INSTRUMENTATION by Ralph H. Müller
Developments in ultrasonic machining, v a p o r phase c h r o m a t o g r a p h y , a n d analytical techniques described
U
LTKASONIC
MACHINING
has
had
many important scientific and industrial applications and now it affords the analyst some new and useful d e vices. According t o the Connecticut Instrument Corp. of Wilton, Conn., the technique permits the manufacture of cheap infrared absorption cells. W e quote extensively from their CIC Newsletter of July 1959 in which they describc t h e construction, uses, advantages and limitations of cavity infrared absorption cells. The cavity cells were originally developed by D r . N o r m a n Jones of t h e National Research Council, Ottawa, Canada and were described in Spectrochimica Acta, Vol. 12, Nos. 2 / 3 , p p . 183-191. I n attempting t o construct a simple microcell of extremely small volume, Jones hit upon t h e idea of forming a cell b y drilling out a single piece of rock salt. When cylindrical cells failed t o transmit enough energy, he turned t o ultrasonic machining—a method capable of producing cavities of any shape—and produced a cell with a fiat sample area. As t h e Connecticut Instrument Corp. specializes in ultrasonic machining and its founders also have backgrounds in spectroscopy, it was a natural step for t h e company to pursue D r . Jones' work and p u t t h e cells into full scale production. I n ultrasonic machining a tool of the desired shape is \'ibrated linearly a t a frequency of about 20,000 cycles per second. Abrasive is circulated b e tween t h e tool and t h e work piece. The high speed motion of t h e tool drives abrasive against t h e work and removes material a t a high rate. T h e cavity produced is shaped precisely like the face of the tool. T o produce a cavity cell, a hole is first drilled into t h e t o p of a block of crystal for t h e stopper. A blade with
the desired cross section is then driven ultrasonically into t h e crystal. After it has been cleaned and buffed, t h e cell is complete. Some limitations are inherent in this technique. As abrasive docs t h e cutting, i t must be continuously supplied to the face of the tool. T h e deeper the
cut, the more difficult this becomes, and the slower t h e cavity is produced. At present, t h e nominal limit of a cut in rock salt is about 15 mm. I n addition, t h e cutting blade must withstand a considerable amount of stress and abrasion. This puts a limit on t h e "thinness" of t h e cell. Currently, t h e
G o l a y column a n d f l a m e ionization d e t e c t o r a r e shown mounted on Perkin-Elmer v a p o r f r a c t o m e t e r . A m p l i f i e r f o r ionization d e t e c t o r is in t h e f o r e g r o u n d VOL. 3 1 , NO. 9, SEPTEMBER 1959
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9 1A
INSTRUMENTATION
5:10 P.M.: Beginning
of a difficult, time-consuming
analysis:
Cary Spectrophotometers Record Spectra Around the Clock...unattended ...with the Program Control Accessory This useful accessory enables CARY SPECTROPHOTOMETERS to automatically repeat spectral scans at predetermined time intervals. Scans may be repeated at intervals ranging from as little as 10 minutes to 24 hours, and may be spaced in any desired program. Some laboratories almost double the usefulness of their CARY SPECTROPHOTOMETERS by using them during the day on routine work, then setting them up with the Program Control for automatic analysis during the night. However, automatic programming is just one feature which demonstrates the unmatched versatility of CARY SPECTRO PHOTOMETERS. The wide wavelength range, high resolution, low stray light, plus the availability of a number of useful accessories for other measurement techniques, enable Cary Instruments to serve a wide analytical field. Complete information on these versatile instruments is yours for the asking. Write for Data File A13-99.
