A Surface Developer for Mass Spectrograph Plates

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Surface Developer for Mass Spectrograph Plates P. R. Kennicott, Geneml Electtic Research laboratory, Schcnectady, N. Y. 12301

HF SPARK SOURCE mass spectrograph TteEhnique utilizes the photographic process for detecting positive ions following their separation by the mass analyzer. The photographic process offers the advantages of simultaneous detection of ions of many different masses, and of integration of the information from a rather widely varying source. The principal photographic requirements are for a plate sensitive t o low energy ions, a plate with high sensitivity and low background fog to give the highest possible signal-to-noise ratio, a plate of relatively high resolution to separate closely neighboring masses, and a plate with a well controlled characteristic curve to permit quantits, tive interpretation of the results. The photographic requirements are currently being met by resorting to the techniques of emission spectroscopy. The plates being used are Schumann plates-Le., the Ilford Q series or Kodak SWR plates which have a very low gelatin content, thus leaving the silver halide grains relatively exposed. These plates are commonly developed in energetic spectrographic developers such as Ilford ID 19 or ID 13 or Kodak D 19. In view of the different method of formationof the image, the photographic .techniques of emission spectroscopy should he re-examined before being applied to the mass spectrography.

A feature in common with all developers in current use fur m w spectrograph plates is the use of an antioxidant for stabilization. These antioxidants exhibit some degree of solvent action on the silver halide grains. An alternative type of developer is the surface developer in which this solvent is omitted. To determine the usefulness of such a developer, the composition in Table I was tested ( 2 , 2 ) . The use of a surface developer resulted in three effects. First, the characteristic curve was both steeper and more linear at medium densities. The resulting curve is better for quantitative work, since an error in the measurement of density results in a smaller error in exposure. Figure 1 shows plots of exposure against the integral of transmission above fog level for Ilford Q2 and Eastman SWR plates developed in both the surface developer and in D 19 developer. These characteristic curves were prepared by the Churchill two-line method with the aid of a computer program described elsewhere (9).

Second, the surface developer resulted in a cleaner plate. Not only is the background fog less, hut a h there is a marked decrease in the intensity of the secondary emission blackening near strong lines. This effect is illustrated hy Figure 2. I n the plate developed by

Table 1.

Component Warm HIO

Developer Composition

Amount 500 cc. 2 . 5 grems 10 grams 35 grsms 1.O gram

I

Elan Ascorbic acid Kodak KBr Add HsO to make 1liter. Developing time, 4 minutes.

chemical developers the AI" line is clearly visible on the shoulder of the Si" matrix line. In the plate developed by D 19, a uniform transmission of 1% prevails throughout this region. Finally, the surface developer resulted in an image of less density. In order to obtain an estimate of the difference in sensitivity of plates developed with the surface developer, one must take into consideration the change in fog level on the plate. The curves in Figure 1 are broken at a density level 0.1 times the plate hackground as measured by comparing transmission of the unexposed plate to transmission with no plate in the densitometer. This is a somewhat arbitrary form of detection limit, hut should give some idea of the relative performance of the surface developer. Another estimate can be made by comparing signal-to-noise ratios from

EXPOSURE I. 104 W I O r n b I

Figure 1. A. 8. C. D.

Characteristic curves

llford I32 plate, D 19 developer Kodmk SWR plde, D 19 developer llford 0 2 plate. turface developer Kodak SWR plote. surface developer

Figure 2. Kodak SWR plates exposed to identical silicon samples VOL 37, NO. 2, FEBRUARY 1965

313

Table II.

Signal-to-Noise Ratio

Signal-to-noise Plate developer Ilford D 19 Ilford Chem. Kodak D 19 Kodak Chem.

10-12 coul. 10-11 coul.

exposure

exposure

0.627 0.056 0.222 0.053

0.752 0.364 0.495 1.324

the two plates at identical exposures (the background fog being considered as noise). The results are given in Table 11. The signal-to-noise ratios at 0.001 X coulomb leave little doubt regarding the superior sensitivity of D 19 developed plates. On the other hand, a t higher densities where one would prefer to obtain quantitative data, the signal-to-noise ratio of the plate developed by the surface developer is as good as that of the plate developed in D 19.

