Use of a Carbon Paste Electrode Modified with Spinel‐Type Manganese Oxide as a Potentiometric Sensor for Lithium Ions in Flow Injection Analysis

A potentiometric sensor constructed from a mixture of 25% (m/m) spinel‐type manganese oxide (lambda‐MnO2), 50% (m/m) graphite powder and 25% (m/m) mineral oil is used for the determination of lithium ions in a flow injection analysis system. Experimental parameters, such as pH of the carrier solution, flow rate, injection sample volume, and selectivity for Li+ against other alkali and alkaline‐earth ions and the response time of this sensor were investigated. The sensor response to lithium ions was linear in the concentration range 8.6×10−5–1.0×10−2 mol L−1 with a slope 78.9±0.3 mV dec−1 over a wide pH range 7–10 (Tris buffer), without interference of other alkali and alkaline‐earth metals. For a flow rate of 5.0 mL min−1 and a injection sample volume of 408.6 μL, the relative standard deviation for repeated injections of a 5.0×10−4 mol L−1 lithium ions was 0.3%.