calcd. N, 25.92; found (D) 24.65, (8 and H) 25.69(;?,, and 1 - p - bromophenyl - 5 - phenyl - 1,2,4 - trizole-3carboxylic acid hydrazide : calcd. N, 19.55; found (11) 18.42, (S and H) 19.4070. LITERATURE CiTED
(1) Albert, A,, Quart. Revs. (London) 6 ,
197 (1952).
(2) Atkinson, 11. R., Polya, J. B., J . Chein. SOC.1952, 3418.
(3) Belcher, It., Bhasin, R. L., West, T., Ibad., 1959, 2585. (4) Brancone, L. M., Fulmor, W,,ANAL. C H E l f . 21, 1147 (1949). ( 5 ) Browne, E. J., Polya, J. B , Chem. & Ind. ( L o n d o n ) 1960, 1085, 1086. J. Chem. SOC.1962, to be published. (6) Challen, E., private communication. ( 7 ) Kirsten, ST-., The Dumas Determination of Nitrogen, in “Commehensive Analytical C h k s t r y , ” C. L. Wilson and D. W. Wilson, eds., Vol. 1, b, pp.
467, 471, and 484, Elsevier, Amsterdam, 1960. ( 8 ) Miher, R. T., Sherman, AI. P.,
ED. 8, 331 (1936). 9) Potts, K. T., C h e m Revs. 61, 87 IN[). E N G . CHEJI., h . 4 L .
i1961). \ - - - - I
10) Ronzio, -1.R.,
I Z D . ENG. CHEM., ANAL.ED. 12,303 (1940) 11) Spies, J. R., Harris, T. H., Z b i d , 9 , 304 (1937). 12) Zimmermann. R..Mikrochemie oer Aiikrochim. A c t i 3 1 , 42 (1943).
E. J. BROWNE J. B. POLYA Chemistry Department The University of Tasmania Hobart, Tasmania, Australia
High-Precision Rapid Injection and Automatic Refill Pipet H. V. Malmstadt and H. L. Pardue, Department of Chemistry and Chemical Engineering, University of Illinois, Urbana, 111.
A
PIPET is described which can operate by remote switching to deliver aliquots of reagent in synchronization with other events. A 1-ml, aliquot is delivered with a precision of 0.002 ml. in 0.4 second. By rotating a switch, a preselected number of aliquots can be added. For example, on dialing “10” ten successive aliquots are added before delivery stops. Any multiple of 1 ml. (or other volume increment) can be dialcd. n ith the maximum number of aliquots depending on the available switch positions. Aliquots other than 1 ml. are pasily obtained with interchangeable cams or syringes.
MICROSWTCH 5 5 1 ACTIVATED)
DELIVERY 3- WAY
TEFLON STOPCOCK OPERATED B Y MOTOR M,
RESERVOIR
The rapid addition of a single aliquot has been especially useful for quantitative reaction rate methods where the analytical results are obtained during the early seconds of a reaction. The accurate selection and pipetting of preset quantities of reagent are essential in automating many analytical procedures. I n other cases, such as for back-titrations, it is desirable to add increments of reagent n i t h good accuracy over a wide range until a n indicator shows a small excess of reagent. For these applications a counter has been connected so that the total number of aliquots from the start to the indicator change is read from a dial. The advantages of this pipet over that described by l l a l m s t a d t and Hicks [ANAL.CHEM.32, 445 (1960)l are the greater precision, the continuous recycling feature with direct readout on a counter, the switching device for preselecting delivery of a fixed number of aliquots, faster delivery times, and the use of a n inert Teflon valve. The Teflon cam and the spring were made as previously described.
