Electroanalysis at salt - cotton - electrode interfaces: preconcentration effects lead to nano-molar Hg(2+) sensitivity

Cotton is employed as a sample absorbent which is analysed sandwiched between a glassy carbon electrode and ammonium nitrate salt in a humidified argon atmosphere (ca. 80% relative humidity). Exploratory experiments show that well-defined voltammetric responses for the Fe(CN)(6)(3-/4-) redox system pre-absorbed into cotton are observed. Experiments with gold plating solution absorbed into cotton reveal the microscopic regions (cotton - glassy carbon contact points) of electrochemical activity where gold microparticles are plated onto the cotton surface. Stripping voltammetry experiments for trace metals such as Hg(2+) pre-absorbed into cotton show a surprisingly high sensitivity with nanomolar detection readily achieved.