Linear Sweep Voltammetric Determination of Heparin Based on Its Interaction with Neutral Red

In this article the interaction of neutral red with heparin was characterized by linear sweep voltammetry on the hanging mercury drop electrode (HMDE) and further used for the determination of heparin. In pH 1.5 Britton‐Robinson (B‐R) buffer solution, neutral red (NR) has a well‐defined second‐order derivative linear sweep voltammetric reductive wave at −0.24 V (vs. SCE). After the addition of heparin into the NR solution, the reductive peak current decreases without the movement of the peak potential and the appearances of new peaks in the scanning potential range. Based on the decrease of the reductive peak current, a new voltammetric method for the determination of heparin is established. The conditions for the interaction and the electrochemical detection are optimized, and the interference substances for detection are investigated. Under the optimal conditions, the decrease of reductive peak current of NR is proportional to heparin concentration in the range of 2.0–10.0 mg/L with the linear regression equation as Δip″(nA)=−172.03+71.49C (mg/L), (n=9, γ=0.997) and the detection limit is 1.34 mg/L. This new method is further successfully applied to the determination of heparin in heparin injection samples with satisfactory results. The binding ratio and binding mechanism of NR with heparin are also discussed.