within 10 seconds, and the new steadystate condition is reached in 3 to 5 minutes. Figure 4 depicts a tracing of the counting rate of the system and its correlation to the Fz concentration presented to the monitor. I n view of the rapidly changing fluorine concentration, the system displayed relatively little lag time. Fluorine rras diluted t o suitable concentrations with room air a t ambient relative humidity.
exhausted after many months of exposure t o a variety of oxidizing gases a t high concentrations. However, under such conditions periodic recalibration of the cells was necessary to account for their reduced reaction efficiency. This method of airborne fluorine analysis through radiological techniques appears to be entirely feasible, sensitive, and noncomplex. An instrument could be designed which is completely portable and adaptable for use in the field.
RESULTS
The effective life of a clathrate cell when monitoring FS a t low levels ( < 2 p.p.m.) is many months. Actually, clathrate cells used in the laboratory at Tracerlab have never completely been
ACKNOWLEDGMENT
The authors express appreciation to Monsanto Research Corp. for furnishing samples of fluorine gas, to Thomas Scavitto for preparation of the Kr8jquinol clathrates. and to Orlando Cuc-
chiara for his assistance in conducting some of the experiments. LITERATURE CITED
(1) Bellack, E., Schouboe, P. J., A Y ~ L .
CHEM.30,2032 (19%’).
( 2 ) Nash, L. K.,
A s . 4 ~ . CHEM. 21, 950 (1949). (3) Powell, H. M., J . Chem. SOC. 1950, 295, 300, 465. (4) Porn-ell, H. hl., Guter, M,, Safure 164, 240 (1949). (5) Slesoer, C., Schram, S., “Preparation, Properties, and Technology of Fluorine and Fluoro Compounds,” National Suclear Energv Series VII-I, p. 135. A!IcGraw-Hill, Xew York, 1951. RECEIVEDfor reviex June 1, 1962. Accepted August 23, 1962. Work conducted under contract (AT-(30-1)-2204’, from the Office of Isotopes Development of the Atomic Energy Commission.
C.
I
Automatic Infrared Analysis of Polymer Films DONALD R. JOHNSON,’ JOHN W. CASSELS,* EDWARD G. BRAME, and DAVID F. WESTNEAT3 E. I.do Pont de Nemours & Co., Wilrnington, Del.
Research and Development Division, Plasfics Deparfment,
b
A versatile and automatic instrument system was constructed to perform routine quantitative infrared analyses on solid samples. An automated infrared spectrophotometer was provided with a digital readout to permit conversion of infrared absorption to concentration on a digital computer. Coordinating units included in the laboratory installation were a master programmer, a sample feed mechanism, an automatic beam balance system, and an auxiliary analog output. Provision was made to convert from one analytical procedure to another by changing a single program sheet. The system was applied to the routine analysis of polymer films from laboratory and pilot-plant operations. Savings of manpower and instrument time were realized through the system’s performance of large numbers of determinations, unattended, on overnight operation.
I
N RECEKT years
industrj- has come to recognize the need for automatic analysis in maintaining desired control of products and processes (81. -1mreness of the need for automatic analysis in the laboratory is growing rapidly (1, 4, 6, ’7,). Laboratory automation can improve the precision of analytical results by making the running of statistically significant replicate determinations economically practical. The technique can improve the accuracy of the analytical data by making the frequent checking of the calibration standards equally feasible. Laboratory automation frees skilled technicians for tasks 1610
0
ANALYTICAL CHEMISTRY
that require their unique human abilities. Finally, automation introduces an untiring uniformity of operations to laboratory analysis that makes possible the use of methods and the undertaking of projects that are outside of the abilities of human operators h key to successful automation of chemical analyseq in the laboratory n a s found to be the ability to change, simply and rapidly, from one determination to another ( 5 ) . Conventional stream analyzers rarely, if ever, have had this ability. Although attempts to automate infrared analysis began early, the systems generally lacked the flexibility that was essential to laboratory use (8, 10) Most attempts covered only parts of the analvtical operations
@,S,6 ) . I n this laboratory, a need n a s recognized for a versatile infrared analyzer that would be capable of performing a variety of analyses and n-orking for long, off-shift periods unattended by human operators. An automatic infrared analyzer meeting these requirements was assembled by coupling a Perkin-Elmer Model 21 infrared spectrophotometer to a digital readout system and computer. The system v a s made fully automatic by mean3 of a simple, but flexible, electromechanical programmer and accessories. APPARATUS
The automated infrared analyzer (Figure 1) consists of three subsystems: a control program, a double-beam spectrophotometer, and a dual readout sys-
tem. These are shown diagrammatically in Figure 2. The control program automatically interprets the analytical procedure, as written by the operator, into electrical commands for the spectrophotometer and readout systems. The spectrophotometer performs its usual function of converting light absorption into an electrical analog and scale reading. The readout system provides a conventional spectrogram and selected digital readings of transmittance for analysis by the operator. It provides the same digital readings on punched paper tape for automatie computation of the analytical results. Programmer. The heart of the automatic infrared analyzer is in the master programmer and the program sheet itself.
