This paper reports the use of unmodified mixed cellulose ester membrane (MCEM) as a simple, novel and efficient substrate in matrix-free pulsed laser desorption/ionization mass spectrometry (LDI-MS) for the detection of lead ions (Pb2+) in water (tap water and coastal seawater) and biological (urine) samples and drinking straws. The discovery of trace amounts of lead in the original MCEM prompted us to investigate the special interactions between the MCEM and the Pb2+ ions. When using an MCEM, first to concentrate Pb2+ ions and then as an efficient LDI substrate, our membrane-based LDI-MS approach exhibited high sensitivity [limit of detection (LOD): 0.05nM] and selectivity (tolerance at least 1000-fold relative to other metal ions) for the detection of Pb2+ ions in aqueous solutions. Based on the special ability of the MCEM, an easy method has been developed to detect Pb2+ ions in drinking straws, by simply rubbing the straws with MCEM and then using LDI-MS. The ability of the MCEM to adsorb metal ions and its interesting surface functional properties should open up new opportunities for its application in LDI-MS for the detection of other contaminants in environmental samples.