Phenol red (Phenolsulfonephthalein) is a pH-indicating dye that relies on a distinct color change from pink to yellow in the event of a positive reaction.

Physicochemical Properties

Molecular Formula	C19H14O5S
Molecular Weight	354.38
Exact Mass	354.056
CAS #	143-74-8
Related CAS #	Phenol Red sodium salt;34487-61-1
PubChem CID	4766
Appearance	Red to reddish brown solid powder
Density	1.5±0.1 g/cm3
Boiling Point	562.8±50.0 °C at 760 mmHg
Melting Point	300 °C
Flash Point	294.2±30.1 °C
Vapour Pressure	0.0±1.6 mmHg at 25°C
Index of Refraction	1.697
LogP	3.02
Hydrogen Bond Donor Count	2
Hydrogen Bond Acceptor Count	5
Rotatable Bond Count	2
Heavy Atom Count	25
Complexity	545
Defined Atom Stereocenter Count	0
InChi Key	BELBBZDIHDAJOR-UHFFFAOYSA-N
InChi Code	InChI=1S/C19H14O5S/c20-15-9-5-13(6-10-15)19(14-7-11-16(21)12-8-14)17-3-1-2-4-18(17)25(22,23)24-19/h1-12,20-21H
Chemical Name	4-[3-(4-hydroxyphenyl)-1,1-dioxo-2,1λ6-benzoxathiol-3-yl]phenol
HS Tariff Code	2934.99.9001
Storage	Powder-20°C 3 years 4°C 2 years In solvent -80°C 6 months -20°C 1 month Note: This product requires protection from light (avoid light exposure) during transportation and storage.
Shipping Condition	Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Biological Activity

ln Vitro	For a fast assessment of the culture's health, phenol red (PR), the standard pH indicator in a variety of cell and tissue culture media, is used. The detection of cellular hydrogen peroxide and human peroxidase enzyme activity has also been accomplished through the use of phenol red in a number of protocols[1].
References	[1]. Caution for the routine use of phenol red - It is more than just a pH indicator. Chem Biol Interact. 2019;310:108739. [2]. Rapid and simple colorimetric loop-mediated isothermal amplification (LAMP) assay for the detection of Bovine alphaherpesvirus 1. J Virol Methods. 2021;289:114041.
Additional Infomation	Phenol red is 3H-2,1-Benzoxathiole 1,1-dioxide in which both of the hydrogens at position 3 have been substituted by 4-hydroxyphenyl groups. A pH indicator changing colour from yellow below pH 6.8 to bright pink above pH 8.2, it is commonly used as an indicator in cell cultures and in home swimming pool test kits. It is also used in the (now infrequently performed) phenolsulfonphthalein (PSP) test for estimation of overall blood flow through the kidney. It has a role as a two-colour indicator, an acid-base indicator and a diagnostic agent. It is a 2,1-benzoxathiole, a member of phenols, a sultone and an arenesulfonate ester. Phenolsulfonphthalein or otherwise called phenol red is a pH indicator commonly used in cell biology laboratories. Phenolsulfonphthalein is being investigated for use clinically due to its weak estrogen mimicking actions. Red dye, pH indicator, and diagnostic aid for determination of renal function. It is used also for studies of the gastrointestinal and other systems.

Solubility Data

Solubility (In Vitro)

DMSO: 50 mg/mL (141.09 mM)

Solubility (In Vivo)

Solubility in Formulation 1: ≥ 2.5 mg/mL (7.05 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL. Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution. Solubility in Formulation 2: ≥ 2.5 mg/mL (7.05 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly. Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.  (Please use freshly prepared in vivo formulations for optimal results.)

Preparing Stock Solutions		1 mg	5 mg	10 mg
	1 mM	2.8218 mL	14.1091 mL	28.2183 mL
	5 mM	0.5644 mL	2.8218 mL	5.6437 mL
	10 mM	0.2822 mL	1.4109 mL	2.8218 mL

*Note: Please select an appropriate solvent for the preparation of stock solution based on your experiment needs. For most products, DMSO can be used for preparing stock solutions (e.g. 5 mM, 10 mM, or 20 mM concentration); some products with high aqueous solubility may be dissolved in water directly. Solubility information is available at the above Solubility Data section. Once the stock solution is prepared, aliquot it to routine usage volumes and store at -20°C or -80°C. Avoid repeated freeze and thaw cycles.