I/EC
Instrumentation
ANALYSIS-1961 by P. H. Stirling and Henry Ho, Canadian Industries Ltd.
Portable low-cost neutron sources bring advanced nucleonic techniques right into the process plant • OR ANALYSIS instrumentation, 1960-61 has been a year of modest development and quiet consolida tion, far removed from the hurried spate of development of 1957-58 occasioned by the rapid acceptance and exploitation of gas chroma tography in that year. Although 1960-61 has not brought forth a major technique development of like significance, nevertheless, sev eral significant milestones have been passed in the progress of analyt ical instrumentation. The most startling of these has been the successful development of portable low-cost neutron sources which promise to bring many ad vanced nucleonic techniques right into the plant. Those who have hitherto considered neutrons at high flux levels as irrevocably connected with the huge complex of a nuclear reactor or large complicated physics accelerator machines must now revise their thinking. The on-site generation of short lived radiotracers which severely reduce the hazards of contamina tion and eliminate the awkward transportation problems usually as sociated with these has been suc cessfully applied to chemical en gineering studies. Dow Chemical reported (Nucleonics, December 1960) the successful use of small accelerator-generated radio-man ganese in mixing studies.
1961 IMA Symposium
The potentialities of the new pulsed tube neutron sources, which are as yet in lusty infancy, were brought sharply to the attention of engineers and chemists who met in Houston (April 17-19) for the Seventh Annual ISA Instrumental Methods of Analysis Symposium. The keynote address and a special session on radiation methods of analysis stressed the growing applica tion of nucleonic techniques.
Portable Neutrons
The recent development of the small black box push-button neu tron source was traced in the key note address (W.W. Meinke). The possibility of online generation of short-lived tracers just prior to count ing using these sources aroused great interest. This effectively promises "cool" radiotracers where specific inert trace "tracer" ele ments are added to the process and later activated just prior to analysis in sample side streams. This re duces equipment contamination haz ards and saves much inconvenience. Three companies (Kaman Nu clear, Phillips, and the Schlumberger Corp.) now offer small sealed tube pulsed neutron sources in the cost range of $8,000 to $30,000. The units somewhat resemble industrial x-ray machines with the tube unit being a cylinder several inches in diameter and between 1 and 2 feet long. The tube units, some of which are specially designed for well log ging, may be used several thousand feet or more away from the main power console. It appears likely that all the manufacturers will soon offer these in explosion-proofed hous ings suitable for field use. The fluxes (108—1010n/sec.), which use the deuterium-tritium reaction for neutron generation, are inter mediate between laboratory ac celerators (108 —1014re/sec.) and isotopic sources (106— lOWsec). The ability to pulse the neutron source (pulses as rapid as 2 microseconds are possible) and to generate neu trons only on demand lends itself to many applications. These tubes virtually eliminate the extensive safety regulations necessary in reactor operation. The fast pulse speed offers possibilities of flow measure ments in awkward situations using pulsed internally generated short lived tracers. At the moment, tube neutron sources are undergoing rapid
development and the available neu tron flux, which is still a little on the low side for some applications, will probably be increased by one or two decades within a year. One proto type delivering better than 10* neutrons sq. cm. per second is reported to be in the final stages of development at Kaman Nuclear. These sources make possible ana lytical schemes involving the γ-ray detection of prompt 7-radiation, gamma decay of a daughter radio isotope, or γ-radiation generated dur ing inelastic neutron-collision proc esses. Alternatively direct neutron detection methods involving fast neutron detection or slow neutron detection are feasible. The former may be made the basis for an ana lytical scheme where a strong neu tron absorber such as calcium or boron is to be analyzed. The latter is useful if one desires to estimate light atoms such as hydrogen in the process stream and has made the basis of moisture determination in certain streams. The determina tion of oxygen in the presence of fluorine and of various trace metals, such as vanadium, copper, alumi num, and iron in oils were men tioned as favorable applications of the neutron activation technique. Onstream boron analysis was mentioned as a suitable neutron absorption ap plication. The latter is not a new application, because isotope neutron sources have already been success fully applied to the problem by the Mine Safety Corp. about 1957. However, the greater sensitivities promised by the larger neutron fluxes of the tube neutron genera tors should extend the range of boron analysis considerably.