r.p.m. reversible Slo-Syn motors (Superior Electric Co., Bristol, Conn.) with instant start and stop. Therefore, the entire sequence of ’/4 turn of stopcock, ’/z turn of cam, reversed turn of stopcock, and reversed turn of cam requires 1.25 seconds, with only about 0.4 second for actual delivery of an aliquot. The basic pipet unit also contains the counter and start switch. The start switch can be pushed for single aliquots or turned to lock in for continuous recycling. Delivery of Single Aliquot. T h e operation of t h e injection pipet to deliver a n aliquot of reagent is de-
DESCRIPTION OF PIPET
MICROSWITCH 53 SPRING
MICROSWITCH I ACTIVATED)
S2
w
TEFLON CAM OPERATED BY MOTOR M,
Figure 1. Delivery and refill system for automatic pipet
The pipet unit delivers one aliquot of reagent b y the upward plunger movement with the syringe connected to the delivery tip. The automatic r e a l occurs when the spring-loaded plunger follows the cam back t o its original position with the syringe connected t o the reagent reservoir as shown in Figure 1. The alternate connections between syringe and either delivery tip or reagent reservoir are made b y 90’ rotations of a T-bore Teflon stopcock. The plunger moves b y 180” rotations of a cam. Both the cam and stopcock are driven by 72
Figure 2. pipet
Basic circuit of automatic
K1. s1.
1 15-volt ax. DPST relay Push button switch for relay contacts of K 1 S2, 53, S4, S5. SPDT microswitches Mn M c . 72-r.p.m., reversible Superior Slo-Syn motor C. 3.3-/lfd., 330-volt R. 250-ohm. 25-watt
VOL. 34, NO. 2, FEBRUARY 1962
299
Table I. Reproducibility of Delivery by Automatic Injection Pipet No. of A V. AiV. Aliquots" Vol., Ml. Dev.,b A i l . 1 0.900 0.001 10 9.001 0.002 20 18.002 0.002 5 For single aliquot preselector box mas
disconnected. Preselector was connected and either 10 or 20 dialed to deliver aliquots automatically by continuous recycling up to selected number. Average deviation of seven measurements for each of selected volumes.
Figure 3. K1. K2-K4. K3, K5. S 1 b.
S5b. S6. X.
Y. R1
c1.
Switching circuit for preselecting number of aliquots
Relay in basic pipet unit (Figure 2) Guardian electrical reset step relay. K 2 i s stepper coil, K 4 is reset coil, t y p e MER1 15, 2 1 -position DPDT 1 15-volt a x . relays SPST switch. Duplicates action of S 1 but is located on switching unit SPST normally open microswitch mounted adjacent to S 5 on pipet unit 2 1 -position rotary selector switch M-500 silicon rectifier TCeZ4E.25 Sodeco electrical counter 1 2 0 ohms 2 5 - ~ f d . ,150-volt, electrolytic condenser
scribed by considering the sequential operations n i t h reference to Figures 1 and 2, Fvhich show t h e syringe, stopcock, and snitches in their standby positions prior to the s t a r t of a cycle. STAND-BYCOKDITIONAXD START. I n the stand-by condition microswitches S 5 and S2 are activated and all contact positions are shown in Figure 2. By operating the relay switch, S I , contacts a and b are closed and the circuit is completed through a, b, c, d, e, and j to connect relay K 1 and valve motor kf,across the 115-volt a x . line voltage. Relay K 1 locks contacts a and b closed during the 90" shaft rotation of JI,. CLOSE REFILLAKD OPEN DELIVERY TUBES. hfotor -Ifv turns the stopcock counterclockwise t o close the refill tube and open contacts i and n and close i and j of switch 85 near the start of rotation, and open the delivery tube and operate contacts of switch S4 after a 90" counterelockwise rotation of stopcock. Contacts c and d open (which opens a and 6 ) and d and g close, so the stopcock motor, X ~stops , and the syringe motor, M,, starts (by completing the circuit through j , e, d, 9, i, j , k , and 1). DELIVERALIQUOT OF REAGENT. The shaft of M, turns the Teflon cam onehalf cycle counterclockwise, which drives the plunger up to deliver an aliquot of reagent. The rotation of the cam operates microswitch S2 shortly after starting and microswitch S 3 at the 300
