Anal. Chem. 1981, 53, 645-650 (32) Roth, C.; Gebhart, J.; Heigwer, G. J. ColloM Interface Scl. 1976, 54, 265-277. (33) Ferrara, R.; Fiocco, G.; Tonna, 0. Appl. Opt. 1970, 9 , 2517-2521. (34) Hinds, E.; Reist, P. C. J. AerosolSci. 1972, 3 , 501-514. (35) Young, T. “An Introduction to Medical Laeraturd’; Underwood and Blacki: London, 1818; p 548. (36) Pijper, A. J. Lab. Clln. Med. 1947, 32, 857-877. (37) Polanyi, M. L. Rev. Scl. Instrum. 1959, 30, 626-632. (38) Dobbins, R. A.; Crocco, L.; Giassman, I. AIAA J . 1963, 7(8), 1882- 1886. (39) Roberts, J. H.; Webb, M. J. AIAA J . 1964, 2(3), 583-585. (40) Silverman. B. A.: ThomDson, B. J.: Ward, J. H. J. A.m. / . Meteorol. 1984, 3, 792-801. (41) Hodkinson, J. R. Appl. Opt. 1966, 5 , 839-844. (42) Talbot, J. H. J . Scl. Instrum. 1968, 43, 744-749. (43) Taylor, M. E. U S . Patent 3469921, 1969. (44) 601, J. U S . Patent 3646352, 1972. (45) Corniliault, J. Appl. Opt. 1972, 7 1 , 265-268. (46) Gravatt, C. G. J. Air Pollut. Control Assoc. 1973, 23, 1035-1038. (47) Davies, R. Am. Lab. (FairfleM, Conn.) 1974, 6 , 73-86. (48) Corniliault, J.; Evrard, P. Cem. Technol. 1975, 6 , 178-179. (49) Wertheimer, A. L.; Wilcock, W. L. Appl. Opt. 1976, 15, 1616-1620. (50) Welss, E. L.; Frock, H. N. Powder Technol. 1978, 14, 287-293. (51) Swkhenbank, J.; Beer, J. M.; Taylor, D. S.; Abbot, D.; McCreath, 0. C. “Progress in Astronautics and Aeronautics”; Zinn, B., Ed.; AIAA: New York, 1977; Voi. 53, p 421.
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(52) Mann, P. J. Foodfng. 1977, 49, 85-88. (53) Caroon, T. A. M.S. Thesis, University of Wisconsin, Madison, 1978. (54) Caroon, T. A,; Borman, G. L. Combust. Scl. Technol. 1979, 19, 255-258. (55) Bachaio, W. D. Appl. Opt. 1980, 19, 363-370. (56) Roberds, D. W. Appl. Opt. 1977, 76, 1861-1668. (57) Mohamed, N.; Fry, R. C. Anal. Chem. 1981, 53, 450-455. (58) Mohamed, N.; Brown, R. M.; Fry, R. C. Appl. Spectrosc. 1981, 35, 153-164.
RECEIVED for review September 17,1980. Accepted January 22,1981. This work was supported in part by FDA Research Contract No. 223-80-2327 CPD (to R. C. Fry) and in part by Kansas Agricultural Experiment Station Project No. 143 (to R. C. Fry). The authors wish to thank the Leeds and Northrup Co. for generous use of the laser diffractometer. This work was presented by N. Mohamed and R. C. Fry in part at the 1979 Pithburgh Conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, OH, in part at the 1979 Rocky Mountain Conference on Analytical Chemistry, Denver, CO, and in part a t EXPOCHEM 80, Houston, TX.
Microcomputer-Controlled Intensified Diode Array Data Acquisition System for Chemiluminescence Spectra D. F. Marino‘ and J. D. Ingle, Jr.” Department of Chemistty, Oregon State University, Corvallis, Oregon 9733 7
A KIM 6502 controlled Intensified dlode array system Is described which Is capable of acquiring a 512-point chemlluminescence (CL) spectrum from 200 to 840 nm In as little as 4 ms under dlrect memory access (DMA) control. Thls system has provlslon for subtraction of the dark current spectrum, automated lnjectlon of the last reagent to Initiate the CL reaction, signal averaglng N spectra, and plotting of the CL spectrum on a strlp chart recorder. The use of the Instrument Is demonstrated with three dlfferent CL chemlcal systems.
