News About Dyes and Stains

Current issues of interest to vendors and users of dyes and biological stains.

Dyes are becoming more expensive!

September 2014. BASF, a major dyestuff manufacturing company, recently announced that it “has increased its prices for many pigments and dyes by up to 15% worldwide. The products affected are predominantly azo pigments … phthalocyanines and dyes. The company said price increases were necessary due to significantly higher raw materials costs and the rising cost of environmental regulation, health and safety, and maintainance.” See http://www.basf.com/group/pressrelease/P-14-316 or International Dyer magazine (ISSN 0020658X), 2014 Issue 7, for details and comment.

Certified dyes

The following changes have been made in certification standards since 2002, the year of publication of the 10th edition of Conn’s Biological Stains and of the detailed account of tests used in the Commission’s assay laboratory (Penney et al. 2002). The following notes (alphabetically by names of dyes) refer to new tests, revised standards, and substances added to the list of stains for which certification is available. Companies that sell dyes for use as biological or microscopical stains should keep in touch with the Biological Stain Commission.

References.

Horobin RW, Kiernan,JA (2002) Conn’s Biological Stains, 10th ed. Oxford, UK: BIOS Scientific Publishers.

Penney DP, Powers JM, Frank M, Willis C, Churukian C (2002) Analysis and testing of biological
stains—The Biological Stain Commission Procedures. Biotechnic & Histochemistry 77(5-6): 237-275.

 

Alcian blue 8G (CI 74240) and other alcian blue dyes.  An additional criterion for identification (formation of an acid-insoluble pigment on addition of alkali) has been introduced, and the acceptable range of the absorption maximum has been extended. Some samples of this dye were received with absorption maxima outside the range (611-620 nm) previously specified (Penney et al 2002) for certification. These dyes passed other tests and performed well in the required staining methods. The acceptable range of the absorption maximum for alcian blue has been extended to 605-630 nm (Lyon & Kiernan 2008). If the alkali-induced precipitate redissolves on acidification, the sample will be tested as alcian blue variant rather than alcian blue 8G. Alcian blue variant is tested in Scott’s critical electrolyte method, but this test is no longer in use for alcian blue 8G.

The production of Alcian Blue 8G has been mainly discontinued due to the toxicity and instability of the reaction to make this molecule.  The main form of Alcian Blue is now characterized as a pyridine (or other) variant.  A complete description of the BSC’s tests and requirements for certification of alcian blue dyes is in preparation and will be submitted to Biotechnic & Histochemistry for independent peer review and eventual publication. This paper will include full explanations of nomenclature of alcian dyes and of the recent changes in the BSC’s tests and standards.

References.

Lyon HO, Kiernan JA (2008) News from the Biological Stain Commission. Biotechnic & Histochemistry 83(3-4):201-203.

Penney DP, Powers JM, Frank M, Willis C, Churukian C (2002) Analysis and testing of biological
stains—The Biological Stain Commission Procedures. Biotechnic & Histochemistry 77(5-6): 237-275.

 

Basic fuchsine and pararosaniline.  High quality pararosaniline (CI 42500, Basic red 9) has been available for many years. Until now, the BSC’s requirement for certification of pararosaniline or basic fuchsine has been a dye content of at least 88%, determined by titration with titanous chloride as prescribed by Peterson et al (1934).

Basic fuchsine traditionally is a mixture containing 2, 3 or 4 of the related aminotriarylmethane dyes pararosaniline, rosaniline (CI 42510), new fuchsine (CI 42520, Basic violet 2) and magenta II
(which has no CI number). Most samples of basic fuchsine submitted to the BSC in recent years contain only pararosaniline. They have been Certified for the required biological applications of basic fuchsine even though they probably would have met the more stringent testing required for samples submitted as pararosaniline.

Samples recently submitted to the BSC as basic fuchsine and found to be mixtures of triphenylmethane dyes have assayed below the previously required 88% but have performed in a satisfactory manner as ingredients of Schiff’s reagent and the endo culture medium for coliform bacilli, and in stains for acid-fast bacteria. Basic fuchsine composed of mixed dyes is a less expensive product than pararosaniline and is suitable for the same biological and medical applications, with the sole exception of preparing Gomori’s or similar aldehyde-fuchsine stains (Mowry and Emmel 1977). To acomodate these batches of basic fuchsine mixtures, the BSC has reduced the minimum dye content for dyes submitted as basic fuchsine from 88% to 80%. These batches will also be evaluated for component percentages, so that batches more heavily composed of pararosaniline and rosaniline are acceptably identified versus unacceptable ones consisting of mostly new fuchsine. For dyes submitted as pararosaniline, the standard remains at 88%. Biological tests for these dyes remain as described by Penney et al. (2002).

Inexpensive basic fuchsine containing mixed triphenylmethane dyes must be sufficiently free of brown and yellow (acridine) impurities to make a clean Schiff reagent (colorless after shaking with no more than 0.5 grams of activated charcoal per gram of the original dye). This test has been a requirement for certification of basic fuchsine (including pararosaniline) for many years (Lillie 1977; Penney et al., 2002).

