1954
Anal. Chem. 1981, 53, 1954-1955
A
NBu4C104decreased below 0.1 mA cm-2 within -1.30 and 2.00 V after two filtrations at -45 “C. Within -1.20 and 1.90 V the current density was even below 0.03 mA cm-2 (cyclic voltammetry, u = 100 mV s-l, T = -45 “C, 1 mm Pt disk electrode, Pt quasi-reference electrode). These data compare very favorable with those recently reported by Tinker and Bard (12). They also demonstrate the low-temperature capabilities (9) of our cell system. The cell has been successfully used for the voltammetric analysis of sigmatropic indene dianion rearrangements (13, 14), the photochemical “in situ” conversion of indenes into isoindenes at low temperatures (14),and last but not least for the electrochemical synthesis of heterocycles (e.g., isoquinolines, oxazoles, phenanthridines) by anodically induced nitrile cycloaddition (14).
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ACKNOWLEDGMENT I am indebted to Ewald Daltrozzo for his support and interest in this work and to Georg Kollmannsberger-von Ne11 for measuring stray light intensities. Last but not least the skilled glass blowing of Erich Harms (Medizinisch-Glastechnische Werkstatten, Berlin) is gratefully appreciated.
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@jcooiant Flgure 4. Schematic representation of the drying operation: A, the cell is assembled and filled with aluminum oxide and with electrolytic solution; B, the electrolytic solution is intermediately transferred Into the cell top by a 90” rotation; C, after back-roation the electrolytic solution flows into the electrode comp_artmentspassing the cooled alumlnum oxide drying tube.
The potential window of a 0.2 M NBu4BF4/MeCNsolution ranges from 2.70 to -3.30 V (vs. Ag/O.Ol M Ag+),the current density being less than 0.1 mA cm-2 between 2.35 and -3.20 V (8). Before filtration the potential window (I < 0.1 mA cm-? was found essentially smaller, ranging from 1.80 to -2.60 V. Also significantly higher background currents within these limits were noted. This fact seems especially important with respect to double layer investigations and kinetic work. Other electrolytic solutions showed similar results. As an example the background current density of liquid S02/0.2 M
LITERATURE CITED (1) Sawyer, D. T.; Roberts, J. L., Jr. “Experimental Electrochemlstry for Chemists”; Wlley: New York, London, Sydney, Toronto, 1974,pl17. (2) Hammerich, 0.;Parker, V. D. Electrochlm. Acta 1973, 18, 537. (3) Bard, A. J. Pure Appl. Chem. 1971, 25, 379. (4) Mills, J. L.; Nelson, R.; Shore, S. G.; Anderson, L. 8. Anal. Chem. 1971, 43, 157. (5) Schmulbach, C. D; Oommen, T. V. Anal. Chem. 11973, 45, 820. (6) Holloway, J. D. L; SenRleber, F. C.; Geiger, W. E., Jr. Anal. Chem. 1978, 50, 1010. (7)Lines, R.; Jensen, B. S.;Parker, V. D. Acta Chem. Scand., Ser. 8 1978, 832, 510. (8) Kiesele, H. Anal. Chem. 1980, 52, 2230. (9) Van Duyne, R. P; Rellley, C. N. Anal. Chem. 1972, 44, 142. Feng, E.; Peet, N. P. J. Org. Chem. 1971, 36, 2371. (IO) House, H. 0;. (11) Woehrle, D. Fortschr. HOChpO&m.-FOf6ch. 1972, 10, 35. (12) Tinker, L. A.; Bard, A. J. J. Am. Chem. Soc. 1979, 101, 2316. (13)Kiesele, H. Chemledozenten-Tagung, Tiibingen, 1981. (14) Kiesele, H. Habllltatlonsschrlft,Unlversitiit Konstanz, 1980,and unpub llshed work.
RECEIVED for review July 28, 1980. Resubmitted April 30, 1981. Accepted July 26,1981. This work was supported by the Deutsche Forschungsgemeinschaft.
