View - ResearchSpace@Auckland - The University of Auckland

5.1
Chapter 5: Methodological assessment of the chemiluminescence analyser
Introduction
The previous chapter reviewed the methods available to measure NO in biological systems
and determined that the most appropriate method for measuring NO in exhaled air using a
chemiluminescence analyser, originally developed to assess NO pollution levels. The
technical aspects of the chemiluminescence analysers were reviewed and the direct correlation
between the intensity of light measured and the concentration of NO described. The
instrument that I ultimately used was the Dasibi Environmental Corporation 'Model 2107'.In
this chapter the characteristics of this analyser will be reviewed, as well as the other
equipment. Connections between a number of analysers were developed to enable
simultaneous measurement of NO, COz, flow and pressure. I will also mention the other
people involved in the work and the role each person undertook.
5.2 The equipment and personnel
5.2.1 Chemilurninescence Analyser'Model 2107'
The chemiluminescence analyser Model 2107 (Dasibi Environmental Corporation, Glendale,
California, USA; local supplier Quantitech Ltd, Unit 3 Wolverton Rd, Old Wolverton, Mlton
Keynes, UK) was designed for measuring NO concentrations within a 2-4000pbb range in a
continuous ambient air sample and operated in ambient temperatures of 5400 C and humidity
of O-9SVo.It had been adapted for online recording with a sampling rate at 240 mls/min and
had a highly stabilised measurement capability (drift without auto zero over 24 hours of
lppb). The original response time of this machine was long at 90 seconds, too long for the
purpose for which it was now required. Modification of the circuitry and the sending of the
pre-computer analogue signal directly to the chart recorder decreased the response time to 6.4
seconds (see below). The estimates of NO concentrations were decreased by lo-l1Vo at IOOVo
humidity; however NO pre-drying of the expirate was not thought to be necessary (this may
have been considered differently if the experiments were conducted in areas of high humidity
such as within New Zealand). I did use a water absorber when doing the reservoir set of
experiments only (see Section 6.4). This machine operated on the same principles as
described in the last chapter. The gaseous specimen was drawn by the vacuum pump into a
reaction chamber where the ozone was generated internally by an electrical discharger. The
NO and 03 wore mixed in front of a red-sensitive photomultiplier tube, the light emission of
this reaction was measured at 660 to 900nm in the red sensitive range, and the signal
110