387
`
`Anal. Chem. 1980, 52, 367-371
`of the decaying portion of the curve and the time to maximum
`deflection, one can distinguish non-first-order kinetics.
`LITERATURE CITED
`(1) Bell, R. P.; Clunie, J. C. Proc. R. Soc. London, Ser. A, 1952, 212,
`16-32.
`(2) Lueck, C. H.; Beste, L. F.; Hall,  . K„ Jr. J. Phys. Chem. 1963, 67,
`972-976.
`(3) Thouvenin, Y.; Hinnen, C.; Rousseau, A. "Les developpements recents
`de la microcalorlmetrie et de la thermogenese”, Vol. 156; Editions du
`C.N.R.S.: Paris, 1967; pp 65-82.
`(4) Camia, F. M. Ref. 3, pp 83-94.
`(5) Mietes, Thelma; Mletes, L.; Jaitly, J. N. J. Phys. Chem. 1969 , 73,
`3801-3809.
`(6) Johnson, R. E.; Biltonen, R. L. J. Am. Chem. Soc. 1975, 97,
`2349-2355.
`(7) Provencher, S. W. Biophys. J. 1976, 16, 27-41.
`(8) James, F.; Roos, M. Comput. Phys. Common. 1975, 10, 343-367.
`(9) Grell, E.; Funck, Th.; Eggers, F. "Molecular mechanisms of antibiotic
`action on protein biosynthesis and membranes"; Elsevier: Amsterdam,
`1972; pp 646-685.
`(10) Moeschler, H. J.; Sargent, D. F.; Tun-Kyi, A.; Schwyzer, R. Helv. Chlm.
`Acta, in press.
`
`56789
`A
`time
`(min)
`Figure 6. Example of a non-first-order reaction. The peak value occurs
`Inset: semi-logarithmic plot of the tail region showing an
`at 55 s.
`apparent exponential decay with a time constant of 140 s. See text
`for details
`pseudo-first-order, then its time constant would also have a
`In this case, however, the calorimeter output
`similar value.
`would peak at about 124 s (Figure 4), whereas the peak ac-
`tually occurred at about 55 s. Thus using the time constant
`
`01
`
`2
`
`3
`
`10
`
`Received for review August 17,1979. Accepted October 30,
`1979. Finanical support of the Swiss National Science
`Foundation and the Swiss Federal Institute of Technology
`is gratefully acknowledged.
`
`Inexpensive Microprocessor Controlled Programmable Function Generators for Use in
`Electrochemistry
`
`A. M. Bond*
`Division of Chemical and Physical Sciences, Deakin University, Waurn Ponds, Victoria 3217, Australia
`
`A. Norris
`Clanor Instruments, P.O. Box 75, Baiwyn, Victoria 3103, Australia
`
`Several review articles on the use of microprocessors in the
`field of chemical instrumentation have been prepared by Dessy
`and co-workers (1-3). The major thrust toward their use in
`many laboratories would be expected to arise from their ex-
`tremely high computing power provided at minimal cost.
`However, in reality, extremely limited use has been made to
`date by chemists working in small, low budget laboratories
`who could actually take direct advantage of the very low cost.
`for very few chemists directly exploiting the high
`The reason
`quality low cost performance of microprocessors has been
`outlined by Dessy et al. (1-3) and the main drawback cited
`is the difficulty of writing the software and the belief that
`access to a larger and rather expensive computer available to
`commercial manufacturers of instruments or
`larger institutions
`is almost mandatory for this task.
`It is certainly true that many manufacturers and chemists
`who have worked in the field have had access
`to rather ex-
`pensive minicomputer systems with facilities for writing in
`high level languages, editors, cross-assemblers, etc., and an
`impression may easily be conveyed that the microprocessor
`is not readily developed on its own
`as an inexpensive com-
`putational component in instrumentation. However, it is
`worth taking time to consider that such aids, while undoubt-
`edly very useful are by no means essential and certainly not
`for the carefully chosen simple tasks we wish to demonstrate
`in the present article.