A typical program sheet, illustrated in Figure 3, consists of a standard recording chart for the Perkin-Elmer Model 21 spectrophotometer on which has been recorded the spectrum of the analytical region. The surface of the chart is covered with a 1-mil layer of Mylar polyester film to improve wear properties and dimensional stability Along the top edge of the chart and parallel to the wavelength axis are punched rectangular holes in four r o w or channels. These holes permit electrical contact between the programmer 1 Present address, Instrument Products Division, E. I. du Pont de Nemours Br Co., Wilmington, Del. 2 Present address, Sadtler Research Laboratories, Philadelphia, Pa. 3 Present address, Department of Cheniistry, University of Akron, Akron, Ohio.
5
Figure I .
Automatic infrared andlyzer
left. Digitol reodout conrole center. Spectrophotometer with progrommer and romple feed system Right.
Analog output
brushes and the recorde; drum at selected ioeations on the wavelength scale. Holes in channel 1 command the instrument to stop scanning for 30 seconds and adjust the attenuation of sample or reference beam so as to place the forthcoming analytical baud a t a desired position on the transmittance scale. Holes in channel 2 instruct the instrument to scan a t top speed. These holes are usually long and are used to conserve time in scanning analytically uninteresting portions of the spectrum. Holes in channel 3 command the digital readout system to record the value of transmittance sensed by the spectrophotometer at the instant electrical contact is established. Holes in the fourth channel provide a special in-
struction to the readout system by signifying the end of a determination and permitting the Flexowriter to execute a carriage return. Start, return, and sample feed commands are indicated on the program sheet, hut are executed by the drum stops and microswitches provided for cyclic operation of the Prrkin-Elmer Model 21 spectrophotometer. The details of the programmer circuit are shown in Figure 4. The four mire contacts, Cr, ride on the program sheet and make contact with the drum throngh holes as described above. The programmer head and contacts are identical to those used for reading program cards in standard IBM keypunch equipment. The contacts actuate
-
601
-t
Fs
Bal
R+SF
any of five relays, R y l - j , which initiate the desired operations. Two RC circuits were added to improve performance. Capacitors C, and resistor R, are placed across the programmer contacts to prevent sparking. Capacitor Cz and resistor R, permit relays RYI and R,, to be fired on a single pulse and prevent the double reading of an analytical point. Both RYLand RYZare actuated by the same contact, CT,. RYI places a small pip on the analog output record to denote the point of readout. RYZ commands the Datex controlier to read and record the signal from the shaft position encoder mounted on the infrared spectrophotometer. R n closes as the last readout point of a determination approaches and permits a carriage return signal to pass to the Flexowriter when R y 2 fires and recording of the last data point is complete. R , determines the scanning speed of the spectrophotometer by introducing an appropriate resistance in the speed control circuit, Ry5 actuates the balancing circuit, This relay circuit contains a thermal time delay. When RYS is closed, the beam balance circuit is actuated for 30 seconds. Beam Balance and Analog Output Systems. The beam balance and analog output systems are essentially identical and operate alternately from a common transmitting potentiometer, Pain Figures 5 and 6 . The basic bridge circuit of each is t h a t described by Westneat (9) for use as an ordinate expaosiou or slave recording system. The common transmitting potentiomet.er is a signal-turn, high resolution Spiralpot (Giannini Controls Corp.) of 1250-ohm resistance and a specified It is mounted on linearity of OS’%. the lower end of the vertical shaft throngh which the comb servomotor of the Perkin-Elmer Model 21 speetrophotometer drives the recording pen and the reference beam attenuator. It is thus coupled directly to the primary transmittance-measuring device and the analog output trace is sufficiently accurate for quantitative measurement. The beam balance system is shown schematically in Figure 5. The double-
’ READOUT
SPECTROPHOTOMETER
ANALOG OUTPUT (SLAVE RECORDER)
OUTPUT \
PERKIN-ELMER MODEL 21 INFRARED SPECTROPHOTOMETER
-[CARRIAGE
PROGRAM
BEAM B A L A N C E L CYCLE CONTROL+
RETURN
PRINTER
I-t Eo%? UT E L------J
Figure 2.
