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F9252 Sigma-Aldrich

Folin & Ciocalteu’s phenol reagent

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



General description

Folin & Ciocalteu′s phenol reagent is most commonly used in the Lowry method for determining protein concentration. It has also been used for the quantification of total phenolics. 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 550-750nm. Normally, absorbance at the peak (750nm) or shoulder (660nm) are used to quantitate protein concentrations between 1-100 mg/ml while absorbance at 550nm 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.
Many modifications of the original assay procedure have been published, including methods for enhancing the color development, for determining the content of insoluble proteins, and for automating the procedure. Compounds including many buffers, chelating agents, detergents, and cyclic organic compounds can interfere with the Lowry protein assay.
Folin & Ciocalteu′s phenol reagent can also be used as a spray reagent in chromatographic procedures.


Folin & Ciocalteu’s phenol reagent has been used for the estimation of total phenolic content in samples.


1 L in glass bottle

100, 500 mL in glass bottle

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.

Safety & Documentation

Safety Information

GHS05  GHS05
Signal word 
Hazard statements 
UN 3264 8 / PGIII
WGK Germany 
Flash Point(F) 
Not applicable
Flash Point(C) 
Not applicable


Certificate of Analysis (COA)

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Certificate of Origin (COO)

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Frequently Asked Questions

What concentrations of proteins does Product F9252, Folin & Ciocalteu's phenol reagent, detect?
Generally, Folin & Ciocalteu's phenol reagent is used to determine protein concentrations between 1 to 100 μg/mL. However, the reagent exhibits a linear response to protein concentration up to 1000 μg/mL when used according to the instructions for kit Product No. TP0200.
Can Product F9252, Folin & Ciocalteu's phenol reagent, be used to detect any protein?
If the protein has an abnormally low tyrosine content, this method would not be suitable.
What should Product F9252, Folin & Ciocalteu's phenol reagent, look like?
The Folin & Ciocalteu's phenol reagent should be a clear yellow solution. If the solution turns green, it may not be suitable and it should not be used.
Does Product F9252, Folin & Ciocalteu's phenol reagent, contain phenol?
The Folin & Ciocalteu's phenol reagent does not contain phenol but reacts with phenol and non-phenolic reducing substances to form chromogens that can be detected spectrophotometrically.
Which document(s) contains shelf-life or expiration date information for a given product?
If available for a given product, the recommended re-test date or the expiration date can be found on the Certificate of Analysis.
How do I get lot-specific information or a Certificate of Analysis?
The lot specific COA document can be found by entering the lot number above under the "Documents" section.
How do I find price and availability?
There are several ways to find pricing and availability for our products. Once you log onto our website, you will find the price and availability displayed on the product detail page. You can contact any of our Customer Sales and Service offices to receive a quote. USA customers: 1-800-325-3010 or view local office numbers.
What is the Department of Transportation shipping information for this product?
Transportation information can be found in Section 14 of the product's (M)SDS.To access the shipping information for this material, use the link on the product detail page for the product.
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Single- & multi-channel pipettes from BRAND
Protocols & Articles


Enzymatic Assay of Protease Using Casein As a Substrate

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 is for determining Proteinase K (EC activity using hemoglobin as the substrate.
Keywords: Immobilization

Protein Determination Modified Lowry Method

1. OBJECTIVE To standardize a procedure for the determination of protein by modified Lowry.
Keywords: Biochemistry, Lowry assay, Precipitation, Protein assay

Peer-Reviewed Papers


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TP0200 Total Protein Kit, Micro-Lowry, Onishi & Barr Modification, sufficient for ~50 manual assays
TP0300 Total Protein Kit, Micro Lowry, Peterson’s Modification

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