AIDS FOR ANALYTICArL CHEMISTS
I
Automation of Existing Atomic Absorption and Emiission Flame Photometers with BCD Punched Tape Output for Computer Processing of Data L. T. Bluuin, C. V. Dostie, W.
W‘
__.... __. ””.,
Parke, Davis & Co., Research Labc.
48IOC
INORDER TO REDUCE the demands on the analyst’s time created by a large workload, we have automated our existing flame photometer (Beckman D U with ERA recorder output) and atomic absorption spectrophotometer (Tectron AA-3) in several steps. The final system places the flame photometer in “piggy-hack” fashion over the optical rail of the atomic absorption unit, such that a single sample input device can service both photometers. The use of polyethylene (P.E. 100) tubing to extend the existing aspirator capillary feed tube for these units does not appreciably alter the aspiration rates, and increases “dead space” only moderately. Good sample flush out and negligible cross-contamination are exoerienced as long as the extension tubing is held to minimum possible lensgh. The phototube output from either Figure 1. Sample input unit instrument is fed (through the respective amplifying systems) . .....~~ ~ - I - I . IO a poinniomerric recorder (Photovolt model 43) which has houette base unit, constructed of stainless steel and alubeen modified by addition of a batter:Ipowered potentiometer minum with Teflon (Du Pont) tubing on the upper rim. (The mechanically coupled to the pen shaft of the recorder. In this hole diameter conveniently was correct without modification manner, the output voltage from thr5 pen follower is stable, to accept high density polypropylene cups used for samples.) c i m r r l + m ~ n l l & , &th normal recorder tracings are obtain-.. o....l..l. A Plexiglas cover was fabricated in an oval shape to accompunched tape data capture, and the recorder serves as an intermodate the two horizontal extremes of travel of the sample facing unit between any photometer that is equipped with carrier, and used to minimize evaporative concentration of the standard recorder output and the digitizing-BCD units. The samples when exposed to the area of the burners and exhaust outnut sirnal from the recorder is fed into a Perkin Elmer ~~~. hood. A dip tube arm, driven by a cam on the dip tube DCR-2 (digital concentration readout) unit for conversion to motor shaft, was added to raise the aspirator tubing out of the digital and binary coded decimal output. A Perkin Elmer sample cup during the indexing sequence. Limit switches on DDR-2c (digital data recorder) unit then conditions the BCD the upper and lower extremes of travel are activated by signal and commands a Royal paper tape punch to record the another cam on the dip tube motor shaft to provide signals for sample information (sample number and concentration). sample advance (at the apex) and for self-arrest, as well as to The end-of-word (EOW) signal, sensed by a microswitch initiate the sample read-out operation of the DCR. mounted in contact with the tape punch shaft, is utilized by a The entire assembly is mounted on a roller plate and the specialized control circuit (which operates in conjunction with sample carrier is affixed to the drive shaft by means of removthe DDR) to initiate and sustain the sequence of events reable pin, to allow ease of sample loading. quired for processing the next sample. This cycle repeats The turn table motor shaft has an indexing microswitch until all samples have been processed (up to ZOO), at which which stops the turn table at each subsequent sample position, time the system automatically deactivates itself. The only once the turn table relay has been activated. Another microrequirement for the analyst’s time is initial sample dilution and switch is provided to deactivate the circuit after position ZOO loading of the diluted samples and standard solutions into the has been passed, and serves as a “fail safe” device in the presautomatic sample input device (GME Model SBl Spiral ent system, should the moveable “last sample’’ detector fail to Collecting Unit, modified to serve as a sample cup holder and stop the turntable at that point. input unit). A detailed description of each of the system Flame Photometer. A Beckman Model D U spectrophocomponents follows : tometer with flame attachment, equipped with a Model 5800 Sample Input Unit. A Gilson Medical Electronics Model Energy Recording Attachment, is elevated on extended legs SBl Spiral Collecting Unit was modified for sample input in piggy-back fashion over the optical rail of the atomic as shown in Figure 1. The mast was shortened to accomabsorption spectrometer (Figure 2). It is positioned to modate an evaporation-suppression cover and “last sample” minimize the distance between its burner aspirator and the microswitch. The test tube holder was disassembled and sample dip tube of the input unit to decrease “dead space” one of the stainless plates containing the 200 spirally arranged and to avoid appreciable diminution of the aspiration rate. holes was incorporated into a new, lower mass, lower silIt had originally been planned to use a booster pump of the peristaltic type if there proved to be a problem with reprol Present address, Bio-Engineering Consultants, Inc., 2378 E. ducibility and aspiration rate, hut this was obviated by the Stadium Blvd., Ann Arbor, Mich. 48104 ~
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ANALYTICAL CHEMISTRY, VOL. 42. NO. 11, SEPTEMBER 1970
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A
A
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B
,
e
,--MOTOR
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R U
U
8 DIP TUBE RELAY
START P.B.