ANALYTICAL CHEMISTRY
end of one-half cycle to open contacts e and f and close f to h near the start of rotation (there is a momentary break of the motor circuit but M , is immediately re-energized through path f - h i j-k-Z) and open contacts k and 1 and close k and m after one-half cycle. This stops M,and starts M , through a path f-h-i-j-k-m, Ivhich causes the stopcock t o rotate in a clockwise direction. CLOSEDELIVERYAND OPEK REFILL TUBES. The stopcock turns in the clockwise direction t o close the delivery tube and open contacts d and g and close c and d near the start of rotation of stopcock, and t o open refill tube and open contacts i and j and close i and n after 90" clockwise rotation of stopcock. This stops JIt and JI,starts clockwise by completion of its circuit through f-h-i-n. REFILLOF SYRIKGEAND RETURXTO STAND-BYCOSDITION. JI, turns the cam clockwise one-half cycle and the spring-loaded plunger follows the cam back to its starting position, thereby refilling the syringe with reagent. hlicroswitches S 3 and S2 return to original positions because S 3 contacts k and m open and k and 1 close near the start of rotation, and switch S2 contacts f and h open and e and f close after one-half cycle rotation. Continuous Recycling with Counter for Number of Aliquots. To recycle continuously i t is only necessary t o hold down or lock SI (Figure 2) closed during the desired interval. T h e number of aliquots delivered can
be determined directly from a n electrical counter which operates b y the on-off action of microswitch S5b (shown in Figure 3 ) during each complete cycle of events. S5b can be either another section of 8 5 or another microswitch adjacent to it. 81 can be closed and opened either manually or as triggered by some phenomenon. Automatic Delivery of Preselected Number of Aliquots. -1ixeselected number of ali'quots c a n Abe automatically delivered by connecting the recycling control shown in Figure 3. The right and left sections of Figure 3 which are in dashed lines indicate components in the pipet unit. The parts connected by solid lines are mounted in a separate control box. A multiple-lead cable is used between the main unit and the preselector unit as shown by dashed to solid line. in Figure 3. The ooeration of the multisle selector is started by closing switih Slb (or 81, Figure 2) which activates relay K1. Activation of K l closes both sets of its contacts a and b and z and y. T h e n contacts a aiid b cloqe, the normal cycle starts as previouqly described. When contacts z aiid y close, relay I i 5 is activated. The activation of K5 closes both sets of contacts p and q and r and s. Contacts r and s short across a and b, so that the refill-delivery cycle repeats until contacts r and s open. Contacts p and q lock relay K5 acroqs the 115-volt a x . line as long as contacts t and I L of relay K 3 are closed. Therefore recycling continues until contarts t and u open momentarily to unlock relay K 5 by opcning its contacts p and q. It is the purpose of the other components to control the number of cydes before contacts t and u opcn. Relay coil K 3 opens contacts t and u only d i e n the armatures of the rotary selector switch, S6. and the stepping relay, K2, are a t the Same numbered contacts which are tied together. Recycling stops when K 3 is activated to open contacts t and u. Activation of K 3 also closes contacts 0 and w, which activates the reset relay, K4, so that the armature of the stepping relay returns t o zero position. Immediately relay Ii3 deactivates and contacts t and I L close and 0 and w open, so that they are back in the stand-by condition ready for the nest operation.