Solution chemiluminescence (CL) spectra are difficult to obtain with discrete sampling instrumentation in which a reagent or the sample is injected into a reaction mixture to initiate the CL reaction. The typical short duration (ca. 1s) and transient nature of the CL signal are not compatible with conventional scanning monochromators. Most investigators (1-7) in this area have invariably employed either photographic detection or conventional scanning spectrometers, both of which require a great deal of time and a number of repetitive CL reactions. Recently however, the first use of a commercially available intensified diode array (IDA) for the acquisition of fast CL spectra was reported (8),and spectra of the lucigenin and pyrogallol CL reactions were presented. Though such spectra provide principally qualitative information about the CL reaction in question, they are nevertheless useful for (i) choosing PMTs for maximum sensitivity at the wavelengths of maximum CL intensity, (ii) identifying reactant or product absorption interferences, (iii) elucidating the nature of nonanalyte interferences, or (iv) obtaining information about CL reaction mechanisms (e.g., identification of the luminescing species). Present address: E. I. du Pont de Nemours and Co., Wilmington, DE. 0003-2700/81/0353-0645$01.25/0
Because the commercial data acquisition system used for previous work did not provide the desired versatility for acquiring CL spectra, an in-house microprocessor control and data acquisition system was constructed. This system is much less expensive and acquires spectra faster than the commerical system. One other &bit microprocessor (8080)control system for a diode array has been reported (9) although the data acquisition rate is much slower than reported in this paper. This paper is concerned with the construction that is specifically designed for acquiring CL spectra with a discrete sampling CL system. The application of the IDA system to three different CL chemical systems is reported to illustrate the information provided by CL spectra that is useful in developing routine CL analysis techniques. EXPERIMENTAL SECTION CL measurements were made with a discrete sampling CL photometer previously described (10,11). The reaction sample and reagents are added to the sample cell with Eppendorf pipets, and the reaction is initiated by injection of the last reagent with a precision liquid dispenser which is TTL controlled. The IDA spectrograph was interfaced to the CL sample module a8 previously noted (8). Absorption spectra were acquired with a Cary 118C W-visible spectrophotometer. The absorption spectra of all reaction constituents were taken in solvents of the same pH as that of their respective CL reaction solutions. INSTRUMENTATION Introduction. A block diagram of the KIM-IDA CL spectra data acquisition and plotting system is shown in Figure 1. The operation and general characteristics of the components of the system will be discussed below. Only circuitry which is unique and which could not be constructed from information in other articles or manufacturer’s information will be discussed in detail. Detailed schematics, flow diagrams, and program listings are available from the authors upon request. 0 1981 American Chemical Society
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Block diagram of KIM-IDA system.
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A Tracor Northern TN-1223-21512 element IDA in conjunction with an f/3 holographic grating spectrograph (TN-1150) and a intensifier gain controller (TN-1710-17)was used for all measurements. The spectrograph dispersion allows the simultaneous acquisition of spectra from 200 to 840 nm. With the 250-pm slit width used, the resolution is about 7 nm. As purchased, the device requires a system clock (SC) which determines the rate of interrogation of the 512 photodiodes in the array, a begin of scan (BOS) pulse which determines when the array will be interrogated and the integration time (Le., time between interrogations),an A/D to digitize the signal information on the video line, and a memory for storage of signal information. The timing diagram shown in Figure 2 will be used for further discussion. Note that in the timing diagram shown in Figure 2 that the first valid data point occurs on the video line after the IDA BOS pulse goes back high and that the EOS (end of scan) signal goes low after the 512th diode is clocked. Additional circuits employed were constructed for another more expensive and sophisticated IDA data acquisition system based on a PDP 11/20 minicomputer and is described elsewhere (12). Only the two parts of that system, a sample-and-hold (S/H) and analog-to-digital converter (A/D) printed circuit (PC) board and parts of a logic and timing (L-T) PC board were used for the KIM data acquisition system and will be briefly described. The S/H-A/D PC board consists of a fast S / H (Computer Labs HTC-0300)
