be made to be ortho, para, meta (12). This type of behavior is not uncommon ( 7 ) and emphasizes that there are conditions where a linear correlation between basicity and retention will not hold. However, it does hold for the amines studied here when chloroform and cyclohexane are the mobile phases.
CONCLUSION While this study was limited in scope, it does indicate that chromatographic conditions can be found which allow a direct correlation between pKb and log of capacity factor for aromatic amines. It established that the relative basicit y of some aromatic diamines can be determined from liquid chromatographic data. This may prove useful in helping to predict the relative basicity of closely related aromatic diamines, especially new amines being synthesized for polymer synthesis. This study also suggests that similar correlations may exist for aliphatic amines and even aromatic and aliphatic acids on slightly basic adsorbents. A
further insight into the separation mechanism of aromatic amines on silica adsorbents has also been obtained.
LITERATURE CITED (1)V. L. Bell, Org. Coatings Plastics Cbern., Prepr., 33 (I),153 (1973). (2)R . A. Dine-Hart and W. W. Wright, Makromol. Chem., 153, 237 (1972). (3)V. Guidofti and N. J. Johnston, Preprints, Amer. Chern. SOC.,Div. Po/ym. Chem., 15 (I),570 (1974). (4)H. Lee and K. Neville, "Handbook of Epoxy Resins,'' McGraw-Hill. New York, N.Y., 1967,Chap. 21,p 25. (5)C. V. Cagle, "Handbook of Adhesive Bonding," McGraw-Hill, New York. N.Y.. 1973,Chap. 9,p 4. (6) R. A. Dine-Hart and W. W. Wright, J. Appl. Polym. Sci.. 11, 609 (1967). (7)L. R. Snyder, "Principles of Adsorption Chromatography," Marcel Dekker, New York, N.Y., 1968,pp 257-334. (8) M. Przyborowska and E. Soczewinski, J. Chromafogr.. 42,516 (1969). (9)J. J. Kirkland. J. Chromatogr. Sci., 10, 129 (1972). (IO)R . T. Morrison and R. N. Boyd, "Organic Chemistry," 3rd ed , Allyn and Bacon, Boston, Mass.. 1973,p 730. (11)D. Kunzru and R. W. Frei. J. Chromatogr. Sci.. 12, 191 (1974). (12)Chromatographic Methods No. 820M6,E. I. du Pont de Nemours & Co., Inc., Instrument Product Division, Wilmington, Del.. March 30,1974,p 4.
RECEIVEDfor review August 15,1974. Accepted December 9, 1974.
A PDP 11 Computer System for the Multiterminal Processing of Several Analytical Instruments in an Interpretative Language Torbjorn Anfalt and Daniel Jagner Department of Analytical Chemistry, University of Goteborg, F a c k
S-40220 Goteborg 5,Sweden
Until recently, automation of analytical instruments by means of computers has mainly been concerned with instruments delivering data a t a very high speed, e g . , mass spectrometers and NMR instruments. Because of the constantly decreasing prices of minicomputers, it is, however, now justifiable to automate almost any analytical instrument. Most analytical instruments, e.g., titrators, spectrophotometers and gas chromatographs, deliver real time data a t a moderate speed, often less than 50 Hz; moreover, after the first reduction, the number of data is not very large (usually of the order of magnitude of less than lo?)). The limited number of data produced in each analysis means that it is not necessary to add an external memory to the system when automating these instruments, which considerably reduces the price. The slow flow of data makes it possible to use an interpretative language in the processing of the instruments, thus drastically decreasing programming difficulties. This is of particular advantage in teaching and in research laboratories where there is a need for frequent reprogramming. If, however, each of the above-mentioned instruments is assigned its own minicomputer, the full capacity of the computer is not exploited, since any minicomputer is capable of processing several such instruments. Simultaneous processing of entirely different analytical instruments, independently of one another has, however, not hitherto been considered in an interpretative language such as BASIC. This paper describes a soft-ware development on a P D P 11 which facilitates the simultaneous use of a maximum of eight processing terminals, all terminals being programmed in BASIC. Each processing terminal consists of an input/ output teletype unit, an A/D converter, a random mode analog multiplexer, and eight random mode programmable relays. Such a terminal is not only sufficient for the interfacing of the analog signals coming from most analytical instruments, but is also capable of processing most analytical
procedures, the programmable relays being used, for example, to process wavelength adjustments of a spectrophotometer by means of a step-motor.