`
`In our electrochemical research, we have seen considerable
`advantage in the use of microprocessors for performing an
`range of tasks at minimal cost, provided we could
`enormous
`confine ourselves to using only the typical microprocessor “kit”
`and instruction set provided by the manufacturer and un-
`dertake all program development work with very restricted
`memory, etc., using accessories and aids that were less ex-
`pensive than the microprocessor kit itself. Working for some
`time within the confines of these restrictions has now con-
`vinced us that outstanding results can be obtained relatively
`easily without access to larger laboratory computers. Fur-
`thermore, we now believe that despite some reports to the
`contrary it is eminently sensible to consider the use of mi-
`croprocessor technology in any low-budget laboratory as a
`means of obtaining high quality performance and versatility
`at extremely low cost. This theme in addition to the actual
`scientific data provided, constitutes one of the main impli-
`cations of the present report.
`In the present paper we describe in detail the use of a
`standard MOS TECHNOLOGY KIM-1 microprocessor kit,
`as well as programming procedures and related approaches
`we have used to develop a programmable function generator
`for use in electrochemistry. The KIM-1 module uses an 8-bit
`microprocessor and is representative of the earlier generation
`kits available at very low cost.
`Indeed our entire system
`including interfaces to a potentiostat can be built at a cost
`
`0003-2700/80/0352-0367S01.00/0
`
`© 1980 American Chemical Society
`
`Vestas Ex 1033-p. 1
`Vestas v GE
`
`

`

`368 · ANALYTICAL CHEMISTRY, VOL. 52, NO. 2, FEBRUARY 1980
`
`CRO TRIGGER
`
`DROP KNOCKER
`
`Figure 1. Microprocessor to analog converter interface. The least significant 8-bit byte, of the 16-bit word to be transferred to the digital to analog
`converter, is put onto the 8 output lines PAD (memory location 1700). These output lines feed both the Intermediate latches and the latches driving
`the most significant 8 bits of the digital to analog converter. PBO, the first output pin of the second 8-bit output part PBD, is set high, which clocks
`the intermediate latches storing the 8 bits. The most significant 8 bits of the 16-bit word are then transferred to PAD replacing the least significant
`that the 16 latches driving the digital to analog converter have the most significant 8 bits of the 16-bit word supplied
`8 bits. This now means
`directly via PAD and the lower 8 bits via the intermediate latches. PBI of PBD is now set high transferring the whole 16-bit word to the digital
`to analog converter. See Figure 2 for further details on PAD and PBD
`
`of less than $500, and is small, portable, and lightweight.
`Much of the field of electrochemistry requires the appli-
`cation of a time dependent potential to a potentiostat and
`analog function generators have been used for this task for
`many years. Digital function generators have also been de-
`their
`scribed (4) and these have substantial advantages over
`analog counterparts. Obviously mini-computers also have been
`used on very many occasions to provide very versatile pro-
`In the fields of polarography
`grammable digital waveforms (5).
`(voltammetry) and corrosion (6), commercially available
`microprocessor controlled systems performing certain tasks
`have been most successful. However, these systems are ded-
`icated to perform certain well defined fixed tasks and the
`function generators in these systems do not allow for the
`extreme flexibility required by many workers in the area of
`Indeed an extremely interesting article by
`electrochemistry.
`Matson et al.
`(7) demonstrates how advantageous a pro-
`grammable function generator could be in electroanalytical
`chemistry. A detailed description of the development of a very
`flexible waveform generator based on microprocessor tech-
`nology is therefore presented to illustrate the use of micro-
`processors to obtain extremely high performance usually as-
`sociated with laboratory computers while preserving the in-
`herent cost advantage gained in the initial purchase of a very
`inexpensive microprocessor module.
`INSTRUMENTATION
`The Mos Technology KIM-1 Module was used as purchased
`from the manufacturer and employs an 8-bit processor. A key-
`board is provided as part of the module for writing programs and
`
`performing certain other tasks. Complete documentation on the
`microprocessor system and a comprehensive instruction set is
`provided by the manufacturer.