KEY: UDTLS & LDTLS = UPPER AND LOWER DIP TUBE LIMIT SWITCHES EOTLS = END OF TRAVEL LIMIT SWITCH
L o SO;€ - s w * c i R t u i T
Figure 2. Arrangement of apparatus
TTLS = TURN TABLE LIMIT SWITCH
j ip DCR "READ": 'L - 4 2 CIRCUIT ;
DIP TUBE MOTOR
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_ _ _ _ _ _ _ _ _ _ _ I
R6-j
TURN TABLE MOTOR
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Figure 5a. Schematic of control circuit
IN2070
Figure 5b. "One shot" 3,6Or pulsing circuit details
Figure 3. Modifications of recorder circuit
L O S PULSING CIRCUIT
16718
IN2070 1 MEG
Figure 5c. Time delay circuit details
Figure 4. Example of calculations performed by computer
10
T
15 TDR CIRCUIT
arrangement of components described. Sampling rate remains essentially unchanged, provided tubing with a lumen no smaller than 0.034 inch (P.E. 100) is used for the flame (emission) photometer. Smaller caliber tubing can be used with the atomic absorption spectrometer because of the aspiratorburner design, which provides greater aspiration force. Atomic Absorption Spectrophotometer. A Tectron Model AA-3 atomic absorption spectrophotometer, which has
ANALYTICAL CHEMISTRY, VOL. 42, NO. 11, SEPTEMBER 1970
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(A) EOW signal o
Initial Conditions
push button starts dip tube up
I
Dip Tube Rising
1
(B) Dip tube (at zenith) stops (C) Turn table starts
Turn
Indexing
1
(D) Turntable stops (E)
R1 energized through START P.B. or EOW switch and through Pos A of UDTLS Dip tube motor starts through R1-1 Dip tube motor cam releases LDTLS to Pos A R1 is now energized through holding circuit consisting of Rz-1(N.C.) in series with LDTLS (Pos A) Dip tube motor runs until the cam operates UDTLS (POSB) RZis energized and Rz-1opens, de-energizing R1; motor stops Rz-2turns on pulsing circuit LOS-1 LOS-1 energizes R3 for approximately 350 msec Re is energized through Ra-1 Turn table operates TTLS to Pos A Rs-1 now opens and Re is held in through TTLS (Pos A) Turn table indexes until TT cam operates TTLS to Pos B, de-energizing Re and the turn table stops Pos B of TTLS turns on pulse circuit LOS-2 Rgcloses, Rs-1 energizes R1 and dip tube motor starts
Dip tube starts down
(F) Dip tube
T
Dip tube is down Upper dip tube limit switch (UDTLS) in Pos A Lower dip tube limit switch (LDTLS) in Pos B R1, Rz,and Ra are de-energized Turn table limit switch (TTLS) in Pos B
t
Dip tube Descending
1
-
Dip tube cam releases UDTLS to Pos A R1 is now energized through Rz-1and Pos A of LDTLS Dip tube cam next operates LDTLS to Pos B, de-energizing Rt and stopping motor Pos B of LDTLS also turns on pulse circuit LOS-3, energizing R4 R4-1 energizes Rt, activating the time delay circuit
stops
t
5 Sec. Time
Delay
1
(G) “Read” sig- -
After delay, Rscloses to complete “Read” circuit for DDR DDR “reads” BCD signal from DCR and commands punch to operate Punch cam closes EOW Switch and cycle begins at (A)
nal to DDR
Figure 6. Flow chart describing operation of control circuit
FLAME EMISSION CONTROL CIRCUIT ATOMIC
VARICORD RECORDER SIGNAL
1
I
“READ” COMMAND
Figure 7. Block diagram showing interrelationship of components
voltage is directly proportional to concentration, with the recorder in the linear mode for emission determinations, and in the log mode for atomic absorption determinations. A series of samples is bracketed by an appropriate set of standards to provide for drift correction. (The assumption is made that factors contributing to drift are relatively slow, and generally unidirectional, such as warm-up drift, changes in aspiration rate, burner gas pressure, etc.) The computer program is designed to compare a given sample to its adjacent standards, correct for drift by comparing standard readings taken before and after the sample series, interpolate its concentration, and print out the value in appropriate concentration units. Figure 4 shows an example of the calculation performed by the computer. Thus : N
recorder output capability, is coupled to the modified Photovolt Recorder (alternately with the flame photometer) and is used primarily for magnesium and calcium concentration measurements in biological samples. The only modification required is the addition of longer polyethylene tubing at the burner aspirator, to allow direct connection to the sample input dip-tube. Recorder. A Photovolt Model 43 Linear-Log potentiometric recorder was modified by addition of a battery powered servo potentiometer to the pen shaft (Figure 3). The output 1300
e
=
(”-’> SI
s4
C
+ S4;
where s3and s4 represent estimated displacement values (based on slopes m a and ma)at point a, n is the displacement for sample N , and Cis a conversion factor from displacement units to concentration units. Digital Concentration Readout. A Perkin-Elmer DCR-2 digital concentration readout unit receives the voltage signal from the pen-follower potentiometer of the recorder, converts to a digital value, and provides a low power BCD (binary coded decimal) signal at its output terminals. It receives a “read”
ANALYTICAL CHEMISTRY, VOL. 42, NO. 11, SEPTEMBER 1970
b
a
Figure 8a and 8b. Recorder traces taken with (magnesium, absorption) and without (sodium, emission) rinsing between samples
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EXPERIMENT Ni). EXPERIHENT TREATMENT
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86 HONKEY DIURETIC SCREEN 5-24 HR 2OMG RXT9646/KG OR I N Y3 SOFT GEL CAPSULEGAVAGE H2O 1 0 HL/K ELECTROLYTE CALCULA,TION CODE
SAMPLE SOURCE CODE
1 URINE 2 PLASMA 3 HdC
-
AN D A T E IMAL NO. 7 1 7 6 9 46 71769 344 7 1 8 6 9 285 81269 34 81269 36 81269 1 3 6
SAMP NO.