X-Rays in Process Analysis
The use of β-isotope sources in various arrangements to excite char acteristic Κ or L x-rays was reported as a new promising laboratory tech nique. At present, resolution of the method appears to be limited to systems where the components are more than eight atomic numbers VOL. 53, NO. 7
JULY 1961
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INSTRUMENTATION apart. The x-rays emitted are very feeble, and quite strong beta sources are required. However, the present availability of cheap high strength beta sources makes this technique attractive. The use of a statis tically steady exciting source elim inates the annoying variations met in the ordinary x-ray excitation methods. This promises to develop into a versatile analytical method which will be considerably cheaper than, but analytically equivalent to, the present x-ray excitation tech niques. The extension of this tech nique to process analysis may prove feasible in the near future. The use of coherent back-scat tered x-radiation (Rayleigh scatter ing) for estimating high atomic number components in process streams was proposed. The in cident x-rays were produced by beta excitation of fluorescent x-rays in a clathrate of uranium oxide, hydraquinone, and the Kr 85 beta emitter. This combination has the advantages of low cost and long life and produces 97-k.e.v. x-rays mixed with a little 520-k.e.v. x-radiation. The 70 to 100-k.e.v. range of xradiations energies is optimum for Rayleigh scattering. Successful tests on process piles carrying solutions of lead salts and tetraethyllead in gasoline have given encouraging results. In the latter case it was estimated that the sys tem could warn of concentrations exceeding 10 ml. per gallon with fair precision. By mixing pulses of uranium or lead compounds into process streams, this technique might possibly be applied to flow estima tions in awkward cases. It pro vides a less sensitive "cool" tracer than neutron activation techniques, but has the great advantage of lower cost. The simple detector system required is merely a conventional sodium iodide scintillation crystal and photomultiplier tube with the usual regulated power source. γ-Radiation Density Gages
The estimation of densities in the polymer range, 0.80 to 1.50 with an accuracy of better than 0.004 units, using a gamma radiation (cesium137) source and the simultaneous monitoring of density and of a fluid interface using two γ-radiation gages, were reported by Union Carbide. The high energy gamma 52 A
sources are normally not usable in pipelines smaller than 3 or 4 inches. The alternative Bremstrahlung gages cannot be used with wall thick nesses above '/< inch or so. An ingenious arrangement of a point source of high energy 7-radiation detector and shields, so as to provide a long diagonal path through the pipeline, was used to enable the 7-radiation technique to be ex tended to pipe sizes down to l/t inch and to thick-walled pipes. The necessary special screening tech niques to reduce back-scattering radiation and direct source radia tion reaching the detector so as to give high sensitivity and the use of simple calibrating absorbing plates of steel were described. All com ponents are mounted externally to the pipeline which need not be dis turbed. The unit was reported to have given over a year's service requiring no maintenance. Routine readjustment of the scale every three months compensates for the slight decay of the source. pH Today
The present status of pH was re viewed. There has been an inter esting European development where in a solution which changes so as to compensate for temperature shifts is incorporated inside the calomel electrode. This enables the glasselectrode pH meter to be used at temperatures other than that at which it was calibrated without com pensating resistors. The successful use of ultrasonic generators under pH electrodes to minimize fouling was reported. The use of thallous chloride and thallous amalgams as reference electrodes at high tem peratures appears to offer advantages over the conventional calomel elec trode which is limited to 80° C. This may help advance high tem perature pH measurement. The dynamics of pH glass elec trodes and pH cells were shown to depend on diffusional and mixing times and to have a definite hys teresis, probably because of the es tablishment or destruction of a boundary layer. The change from acid to water is faster than the change from water to acid. The dynamics in the latter case were flow-rate dependent and appear to correlate with film thickness.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Chemical Methods of Analysis
The "chemist in a box" analytical systems for wet chemical analysis have taken great strides forward in the last year. Fisher Scientific Co. developed an improved and highly accurate piston displacement sys tem which forms the basis of their automated digital read-out wet ana lyzer. This is capable of at least the same precision as a well trained technician, if not better, and can be adapted to the onstream analysis of practically any wet system pres ently analyzed in the laboratory. A less accurate but less costly, wet analysis is provided by the Technicon Co. Autoanalyzer which uses a colorimetric estimation. This has a multi-channel proportioning pump of the peristaltic type which squeezes multiple Tygon tubes so as to proportion reagents to a flow system. The color developed is monitored by a twin photocell sys tem. The successful application of this system to the chemical analysis of hardness, silica, phosphate, chlo ride, copper, iron, and hydrogen and similar constituents in boiler feed water was described. The Milton-Roy Co. described a new technique of intermittent analysis using a sample-injection valve similar to a gas chromato graphic system but using a dual valve which also automatically diluted the sample. This system has better reproducibility than the usual man ual dilution techniques used in volumetric analysis. The combina tion of such valves and the specially designed mixing and holding cham bers which are available enables a wide variety of wet analyses to be carried out. The great versatility of these combinations will undoubt edly lead to broader application. Electrolytic Hygrometry
The electrolytic hygrometer using the twin-wire phosphoric anhydride cell (Consolidated Electrodynamics Corp.) has been utilized as a basic detector for the elemental deter mination of hydrogen and carbon in organic compounds. The H2O gen erated on combustion using cata lytic afterburners is determined in the usual manner and the CO2 is either made to liberate quantita tively an equivalent quantity of H 2 0 from a heated (250° C.)