`To develop and fully use on a routine basis the complete
`function generator described, an audio cassette to store programs
`was connected via the port provided by the manufacturer. A
`standard power supply was built to power the microprocessor kit
`and this completed an inexpensive construction technique enabling
`complete program development.
`The microprocessor kit plus cassette, plus power supply and
`interfacing, where necessary, achieved an objective of performing
`all tasks with a minimum of monetary outlay and requires no
`nonstandard electronics.
`In voltammetric measurements, it is probable that the waveform
`will need to be applied to a potentiostat, so in most instances the
`digital output from the microprocessor was converted to an analog
`signal with a 16-bit Datel DAC 169-16B D-A converter. Figure
`1 provides a diagram of the analog interface. During development
`of the waveform generator and to verify the fidelity of all software
`programs, the analog output was displayed on an Tektronix D13
`Storage Oscilloscope.
`RESULTS AND DISCUSSION
`Figure 2 is a flow diagram of a program suitable for applying
`a range of polarographic and voltammetric techniques at a
`dropping mercury electrode. Table I provides a copy of the
`input for the program.
`zero page or
`A complete and extensively documented listing of the
`software used with the KIM-1 Module to construct
`the
`function generator described in this paper
`is available.
`Versions of this program on cassette tape or paper tape and
`
`Vestas Ex 1033-p. 2
`Vestas v GE
`
`

`

`ANALYTICAL CHEMISTRY, VOL. 52, NO. 2, FEBRUARY 1980 · 369
`
`SET OUTPUT REGISTERS
`
`I
`TRIGGER CRO SYNC PUlSE
`
`I
`CALCULATE CONTROL WORDS 1 AND 2
`
`I
`INPUT PARAMETERS TRANSFER WITH
`DECIMAL  0 BINARY CONVERSION
`
`I
`CHECK AND TRANSFER REPLICATION NUMBER
`
`I
`CHECK ®0R SAWTOOTH (STAIRCASE) OR
`TRIANGULAR (CYCLIC) RAMP
`
`SAWTOOTH
`(8)
`
`(0)
`
`REPLICATION
`NUMBER BY 2
`
`MULT 5 P L-*
`
`INITIAL CONDITION BY 1G
`I
`CHECK POLARITY 0® INITIAL CONDITION
`
`POSITIVE
`(8)
`
`NEGATIVE
`(0)
`
`80
`
`S COMPLEMENT
`' IAL CONDITION
`
`CORRECT INITIAL
`
`CONDITION OFFSET
`
`I
`LOAD NUMBER OF RAMP STEPS
`
`I
`JUMP TO SUBROUTINE FOR INITIAL
`CONDITION TO OUTPUT (PAD>
`
`CHECK ]® PULSE FOR KNOCKING
`OFF DRC® REOUlRED
`
`pulse4TE
`
`JO
`
`STEP WIDTH DELAY
`
`OOLAROGRAPH1»
`(8)
`
`VOLTAMMETRY
`(0)
`
`HO
`
`CHECK ®0R SIGN
`(
`
`CF  
`
`RAMP   PULSE
`1(8)
`
`Cl
`
`RAMF -
`PULSE
`(0),
`
`i
`
`CHECK FOR
`FOLAROGRAPHY
`OR VOLTAMMETRY
`
`in
`lv
`
`NEW
`DROP
`
`SAME
`DROP
`(u.
`
`REPLICATION TO
`OCCUR BEFORE OR
`ACT£R DROP TO
`BE KNOCKED OFF
`
`PULSE TO CUTPUT (PBO
`
`PULSF y
` 
`
`CHECK FOR SIGN (')
`OF RAMP INCREMENT
`
`RAMP +
`
`INCREMENT
`(8)
`
`RAMP -
`
`INCREMEN*
`f0)
`
`02
`
`-1-
`CHECK FOR NORMA,.
`OR DI®®ERENT1AL PU.SE
`
`r-—^-i
`
`NORMAL
`(8)
`
`DIF®ERENT|AL
`(C>
`
`OH
`
`-r
`
`PULSE 0® F
`
`CHECK NO.
