1750
ANALYTICAL CHEMISTRY
Table IV. Comparison of Glucose Test Paper and Benedict's Test on Urine Specimens in Diabetic Clinic Test Paper Glucose, 07 No.
Keg.
Trace
+
++ +++ ++++
Benedict's Test
every 15 seconds diiring thP s c ~ o n Jminiitr. In the timing int,erval the moist paper can Lie foldrd and himy from the edge of the specimen container 01' plared in order on adhesive cellophane tape. The stability of the paper, as indicated by t,esting at intervals over a period of 6 months, was found t,o be satisfactory a t room temperature, 37" C, and 50" C. when protect,ed from light. Direct sunlight causes a gradual deterioration of the paper, but the opaque plastic dispenser, in which the commercially available paper is packaged, serve8 to prot'ect it. LITERATURE CITED
Urine specimens received a t a diabetic clinic were tested with the Benedict's test and the test paper. Table IT' lists the number of observations for the test pnper and the corresponding observations for the Benedict's test. Again, better differentiation is evident by the test paper a t the lon-er concentrations and by the Benedict's test for the range from 1 to 2 % not covered by the color chart for the test paper. For better differentiation R ith the test paper a t higher glucose concentrations, dilutions of the urine are necessary. The test paper can be dipped conveniently into the specimens as they are received in the normal variety of containers. Four determinations can be made every 2 minutes by dipping one strip cvery 15 seconds during the first minute and reading one strip
(1) Bentley, R., Seuberger, .4.,Riochem. J . 45, 584 (1949). (2) Coulthard, C. E., Michaelis, R., Short, W. F., Sykes, G., Skrimshire, G. E. H., Standfast, -1. F. B , Birkinshaw, J. H., Raistrick, H., I b i d . , 39, 24 (1948). (3) Feigl, Fritz, "Qualitative Analysis by Spot Test, Inorganic and Organic Applications," 3rd English ed., Elsevier, Kew York, 1947.
(4) Keii;, D., Hartree, E. F , Biochem. J . 42, 230 (1948). (5) Ibid., 50, 331 (1952). ( 6 ) Keston, .1.S., Abstracts of Papers, 129th Neeting, ACS, Dallas, Tex., p. 31c, -4pril 1956. (7) Theorell, Hugo, -4rkio Kenai, Mineral. Geol. 2, 1 (1942). (8) Whistler, R. L.,Hougli, I,., IIylin, J. IT., ASAL. CHEM.25, 1215 (1953).
RECEIVED for review March 14, 1956. Accepted August 3, 1956. Dir-ision of A~ialyticalChemistry, 1 2 9 t h Neeting, ACS, Dallas, Tex., April 1956.
Boron Hydride Monitoring Devices Employing a Triphenyltetrazolium Chloride Reagent L. J. KUHNS, R. H. FORSYTH, and J. F. MAS1 Callery Chemical Co., Callery, Pa.
Two instruments may be used to monitor atmospheres contaminated with boron hydrides: a portable, field model with a hand-operated pump and a continuous analyzer which automatically records boron hydride concentration. Both were designed to make use of the nonspecific reduction of triphenyltetrazolium chloride by boron hydrides to form the red-colored formazan. Metered air samples are passed through filter paper or cloth tape impregnated with the reagent solution. The red color produced is measured by visual means with the field model and by a differential reflectance photometer with the automatic instrument. The instruments w-ere calibrated with diborane, pentaborane, and decaborane; although they are relatively insensitive to diborane, very low concentrations of pentaborane and decaborane can be detected. The field model can detect 0.1 p.p.m. of decaborane and 0.5 p.p.m. of pentaborane, while the automatic instrument is capable of detecting 0.1 p.p.m. of either compound.