A model of the development process which explains the differences noted between the commonly used developers and the surface developer is as follows: Each of the commonly used developers contains an antioxidant, such as sodium sulfite, for stabilization of the solution. These materials exhibit a certain degree of solvent action for the silver halide grains in the emulsion. Any image which resides in the interior of a grain thus may become exposed to the developing solution as a result of this solvent action. Because of the low energy of the ions used to expose the plate, it is likely that the desired image will reside almost exclusively at the surface of the silver halide grain. ilny internal image thus is the result of other image formation processes and contributes only to the general fog of the plate. The results presented here show the superiority of the surface developer for quantitative work while leaving some

doubt as to its usefulness in qualitative work, except in special cases where secondary emission blackening is a problem. It should be emphasized that these results are from a limited number of plates and must, therefore, be considered preliminary. However, they seem interesting enough to encourage others to consider the photographic process in terms of low energy ions. ACKNOWLEDGMENT

I express my appreciation to J. W. Mitchell for helpful suggestions and discussions. LITERATURE CITED

( 1 ) James, T. H., Vanselow, W., Photographic Science and Technique, Series 11, 2-135 (1955). (. 2,) James. T. H.. Vanselow. W.. Photo. Sci. Eng.,2, 1-104 (1958). (3) Kennicott, P. R., General Electric RL Rept. 37660, Schenectady, N. Y., 1964. I

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High Frequency Electrodeless Discharge System for Ashing Organic Matter Chester

E. Gleit,

Department of Chemistry, North Carolina State, of the University of North Carolina at Raleigh, Raleigh, N. C:

exists in the use of the high Ia substitute frequency electrodeless-discharge as for conventional ashing NTEREST

methods and as a means of producing free radicals and thermally unstable compounds (4). In this technique gas a t low pressure is inductively coupled to a radiofrequency field. To oxidize organic matter, oxygen is passed through an intense oscillating field and then reacted with a solid specimen a t low temperature ( 2 ) . This technique greatly reduces the volatility losses inherent in dry ashing, (2) permits low temperature decomposition of difficultly oxidizable substances such as pyrolytic graphite and other carbonaceous material (3, 6),and provides a method for ashing biological tissue without distortion of the associated mineral microstructure ( 7 ) . Applications of this technique have been restricted by lack of suitable laboratory equipment. The principal difficulty has been in the design of an efficient and flexible means of transferring power from the electronic generator to the gas. In early work a direct connection between the radiofrequency power amplifier and a resonant LC-tank was employed (1, 6). Since the plate impedance is several thousand ohms and the LC-tank and associated gaseous discharge approximates a several hundred ohm termination, only a small portion of the generated power was delivered to the 31 4

ANALYTICAL CHEMISTRY

Figure 1 .

Basic coupling circuit.

Coil Lt surrounds the gas discharge tube

load. This impedance mismatch also led to overheating of the power amplifier from reflected power and excessive radiation. Other methods such as link coupling and the use of polygonal inductors ( I ) have been employed. Such circuits are difficult to adjust, and standing-wave ratios (ratio of load impedance to line impedance) of less than two have not been achieved. A simple autotransformer-resonant LC-tank has been found to be an efficient means of transferring power to the gaseous discharge over a wide range of frequencies and gas conditions. This circuit can be used with most commercial radio transmitters and laboratory radiofrequency oscillators. The standard transmitter terminating network, which is shown on the left side of Figure 1, consists of a capacitor CI to remove d.c. high voltage from the out-

put and a r-network, composed of variable capacitors Czand CJand tapped coil L1. This network suppresses undesired harmonics and lowers the output impedance to 52 ohms. A coaxial cable of suitable impedance, such as type RG8/U or RG58/U, is generally employed to connect the transmitter to the antenna. For use in an electrodeless discharge system, the antenna is replaced by a resonant circuit composed of solenoid, Lz, and variable capacitor, C,. The inductor is tapped at an appropriate point to provide proper impedance match. CONSTRUCTION AND ALIGNMENT

For operation a t 13.56 Mc. per second an output network consisting of a Hammarlund HFBD 25 picofarad variable capacitor and a silver plated coil