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F9252 Sigma-Aldrich

Folin & Ciocalteu’s phenol reagent

suitable for determination of total protein by Lowry method, 2 N



Frequently Asked Questions

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Other Notes

Folin & Ciocalteu′s phenol reagent does not contain phenol. Rather, the reagent will react with phenols and non-phenolic reducing substances to form chromogens that can be detected spectrophotometrically.


This product is also available as part of a kit.


1 L in glass bottle

100, 500 mL in glass bottle


Folin & Ciocalteu′s phenol reagent is most commonly used in the Lowry method for determining protein concentration.1 In this method, protein is pretreated with copper(II) in a modified biuret reagent (alkaline copper solution
stabilized with sodium potassium tartrate). Addition of the phenol reagent generates chromogens that give increasing absorbance between 550-750 nm. Normally, absorbance at the peak (750 nm) or shoulder (660 nm) are used to quantitate protein concentrations between 1-100 mg/ml while absorbance at 550 nm is used to quantitate higher protein concentrations.
In the absence of copper, color intensity is determined primarily by the tyrosine and tryptophan content of the protein, and to a lesser extent by cysteine and histidine. Copper(II) has no effect on color formation by tyrosine, tryptophan, or histidine, but reduces color formation due to cysteine.1,2,3,4,5

Many modifications of the original assay procedure have been published,2 including methods for enhancing the color development,4,6 for determining the content of insoluble proteins,1,7 and for automating the procedure.8 Compounds including many buffers, chelating agents, detergents, and cyclic organic compounds can interfere with the Lowry protein assay.2
Folin & Ciocalteu′s phenol reagent can also be used as a spray reagent in chromatographic procedures.

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Safety & Documentation

Safety Information

GHS05  GHS05
Signal word 
Hazard statements 
Precautionary statements 
Hazard Codes (Europe) 
Risk Statements (Europe) 
Safety Statements (Europe) 
UN 3264 8 / PGIII
WGK Germany 


Certificate of Analysis

Certificate of Origin

Protocols & Articles


Enzymatic Assay of Protease Using Casein As a Substrate

1. OBJECTIVE To standardize a procedure for the enzymatic assay of Protease using Casein as a substrate at Sigma-Aldrich St. Louis.

Enzymatic Assay of Proteinase K (EC

This procedure may be used for determination of Proteinase K activity using hemoglobin as the substrate. It is not used to assay the activity of immobilized Proteinase K products, such as Catalog Num...
Keywords: Immobilization

Protein Determination Modified Lowry Method

1. OBJECTIVE To standardize a procedure for the determination of protein by modified Lowry at Sigma-Aldrich, St. Louis, MO.
Keywords: Biochemistry, Lowry assay, Precipitation, Protein assay

Peer-Reviewed Papers


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1. Protein measurement with the Folin phenol reagent. Lowry, O.H., et al. J. Biol. Chem. 193, 265-275, (1951)


2. Review of the Folin phenol protein quantitation method of Lowry, Rosebrough, Farr and Randall. G.L. Peterson Anal. Biochem. 100, 201, (1979)


3. Analysis of phenolic compounds of interest in metabolism. BRAY HG and THORPE WV Methods Biochem. Anal. 1, 27-52, (1954)


4. A simplified method of quantitating protein using the biuret and phenol reagents. Ohnishi, S. T., Barr, J. K. Anal. Biochem. 86, 193-200, (1978)


5. Lowry's method of protein estimation: some more insights. Sengupta S and Chattopadhyay MK J. Pharm. Pharmacol. 45(1), 80, (1993)


6. Artificial reductant enhancement of the Lowry method for protein determination. Larson E, Howlett B, and Jagendorf A Anal. Biochem. 155(2), 243-8, (1986)


7. A simplification of the protein assay method of Lowry et al. which is more generally applicable. Peterson, G.L., et al. Anal. Biochem. 83, 346-356, (1977)


8. Lowry protein assay using an automatic microtiter plate spectrophotometer. Fryer HJ, Davis GE, Manthorpe M, et al. Anal. Biochem. 153(2), 262-6, (1986)


Bioactive compounds from culinary herbs inhibit a molecular target for type 2 diabetes management, dipeptidyl peptidase IV. Bower AM, Real Hernandez LM, Berhow MA, et al. J. Agric. Food Chem. 62(26), 6147-58, (2014)


Antioxidant activity and free radical-scavenging capacity of Gynura divaricata leaf extracts at different temperatures. Wan C, Yu Y, Zhou S, et al. Pharmacogn. Mag. 7(25), 40-5, (2011)


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TP0200 Total Protein Kit, Micro-Lowry, Onishi & Barr Modification, sufficient for ~50 manual assays
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