INSTRUMENTATION alkali hydroxide (LiOH supported on carborundum) or is determined by gas chromatography. The determination of water in jet fuels has also been successfully accomplished by CEC. The prob lem of suspended water has been over come by special filtering methods. The electrolytic hygrometer gives readings of both entrained water and dissolved water by stream switching. The water in the fuel is transferred to a dry nitrogen stream, which then continues to the analyzer cell, in a specially constructed high efficiency falling film absorber. Ranges of 0 to 10, 0 to 100, or 0 to 1000 p.p.m. may be indicated. Extensive light-scattering tests to examine the efficiency of the filtra tion technique could not detect any suspended material. Gas Chromatography
Attention is still centering on high speed chromatography and ioniza tion detectors. The development of columns for high speed determina tion of C4 paraffins and olefins was reported by Texas Butadiene, and a medium 60-80 mesh support was found to give best results. Par tition columns give best results at 10% loading, and acid-treated Chromosorb Ρ was needed for good separation in less than 2 minutes. The development of several new sample injection valves based on the sliding-plate principle was described (Monsanto and Beckman Instru ment) as was the development of sample valves for direct liquid injection (Micro-Tek Instruments). A versatile tape programmed con troller unit for a process chromatograph using a loop of photographic film and a reading photocell was described by Mine Safety Appli ances. Although this is a recent development, the versatility and con venience of the unit for repetitive laboratory gas chromatography was soon realized. A description of an ingenious modification of this pro gramming unit to make it suitable for wide-range laboratory gas chro matography was given by the Mon santo Co. The modification in volved setting up a relay matrix and incorporating a unit which allowed either automatic or the conven tional manual switching of attenua tion in a facile manner.
A description of a simple mathe matical system for predicting separa tions of gas chromatography col umns was given by the PerkinElmer Corp. This system guides the manipulation of retention times by using mixed partition liquids so as to give optimum separations in difficult cases. It forms a sound basis for the initial selection of a column for a new analysis. The use of capillary columns is becoming more widespread and many are being tried out in plants as was evident from the panel dis cussions. The relative virtues of ionization detectors seem to now be well established. This meeting as well as that of the ACS in St. Louis and the Pittsburgh Analytical Con ference offered the majority con clusion that the argon ionization detector is the more sensitive by about a decade, but that the flame ionization detector is of more value in hydrocarbon analysis because of its wider dynamic range. Temperature programming is now widely accepted in the laboratory but as yet has not appeared in com mercial process units. Flame ion ization detectors are now available on process chromatographs (Perkin-Elmer), and improved hot wire katharometers of some 20 times higher sensitivity than those of two years ago are now available (Beckman Instrument). At the Pittsburgh Analytical Con ference, the use of a preliminary column of calcium carbide main tained at 200° C. prior to another conventional gas chromatographic column was reported. This enables the analysis of aqueous solutions to be carried out satisfactorily and is particularly suited to the analysis of fermentation liquors. The use of low temperature gas chromatograph ( — 78° C.) was re ported by the California Research Council at the St. Louis ACS meet ing. Separation of the lighter gases on η-heptane partition columns us ing either firebrick or glass-bead supports was studied.
offers, for about one third or less cost, the full capability of the $100,000plus mass spectrograph of several years back. A detection level of 5 to 10 p.p.m. is possible with this instrument which covers the mass range from 2 to 230 in three ranges. CEC also now offers a new high temperature gas chromatograph, Type 26-203, with any options, capable of attaining 500° C. so that analysis of substances which boil up to 600° C. is possible. There are three new temperature programmed units available (Perkin-Elmer, Beckman, and F & M Scientific). Of these the Beck man Thermotrack instrument ap pears to offer the maximum ver satility in programming as it uses a photoelectric curve-follower. The new Perkin-Elmer, Model 184, high-speed gas chromatograph is now available with a flame ion ization detector giving it parts per million sensitivity. Greenbrier Instrument Co. brought out two new instruments at the IMA show which aroused great interest. One is an improved elec trolytic hygrometer which uses large planar electrodes transverse to the stream and which is much more tolerant to overloads and minor contaminants than the usual twinwire cells. The second instrument is a new twin-cell oxygen analyzer with rapid response based on a silverlead galvanic cell. Detec tion of 0.1 p.p.m. is possible and the dual cell arrangement allows rapid checking or simple calibra tion procedures. The output is approximately 10 microamperes per part per million of oxygen into 100 ohms load. Range is 0 to 100 p.p.m. A small chromatograph, the chromofrac, by the Precision Scien tific Co. also aroused considerable interest because of its low price and simplicity. As a basic unit for simple routine analyses or for teach ing purposes this is a good unit with fair capabilities.
New Instruments
The extent of the quiet but steady progress that has been made in the last few years may be gaged from a comparison of the new Consolidated Electrodynamics Corp.'s mass spec trograph, Type 21-130, which now
Our authors like to hear from readers. If you have questions or comments, or both, send them via The Editor, l/EC, 1155 16th Street N.W., Washington 6, D.C. Letters will be forwarded and answered promptly. VOL. 53, NO. 7
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