Methyl Red sodium salt is the sodium salt of Methyl Red. Methyl red is an indicator dye that turns red in acidic solutions. It is a pH indicator, turning red under pH 4.4, yellow over pH 6.2, and orange in between those values. It is used in microbiology in the Voges-Proskauer test to identify bacteria that produce stable acids through mixed acid fermentation of glucose. Methyl-red positive bacteria include Proteus vulgaris and Escherichia coli. Methyl-red negative bacteria include Enterobacter aerogenes and Serratia marcescens.

pH Indicator
Identification of bacteria in Microbiology

C.I.13020

Dye Content: >90%
Molecular Formula: C15H14N3NaO3
Molecular Weight: 291.29 g/mol
Transition Range: pH4.2 (Violet Red) – pH6.2 (Brownish/Yellow)
Maximum Absorption (pH4.2): 523-527nm
Maximum Absorption (pH6.2): 430-434nm
Absorptivity(A1%/1cm@pH4.2): 1200-1300
Absorptivity(A1%/1cm@pH4.2): 675-735
Loss on Drying: <5%

Hazard Phrases: Not considered harmful under normal laboratory conditions

Cas No: 845-10-3
Einecs No: 212-682-9