and a fast (2 ps acquisition time) 12-bit A/D (Date1 EH12B3) with an additional voltage amplifier between the S / H and A/D. The video line of the IDA is connected to the input of the S/Hand a full scale or saturated signal from a photodiode causes 10 V to be input to the A/D which is full scale for the A/D. The A/D requires a clear-start (Cl-ST) logic 1 pulse. Additional circuitry on this PC board is used to generate a logic 1level DONE bit from the A/D DATA READY signal which is cleared by a logic 1 handshake (HS)pulse from the direct memory access (DMA) module after the data are transferred. The S / H also requires a logic 1 HOLD pulse during which time the S/H tracks the signal on the IDA video line. The L-T board contains one monostable which converts a logic 1 start (ST) pulse from the computer into a 2-ps logic 0 BOS pulse that goes to the IDA and the KIM-IDA adapter. Two more monostables on the L-T board produce the 0.4-ps logic 1HOLD pulse that is delayed 0.6 pus from the falling edge of the SC. This ensures that the photodiode signals on the video line (about 1p in duration) are sampled at their peaks. The microprocessor system consisted of a KIM 1 (MOS technology) single-board microcomputer (6502 microprocessor) plus a Memory Plus expansion board (Computerist)mounted in one box. The KIM 1(13)includes 14 bidirectional 1/0lines, a cassette tape interface, a 20-mA teletype interface, 1K of static RAM, an interval timer, and a 2K ROM operating system. The expansion board provides 8K of RAM (denoted system RAM), 8K of EPROM, 16 more bidirectional 1/0(3 of the original KIM 1/0bidirectional lines are used by the expansion board). The EPROM was loaded with an 8K BASIC from Microsoft. The 16-bit address buss of the KIM was modified by using 74126 Tri State buffers to allow for external address and read/write (R/W) line control by the DMA module described later. Communication with the computer system is carried out with an in-house keyboardprinter (14) connected to the teletype interface. A tape cassette was used to load the operating program into system RAM, Spectral data were plotted on a recorder (Heath, Model SR-205) with a 12-bit DAC (Burr Brown 8OCBl) whose inpub are latched with 7475 quad latches that are strobed with a logic 1 STROBE pulse via a KIM 1/0line. KIM-IDA Adapter. The KIM-IDA adapter is shown in Figure 3. It prevents any A/D conversions until the second SC negative edge after EOS (end of scan) and BOS lines go high, and allows A/D conversions only when valid data are present. If the A/D ran continuously rather than only when valid data are available, the DMA would always have control of the KIM and fdl its RAM with meaningless data. Referring again to Figure 3, the BOS start pulse from-the L-T board is applied to the preset pin of IC3, driving Q low. Directly after th_e pulse, the next falling edge of the S / H pulse train drives Q of IC3 high. Provided that EOS is high, this clocks Q of IC4 high, enabling IC5. The next falling edge of the S/H
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(KIM)
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IC5
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Figure 4. DMA address generation circuitry: IC1-IC4, 74191 up/down counter; IC5, IC12, IC20, 7404 hex inverter; IC6-IC9, IC19, 74126 TRI-STATE buffer; IC10, IC11, 7485 4-bit magnitude comparator; IC13, 7408 AND gate; IC14, IC17, 7474 dual D flip-flop; IC15, 7407 open collector buffer; IC16, IC18, 7400 NAND gate; IC21, 74121 one shot; R1, 1.2 kO; R, 1 kO; R3, 2 kO, internal to 74121; C1, 40 pF ceramic.
pulse train will then trigger IC6, producing a short (1.4 ps) A/D clear and start pulse. When all 512 diodes in the array have been interrogated, EOS goes low, setting Q of IC4 low and halting the A/D start pulses. DMA Module. In cases where a very fast A/D is employed with the KIM, data acquisition rates are limited by the rate at which the 6502 microprocessor can load and transfer the data to memory. The loading and storing of a single 16-bit word requires 30 ps without page crossing and 46 ps with page crossing, providing a maximum data collection rate of 22K bytes/s for over 128 16-bit data words. This data limitation was circumvented through the use of a DMA module which is basically concerned with “stealing” the address and data buss from the 6502 and writing directly into system RAM under hardware control, beginning at the highest address of a page selected by the operator, and loading data in successive memory locations down from the initial address until the lowest address of a page selected by the operator is filled. Figures 4 and 5 are schematics of the address generation and data manipulation portions of the device constructed for this purpose. A hardwired DMA circuit had to be constructed since a DMA chip is not available for the 6500 family of chips although a 8080 DMA chip could probably be used with additional external circuitry. The DMA module consists of two PC boards mounted in one box. Three 37-pin amphenol connectors provide connections between the DMA and, (1)the data buss, address buss, read write (R/W), processor clock (42),and RDY lines of the KIM, (2) the data outputs, DONE bit and HS of the fast A/D, and (3) 19 KIM 1/0 lines, which control the DMA upper and lower page boundaries (eight lines each), the pro-