SAMP SRCE 1 1 1 1 1 1
4 5
1 UEPIK/T 2 HEWL
6
3
TIME 19 19 19 19 19 19
HR HR Hi HR HR HS
WEIGHT OR 5.1.
VOLUCT
4.750 6.950 5.600 4.700 4.600 4.700
29.09 22.35 40.71 27.45 95.43 35.11
ncr
VOL CAL
NA 488.1 2195.7
2307.6 1 1
459.9 1479.7 1201.8
0 8 / 1 9 169 KESEARCHr ANN A R B O R
voLunE CALCULATION CODE
4 UEO/K/UT 5 UEP/H2/T 6 UEP/H2/UT
EL1 CAL
P.0.
1 NO voLunF: 4 MLIKIUT 2 HL/K 5 MLlM2 3 HL FLUSH 6 HL/M2/UT
-
K 1005.0 1036.6 1131.8 718.2 1204.3 839.3
NA/K 0.49 2.12 2.04 0.64 1.23 1.43
CA
2 6.43 158.34 80.38 310.85 211.00 400.85
HG b7. 11 194.56 61.34 192.37 268.35
301.01
CL 516.5 1752.1 2042.1 798.3 1122.1 1644.5
HC03 94.0 434.5 167.5 347.1 548.5 405.7
Figure 9. Example of computer printout sheet command from the control circuit after aspiration into the flame has been initiated for each successive sample. The DCR-2 has several built-in options which made it quite flexible. In the event that curve linearization is desired, it can be operated in the log mode for absorption determinations, and adjustments made for linearization. It also “reads” the samples in successive increments of 2 seconds, and can be set to “read out” the average of any multiple of such readings from 1X to 16X. Thus, for any given determination, the optimum setting can be selected for the best compromise between reproduciblity and economy of sample and time. Generally an 8-second “read” period (4X) has been suitable for the work herein described. Signal Processing and Command Unit. A Perkin-Elmer DDR-2c (digital data recorder) reads and conditions the BCD signal from the DCR and commands a table tape punch unit (Royal, equipped with a Perkin-Elmer manual-enter keyboard) to punch the BCD information on tape. The operator adds the date, identification number for a group of samples, and “end of tape” code by means of the manual keyboard. It is also possible to delete any given sample by providing that information on a log sheet for the key punch operator, who supplies such additional information to the computer as: element (Na, K, Mg, etc.) assayed, animal identification (species and number), experiment number, sample type (plasma, urine, etc.) etc. In this manner, the additional option of rinsing between samples is provided by simply positioning cups containing diluent alone in every other hole of the spiral plate.
Control Circuit. A specialized circuit was designed and fabricated to integrate and control all of the other components (Figure sa). Details of the “one shot” and time delay circuits appear in Figures 5b and 5c. A flow chart describing its operation appears in Figure 6. A block diagram showing the sequential interrelationship of the system components is given in Figure 7. An example of an actual recorder chart for a group of samples appears in Figures 8a and 86. This is a redundant “fail safe” recording which serves two purposes: ( 1 ) allows the operator to inspect sample readout to check on noise or other artifacts, drift, etc., and (2) provides recorded data for manual processing in the event that anything goes wrong with the computer processing of tape punched data. An example of a final print-out sheet from the computer is shown in Figure 9. The program we use was written for an IBM 360 computer. ACKNOWLEDGMENT
We thank Arnold E. Essenburg for helpful suggestions in design and for evaluation of the performance of the equipment, and Herbert Simonds and Lloyd Olson for much of the fabrication and wiring of the apparatus. RECEIVED for review January 8, 1970. Accepted June 10, 1970.
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