a Block diagram of automated infrared spectrophotometer
VOL 34, NO. 12, NOVEMBER 1962
.
1611
PEN ON PE-21
AUX. REC.
- . PULSE
. ._._
r-----i . 1
CI t :
d
11
I
tb
0 '
'
, ' I
100?e' T Pa, PEN TRANSMITTING POTENTIOMETER
DATEX READOUT
P 4 , BALANCE SETTING POTENTIOMETER
Figure I
5o:V
&
Figure 4. C1. Cp.
5.
Block diagram of beam balance system
DC
Programmer circuit
0.1 mfd. 300 mfd.
R,I Rz. 5000 ohms R ~ I - ~ .10,000-ohm, SPDT relay Amperite 1 15C60 thermol relay SPDT Ry6. R y e . 650-ohm, 4-PDT relay
wedge attenuator is mounted in the sample compartment of the spectrophotometer, as far away from the image of the monochromator slit as possible. The attenuator is driven into or out of the appropriate beam by rotation of the drive screw on which it hangs. At balance, the output of the transmitting potentiometer, P3,matches that of the balance-setting potentiometer, P4, located on the programmer control panel. This control is set to ensure the recording of the analytical band in the portion of the transmittance scale giving maximum accuracy. The circuit of the combined beam
balance and analog output system is shown in Figure 6. SR'l-SW4 are the contacts of R Y ~ ,the four-pole, double-throiv relay of Figure 4. In the scanning position shown, switch 1 permits normal operation of the spectrophotometer scannmg motor and sm-itches 2 and 3 connect the transmitting potentiometer, P3, into the active analog output circuit. The auxiliary recorder pen thus duplicates the motion of the pen and optical attenuator system of the spectrophotometer. Switch 4 is open under these conditions. When the wavelength selected for balancing the beam is reached, Ryg
TO SCANNIb!!G MOTOR INPUT VIA.Ki RLLA'I IN CONTROL HoUSING IN M O D E L L INPUT OF AUXIL. RECORD
T
!
_A_
I
B A L A N C IN G CIRCUIT
BROWN
1 MOTOR I
-
Recycle and Sample Feed Systems. Completion of a sample scan requires three Operations to initiate the next sample cycle: 1. reverse scanning to the starting wavelength, 2. lifting of the programmer contacts to prevent their catching in the holes of the program sheet, and 3. insertion of the new sample. Reverse scanning is accomplished with the drum stops and cycle system provided by the manufacturer. The circuit for 'operations 2 and 3 is shorrn in Figure 7 . Relay Ryi.is actuated by the reverse scan contacts of the cycle system relay, K B ,in the spectrophotometer. Closure of Ri7 lifts the programmer contact bar by means of a low voltage solenoid. The same closure sends a pulse to the trigger solenoid of the sample feeder, lT-hich is a 35-mm. slide changer (Airequipt Electrochanger) modified as described by Cassels, Brame, and Day
ANALOG OUTPUT CIRCUIT
A.C.
is actuated by the programmer. This in turn actuates Rys for 30 seconds. Switch 1 opens the scanning motor circuit and stops the wavelength drive. Switches 2 and 3 connect P3 into the balancing circuit described above and switch 4 closes to energize the field coils of the Brown motor. The field coils are disconnected a t all other times to prevent drifting of the balancing attenuator. h i t c h 4 also energizes the heater of the thermal relay of Ry6. After 30 seconds of heating, the contacts in the thermal relay open. RYS and Ri6 return to their original positions and the scan is resumed.
1
I N P U T TO BROWN AMPLIFIER
L*,&
H E A T E R FOR T H E R M A L RELAY (30 SEC.)
