Differential pulse polarographic determination of poly(8-hydroxyquinoline) in the presence and absence of an insulating poly(vinyl alcohol) matrix

The electrochemical activity of poly(8-hydroxyquinoline) (PHQ) in acid and alkaline media has been investigated by use of differential pulse polarography (DPP). The reduction peak height (I(p)) of PHQ in universal buffer solutions is not useful as an analytical signal, because it is highly affected by hydrogen evolution in acid media and appears as a small peak located at more negative potential values in alkaline media. A new and highly sensitive reduction peak (E(p)=-0.45, pH 9.25) appears, however, after addition of trace amounts of PHQ to Cu(II), or vice versa. This reduction peak is a result of the reduction of Cu(II) chelates in the PHQ-Cu(II) complex and is highly promising for the trace determination of PHQ at nanomolar and submicromolar levels. The response current (I(p)/mu A) for the reduction peak of Cu(II) chelates in a PHQ-Cu(II) matrix results in sensitivity to the concentration of PHQ at least three orders of magnitude higher than that for the reduction peak of PHQ alone under the same conditions. The limit of detection is as low as 5.264 ppb (microg L(-1)). The effect of a variety of anions and cations and of an insulating poly(vinyl alcohol) (PVA) matrix has been investigated. Electroactive PHQ-Cu(II) at a level of 0.685% could induce a current of approximately 240 nA in an insulating PVA matrix, suggesting possible application for the preparation of a PHQ-Cu(II)-PVA electroactive composite.