Pyrocatechol violet-metal protein assay

A protein assay reagent composition comprising

• pyrocatechol violet at a concentration of 0.26 mM;
• sodium molybdate at a concentration of 0.16 mM;
• polyvinyl alcohol at a concentration of about 0.2% w/v;
• methanol at a concentration of about 4%;
• succinic acid at a concentration of about 50 mM;
• sodium oxalate at a concentration of about 1.0 mM;
• sodium benzoate at a concentration of 3.5 mM;
• and
• polyvinyl pyrrolidone at a concentration of about 0.1% w/v,
• wherein the pH of the protein assay reagent composition is about pH 2.5.

A method for determining protein concentration in a sample, the method comprising

• (a) combining the sample with a protein assay reagent composition comprising
• pyrocatechol violet at a concentration from about 0.1 mM to about 0.5 mM;
• a metal at a concentration from about 0.05 mM to about 0.4 mM;
• polyvinyl alcohol at a concentration from about 0.05% w/v to about 0.4% w/v;
• optionally methanol at a concentration from about 0% v/v to about 10% v/v,
• polyvinyl pyrrolidone at a concentration from about 0.05% w/v to about 0.2% w/v,
• a buffer at a concentration from about 25 mM to about 200 mM,
• and at least one of
• a chelator at a concentration from about 0.05 mM to about 2 mM, or
• sodium benzoate at a concentration from about 1 mM to about 6 mM,
• wherein the pH of the protein assay reagent composition is from about pH 1 to about pH 4, and
• wherein combining the sample with the protein assay reagent composition results in a protein determination mixture;
• (b) incubating the protein determination mixture for a time sufficient to form a colored complex;
• (c) measuring the absorbance of the colored complex;
• and
• (d) determining the protein concentration in the sample by comparing the measured absorbance with the absorbance obtained from at least one sample containing a known concentration of protein.

A method to enhance compatibility of a protein determination assay with a sample containing at least one interfering substance, the method comprising

• (a) combining the sample with a protein assay reagent composition comprising
• pyrocatechol violet at a concentration from about 0.1 mM to about 0.5 mM;
• a metal at a concentration from about 0.05 mM to about 0.4 mM;
• polyvinyl alcohol at a concentration from about 0.05% w/v to about 0.4% w/v;
• optionally methanol at a concentration from about 0% v/v to about 10% v/v,
• polyvinyl pyrrolidone at a concentration from about 0.05% w/v to about 2% w/v,
• a buffer at a concentration from about 25 mM to about 200 mM,
• and at least one of
• a chelator at a concentration from about 0.05 mM to about 2 mM, or
• sodium benzoate at a concentration from about 1 mM to about 6 mM,
• wherein the pH of the protein assay reagent composition is from about pH 1 to about pH 4, and wherein combining the sample with the protein assay reagent composition results in a protein determination mixture;
• (b) incubating the protein determination mixture for a time sufficient to result in the formation of a colored complex;
• (c) measuring the absorbance of the colored complex;
• and
• (d) determining the protein concentration in the sample by comparing the measured absorbance with the absorbance obtained from at least one sample containing a known concentration of protein, wherein the interfering substance is selected from the group consisting of detergents, reducing agents, chelating agents, buffers, reagents, solvents, and combinations thereof, and wherein the method enhances the compatibility of the protein determination assay with a sample containing at least one interfering substance.