RECORDING SPECTROPHOTOMETERS
A P P L I E D
P H Y S I C S
C O R P O R A T I O N
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Circle No. 14 on Readers' Service Card 92 A
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ANALYTICAL CHEMISTRY
thinnest practical cell is a nominal 0.10 mm. or about 0.003 inch. Very thin cells have a slight taper but in a 1-ml. cell, the taper averages only a few per cent. One of the obvious advantages of cavity cells is low cost. The average cost is about the same as that of a single window in a conventional sealed cell and it is usually cheaper to buy a new cavity cell than to rebuild a con ventional one. Because there are no seals, leakage problems cannot arise. Teflon is used as the stopper material. Another advantage of cavity cells is the. small sample volume. Micro colls of this type can be made having vol umes of less than 5 ^1. Compensation plates for use with cavity cells are available in all infrared transmitting materials such as NaCl, TCBr, CaFo," BaF 2 , CsBr, Ge, glass, and fused quartz. Cavity cell holders are also available for use with Perkin-Elmer models 12, j 112, 13, 21, 221, 321, and 137, and for the Bcckman models, IR-4, IR-5, and 1R-7. Four bulletins are available from: Editor, CIC Newsletter, Box 66, Wil ton, Conn., on these cells, and a related bulletin, U-l, describes "A Machining Service for 'Enmachinable' Mate rials." V a p o r Phase C h r o m a t o g r a p h y Developments
The practicing analyst is usually happy when instrument development has settled down and becomes stand ardized. Then he can go on with his work and no longer worry about the technical details. Although vapor phase chromatographs are now in a high stale of development and arc used in a dozen or more fields, there is no indica tion that instrumental developments are slowing down. Two new develop ments afford extremely high resolution and sensitivity and have been designed for use with the Perkin-Elmer Vapor Κ Tactometers, Models 154 Β and 154 C. The new unit, developed by PerkinElmer comprises a Golay column and an ionization detector. The new unit is normally capable of producing chromatograms with at least five times better resolution than packed columns and in less time. Conversely, if time is a critical factor, it can provide resolu tion equal to that of packed columns in a tenth of the normal operating time. Two new types of detectors are avail able with the unit. In one, the column effluent is thermally ionized in a hydro gen flame to produce changes in the ion current of an electric field. This de vice, which uses nitrogen as the carrier, is called the flame ionization detector.
INSTRUMENTATION
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94 A
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ANALYTICAL CHEMISTRY
Education Research Development
-* Organic Chemicals Solvents Glass Oil Contamination Hydraulic Fluids Petroleum Derivatives Plasticizers Chlorinated Solvents Silicones Nylon Cocoa and Chocolate Salt Solutions Polymers Proteins Waxes Essential Oils Peroxide Solutions Coffee Solids Polyester Resins Paint Solvents Pharmaceuticals Biologicals Flours
I n the beta-ray ionization detector, metastable argon atoms (argon is the carrier) are produced by the impact, of accelerated electrons from a krypton 85 source. Collision of sample mole cules of lower than 11.7 electron-volt potential with the argon atoms ionizes the sample molecules, again creating a measurable change in ion current of the detector circuit. Both new detectors arc characterized by high sensitivity, low sample volume, fast response, and versatility, required to realize the capabilities of the Golay column. T h e beta-ray detector has a detectability of the order of 1LV14 mole of sample in carrier gas, and t h e flame detector is somewhat better. Effec tive volume of the flame detector is 1 to 3 cu. m m . against 5 eu. m m . for the beta-ray device. Electrical re sponse time for both is 1 millisecond. Though both are differential detectors, they have such high signal/noise ratios and stability t h a t no reference cell is required. T h e flame detector is completely free of drift, the b e t a - r a y detector is essen tially so. T h e new detectors permit use of economical wide-span (0-100 mv.) recorders or high-speed recording milliammeters. T h e Golay column is wound on a spool about the size of a fishing reel to conserve space and permit rapid warmup and cooling. I t provides resolution of u p to 150,000 theoretical plates with a 150-foot column. T h e column accessory includes a unique device called a "stream-splitter" designed to overcome problems of a small sample size and low injection volume encoun tered with capillary columns. The stream-splitter is adjustable to permit varying of the initial injected sample size or of the splitting ratio. It is felt that low concentration analysis and in organic analysis will be greatly im proved by these new techniques.
New Analytical Techniques We enjoyed reading ''Analytical Chemistry—Some New Techniques," by A. G. Jones (New York: Academic Press I n c . : London: B u t t e r w o r t h Sci entific Publications, 1959). T h e tech niques discussed are—flame photom etry, differential spectrophotometry. gas chromatography, the analytical uses of ion exchange resins, acid-base titrations in nonaqueous media, coulometric titrations, and the determina tion of oxygen and lrydrogen in metals. A chapter on differential refractometry is the only account we have seen in which the various techniques and in struments are described and com pared.
