Process Biochemistry 35 (2000) 897 – 905 Trace metal analysis: selective sample (copper II) enrichment on an AlgaSORB column Rachana Singh, B.B. Prasad * Analytical Diision, Chemistry Department, Banaras Hindu Uniersity, Varanasi 221 005, India Received 24 August 1999; accepted 14 November 1999 Abstract A new approach to sample enrichment for copper(II) determination at trace level is reported. The silica-immobilised cationic polyelectrolyte, [poly (N-xylene-N,N dicyclohexyl ethylenediamine dibromide)], capable of electrostatic binding with the biofilm of a natural alga Spirogyras sp is used in column separation for enrichment of trace analyte for accurate detection by differential pulse anodic stripping voltammetry. Algae – silica preparation termed as AlgaSORB-sp involves the molecular-level polymer coating as ‘spacer’ between algae and silica gel. This enables the entire algal film to be accessible for metal uptake and prevents the trace analytes becoming entrapped into the inner-core of the macroporous silica gel. The unique Cu 2 + ion-selectivity from multi-elemental complex matrices circumvents the usual problems of overlapping peaks and intermetallic effects. Effects of flow rate, pH, equilibration time and other variables are reported. The system has attractive features for application in single-column ion-chromatography with high durability, simplicity and economy. © 2000 Elsevier Science Ltd. All rights reserved. Keywords: Spirogyra ; Biosorption; AlgaSORB; Trace metal analysis; Selective enrichment; Stripping voltammetry www.elsevier.com/locate/procbio 1. Introduction The binding of metal ions through biological pro- cesses has been reported to involve biosorption, intra- cellular uptake and chemical transformations [1 – 6]. In particular, biosorptive interactions of several heavy metals with various algae and their applications in waste-water treatment and metal recovery have been illustrated [3,7]. Several cell-wall constituents were found to be involved in metal binding, particularly through amino and carboxyl groups from both amino acids and polysaccharides [8], sulphydryl [9] groups and unmethylated pectins [10]. The pre-concentration of copper and several other elements on green algae has been reported [10,11]. Different algae exhibit different affinities towards dif- ferent metals and different metals exhibit different pH- binding profiles. Although the usual mechanism of metal uptake by the chemically complex matrices of algae is often ionic-bonding, the existence of covalent bonding in some cases has also been known [8]. Such algae – metal interactions are being utilised for techno- logical advancements to develop electrochemical sen- sors [4,12]. In view of the fact that the non-immobilised algal cells may clump together during flow-analysis, the present paper describes the utility of algal biomass when immobilised as a biofilm on silica gel. The use of polyelectrolyte as ‘spacer’ in between the algal cells and silica gel apparently obviates the usual problems of column clogging and rapid deterioration caused by the irreversible adsorption of interfering organic and inor- ganic particulates present in complex matrices of the samples under study. Furthermore, the polymeric spacer also serves as an ‘armour’ around silica gel restricting any percolation of metal analyte into its macroporous structure. From the economic point of view, the proposed algae-silica preparation referred to as AlgaSORB-sp, is deliberately made from the natural dead cells of multi-cellular filamentous green algae, Spirogyra, which provides a biofilm (in dimethylfor- mamide) of excellent durability after immobilisation over the polymer-modified silica gel. The system is well suited for the continuous monitoring of heavy metals * Corresponding author. Fax: +91-542-317074. 0032-9592/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 3 2 - 9 5 9 2 ( 9 9 ) 0 0 1 5 0 - 8