IL gives you fits
COMMENTARY by Ralph H. Muller
And on We make
by Drs. Stevens and informative and encouraging view of what may be expected of second-generation air pollution moniWo were particularly intrigued tors. by Hodgeson, Stevens, and Krost’s improvement of the Regener ozone detecFor many years, the Regener tor. ozone radio sonde has been sent aloft in all comers of the earth. In ignorance of much which has been done with the device, we wonder if the analyst has been too much concerned with the chemical aspects of this detector. mere To what extent have the many collateral aspects of the radio sonde been utilized ? Modem radio telemetry is a vast and highly developed subject. It is entirely possible, in addition to the recording and transmission of ozone concentration, to transmit azimuth, altitude, slant range, temperature, pressure, wind direction and velocity, as well as the intensity of solar radiation. It would seem that a detailed vertical profile of ozone concentration could be recorded which would provide important information on the formation of ozonides, peroxides, and other obnoxious and lacrimatory products. The full resources of computer analysis of the data could furnish far more information than the mere ‘‘spot” determination of ozone concentration. Much of this is done routinely in meteorology and weather forecasting, but, in the latter, the chemical factors are of negligible interest. The other chemiluminescent reactions, such as S02 in a hydrogen flame, are good examples of the second-generation approach, and it is to be hoped that the NAPCA in-housc scientists and their out-of-house scientists under contract, will continue and redouble their efforts in this direction. This is important because all too much work is being done by conventional instrumental methods, and the state of the art is limited by the capabilities of commercially available instruments. We wonder what might be done with abridged mass spectrometers which could be sequentially set for selected mass numbers, says a parent peak or one or two prominent fragment peaks for a given substance. The helium leak detector is a portable single mass spectrometer, and its extension to a limited number of other masses might be reasonably economical. It would, report
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of course, be quite impractical for CO whose mass differs from nitrogen only in the second or third decimal place.
Another approach which might merit
serious attention is a phenomenon long known to spectroscopists. This is the effect of foreign gases on the spectrum of the rare gases. Helium admitted to a high-vacuum system can be excited to luminescence and, even if unresolved by a spectroscope, yields a brilliant yellow-pink glow. If the region around a suspected crack or leak is exposed with a
purpose, too!
tiny unignited jet of illuminating
will at once attain a dull slate color due to the presence of CO. This is about as sensitive as the modern helium leak detector (mass spectrograph) except that in the latter, helium gas has a much higher diffusion coefficient. Band spectra of the foreign gas are excited partly by direct electron bombardment but principally by collisions of the second kind with helium ions. The ionization potential of He (24 eV) is the highest of any known gas and will, therefore, excite them to luminescence. Indeed, at high concentrations of foreign gas, the bulk of the current is carried by the contaminant. It would seem a simple matter to photograph the spectrum of the pure He and then, after photographic intensification of the spectrum plate, to use it as a mask in the image plane, thus obscuring most of the helium radiation. Refocusing all other regions into a slit in front of a phototube would record the radiation of the contaminant. The arrangement could be simple and inexpensive. However, it is not likely that the information would be simple to interpret. Much empirical calibration would be required with mixtures of contaminants. With sufficient data, it might be possible to select a series of readings in different spectral regions. Once more, wo emphasize the sensitivity of the method. It was many years before the correct values of the ionization potentials could be obtained by direct electron bombardment, (true values arc known from spectroscopic data). It was a question of rare gas purity. The rare gases even affect each other. Certain aspects of electron spectroscopy, discussed in detail in the JanuChemary 1970 issue of Analytical istry (pages 20A, 43A), would also appear to have a role in future air pollution studies. gas, the discharge
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ANALYTICAL CHEMISTRY, VOL. 42, NO. 2, FEBRUARY 1970
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