HARDWARE DESCRIPTION The Computer. A diagram of the computer set-up is shown in Figure 1. The computer is a Digital Equipment P D P 11/10 with a 16-K core memory, the word size being 16 bits. All peripherals are connected to the computer unibus, i.e., they all have unique core memory addresses ( I ) . Real-time is obtained by means of a line-frequency clock, the time duration for one increment being 20 msec a t 50 Hz. The paper tape reader and punch (Digital Equipment PC-11) have maximum speeds of 300 and 50 characters/sec, respectively. Hitherto, only three processing terminals have been connected to the system ( c f . Fig. 1).A fourth terminal has been used for computation only. The Processing Terminals. The configuration of the terminals is shown in Figure 1. Input and output operation a t each processing terminal is facilitated by means of teletypes ASR 33 or Olivetti TE-308, both having a maximum speed of 10 charactershec. The terminals have access to the tape reader and punch of the computer to enable more rapid reading and punching. Each terminal has an integrating voltmeter as an A/D converter, Fluke 8300 or Fluke 8200, with maximum conversion speeds of 0.3 and 400 readingdsec, respectively, in the millivolt range. All voltmeters are equipped with automatic ranging, remote control, and isolated data output. The resolution is 1 p V and the input impedances are close to 10000 M a . Each terminal has a random mode scanner, facilitating measurements on eight different analog inputs, and a short-circuiting relay register, facilit,ating the random mode processing of eight different electromechanical devices. Scanners and relays a t all terminals are processed by ANALYTICAL CHEMISTRY, VOL. 47. NO. 4, APRIL 1975
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Figure 1. Hardware configuration
___-___ hhemonic
ADC (X) TIM (XYZ) TIC (XYZ) INR (XOZ)
Comment
Read voltmeter at terminal No. X Start (Y = 0) or read ( Y = 1) clock No. Z at terminal No. X at one second intervals Same as TIM but with 20-msec increments Open scanner channel No. Z at terminal No. X
RNR (XYZ) S E T (X)
Open (Y = 0) or close (Y = 1) relay No. Z at terminal No. X Transfer the function X into an unimplemented mode
the same general purpose input/output interface, Digital Equipment DR-11-C ( I ) . An 8-bit output from this register is decoded into 48 bits, half of these being used for the three scanners while the other half are used for the three relay registers.
SOFTWARE DESCRIPTION The purpose of the software is to allow all peripherals, including the processing terminals, to be programmable in BASIC, independently of each other, Le., measurements on one terminal should not be hindered by measurements or teletype output on another terminal. This has been achieved by the modification of the P D P 11 1-8 user BASIC interpreter. This interpreter is normally used for performing calculations only. I t provides a multiprocessing capability by executing one BASIC instruction from one terminal and then jumping to the next terminal to execute another BASIC command a t this terminal and so on until it has jumped back to the first terminal where the next BASIC command in line of its program is executed. Details of the interpreter reprogramming and Assembler handlers will not be given in this paper, but a full documentation can be obtained from the authors on request. Only the use of the BASIC-callable Assembler routines for the processing of the terminals will be illustrated. These routines are summarized in Table I, and an example program is given in Table 11. The modified BASIC interpreter, which is capable of operating 4 to 8 times more rapidly than normal single-user BASIC interpreters, occupies 5.5 K word core memory, the memory area available for programming thus being 10.5 K word. When the system is loaded, which is done via a highspeed paper-tape reader, one can choose the number of terminals for sharing the programmable memory area. If the four terminals are operated simultaneously, each user thus has 2.7 K word core memory available. 760
-~
~-
Table 11. Example of a Basic Program at Terminal No. 2
Table I. Basic Handlers
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10 20 30
L E T E l = 10000 S E T INR (207) S E T TIC (213)
40
S E T RNR (204)
50
I F TIC (203) i 5 THEN 50 S E T RNR (214) S E T TIC (213). S E T TIC (214) I F TIC (204) < 50 THEN 80 S E T TIC (214)
Open cliannel 7 i n scanner 2 Clear and start clock No. 3 at terminal No. 2 Open relay N o . 4 at terminal No. 2
60 70
80 90 100 110 120 130 140
Wait 5 x 20 msec Close relay N o . 4 Clear and start clocks Nos. 3 and 4 W a t 50 X 20 msec Clear and start clock No. 4 at terminal No. 2 Read voltmeter No. 2
L E T E2 = ADC (2) IF ABS (E2-El) ’ Compare two consecutive 0.05 THEN 140 values LETEl =E2 G O T 0 80 PRINT TIC (203) Print total time (seconds) and 50, E 2 steady value
The BASIC callable Assembler routines are not protected from interference of other users and, since each terminal has its own A/D converter, relays, and clocks, little need for protection is required. However, such protection can easily be incorporated into the software system. Real Time. The real time processor is a 50-Hz line-frequency clock generating a system interrupt each 20th msec and incrementing a time accumulator. This means that the real time resolution is 20 msec only. A crystal frequency clock, which could be incorporated into the system a t reasonable price, would indeed improve the time resolution. Such a clock would, however, be of limited practical value, since the interpreter is capable of handling floating point data only. This means that the integer representation from any A/D converter must be transformed into floating point representation, the time duration for such a conversion being in the order of magnitude of a few milliseconds. Thus, from a practical point of view, a time resolution of 20 msec is reasonable. It should be pointed out that limited real time resolution is, of course, the main sacrifice one has to make when using the BASIC interpreter for multiterminal operations.
