Development of instrumentation for NQR spectroscopy and multiplex sample NMR

George Gregory Fisher, Purdue University

Abstract

This thesis describes the development and construction of a computer controlled, fully automated, Nuclear Quadrupole Resonance (NQR) spectrometer. The spectrometer features phase locked, superheterodyne detection using a commercial spectrum analyzer and a fully automatic, computer controlled tuning and matching network. The tuning and matching network employs stepper motors which turn high power air gap capacitors in a “moving grid” optimization strategy to minimize the reflected power from a directional coupler. In the duplexer circuit, digitally controlled relays are used to switch different lengths of coax cable appropriate for the different radio frequencies. A home-built pulse programmer card controls the timing of radio frequency pulses sent to the probe, while data acquisition and control software is written in Microsoft Quick Basic. A sampling of a variety of different applications of this NQR spectrometer is provided to demonstrate its versatility. ^ In Part II of this thesis, a dual channel liquid NMR probe for the simultaneous acquisition of NMR data from multiple liquid samples is demonstrated. This multiplex probe consists of two non-interacting sample coils that are each capable of detecting NMR signals at the same resonant frequency with good sensitivity and resolution. 13C free induction decays for the two samples, methanol (13C, 99%) and carbon tetrachloride ( 13C, 99%), were acquired simultaneously at 75.44 MHz using a single transmitter pulse and separate NMR receivers. The NQR spectrometer described in Part I of this thesis is used as one of the receivers. S/N measurements are comparable to those observed using single coils. No evidence of cross talk is evident in the spectra even after considerable signal averaging. The probe demonstrates the feasibility of significant parallelism in NMR, which will be of interest in situations where high throughput analysis is desired. ^

Degree

Ph.D.

Advisors

Major Professor: M. Daniel Raftery, Purdue University.

Subject Area

Chemistry, Analytical|Chemistry, Nuclear

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