Ten-Bit Interface to an Eight-Bit Microcomputer in One Clock Pulse Mark M. Doxtader and R. Ken For&* Department of Chemistry, University of Rhode Island, Kingston, Rhode Island 0288 1
Advances in microelectronics in the past few years and the wide commercial availability of fairly sophisticated and inexpensive microcomputers has made it possible for many laboratories to interface laboratory instrumentation to microcomputers. However, many of the microcomputers are eight-bit machines which limits the input resolution to one part in 256. In many cases, the instrumentation yields a higher resolution signal. Also, some high-speed data collection systems, such as transient recorders, have memory units with larger bit words than can be accommodated by the computer on hand. One possible compromise is to use only the most significant bits disregarding the information contained in the balance or change memory size to fit that of the computer. In our laboratory, we have successfully interfaced a 10-bit transient recorder (TR) to an 8-bit Commodore Model 2001-8K PET microcomputer without loss of the information 0003-2700/81/0353-1954$01.25/0
contained in the two least significant bits of the TR. The TR used in this application is a modified version of the design of Betty and Horlick (1). Interfacing is accomplished by means of three integrated circuits, two hex noninverting tristate buffers (National Semiconductor MM80C95, DM80C97) (2) and an inverter (7408). The outputs of the ten bits from the TR are used as the inputs to the two buffers. The third through eighth bits go to inputs 1-6 on the MM80C95, while the seventh through tenth (LSB) bits go to inputs 1-4 on the DM80C97. The two most significant bits, 1 and 2, are used as inputs 5 and 6 on the DM80C97. The computer clock line (CB2) which controls the movement of the 10-bit words from the TR serial memory is also attached directly to three disable lines 1, 2, and 3 located on the two buffers. An inverted clock is used to control disable 4. Figure 1 shows a schematic of the interface and 0 1981 American Chemlcal Society
11955
Anal. Chern. 1981, 53, 1955-1957
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the truth tables for the two buffers. The computer intenface cable is so arranged that, after exiting from the tristate buffers, TR bits 1(MSB) and 2 are on the same lines as 9 and 10 (LSB), respectively, with bits 3-8 on their own individual lines to the computer. Figure 2 shows this arrangement in conjunction with the parallel user port located on the back of the PET. The transient recorder in our laboratory is capable of transferring data at rates up to 1.5 MHz. The PET under complete control of BASIC can accept double precision words a t data rates of about 2160words per second (wps). With the addition of an msaembly language data transfer routine, data transfer rates of a t least 10 K wps can be achieved. The recorder advances to the next word on the clock 1-to-0 transition. Transfer of the 10-bi1tword is accomplished by applying a clock pulse to the system. Thus, a clock pulse is obtained a t the memory wid simultaneously to the buffer disable lines 1, 2, and 3. At disable 4, an inverted clock is received. As shown in the truth tables, when the clock is low, “O”, a t the disable lines, input follow output. However, disable 4 is high, “1”(ie., inverted), at tlhis point, and as shown in the truth tables outputs 5 and 6, which contain the information in bits 1and 2, are in a high impedance (or Hi-Z) state. As a result, bits 3-10 are read during the “0” logic level of the pulse. When the clock transition to “ 1” occurs, disable lines 1,2, and 3 are “1”while disable line 4 is “0”. The truth tables indicate that bits 3-10 will be in the Hi-Z state while bits 1and 2 are read. Thus, in one complete clock pulse, bits 3-10 and then bits 1 and 2 are read. As an example, the binary equivalent to 512 being lOOOOOOOOO would1 be read as 00000000 = 0, at the “0” level of the pulse and 11111110 = 254 at the “1”level of the pulse since the second bit is located at the LSB of the corn-
Figure 2. Cable connection from the transient recorder to the computer. The output from bit 1 (MSB) and 2 (next MSB) are hardwired to PA0 and PA1 of the computer (the computer LSB and next LSB, respectively).
puter and the Hi-Z state input is read as a “1”by the PET. With the proper peek and poke routines used by the PET computer, the data obtained in the “0” portion of the clock pulse can be placedl in one array while that information obtained in the “1”ltwel can be placed in another. The beginning of the program which accomplished this task opens and clears two arrays that will be used to store data. Once these arrays have been cleared, the program enters into a loop which controls the clock and data collection. CB2 is instructed to go low at which time bits 3-10 are read. CB2 is then brought high and bits 1and 2 are read. This process continues until the program exits from the loop. By a simple arithmetic statement, the two arrays are then joined into one decimal equivalent for each 10-bit word. If we let A(1) = 0 and B(1) = 254, then C(1) = (B(1) 252)*256 + A(I), C(1’) = (254 - 252)*256 + 0 = 512 + 0, which is equivalent to the original 10-bit word (1000000000). The correction factor (B(1) - 252) is employed because there are four possible valuesr for B(1) (255, 254, 253, 252). As well as increasing the resolution of our measuremeiits read by the cornputper,this system has also maintained the same data collection frequency as would be anticipated by just reading the first eight bits. Here we have utilized both levels of the clock pulse for reading the memory of the transient recorder. With our present system, the 10-bit word without the aid of the buffers could only be read as 8 bits on the falling edge of the clock. With the buffer interface system, the complete 10-bit word is read in one clock pulse.
LITERATURE CITED (1) Betty, K. R.; Horllclk, G. Anal. Chem. 1977, 47, 342-345. (2) “CMOS Integrated Clrcults Handbook”; National Semlconductor Gorp.: Santa Clara, CA, 1975; p 113.
RECEIVED for review July 18, 1980. Resubmitted June 2!9, 1981. Accepted June 29,1981.
Determination of Water in Solids by Automatic Karl Fischer Titration Frank E. Jones National Engineerhg Laboratory, National Bureau of Standards, Washington, D. C. 20234
The specificity of the Karl Fischer reagent (KFR) titration method for HzO, its high precision, and its applicability to
rapid determination make it the preferred method for the absolute determination of HzO. Several significant develop-
This artlcle not suhject to US. Copyright. Published 1981 by the American Chemical Society
