Novel flow-through bulk optode for spectrophotometric determination of lithium in pharmaceuticals and saliva

A new flow-through spectrophotometric bulk optode for the determination of lithium is reported. The optode membrane incorporates a lipophilic pH indicator (chromoionophore XIV), a lipophilic neutral ionophore (lithium ionophore VIII) and potassium tetrakis[3,5-bis(trifluoromethyl) phenyl] borate (ionic additive) as active constituents in a plasticized poly(vinyl) chloride membrane, entrapped in a cellulosic support. The composition of the membrane was tested using two different plasticizers. The optode was incorporated in a flow-injection system optimized for the determination of lithium. The analytical performance of the optode was evaluated, obtaining a linear concentration range of two decades of concentration (1 × 10−4 to 1 × 10−2 M), a limit of detection of 1.4 × 10−4 M, a fast sample throughput (25–4 samples h−1) and good reproducibility and selectivity. The sensor was seen to exhibit a fully reversible response. The proposed FI method is applied to the determination of lithium in pharmaceuticals and human saliva with satisfactory results.