Figure 6. output
Combined circuit of beam balance-analog
IiOV. A . C . 1 FROM R E L A Y K 2 IN CONTROL
SW
7-SW 4. Contacts of 4-PDT relay ( R y e of Figure 4) 10-turn potentiometers, 1000 ohms PI,P~,PcP~. Pa. Single-turn, high resolution potentiometer, 1 250 ohms, 0.1 % linearity (Giannini Controls Corp., Spiralpot)
1612
ANALYTICAL CHEMISTRY
45 v. -=-
Figure 7.
CONTACT BAR L I F T SOLENOID
S L I D E CHANGER SOLENOID
Recycle-sample feed circuit
(3). The RC-generated pulse ensures that only one sample change is made for each analytical cycle.
Consirnetion details and arrangement of the programmer head, sample changer, and heam attenuator are shown in Figure 8. Digital Readout System. The digital readout system incorporates standard Giannini Dates components. A Datex Illode1 C-104, lOOO-point, singleturn shaft position encoder is mounted on the pen-wedge drive shaft of the spectrophotometer along with the transmitting potentiometer, Pa. The encoder is interrogated by a Datex K-155 control system. .\ Datex Model PC105 programmer drives a standard Flexowriter. A patchboard coupling is used between the programmer and Flexowriter t o provide a choice of output format. The transmittance values are typed as three-digit numhen in a.ppropriate columns by the Flexowriter and are punched on eight-channel paper tape in standard IBM code. PROCEDURE
In principle, any infrared spectrophotometric analysis which can he performed manually can he automated with this apparatus. Three basic steps :ire involved: programming, scanning of samples, and computation. Opera& ing procedure can be described best by considering the case illustrated in Figure 3: the determination of a minor component, X, in a matrix, M. The ratio of the absorbance of hand X to that of the internal standard, hand M, is taken as a measure of the concentration of X and is assumed to he linear over the range of concentration of X. Programming. The portions of the spectrum of analytical interest are recorded under the actual analytical conditions with the greatest expansion of the abscissa that will permit inclusion of all hands on a single scan. The expanded abscissa improves the reproducibility of peak transmittance measurements on sharp absorption hands. Start and finish of the scan are marked on the chart and sharp bands of suitahie reference standards are recorded to provide wavelength calibration checks. If transparent Mylar tape is used for the lamination, it can be added at this time. The chart is removed from the drum of the spectrophotometer and the holes are punched in the appropriate cha.nnels to execute balance, readout, fast scan, and carriage-return operations. The short-wavelength edges of the holes coincide with the exact wavelength a t which the operation is desired. Scanning of Samples. Once the program sheet has been constructed, routine operation is simple and flexible. The program sheet for the desired analysis is selected from the file and placed on the drum of the spectrophotometer. Ilhvelength alignment is made by sett.ing the drum of the
Figure 8. attenuator
Detail of programmer head, sample changer
spectrophotomctcr so that an indexing mark on the programmer head coincides with the recorded wavelength reference hand on the program sheet when the spectrophotometer records the maximum absorbance of that reference hand. Sample preparation requires no more Cx = K -A x AM
=
puter reads the six values of transmittance, T, through Ts,for each determination from the punched tape or from cards prepared from the tape. The concentration of component X is then calculated from an equation of the form:
log
[(e;) +
log
[(E;)- h
K-
and beam
(Ta - TI)
h6
time than for manual operation, Films are mounted on cardboard inserts in the 2 X 2-incl1 aluminum Airequipt slide holders, and are then loaded in the feeder magazines interspersed with calibration standards and occaqionnl opaque “dummy” samples. The standard samples normally provide a check on the accuracy of the analysis. They may he used to reset the calibration constant, if necessary. The opaque samples provide a check of the instrument zero at selected times during unattended operation and verify that no sample has been missed or recorded twice. The sample identification list is logged on the feeder magazine for filing purposes and on a computing sheet for identification of the analytical results. The system is started on automatic operation and it proceeds to record the analytically significant data on as many as 72 samples without further operator attention. Computation. On completion of a series of samples, the punched tape is collected, edited if necessary, and sent to the computer along with information on sample identification, computer program number, and instrument zero reading. Values of XI through XS may he carried in the computer program or submitted with the preliminary information. The com-
(T,- T J
- PI
- log (T>- F )
+ T
