one aspect of the present invention is a method for detecting a class of target species containing quadrupolar nuclei in a specimen by nuclear quadrupole resonance , comprising : generating a random or pseudo - random train of rf pulses ; irradiating the specimen with the train of rf pulses ; detecting an nqr signal in response to irradiating the specimen ; cross - correlating the nqr signal with the random or pseudo - random train of rf pulses , thereby generating a free induction decay signal ; and converting the free induction decay signal into a frequency domain signal . another aspect of the present invention is an apparatus for carrying out the method of the invention .