Patent ID: 7258726

Claim:
A method of thermal modulation for generating chemical pulses in a fluid stream flowing through a modulator tube, said method comprising the steps of: a. providing a modulator tube comprising an inlet, a first portion in communication with said inlet, a second portion in communication with said first portion, and an outlet portion in communication with said second portion; b. creating a fluid stream in a direction through the modulator tube to produce a carrier fluid stream; c. introducing a sample into the carrier fluid stream, said sample comprising one or more chemical substances; d. manipulating the temperature of the first portion to cause at least a portion of the sample to be retained therein; e. manipulating the temperature of the second portion such that at least a portion of the sample will be retained therein; f. accumulating a sample component in the first portion for a period of time to form a first concentration, the accumulated sample component being carried into the first portion by the carrier fluid stream; g. manipulating the temperature of the first portion to release the first concentration into the carrier fluid stream in the form of a first chemical pulse; h. causing the first chemical pulse to be carried in the direction of the carrier fluid stream flow toward the second portion; i. accumulating the first chemical pulse in said outlet portion so as to focus and hold the first chemical pulse therein for a period of time and form a second concentration which is more compact in distance than the first chemical pulse, sample components of the first chemical pulse being carried to the outlet portion by the carrier fluid stream; j. manipulating the temperature of the first portion to accumulate at least one second sample component therein for a period of time, the at least one second sample component being carried into the first portion by the carrier fluid stream; k. manipulating the temperature of the second portion so as to release the second concentration into the carrier fluid stream in the form of an outlet chemical pulse, the outlet chemical pulse being of shorter duration than the first chemical pulse; l. manipulating the temperature of the second portion such that a subsequent chemical pulse is retained therein; and wherein travel of a first concentration from the first portion to the second portion in step (h) is delayed such that: steps (d), (e), (j) and (l) occur simultaneously during an interval of time; and steps (g) and (k) occur simultaneously during an interval of time.