grammable read/write line (PR/W), the Dh4.4 8/16-bit control line, and the DMA address load (ADD LD) line. The operation of this DMA module will now be discussed. When the KIM RDY line is pulled low (Figure 4) the KIM is effectively disconnected from the external RAM address buss and R/ W line. In addition, the 6502 is halted when RDY is pulled low provided that (I)R/W is high (a read cycle) and (2) 42 (KIM 1-MHZ clock) goes through a positive edge. Referring to Figure 4, IC14-IC17 act to pull the RDY line low on the zero to one transition of the A/D DONE bit and generate a buss available (BA) signal when the above requirements are met. This DONE bit signal appears at the clock (CL1) input of IC14, and drives high, providing that preset one (Pl) is high. When R/W is high and is NANDed with the output of at IC16, a low signal is presented to data two (D2) of IC17. On the next positive 42 transition, CL2 clocks in these data, driving high and Q2 low. This simultaneously generates the BA signal and pulls RDY low through IC15 Note that a high on BA “locks” IC17 in the event that R/W changes during the DMA operation. If &1 of IC14 is still high and BA is high at IC18, C2 of IC17 is forced low, “locking” BA high and RDY low. If at some later point, P1 of IC14 is driven low, @ w i l l go low and the BA and RDY lines will be “unlocked”. This occurs during the DMA handshake (HS) operation, to be discussed later. At the same time, P2 of IC17 is driven low, forcing BA low and RDY high and returning control of the data and address busses to the 6502. The four 74191 up-down counters (IC1-IC4) and two 7485 parity checkers (IC10, IC11) constitute the address generation portion of this circuit. An initial page address (starting point
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DMA data control circuitry: IC22, IC23, 741 12 J/K flip-flop; IC24, IC26, IC31, IC32, 7408 AND gate; IC25, IC30, 7404 hex inverter; IC27, 7432 OR gate; IC28, IC29, DM 7123 TRI-STATE one of two gate: I C 3 3 d C 3 6 , 74126 TRI-STATE buffer.
for data read or write operation) from $20 (2OI6) to $FF is selected and loaded into IC1 and IC2 via eight KIM 1/0bits when the ADD LD line is high. The lower address page (final address for data read or write operation) is loaded into IClO and IC11 in the same manner. As an example, if $3F is loaded into IC1 and IC2 and $ l F is loaded into IClO and IC11, address $3FFF through $2000 will be accessed by the DMA. After $2000 has been accessed, the DMA will halt all operations and return to the 6502 until reprogrammed. Once a device triggers the DMA and BA goes high, IC6-IC9 are enabled, and the first 74191 address is placed on the buss, which occurs while 42 is high. The address will decrement by one when 42 goes low (rising edge of 41). If it is desired to write or read only one address per DONE bit (8-bit transfer), IC21 is programmed to send out a short pulse just after the rising edge of 41, “handshaking” the A/D and returning control of the buss to the 6502. This is accomplished with the 8/16 bit control line, which is under KIM 1/0control, and IC22-IC27 (Figure 5 ) , which will be discussed later. Control is passed to the KIM when Q of IC21 drives P1 of IC14 and P2 of IC17 low, which drives BA and RDY high. At the same time, Q of IC21 “handshakes” (resets the DONE bit of) the A/D. Note that one selects a DMA read or write (data transfer from or to KIM RAM, respectively) by setting or clearing, respectively, the programmable read/write line (PR/W), which is done by using another KIM 1/0bit. The status of the PR/W bit is independent of the 6502 R/W status. By making use of two 7123 TRI-STATE one-of-twoselectors, (IC28, IC29, Figure 5), the DMA may read or write (1) consecutive eight-bit words in consecutive RAM locations or (2) the low eight bits followed by the high eight bits of a 16-bit word in consecutive RAM locations. Using another KIM 1/0 bit, one may set the 8/16 bit DMA line low, resulting in the
consecutive eight-bit transfer of data. If the 8/16 line is set high, the A/D HS and BA clear pulses are generated every other 42 positive edge, allowing two addressesto be generated and two eight-bit words to be transferred per DMA cycle. If the 8/16 bit control line is set low, each 42 clock pulse passes through IC26 and IC27, triggering IC21 of Figure 5 and “handshaking” the A/D. In addition, C1 or IC23 and C2 of IC22 are forced low, essentially disabling IC23 and forcing Q2 of IC22 low, which forces IC28 and IC29 to deliver only the data present of the “ A lines to the KIM. If the 8/16 bit is set high, 42 is blocked from IC27 by IC26. Instead, IC23 “toggles” every 42, resulting in a “handshake” ever other 42. In addition, Q2 of IC22 “toggles”, resulting in “A” data and “B” data being presented to the system RAM on alternate 41 edges. The timing diagram of Figure 6 summarizes the above discussion and illustrates the speed of DMA data transfer. In this example, a 16-bit data word is being taken every 3.5 ps, a worst case figure, since the triggering device “done” bit requests a DMA just after a read cycle and just before a write cycle. A best case figure would be 1.5 I.LS. Even so, this results in a data acquisition rate of 571K bytes/s, a factor of 25 faster than obtainable under 6502 control of the data transfer. Analysis of the pulse widths in Figure 2 considering the time delays in the S/H HOLD and A/D clear and start signals and the A/D conversion time will show that, in conjunction with the DMA, one may clock through4he array at 137 kHz, resulting in a complete spectrum in 3.7 ms. A SC rate of 125 kHz was used for actual experiments. Software. The operating program (CLIDA) allows the user to collect and sum N net CL spectra from 200 to 840 nm under DMA control and then to plot the resulting spectrum by using a simple chart recorder. The difficult interaction and calcu-