T
HE high toxicity of boron hydrides makes it desirable to have monitoring devices for the detection of very low concentrations of these compounds in areas where they may contaminate the atmosphere. The instruments described here are capable of detecting pentaborane and decaborane a t least a t the maximum allowable concentrations (MAC). For decaborane this concentration is less than 1 p.p.m. (8) and for pentaborane may be set a t less than 0.2 p.p.m. ( 6 ) . It was first established by Hill that triphenyltetrazolium chloride (TTC) in alkaline solntion is reduced by boron hydrides to
form the red-colored formazan and it was employed by him in the quantitative estimation of these compounds ( 3 ) . The color reaction is not specific for boranes; methods are reported in the literature for its use in the quantitative determination of sugars and of enzyme (dehydrogenase) activity (5, 7 ) . Although it is not specific, the high sensitivity of the reagent for these compounds justifies its use. A reagent developed in this laboratory is employed as the detecting element for the instruments described in this paper. The reagent, which contains triphenyltetrazolium chloride, quinoline, pyridine, and water, is particularly suited for monitoring devices of this kind. It has a low volatility of the necessary alkalinity without being as unstable as an aqueous alkaline solution of the salt. The salt and its reduced form are both soluble in the solution, whereas the reduced form precipitates out of an aqueous solution. A silver nitrate reagent is reported by Etherington and McCarty ( 2 ) for boron hydride detection with a monitoring device. Instruments similar to the automatic recording analyzer described here are available commercially for the detection of compounds other than boron hydrides (hydrogen sulfide analyzer, Rubicon Co., Philadelphia 32, Pa.; Microsensor, Vitro Corp., 233 Broadway, New York 7 , N. Y.) Some parts of the devices reported on in this paper had to be fabricated from stainless steel and Teflon, because of the action of the reagent on other metals, rubber, etc. FIELD MODEL
The portable model consists of the sensing unit and the handoperated vacuum pump (Figure 1). The stainless steel sensing
V O L U M E 28, NO. 11, N O V E M B E R 1 9 5 6
1751 The analyzer has the following operational sequence:
FILTER PAPER CHECK VALVE
ACTIVATED CARBON
9
SENSING UNIT
' \
GLASS 'WOOL
W
RUBBER PLUNGER
M S A SAMPLAIR PUMP
The tape is moved into position by the tape-pulling mechanism and clamped into place by the lowering of the scanning stage cover. During this operation, the sample flow is bypassed through a solenoid valve, and sample is not pulled through the tape until a 15-second zeroing time has elapsed. After the zero point is established, the sample is pulled through the tape for 3.5 minutes, and any deflection is recorded. The sequence is then repeated automatically. Reflectance Photometer and Recorder. The reflectance photometer is composed of two Photovolt 610D search units with matching photocells. The original light filters are replaced with Corning 4 9 0 - m ~glass filters (filter glass No. 4445 CS 4-74, 23/16i~ 1/32 inch, polished stock thickness of 2.1 to 2.9 mm., edges ground standard quality). Unexposed tape is scanned by the reference photocell, and the exposed tape by the other. The two photocells are in a bridge-type circuit, and when no reductant is
Figure 1. Hand-operated monitor for boron hydrides
Figure 2. Schematic diagraiii of automatic recording monitor for boron hydrides
unit is designed to clamp the filter paper ( 3 / 4 inch in diameter) tightly in position and to allow air to be drawn only through an area of the paper inch in diameter. Observation of the paper was made easier by dishing the top of the cap. The vacuum pump used for this device is part of the iLlS-4 Samplair, an instrument for detection of chromic acid mist. The sensing unit is inserted into a rubber stopper, which is in turn inserted into the neck of the pump. A layer of activated carbon placed between two layers of glass wool in the neck of the pump prevents the quinoline and pyridine in the reagent from attacking the rubber components of the pump. In operation, a filter paper disk is placed in the sensing unit cap. Two drops of reagent are placed on the paper, and the cap is screwed on the body of the unit. Sample air is drawn through the reagent paper by means of the pump, and the paper is observed after each stroke. The number of strokes required to produce a definite, uniform pink color is recorded and compared with a calibration chart. AUTOMATIC RECORDING MODEL
Description of Analyzer. Atmospheric boron hydridc pollution is automatically measured and recorded by the automatic reflectometric analyzer, and it is possible to install easily an alarm circuit to be actuated a t any boron hydride concentration within the instrument's range. A4 schematic drawing of the analyzer is shown in Figure 2. When boron hydride-contaminated air is drawn through the tape impregnated with reagent, a red color is produced which changes the reflectance of the tape. A potential difference is obtained between the two photocells of the double-beam photometer and this potential is recorded. The rate of sample flow and exposure time are kept constant, and calibration data are obtained by relating recorder readings to the corresponding boron hydride concentrations.
