Abstract: Techniques for simultaneously detecting direct and reflected ions in a time-of-flight tube (120) and a source (110) for generating an ion beam of ions of a sample and introducing the ion beam into a first portion of the flight tube. A reflector (126) reflects ions from the ion beam in a second portion of the flight tube. A plate (140) substantially perpendicular to an axis of the ion beam is located between the first portion of the flight tube and the second portion of the flight tube. The plate has a hole through which some ions in the ion beam may pass from the first portion to the second portion of the flight tube. Each of two opposite faces of the plate includes a set of one or more ion detectors (140). The technique allows rapid, reliable detection of complex agents in a small number of samples.