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DIODE I
DIODE 512 WAVELfNOIH NM
CL spectrum of the luminol-OCI- CL reaction and relatlve absorption spectra of OCI- and luminol: [OW] = 25 mg/L; [IUminOl] =2X M; pH 10; ten summed scans; 0.8 s integration time. Flgure 7.
S/H OUT
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11
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Figure 6.
Worst case timing diagram for 16-bit DMA write.
lation functions are accomplished in BASIC while machine language subroutines are used for 1/0 port control, DMA control, and plotting the spectrum. The operator may choose the array integration time (T) and number of CL reactions to be run (N). Once the cell has been filled with all but one of the CL reagents, the operator commands the KIM to begin acquisition. The array is cleared with three refresh scans to totally discharge the diodes (12)and the diodes are allowed to integrate dark signal for T ms. This dark spectrum is then transferred to the KIM under DMA. The KIM then injects the final CL reagent, beginning the CL reaction, and allows the array to integrate the CL signal for T ms. The CL spectrum data are then transferred to the system RAM under DMA. The KIM then performs a point by subtraction of the dark and CL signal spectra and adds the resulting net spectrum to any previously acquired spectra in a “net spectrum bank’, This process is then repeated N - 1times. Once N net spectra have been acquired and summed, the resultant CL spectrum is plotted by using the 12-bit DAG and chart recorder. The operator is asked if he would like to plot a spectrum. If so, the operator commands the KIM to plot a spectrum via the 12-bit DAG to the recorder on the 10-V scale. The 512point spectrum is plotted in ca. 100 s. A 0.1-V offset is added to each data point before plotting to ensure that negative values (due to random noise in the dark signal) are not plotted erroneously. At this point the operator can sum N more spectra on top of the spectra already in memory if the net CL spectrum is too weak and replot the new spectrum. Once all of the spectra desired have been taken, summed, and plotted, BASIC executes a “peak maximum” search which compares the signal from each diode to its four nearest neighbors and to an operator defined “discriminator level”, D, which may be viewed as the minimum signal value a diode must have to even be considered as a maximum. Inclusion of D merely speeds up the peak maximum search. If a diode signal is greater than all four nearest neighbors, its number, wavelength, and value in millivolts are printed. If the operator wishes to change D and try again, he is then given the option of doing so. The operator must be sure that no value in the “net spectrum” bank exceeds 212,which is the full-scale range of
CL spectrum of H,O,-OCI- singlet oxygen CL reaction: [OCI-] = 0.1 M; [H202]= 0.1 M; pH 8.0; five summed scans; 2.0-9 integration time. Figure 8.
the DAC. The CLIDA program occupies about 5K of RAM leaving about 3K bytes for data storage. This amount of memory is totally consumed by the double-precision,512-point “dark” spectrum, signal spectrum, and “net” spectrum, which leaves no room for any other spectra unless more RAM is interfaced to the KIM. Note that although 16 1/0 lines are required for DMA address programming, these same 1/0 lines are used for the DAC, i.e., the DMA and DAC data 1/0 lines of Figure 1are placed in common. This may be done since the DMA and DAC are both strobe controlled by separate 1/0 lines which load these devices at totally different points in the program, allowing these common 1/0lines to perform a double duty. The primary advantages of the KIM data aquisition system compared to the one previously used are that the dark spectrum is subtracted from each CL spectrum for each CL run and the CL spectrum is synchronized to the start of the reaction by control of the injector. Thus the CL spectra are taken only when the CL signal is present and unnecessary dark signal and noise are not accumulated. Also the dark and CL spectra are separated only by the time necessary to activate the dispenser. This is crucial since dark current drift although small was found to degrade the S/N if N CL spectra were first taken and then N dark spectra followed by subtraction or if there was considerable time between a CL and dark current spectrum (8).