The stepper coil, K2, is in series with niicroswitch S5b, which closes shortly after the start of rotation of the stopcock. Each time the stopcock starts a cycle the armature of the stepping relay moves one position. Therefore if the 5 position is dialed on S6, the pipet will recycle to deliver 5 aliquots before terminating automatically. The pipet is immediately ready to deliver the exact number of aliquots preset on the dial. DELIVERY DATA
Typical data for delivery of single and multiple aliquots using a cam cut to deliver 0.9 ml. per cycle are shown
in Table I. These data were obtained by weighing water delivered into a rveighing bottle and show reproducibility of delivery within 0.002 ml. for both single and multiple deliveries. The pipet has been in use for more than a year and the reproducibility has remained the same. During this time the absolute volume delivered per stroke has changed by a few thousandths of a milliliter. This would be expected because of slight changes in cam and syringe. For all applications in our laboratories the delivery of a constant volume for a few days or a week with
errors not exceeding those in Table I has been the only requirement. The actual volume delivered can be checked within a couple of minutes every few days b y weighing aliquots. If i t is necessary to deliver a specific volume, such as 1.000 f 0.001 ml.. over a long period, i t would be necessary to provide a calibration adjustment for the cam. ACKNOWLEDGMENT
The authors thank Verle Kalters for valuable suggestions and construction of the unit.
Versatility of Dynamic Sorption Method for Routine Measurements on Solids K. V. Wise and
E. H.
Lee, Hydrocarbons Division, Monsanto Chemical Co., Texas City, Tex.
HE dynamic rorption method has been used primarily for rapid surface area determinations of solids (9, 11, 12); and in this connection, the reported uses h a w been limitpd to the higher range of specific surface areas, about 1 to 1300 sq. meters per gram. By using krypton, n e have extended the dynamic surface area technique to the measurement of evtremely low surface areas (about 6 sq. em.). We have alqo used the dynamic sorption method for determining chemisorption characteristics of catalysts. Modification of the surfave nrea technique for pore volume niewurciiients has also been described (12). Thc major adan tag^ of the dynamic method over the itatic method are simplicity, speed. and greater versatdity. In general. the dynamic method in\ olver the nieasurement of sorbed gasei by a cooled (or heated) solid from a floning mixture of adsorpt;on and inert carrier gasps If the solid sample is interposd betn een tivo arms of a Wheatstone bridge arrangement of a thermal cwnductirity ccll, tlic amount of sorbed gas can bp easily dcterniined by ccmparing the bridge unbalance due t o sorption to tlic unbalances obtained from ii,jwting k n m n volumes of the adsorption gas downstream from the sample. To niinimize any errors emanating from nonlincw rcsponse-concentration relationships, the calibration volumes should be close to the observed sorption volumes. This work involred the use of a PerkinElmcr-Shell Sorptometer (Modcl 212, Perkin-Elmer Corp., Korwalk, Conn.) n i t h grade A helium as the carrier gas. As little as 10 p.p in.of krypton or 50 p . p m of nitrogen in helium could be detected when a 12-volt battery was the current source.
Table I.
ildsorbent Activated carbon, Pittsburgh BPL Activated alumina
adsorbate Nitrogen
Red Chromosorb
Kitrogen
Pumice Platinum gauze Glass tubing
Specific Surface Areas
Nitrogen
Nitrogen Krypton Krypton Krypton
SURFACE AREA MEASUREMENTS
As shown in Table I, the entire range of specific surfacc. areas n as reliably determined by the dynamic sorption method. Both the nitrogen and krypton sorption measurements w r e made a t liquid nitrogen tempwatures. using reduced pressures of the adsorbates bctween 0.05 and 0.35. Isotherms and specific surface arcas were calculated according to the equations advanced by the RET theory ( 2 ) . The values 4 38 and 5.52 vere used for the areas (in square meters) corered by 1 nil. (STP) of nitrogen and krypton, respectively (7, 23). Adsorbate saturation pressures were determined from vapor pressure-t~,mperature relationships (8, 10); the temperature of the liquid nitrogen bath was determined n i t h a nitrogen thermometer. For the krypton measurements, a mixture of 0 570 krypton in helium n-as used as the adsorption gas. All samples were outgassed in a stream of helium a t 250'
Method Dynamic Static Dynamic Static Dynamic Static Dynamic Dynamic Dynamic Dynamic
Surface Area, sq. M . / G . 1372 1360 218 195 4.6
4.8 0.41 0.40 49 sq. cm./g.