The reduced assay requirement for basic fuchsine may make BSC-certified batches of the dye mixture available for clinical diagnostic purposes in places where pararosaniline cannot be afforded.

A complete description of the BSC’s tests and requirements for certification of basic fuchsine and pararosaniline is in preparation and will be submitted to Biotechnic & Histochemistry for independent peer review and eventual publication.

Pararosaniline and new fuchsine are the only members of the basic fuchsine group commercially available as single dyes. New fuchsine is the preferred amine for making a diazonium salt widely used in immunohistochemistry to localize secondary antibodies labelled with alkaline phosphatase. The BSC does not currently offer testing of new fuchsine. Is there a demand for
certified new fuchsine? Please let us know.

References.

Lillie RD (1977) Conn’s Biological Stains, 9th ed. Baltimore: Williams & Wilkins.

Mowry RW, Emmel VM (1977) The production of aldehyde fuchsin depends on the pararosaniline (C.I. No. 42500) content of basic fuchsins which is sometimes negligible and is sometimes mislabeled. Journal of Histochemistry and Cytochemistry 25: 239.

Penney DP, Powers JM, Frank M, Willis C, Churukian C (2002) Analysis and testing of biological stains – the Biological Stain Commission procedures. Biotechnic & Histochemistry 77: 237-275.

Peterson AR, Conn HJ, Melin CG (1934) Methods for the standardization of biological stains. Part IV. The triphenylmethane derivatives. Stain Technology 9: 41-48.

 

Carmine (CI 75470).  This is used as a food dye, with the name “carmine” applied to carminic acid, carmine or sometimes aminocarminic acid. Only true carmine is certified by the Biological Stain Commission. A new spectrophotometric test (Dapson 2005) distinguishes the three dyes and also provides an assay. For a review of carmine and related dyes, see Dapson (2007).

References.

Dapson RD (2005) A method for determining identity and relative purity of carmine, carminic acid and aminocarminic acid. Biotechnic & Histochemistry 80(5-6): 201-205).

Dapson RD (2007) Thr history, chemistry and modes of action of carmine and related dyes. Biotechnic & Histochemistry 82(4-5): 173-187.

 

Nuclear fast red (CI 60760)  has been added to the list of dyes for which the Biological Stain Commission offers testing and certification (Frank et al., 2007). The criteria for certification were published in 2007. This dye is a component of a red nuclear counterstain for histochemical methods that provide blue end-products in cytoplasm (iron, mucus, heparin etc) and in extracellular materials such as cartilage matrix. Some batches of another (and very different) red dye may be sold as nuclear fast red. Caveat emptor, especially if emptor (buyer) is a company that also is a vendor (seller) of staining solutions.

Reference.

Frank M, Dapson RD, Wickersham TW, Kiernan JA. (2007) Certification procedures for nuclear fast red (Kernechtrot), CI 60760. Biotechnic & Histochemistry 82(1): 35-39.

 

Sirius red F3B (CI 35780) has been added to the list of dyes for which the Biological Stain Commission offers testing and certification. The criteria for certification have been published (Dapson et al., 2011). This dye has been used in the best easy stain for collagen fibres (even very thin ones, such as reticulin) for more than 40 years.

References.

Dapson RW, Fagan C, Kiernan JA, Wickersham TW (2011) Certification procedures for sirius red F3B (CI 35780, Direct red 80). Biotechnic & Histochemistry 86(3): 133-139.

 

Thionine (CI 52000).  The spectrophotometric assay developed for this dye in 1950 was for the chloride (MW 263.7 ), which was the usual form of the dye at that time. Since about 1960, however, thionine has been manufactured as its acetate (MW 287.3). For assaying thionine (Stotz 1950), the absorbance (at maximum) of a 5 mg/l solution in water (in a 1.0 cm cell) was multiplied by 97 to calculate the percentage (w/w) content of thionine chloride in the dye powder. For thionine acetate the correct factor is 106, which is now being used. The dye contents of previously assayed batches of thionine acetate were underestimated by about 7%. Fortunately this error did not result in rejection of any samples, because the minimum dye content for certification is 85% whereas thionine acetate is usually manufactured with dye content close to 99% (Lyon & Kiernan 2008).

References.

Stotz E, Conn HJ, Knapp F, Emery AJ (1950) Spectrophotometric characteristics and assay of biological stains. Stain Technology 25: 57-68.

Lyon HO, Kiernan JA (2008) News from the Biological Stain Commission. Biotechnic & Histochemistry 83(6): 285-288.

 

Dyes are becoming more expensive!

September 2014. BASF, a major dyestuff manufacturing company, recently announced that it “has increased its prices for many pigments and dyes by up to 15% worldwide. The products affected are predominantly azo pigments … phthalocyanines and dyes. The company said price increases were necessary due to significantly higher raw materials costs and the rising cost…Continue Reading

Certified Dyes

The following changes have been made in certification standards since 2002, the year of publication of the 10th edition of Conn’s Biological Stains and of the detailed account of tests used in the Commission’s assay laboratory (Penney et al. 2002). The following notes (alphabetically by names of dyes) refer to new tests, revised standards, and…Continue Reading