`RAMP STEPS
`
`0®
`
`\
`
`CHECK FOR SAWTCO'M
`OR TRIANGULAR (CYC.
`
`CYCLIC
`(55
`
`SAWTOOTH
`(8)
`
`CONDITIONS
`TO RAMP
`
`I
`
`08
`
`RELOAD HUMBER
`OF RAMP STEPS
`L
`
`Figure 2. Flow diagram of a program for developing a function generator
`using a microprocessor
`
`Vestas Ex 1033-p. 3
`Vestas v GE
`
`Table I. Zero Page Listings of Input Values of Parameters
`with a Typical Program for Generating a Very Easily Used
`Microprocessor-Controlled Function Generator
`control
`word
`assign-
`ment
`01
`
`memory
`location
`0000
`
`0001
`
`02
`
`0002
`
`04
`
`instruction and comments
`Set sign (±) for pulse.
`8 for
`positive, 0 for negative.
`LH digit for second con-
`trol word. RH digit for
`first control word.
`Set sign (± ) for ramp incre-
`8 for positive, 0
`ment.
`for negative. LH digit for
`second control word. RH
`digit for first control
`word.
`Set normal or differential
`(Staircase ramp is
`pulse.
`differential pulse with ze-
`ro pulse amplitude) 8 for
`normal, 0 for differential.
`Set sawtooth (staircase) or
`triangular (cyclic) ramp.
`8 for sawtooth, 0 for cy-
`clic.
`Set for repetitive scans
`to
`on same drop or on
`occur
`8 for same
`new drop.
`drop, 0 for new drop.
`Set pulse to knock off drop.
`8 bypass drop knock, 0
`knock off drop.
`Set polarography or voltam-
`8 for polarogra-
`metry.
`phy, 0 for voltammetry.
`Set sign of initial potential.
`8 for positive, 0 for nega-
`tive
`MS digit) Initial potential.
`LS digit f Resolution 1 mV,
`3.277 V.
`max
`MS digit) No. of ramp steps.
`LS digit f 0 to 9999.
`MS digit\ Ramp increment
`value
`>
`LS digit * Resolution 0.1
`mV, 0 to
`999.99 mV
`MS digit 1 Pulse increment
`value
`>
`LS digit / Resolution 0.1
`mV, 0 to 999.9
`mV
`MS digit \ Pre-sweep delay
`time
`>
`LS digit / Resolution 1 s, 0
`to 9999 s
`MS digit i Ramp step width
`(time)
`>
`LS digit / 10-ms resolution,
`0 to 99.99 s
`MS digit) Pulse width (time)
`LS digit 1 1-ms resolution, 0
`to 9.999 s
`No. of replications, maxi-
`8, Default is 1
`mum
`programs with specifically requested modifications or even
`a complete unit with interfacing may also be available. Write
`to the authors for further information.
`With the microprocessor system, the program and inter-
`facing to the D-A converter, the operator specifies via the
`keyboard input initial potential, pre-sweep delay, step height,
`step width, pulse height, pulse width and determines the
`potential range, drop time, scan rate, etc. Furthermore, it is
`
`08
`
`10
`
`20
`
`40
`
`80
`
`-
`
`-
`
`-
`
`-
`
`0003
`
`0004
`
`0005
`
`0006
`
`0007
`
`0008
`0009
`
`000A
`000D
`OOOC
`
`000D
`
`OOOE
`
`OOOF
`
`0010
`
`0011
`
`0012
`
`0013
`
`0014
`0015
`
`0016
`
`i { { { { { i
`
`

`

`370 * ANALYTICAL CHEMISTRY, VOL. 52, NO. 2, FEBRUARY 1980
`
`Table II.a Typical Specifications Available Using a
`Function Generator Based on Mos Technology 8-bit
`Microprocess Module, Datel 16-bit D-A Converter and
`Program Described in This Paper
`Initial conditions can be set within range ±3.277 V.
`1.
`Ramp range determined by initial condition plus
`number of steps times step height and can be set
`to values in the range ±3.277 V.
`0.1 mV.