Using the line-frequency hardware clock the interpreter has been modified so that each processing terminal has been given eight independent software clocks. These clocks can operate either with a time resolution of 20 msec (TIC clocks) or 60 sec (TIM clocks). These clocks restart automatically after 10 min and 24 hours, respectively. The BASIC calls used to start and read the clocks are illustrated in Tables I and 11. Voltmeter Handlers. For each line frequency clock interrupt, the current status of each of the voltmeters is stored in two memory cells whereafter a strobe pulse immediately triggers the voltmeters again. The time duration between interrupt and strobe pulse is negligible on the interpreter time scale. The maximum hardware reading rate in real-time is thus limited to 50 readingdsec at each terminal. After each reading, it is, however, necessary for the interpreter to convert the stored BCD information into floating point representation. This is achieved by means of the implemented BASIC call ADC (cf., Tables I and 11). These software manipulations in BASIC take approximately 15 msec. Consequently, the software limitation of the reading rate is almost equal to the hardware reading rate limitation of 50 readingdsec. The software limit does, however, refer to maximum possible reading rate at all terminals. This means that the maximum real time reading rate of 50 readings/sec is possible only if only one processing terminal is operating. If two terminals are operating, the maximum reading rate a t each of them is 25 readingdsec, etc. Scanner and Relay Handlers. The random mode scanners and short-circuiting relays are called by the implemented INR and RNR statements, respectively (cf., Tables I and 11). The calling of a new channel automatically closes the channel used previously. The response time of all relays is considerably less than one millisecond. The SET Statement. Some of the handlers discussed above, such as starting a clock or opening or closing a relay, can be used in an unimplemented mode, Le., these instructions do not return a parameter value to the BASIC program. Reading of a clock can, of course, not be performed in this mode since this function returns the real time value to the program. When placed before a handler function, the S E T statement transfers this function into an unimplemented mode. In this way, it is possible to avoid dummy variables in the handlers which can be operated equally well in an unimplemented mode. The use of the S E T statement is illustrated in Tables I and 11.
Example of BASIC Programming at a Processing Terminal. An example of the use of the BASIC callable handlers is given in Table 11. This program starts by delivering a shortcircuiting pulse of 100-msec duration, after which two software clocks are set equal to zero. One of these clocks is used to measure the total time needed to obtain a steady reading on the voltmeter, while the other clock is used to process a time duration equal to one second between two consecutive voltmeter readings. The criterion for a steady reading is that two consecutive readings differ by less than 0.05 unit (e.g., mV). DISCUSSION The suggested modifications of the multi-user BASIC interpreter can easily be adopted to all computers in the P D P 11 series. The number of Assembler instructions needed to modify the BASIC interpreter is about 400. The time required achieving the modification can be estimated to be two months. Experience in our laboratory has shown the processing terminals to be suitable for many kinds of spectrophotometrical and electrochemical analysis. They have been extensively used for titration procedures, the determination of stability constants, and column chromatography. In all these applications, the drawback of low real-time resolution has been more than compensated for by the advantage of being able to operate the instruments in an interpretative language. A comparison of the cost of a multiterminal system to several single-terminal systems shows that addition of a new terminal to a multiterminal system is much cheaper than a new single-terminal system. A new terminal to a multiterminal system also has access to all common peripherals in the system, i.e., high-speed reader and punch. This can also be done with several single-terminal systems but for a much higher price. In the near future, it will be advantageous to let all terminals be guided by microcomputers and, in this way, achieve some of the advantages of separate systems without loss of access of a larger system.
LITERATURE CITED (1) Manuals PDP 11, Digital Equipment Co., Maynard, Mass.
RECEIVEDfor review June 24, 1974. Accepted November 18, 1974. Financial support from Knut och Alice Wallenbergs Stiftelse and the Swedish Natural Science Research Council (NFR) is gratefully acknowledged.
Study of Diffusional Shielding Effects at Micrometer Fed Capillary Mercury Electrodes Leon N. Klatt' and John B. Carraway Department of Chemistry, University of Georgia, Athens, Ga. 30602
The hanging mercury drop electrode (HMDE) has been shown to be a useful electrode in numerous electroanalytical studies ( I ) . Based upon the results of chronoamperometric experiments in our laboratory, electrodes of very reproducible area are easily prepared by using a micrometer fed Author to whom correspondence should be addressed at his present address, Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tenn. 37830.
capillary to obtain the mercury drops. However, because of reports by Martin and Shain ( 2 ) and Murray and Gross ( 3 ) that diffusional shielding becomes an important factor as the size of the support increases, relative to the mercury drop, a glass-platinum support with a tip width of ca. 0.5 mm continued to be used as the mercury drop support. acid media, the Occurrence of hydrogen However, in discharge on the platinum wire is observed rather frequentANALYTICAL CHEMISTRY, VOL. 47. NO. 4 , APRIL 1975
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