What is the pH of the reaction in the Evelyn-Malloy method?

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Multiple Choice

What is the pH of the reaction in the Evelyn-Malloy method?

Explanation:
The essential idea here is that the color reaction in the Evelyn-Malloy bilirubin assay relies on a diazo coupling step that only happens readily in strongly acidic conditions. In this method, a diazonium ion is formed from an aromatic amine (like sulfanilic acid) under acidic conditions. Bilirubin then reacts with that diazonium ion to produce a colored azobilirubin complex. The acidic environment stabilizes the diazonium ion and enables the coupling reaction, yielding a color whose intensity is proportional to bilirubin concentration. If the medium were neutral or basic, the diazonium ion would be unstable or decompose, and little to no color would develop. Therefore, the pH of the reaction is acidic.

The essential idea here is that the color reaction in the Evelyn-Malloy bilirubin assay relies on a diazo coupling step that only happens readily in strongly acidic conditions. In this method, a diazonium ion is formed from an aromatic amine (like sulfanilic acid) under acidic conditions. Bilirubin then reacts with that diazonium ion to produce a colored azobilirubin complex. The acidic environment stabilizes the diazonium ion and enables the coupling reaction, yielding a color whose intensity is proportional to bilirubin concentration. If the medium were neutral or basic, the diazonium ion would be unstable or decompose, and little to no color would develop. Therefore, the pH of the reaction is acidic.

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