`2. Resolution:
`3. Technique Type: DC (Staircase), Normal Pulse,
`Differential Pulse, Cyclic, Polarography or Vol-
`tammetry, etc.
`4. Drop Time: Variable with pulse duration to
`knock off drop also variable.
`5. Minimum Step Width (pulse plus DC):
`0.16 ms.
`6. Maximum Step Width:
`of 1 h.
`in excess
`7. Maximum Number of Steps:
`Limit 65K (0.1 mV)
`Steps.
`8. Minimum Pulse Width:
`80 ms.
`±3.277 in 0.1-mV incre-
`9. Range Pulse Heights:
`ments.
`a All parameters such as initial potential, final potential
`rate, ramp and pulse direction, technique, drop time,
`scan
`etc., can be set up and/or derived during the initialization
`process and altered as required. The only limitations
`on
`the initial conditions, ramp, and pulse is that their total
`value at any time does not make the output try to exceed
`±3.277 V.
`
`Identical sawtooth waveforms used in staircase voltammetry
`Figure 4.
`with (lower) and without (upper) pre-sweep delay. Upper traces without
`pre-sweep delay have an initial potential of +2.000 V and consist of
`twenty (50-mV) steps, 250 ms wide with a negative scan direction.
`Lower traces have a 1.0-s pre-sweep delay and commence
`at 0.000
`In other respects, they are the same as the upper traces
`V.
`
`Figure 5. Waveform used in normal pulse polarography (voltammetry).
`Initial potential = 0.000 V. Delay between pulses = 250 ms. Pulse
`width = 25 ms. Fifty steps with 50-mV increments. Negative pulse
`direction
`
`Figure 3. Triangular waveform used in cyclic (staircase) voltammetry.
`From top to bottom:
`Initial potential = 2.000 V, 1.000 V, 0.000 V,
`-1.000 V respectively,
`in each case fifteen (100-mV) steps, 250 ms
`wide, are shown and initial scan direction is negative.
`possible to generate the waveforms required to perform DC
`polarography, normal pulse polarography, and differential
`pulse polarography. Alternatively, the waveform for fast sweep
`staircase voltammetry, initiated at any point in the drop life,
`fast sweep differential pulse
`fast sweep normal pulse, or
`voltammetry using positive going sweeps, negative going
`sweeps, or cyclic versions, including pulses of either positive
`or negative direction superimposed on a staircase ramp can
`be generated. The potential range can utilize up to 65K steps
`so excellent resolution and high approximation to a linear
`ramp is possible if required. Waveforms for stationary elec-
`trodes are also available. The program calculates all the
`control words and provides routines for decimal to binary
`conversion so that parameters conveniently may be input in
`decimal form. Also provided are pulses to knock off mercury
`drops and to trigger the oscilloscope or other recording device.
`The presentation of a flow diagram as in Figure 2 with
`comments as to what various statements achieve, as well as
`Table I is believed to be an ideal way of demonstrating how
`and what can be performed under software control as well as
`conveying the essential idea as to how the various tasks are
`In the presence of these items, little additional
`achieved.
`comment appears to be required apart from providing a typical
`list of specifications that we have found to be obtainable with
`the Mos Technology 8-bit system. This information is con-
`tained in Table II. Clearly the ability to provide pulses of
`
`Figure 6. Waveform used in differential pulse polarography (voltam-
`Initial potential = 0.000 V. Positive ramp, positive
`metry). Upper trace:
`pulse. Ramp increment, 5 mV. Pulse amplitude, 500 mV. 50 steps.
`-2.000 V. Negative ramp, negative
`Initial potential =
`Lower trace:
`pulse. Ramp increment, 5 mV. Pulse amplitude, 500 mV. 50 steps
`any width down to 80 µ& enables fast sweep differential pulse
`techniques previously presented with a mini-computer system
`(8) to be performed at relatively negligible expense. Almost
`all other “tricks” with respect to waveforms in pulse po-
`larography and voltammetry, DC polarography, cyclic
`(staircase voltammetry) that have been achieved with mini-
`computers can also be implemented with the program shown
`in Figure 2 or with a slightly modified version. The main
`attraction is the enormous
`cost saving gained and speed.
