A concentrator and sensor assembly are disclosed that use phased heaters to multiply the concentration levels that can be eluted, relative to operation with a single interactive element having a sorbent material to increase the concentration of desired gas constituents at a detector. This is accomplished here by providing two or more interactive concentrator elements that are selectively heated in a time phased sequence so that each of the interactive elements becomes heated and desorbs gas constituents into the sample fluid stream at substantially the same time that an upstream concentration pulse, produced by heating one or more upstream interactive elements, reaches the interactive element. This produces a multiplication effect that significantly increases the concentration of the gas constituents at the detector, thereby increasing the effective sensitivity of the detector.