being sampled, a zero potential is obtained. A manual control is provided for setting this zero potential by balancing the output of the two photocells. The photometer lamps are fed from a constant-voltage transformer and are connected in series to eliminate the effect of current fluctuations. The output of the photocells is fed into a Leeds & Xorthrup recorder with the range set a t 0 to 10 mv. Tape-Drive Mechanism. The tape-drive mechanism is controlled by the timer that controls the duration of the exposure. The sequence of the operation is initiated with the cover solenoid and the tape-drive motor being energized. The cover is lifted by the solenoid and the tape is drawn through the slot above the storage compartment, across the scanning stage, and through the drive and tension rolls and is then wound on the tape-rewind spool for easy disposal. The drive roll and rewind roll are turned by means of the same motor; a spring belt used on the motor allows for the increasing diameter of the tape-rewind roll. After the unexposed tape is positioned, the solenoid is deenergized and the cover is pulled into place by the two springs. At the end of the exposure period, the solenoid and motor are again energized, and the sequence is repeated. Gas-Sampling System. Gas sample is drawn through the inlet, into the reaction chamber by way of an annular slot, and through the reagent tape. The spent sample then passes through a charcoal filter, and a vacuum pump which leads to a vent. Flow rate is regulated a t 1 liter per minute by means of the needle valve and a Flowrator inserted in a sample line attached to the inlet. Solvent vapors and boron hydrides are removed by the charcoal filter to prevent them from going into the pump. The reaction chamber is sealed a t the bottom by a Teflon gasket and the glass light filter, which are held in position by the photometer assembly and sealed a t the top by a Teflon gasket seal between the scanning stage and the stage cover. The reagent tape is held in position by the latter seal, which also stretches the tape to give a uniform reflection. An absolutely tight seal is not obtained, because of the fibrouE nature of the tape, but the leakage is not variable nor too great. Circular sections on the stage cover directly above the tape are painted white to provide a suitable reflectance background for the tape.
1752
ANALYTICAL CHEMISTRY IO
I
I
I
I
I
I
I
1
I
I
and 11. The instruments were so insensitive to diborane that complete calibrations were not made for this compound, but they can detect very low concentrations of pentaborane and decaborane and should be useful monitoring devices for these compounds. Calibration curves for pentaborane and decaborane obtained with the automatic analyzer are shown in Figure 3.
Table I.
Calibrations for Field Model Borane Detector
of Strokes KO.
I x
PEN'TABORA N E
0
DECpBORANE
Diborane, P.P.31.
Pentaborane, P.P.hZ. 10.0 7 0
100
1
.. ..
