture of 8gx by ici had stopped by mid-1970s because of environmental hazards and very small lots were available that were received from alternate sources. only recently alcian blue has been re manufactured in bulk using safer procedures but the newer product does not have the suffix x (or s) since the manufacture process (and the exact product composition) is somewhat different. material safety alcian blue is an eye and respiratory tract irritant. solid alcian blue is a combustible powder and should never be handled close to heat or a naked flame. heating alcian blue produces toxic fumes of nitrogen compounds. it can react violently if mixed with oxidising materials. the solution of alcian blue is a skin sensitiser and corrosive (partly due to the acidic ph needed to maintain it unhydrolyzed in solution) and harmful by skin absorption. most vendor msds (material safety datasheet) mention that effect of ingestion not known or target organ not known. however some do mention that potential target organs are teeth and kidneys. uses in dye industry this stain was originally discovered by ici in the 1940s as a member of the competitive dye industry for the purpose of industrial dying. it was used for some time for staining textiles, leather products and inks. ici sold thousands of tons of alcian blue and filed multiple patents regarding its manufacturing process to keep its chemistry a tight secret. however ici had had trouble with the dye's solubility under textile dyeing conditions, and various process changes in manufacturing were made during the 1950s and 1960s. uses in biological staining uses other than as a dye or stain in addition to its use as a dye or stain alcian blue also finds other material science uses. adhesive alcian blue has been used as an adhesive to help stick glycol methacrylate sections to glass slides (which have negatively charged silicate groups). coating agent alcian blue carrying a large aromatic surface that can participate in van der waal's interaction as well as multiple localized charges. thus it can be coated onto surfaces and significantly modify surface property and charge. some cells in culture grow better on surfaces coated with positive charge like poly-l-lysine or polyornithine or alcian blue. alcian blue coated surfaces hold onto the negatively charge glycocalyx so tight that it can even be used to cover a layer of cells and then float it up to peel off the roof ("unroofing") to study the cytoplasmic side of the plasma membrane. gelling or lubricating agent alcian blue has been used as a gelling agent for lubricating fluids likely due to the stacking properties of this macrocylic aromatic compound. electrode component another application is "alcian blue modified carbon paste electrode" (abmcpe), which acts as a highly sensitive redox sensor compared to bare carbon paste electrode (bcpe) and exhibits strong "promoting" effect and stability.