`Figures 3 to 6 show some representative oscilloscope displays
`of typical waveforms generated.
`Hopefully, the above data adequately demonstrate that
`extremely high quality performance superior to that available
`on a mini-computer is likely to be obtainable on many occa-
`sions using microprocessors and that intrinsic cost savings are
`available to all chemists working on any given project provided
`costs of auxiliary devices are kept to a minimum, and some
`inconvenience can be tolerated. For example, we are prepared
`to accept a cassette tape for storage of programs and the
`tediousness of writing programs without the aid of high level
`It goes without
`languages such as basic
`etc.
`fortran,
`or
`saying that the final electrochemistry unit we have constructed
`is easily used by workers in our
`laboratories, including those
`who have no knowledge whatsoever of the operations of a
`microprocessor. The latter class of workers is obviously
`confined to working within the specifications established by
`Table II if using the program provided for them as per Figure
`2. That is, none of the disadvantages of employing a micro-
`processor are associated with the end product, but with the
`greater tediousness of software development when it is un-
`
`Vestas Ex 1033-p. 4
`Vestas v GE
`
`

`

`Anal. Chem. 1980, 52, 371-373
`dertaken without the aid of high level languages.
`LITERATURE CITED
`(1) R. E. Dessy, P. J. Van Vuuren, and J. A. Titus, Anal. Chem., 46, 917
`(1974).
`(2) R. E. Dessy, J. A. Titus, and P. J. Van Vuuren, Anal. Chem., 46 1055A
`(1974).
`(3) R. E. Dessy, Science, 192, 511 (1976).
`(4) W. G. Sherwood, D. F. Untereker, and S. Bruckenstein, Anal. Chem.,
`47, 84 (1975) and references cited therein.
`
`371
`
`"Computers in Chemistry and Instrumentation”, J. S. Matheson,  . B.
`(5)
`Mark, Jr., and H. C. MacDonald, Eds., Marcel Dekker, New York, 1972.
`(6) Princeton Applied Research Corporation, Princeton, N.J.
`(7) W. R. Matson, E. Zink, and R. Vitukevitch, Am. Lab., 10, 59 (1977).
`(8) K. F. Drake, R. P. Van Duyne, and A. M. Bond, J. Electroanal. Chem.,
`89 231 (1978).
`
`Received for review March 26, 1979. Accepted October 26,
`1979.
`
`Portable Fluorometric Monitor for Detection of Surface Contamination by Polynuclear
`Aromatic Compounds
`
`Daniel D. Schuresko
`Chemical Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830
`
`Uptake of polynuclear aromatic hydrocarbon (PNA) com-
`pounds via contact with contaminated surfaces in the work-
`place has been identified as a major mode of worker exposure
`(1). The need for instrumentation to monitor PNA buildup
`on surfaces has also been recognized (1, 2). Such an instru-
`ment must be capable of:
`(a) functioning during actual plant
`operation in varied working environments;
`(b) detecting
`material spilled on different work surfaces, including ma-
`chinery, plumbing, construction materials, and on personnel
`and clothing; and (c) being easily and reliably operated by all
`plant personnel.
`The fluorescence spotter described in this paper (U.S.
`Patent applied for) has these capabilities. This instrument,
`which consists of a hand-held optics unit connected via an
`umbilical cable to an electronics console, enables remote
`monitoring of work area surfaces at distances <3 m. A
`portable, rechargable, battery-powered electronics module,
`which will replace the electronics console, is also being de-
`veloped.
`It is anticipated that portable fluorescence spotters will be
`used extensively to detect surface contamination in changing
`areas, lunch rooms, control rooms, and other “clean” areas
`in coal conversion facilities, and to monitor skin contamination
`of coal plant workers. The currently used method of detecting
`spills is to turn off the ambient lighting and scan the suspected
`area with a black light.
