Stable colored reference standard for enzymatic determinations

A colored reference standard for use in diagnostic determinations involving enzymatic reactions in which 1-(p-iodophenyl)-5-(p-nitrophenyl)-3-phenylformazan is produced, which comprises an aqueous solution of;

• A. from about 0.001% to about 0.020% by weight of 1-(p-iodophenyl)-5-(p-nitrophenyl)-3-phenylformazan;
• B. from about 0.01% to about 0.10% by weight of serum albumin;
• C. from about 1.76% to about 10% by weight of solvent selected from the group consisting of N,N'-dimethylformamide and dimethylsulfoxide;
• D. from about 1.45% to about 10% by weight of isopropyl alcohol;
• and
• E. from about 5% to about 20% by weight of an inert bulking agent;
• said percentages by weight being based on the weight of the total solution;
• said aqueous colored standard solution having the absorbence maximum at 500 nanometers.

A lyophilized colored reference standard for use in diagnostic determinations involving enzymatic reactions in which 1-(p-iodophenyl)-5-(p-nitrophenyl)-3-phenylformazan is produced, obtained by a process which comprises:

• A. completely dissolving from about 0.001% to about 0.020% by weight of 1-(p-iodophenyl)-5-(p-nitrophenyl)-3-phenylformazan, in about 1.76% to 10% by weight of solvent selected from the group consisting of N,N'-dimethylformamide and dimethylsulfoxide;
• B. adding from about 1.45% to about 10% by weight of isopropyl alcohol to (A) slowly, and mixing thoroughly;
• C. dissolving from about 0.01% to about 0.1.0% by weight of serum albumin and from about 5% to about 20% by weight of inert bulking agent in water;
• D. adding solution (B) to solution (C) slowly, with stirring;
• and
• E. lyophilizing the solution of (D);
• said percentages by weight being based on the weight of the total solution, prior to lyophilization.

A process for preparing a colored reference standard for use in diagnostic determinations involving enzymatic reactions in which 1-(p-iodophenyl)-5-(p-nitrophenyl)-3-phenylformazan is produced which comprises:

• A. completely dissolving from about 0.001% to about 0.020% by weight of 1-(p-iodophenyl)-5-(p-nitrophenyl)-3-phenylformazan, in about 1.76% to 10% by weight of solvent selected from the group consisting of N,N'-dimethylformamide and dimethylsulfoxide;
• B. adding from about 1.45% to about 10% by weight of isopropyl alcohol to (A) slowly, and mixing throughly;
• C. dissolving from about 0.01% to about 0.10% by weight of serum albumin in water;
• D. adding solution (B.) to solution (C.) slowly, with stirring;
• said percentages by weight being based on the weight of the total solution.

A process for preparing a lyophilized colored reference standard for use in diagnostic determinations involving enzymatic reactions in which 1(p-iodophenyl)-5-(p-nitrophenyl)-3-phenylformazan is produced which comprises:

• A. completely dissolving from about 0.001% to about 0.020% by weight, of 1-(p-iodophenyl)-5-(p-nitrophenyl)-3-phenylformazan in about 1.76% to 10% by weight of solvent selected from the group consisting of N,N'-dimethylformamide and dimethylsulfoxide;
• B. adding from about 1.45% to about 10% by weight of isopropyl alcohol to (A) slowly, and mixing thoroughly;
• C. dissolving from about 0.01% to about 0.10% by weight of serum albumin and from about 5% to about 20% by weight of an inert bulking agent in water;
• D. adding solution (B) to solution (C) slowly with stirring;
• and
• E. lyophilizing the solution of (D);
• said percentages by weight being based on the weight of the total solution, prior to lyophilization.