A device for detecting a class of target species containing quadrupolar nuclei in a specimen by nuclear quadrupole resonance, comprising a pulse generator for generating a three-pulse-composite-pulse to refocus signals that were excited by another pulse, an irradiator for irradiating a specimen with the three-pulse-composite-pulse, a detector for detecting an NQR signal in response to irradiating the specimen, a coupler for transmitting the three-pulse-composite-pulse to the irradiating means, and a transformer for converting the free induction decay signal into a frequency domain signal. A method for detecting a class of target species containing quadrupolar nuclei in a specimen by nuclear quadrupole resonance, comprising generating a three-pulse-composite-pulse, irradiating said specimen with said three-pulse-composite-pulse, detecting an NQR signal in response to irradiating said specimen and converting said free induction decay signal into a frequency domain signal.