RESULTS AND DISCUSSION For this work, the uncorrected CL spectra of the luminol-OC1- (15), H2Q2-OC1- (16),and lophine-Cr(V1) (17)reactions were acquired and are presented in Figures 7-9, re-
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Figure 9, CL spectrum of lophine-Cr(V1) CL reactlon and relative absorption spectrum of Cr(II1): [Cr(VI)} = 100 mg/L; [lophine] = 4 X lo-‘ M; [KOH] = 0.8 M; [H202] = 0.04 M; five summed scans; 2 . 5 s integration time.
spectively. The solution reaction conditions and data acquisition variables are given in the figure captions. Detailed discussion of the above chemical systems are found in the references cited above. All spectra are relative noisy due to the low light levels of CL and the diode-to-diode sensitivity variations even though analyte concentrations were chosen to maximum CL intensity and the full intensifier gain was used. Also the integration time was chosen to include about 90-95% of the total integrated CL intensity. Figure 7 presents the spectrum of the luminol-0Cl- CL reaction, along with the relative absorption spectra of luminol and OC1-. The peak CL wavelength of 476 nm agrees well with the fluorescence maximum of 3-aminophthalic acid, the proposed luminescing species in luminol reactions (3). As Figure 7 illustrates, luminol does not appear to absorb in the region of CL nor does OC1- and thus the reactants do not cause postabsorption problems. Figure 8 presents the spectrum of the OC1--H202 singlet oxygen CL reaction. Two peaks a t 636 and 703 nm appear in agreement with the work of Khan and Kasha (18) and Seliger (6). This is the first spectrum ever obtained of singlet oxygen CL by use of a multichannel detector. These peaks are due to a two-molecule, one-photon process (19)
H202+ OC1200C1202(lAg)
k3
H20 + OOC1-
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202(32,)
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The production of OOC1- has been proposed to be rate limiting (20), which would result in an overall first-order dependence on OC1-. Work in our laboratory, however, has shown a 1.4order dependence on OC1- a t low concentrations (16). This would indicate that reactions 2 or 3 are partially rate limiting. The wavelengths of CL emission suggest that with routine
quantitative work with a PMT, a red-sensitive PMT should be used if the ratio of responsivitiy at these wavelengths to the dark current noise is higher than for a conventional PMT. Figure 9 presents the uncorrected spectrum of the lophine-Cr(VI) CL reaction, along with the relative absorption spectrum of Cr(III), a product of the reaction. As can be seen, Cr(II1) absorbs in the region of CL. Fortunately, although Cr(II1) is a product in this reaction, it is a very weakly absorbing species and reduces the CL signal only when very high Cr(V1) concentrations are used (9). The peak CL wavelength of 561 nm in water reasonably well with the reported CL maximum of 530 nm (21) in ethanol which is also the maximum of fluorescence emission of the proposed luminescent product, an amidine salt. These spectra illustrate that one must consider the absorption characteristics not only of the reactants or self-absorption of the luminescence precursor but also of “dark” products of the reaction. The interference effects of some species in CL work may be due to the absorption of CL radiation by these species or products of these species formed in the CL reaction mixture. Thus the absorption spectrum of the final reaction mixture with and without potential interferents added or individual products can be compared with CL spectra obtained with the KIM-IDA system to more precisely identify causes of interference.
LITERATURE CITED Seliger, H. H. Anal. Blochem. 1960, 7 , 60-65. White, E. H.; zafiriou, 0.; Hagi, H. H.; Hill, J. H. Seliger, H. H. “Light and Life”; McElroy, W. D., Gloss, B., Eds.; John Hopkins Press: Baklmore, MD, 1961; pp 200-205. Khan, A. U.; Kasha, M. J . Chem. Phys. 1963, 3 9 , 2105-2106. Arnold, S. J.; Ogryzlo, E. A,; Witrke, H. J . Chem. Phys. 1964, 40,
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RECEIVED for review September 17,1980. Accepted December 23,1980. Acknowledgment is made to the National Science Foundation (Grant No. CHE 7617611and 7921293) for partial support of this research.
