University of California

The picric acid method for determining minute amounts of hydrocyanic acid in fumigated insects


Walton B. Sinclair
R. C. Ramsey

Authors Affiliations

Walton B. Sinclair was Associate Biochemist in the Experiment Station; R. C. Ramsey was Principal Laboratory Technician, Citrus Experiment Station.

Publication Information

Hilgardia 16(6):291-300. DOI:10.3733/hilg.v16n06p291. September 1944.

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In studies on the toxic effect of different concentrations of HCN (hydrocyanic acid) on fumigated insects, determinations of the amounts of the gas absorbed and retained are important. To secure these facts, an accurate method of determining amounts of HCN in the range of 0.005 to 0.200 mg is essential. Extensive preliminary investigations showed that the picric acid method had the greatest promise.

Picric acid in alkaline solution has been widely used as a reagent in colorimetry. It has been commonly used in determining soluble sugars in plant extracts and creatinine in animal fluids. In the procedures for determining reducing sugars, the reaction involves the reduction of the nitrophenol to aminophenol. In the presence of reducing sugars, picric acid (trinitrophenol) is reduced to picramic acid when heated in alkaline solution. The same basic reaction is involved in the determination of creatinine. According to the literature, a different reaction occurs between HCN and picric acid in alkaline solution.

Hlasiwetz (1859) 5 was the first to note the formation of isopurpuric acid according to the following equation:

C6H3N307 + 3KCN + 3H20 ? C8H4KN506 + CO2 + NH3 + 2KOH
Picric acid Potassium

Rosenthaler (1923), also, noted that blood-red isopurpuric acid is formed when picric acid and KCN are heated in alkaline solution. Some disagreement exists about the formation of isopurpuric acid. According to Chapman (1911), the reaction is identical with the reducing reaction between picric acid and reducing reagents, resulting in the formation of 2-amino-4,6-dinitrophenol.

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Sinclair W, Ramsey R. 1944. The picric acid method for determining minute amounts of hydrocyanic acid in fumigated insects. Hilgardia 16(6):291-300. DOI:10.3733/hilg.v16n06p291
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