2
3
5.0
Decaborane, P.P.M. 20 8 4
3.0
2I
0.9 0.8 0.7 0.6 0.5
0.8 0.6
1 .o
2
3
4
5
6
p a r t s per m'illion Figure 3. Calibration curves for automatic monitor
Sample flow through the reaction chamber is discontinued by means of a solenoid valve during the positioning of the tape and the 15-second zeroing time. Timing Mechanism. For ex erimental purposes an automatic reset timer (Industrial Timer Eorp., Model P-5M-Fig. 6) and a recycling timer (Industrial Timer Corp., Model MC3-814-4, cams, 46.5 seconds) were used. After the 3.5-minute exposure period, the solenoid valve is positioned so that sample is not pulled through the instrument. At the same time, the motor that pulls the tape and the solenoid that lifts the scanning stage coveiare put into operation for 2 seconds. Fifteen seconds later the solenoid valve is positioned to allow sample air to flow through the instrument for the 3.5-minute exposure period. EXPERIMENTAL
Diborane and pentaborane calibration samples (approximately 1000 p.p.m. in nitrogen) were contained in 4liter steel cylinders a t initial pressures of 1000 pounds per square inch gage. Lower concentrations were obtained by diluting with air using criticalorifice flowmeters ( ressure drop greater than 1 atm.). These compounds were a t feast 98% pure, and as the concentrations in the cylinders were determined by analysis, no attempt a t further purification was made. Diborane and pentaborane samples were determined as boric acid by the dianthrimide method ( 1 ) . Decaborane (resublimed) samples were obtained by passing nitrogen through decaborane cr stals held a t 25" or 35" C. and diluting the nitrogen stream ?not over 30 ml. per minute) with air, using critical-orifice flowmeters. Concentrations of decaborane were determined by Hill's quinoline method (4). Boron hydride samples for calibration were diluted a t least 90% with air; erroneously high sensitivities were obtained when samples were diluted entirely with nitrogen. Triphenyltetrazolium chloride was a product of Eastman Organic Chemicals, Rochester 3, N. Y . , and the quinoline and pyridine were reagent grade and obtained from Fisher Scientific Co., Pittsburgh, Pa. The filter paper (grade FF 3, lot 3097) used in the field model is manufactured by the Hollingsworth and Vose Co., 41 Park Row, S e w York 7 , N. Y. Preparation of Reagent. The reagent is prepared by dissolving 0.5 gram of triphenyltetrazolium chloride (Eastman Organic Chemicals) in 2.5 ml. of pyridine (reagent grade) and 2.5 ml. of distilled water and then adding 25 ml. of quinoline (reagent grade) and shaking. This solution will keep indefinitely if stored in a dark bottle away from light. Preparation of Reagent Tape. Reagent tape is prepared by placing one drop of reagent a t l/a-inch spacings along the tape. The tape is then rolled on a spool and allowed to stand overnight before using. It is recommended that the reagent tape be used within 1 week after preparation. The tape (Rubicon Co., Catalog S o . 4805) is the same as in the hydrogen sulfide analyzer except for the absence of lead acetate reagent. RESULTS AND DISCUSSION
The data obtained in the calibration of the instruments with diborane, pentaborane, and decaborane are given in Tables 1
0.4 0.2
0.1
Table 11. Calibrations for Automatic Reflectometric Borane Analyzer AV. Deflection,
P.P.hI.
MV.
No. of Analyses
Diborane Calibration
B2Ha 30
0.2 1.0
100
2 4
Pentaborane Calibration
BsHp 6.4 3.2
9.3 7.2
1.6 0.8 0.4
5.6
3.5 2.3 1.1
0.2 0.1
0.5
Decaborane Calibration 3.2 1.6
5.2 4.6 3.5 2.6
0.8
0.4 0.2 0.1
1.7 1.0
It would be possible to increase the sensitivity of the field model somewhat by increasing the number of strokes and that of the automatic model by increasing either flow rate or exposure time. The amount of increase is limited by the fact that the reagent solvents gradually evaporate, making the reagent insensitive. Xew calibrations are required whenever operating conditions are changed, because any change greatly alters them. No long-term studies of reproducibility were made, but the small number of tests made show that the precision of the field model was about 340% and of the automatic model within &20$4 even a t low concentrations. LITERATURE CITED
(1) Ellis, H. E.,Zook, E. G., Baudisch, O., ~ ~ N ACHEM. L. 21, 1345 (1949). (2) Etherington, T.L.,NcCarty, L. V., Arch. Ind. H y g . and Occupatied Med. 5, 447-50 (1952). (3) Hill, W.H.,private communication, 1953. (4) Hill, W. H., Johnston, A I . S., ANAL.CHEM.27, 1300-5 (1955). (5) Jensen, C. O., Sacks, W., Baldauski, F. A., Science 113, 66-6 (1951). ( 6 ) Levinskas, G. J., personal communication. (7) Mattson, A. M., Jensen, C.O., ANAL.CHEM.22, 182-5 (1950). (8) Svirbely, J. L., personal communication.
RECEIVED for review March
12, 1956.
Accepted July 18, 1956.