`In contrast, the newly developed
`spotter (a) can be operated outdoors in direct sunlight or
`indoors in the presence of strong background illumination;
`of the amount of
`(b) can provide a quantitative measure
`(c) will discriminate between the
`fluorescent material;
`fluorescence of organic materials and some inorganic com-
`pounds based on their fluorescence lifetimes; and (d) does not
`present a vision hazard to personnel.
`EXPERIMENTAL
`The spotter induces and detects the fluorescence of PNAs that
`characteristically absorb light in the 350- to 440-nm region of the
`spectrum and fluoresce with high efficiency in the blue-green
`region of the spectrum. Multiring heteroatom aromatic com-
`pounds, including acridines, are also detected, although they
`generally absorb light and fluoresce at longer wavelengths than
`do their pure hydrocarbon counterparts.
`The optics unit, shown in Figure 1, consists of two subunits:
`(a) a UV illuminator, which produces a beam of amplitude-
`modulated light; and (b) a fluorescence detector, which detects
`380- to 600-nm fluorescence induced by the UV light. The op-
`eration of the spotter is depicted in Figure 2, as are the signal
`traces corresponding to the radiated UV intensity (trace A) and
`
`to the fluorescence (trace B) that is produced when a spill has
`been “sighted”. The radiated UV beam is amplitude-modulated
`at 1 kHz by a mechanical chopper; thus the induced fluorescence
`is also modulated at 1 kHz. This  -kHz fluorescence signal is
`superimposed on a much stronger signal from reflected back-
`ground illumination of the viewed surface. The electronic fre-
`quency spectrum of ac-powered fluorescent or
`incandescent room
`lighting consists of a 120-Hz frequency component and its har-
`monics superimposed on white noise (dc-powered lamps and
`sunlight produce only white-noise background); hence, it is possible
`to separate the fluorescence signal from the background signal
`by electronic filtering (trace C). Demodulating and low-pass
`filtering of this signal (trace D) effectively averages each 1/2-ms
`pulse and allows detection of fluorescence only 3 % as intense as
`the background illumination in the optical wavelength band of
`interest.
`A schematic diagram of the prototype spotter optics unit is
`shown in Figure 3.
`The illuminating beam, produced by a
`lamp, is modulated by an electro-
`high-pressure mercury arc
`magnetic, tuning-fork chopper. A dichromatic beam splitter
`reflects the illuminating beam to the telephoto output lens. The
`longer wavelength fluorescence from the sample is collected by
`the telephoto lens, passed through the dichromatic splitter and
`emission filters, and detected by the photomultiplier tube.
`The 4% beam splitter and photodiode assembly provides a
`reference signal that is used to offset the background fluorescence
`of the dichromatic splitter and to correct fluorescence measure-
`ments for lamp output drift. Optical filters in both units are
`mounted in interchangeable dovetailed filter slides, allowing for
`filter selection appropriate to the class of compounds being
`monitored while the unit is in use.
`Using a simple resistor network, a photomultiplier signal
`component, which is caused by the fluorescence of the dichromatic
`beam-splitter and telephoto lens, is cancelled by subtracting a
`preset fraction of the photodiode signal from the photomultiplier
`signal. The difference signal is then fed into an Ithaco Model
`Dynatrac 3 lock-in amplifier (Ithaca, N.Y.) which filters and
`demodulates at 1 kHz. The lock-in reference signal is provided
`by the chopper oscillator circuit. The lock-in output drives a
`voltage-to-frequency converter coupled to a small speaker, which
`provides an audio signal whose frequency increases with the
`In addition, the lock-in output
`measured fluorescence intensity.
`is measured on a front-panel meter.
`RESULTS AND DISCUSSION
`The spotter has been laboratory tested with pure com-
`pounds and with several coal and oil shale products and
`illuminated by
`wastes. When operated in a laboratory area
`fluorescent lighting, the spotter can typically detect 0.2 µg of
`perylene (in dilute solution in cyclohexane); in darkened areas,
`it is sensitive to 0.001 µg of perylene. Considering that 10^g
`
`0003-2700/80/0352-0371 $01.00/0
`
`&copy; 1980 American Chemical Society
`
`Vestas Ex 1033-p. 5
`Vestas v GE
`
`