the acidified sample yields 237 - 203 = 34 ppm C as formate (33 ppm C theoretical). A second bath prepared as above, but with no copper salt, produced identical results. Thus, the large excess of copper salt present in the original bath caused no deleterious effect. These excellent results demonstrate the useful function a TOC analyzer serves in industrial process control. Specifically, both the tartrate and formate contents of the bath can be quantitatively determined using a TOC analyzer,
which can affect the separate analysis of volatile and total components.
LITERATURE CITED (1) Fed. Regist., pp 34541-34558, Dec. 14, 1973. (2) Fed. Regist., pp 28758-28760, Oct. 16, 1973; Note 1 (3) M.K. Carter and C.Goodell, Am. Lab., 6, 43 (1974).
RECEIVEDfor review November 7 , 1974. Accepted March 21, 1975.
Low Power, Programmable, Non-Reactive Air Sampler for Field Use S. 0. Farwell,’ H. H. Westberg, and R. A. Rasmussen Air Pollution Research, Engineering Research Division, Washington State University, Pullman, Wash. 99 163
The need for an inexpensive, yet versatile, air-sample collection system originated as a result of our current research in the analysis of ambient air for ozone and light hydrocarbons ( I , 2). For example, in addition to extensive aircraft monitoring along different flight paths and routine sampling at the location of the mobile field laboratory, integrated bag samples of air would be collected for variable sampling times at several remote sampling sites. These bag samples would be collected for subsequent analysis at the mobile field laboratory. In order to satisfy our sampling requirements, the collection system would incorporate the following design features: (a) low power consumption to permit battery operation, (b) adequate temperature stability for field use, (c) automatic collection of an integrated air sample, (d) programmable sampling times, (e) a cycle timer with sufficient noise immunity to operate in a relatively high noise environment (e.g., close proximity to the dc pump motor), (f) both the controller and the pump should be capable of operating a t the same dc supply voltage, (g) optimum operational simplicity and reliability, and (h) small in size and light-weight. In addition, the sampling pumps and sample bags should not contaminate or destroy the gases being collected. A digital timer constructed with integrated circuits, a non-reactive sampling pump with gas-contacting parts of Teflon, and a Teflon sample bag have been combined to produce an air collection system with the above-mentioned characteristics. Timer Circuit Design and Operation. Figure 1 shows the detailed circuit diagram of the programmable, control timer. This sampling controller actually consists of two individual timers: (a) the two uppermost XR-2340 integrated circuits in Figure 1 have been cascaded to generate the longer time delays associated with the specific time intervals between initial field triggering and the period of time before the sampling pump is turned on; (b) the lower XR2340 unit in Figure 1 controls the shorter duration of the actual sampling period, or the length of time that the pump motor operates. The two cascaded XR-2340 units are connected for low-power operation by leaving the Vf+ terminal (pin 16) of the second XR-2340 open-circuited; thus the second XR-2340 is powered from the regulated output of the first XR-2340 by connecting pins 15 of both units ( 3 ) .
Author to whom correspondence should be addressed. 1490
ANALYTICAL CHEMISTRY, VOL. 47, NO. 8, JULY 1975
Unlike integrated circuit timers such as the popular 555 ( 4 ) that have a time delay which is determined by a single charging cycle of the external timing capacitor, the XR2340 uses a time-base oscillator to provide multiple cycles. These multiple cycles of the XR-2340 permit reasonable values of timing capacitance for time delays in excess of several days without a deterioration in timing accuracy because of excessive leakage contributed by the circuit components. The XR-2340 timer/counter circuit consists of three basic sections: (a) a time-base oscillator, constructed from two voltage comparators and a R-S flip-flop, that acts as a relaxation oscillator; (b) a control flip-flop that includes a trigger input and a reset input; and (c) a programmable %bit binary counter. Prior to the application of a trigger input, the circuit is in its reset state where both the time-base and the counter sections are disabled and all the counter outputs are at a high logic state. The timing cycle is initiated by a positive-going pulse at the trigger input which in turn actuates the time-base, enables the counter section, and sets all the counter outputs to their low logic state. The time-base oscillator generates precise timing pulses of period T , where T is equal to the time constant determined by an external timing resistor and timing capacitor. The clock pulses coming out of the time-base oscillator are counted by the binary counter section. Two XR2340 circuits can be cascaded in which case the delay provided is increased in a geometric rather than an arithmetic progression. When the pre-programmed count is reached, the circuit completes the timing cycle and resets itself. The XR-2340 integrated circuit has been recently described in a laboratory timer designed by Karlsson (5). His timer was constructed by combining a XR-2340 with standard T T L logic devices, and consequently is designed for applications in the laboratory. The CMOS circuit components shown in Figure 1 were selected so that the resulting timer would be suited for field application rather than use in a ordinary laboratory. The advantages of the CMOS logic family over their equivalent T T L designs for low power, portable equipment have been recently demonstrated and reported (6, 7). The delay function of the timer is programmed by selectively shorting any one of the switches, S5-Sl2, or any multiple of these switches from the second XR-2340 circuit to its output bus. In this manner, one can program the delay timing cycle from T2 I T,ff I 255 TP,where Teff is the total time delay and T2 is the time-base period of five min-
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Figure 1. Schematic diagram of the programmable, control timer. Circuit components: Three XR-2340 monolithic timers (Exar); one CD4027A dual J-K flip-flop (RCA); gates G1, G2, G3. and G4 are provided by one CD4030A quad exclusive -OR package (RCA); 01, Q3, 2N3642 (Fairchild); Q2, 2N3640 (Fairchild); Q4, SK3024 (RCA); D1. D2, RL-209 (Litronix); D3, IN458 (Motorola): RLY, PRB-2510 (Clare). All the resistance values are in ohms and all the capacitor values in microfarads. The I M and 475K resistors are 1 YO tolerance, all other resistors are 5 % tolerance. The 1 pF and 100 pF capacitors in the R-C networks are high-quality polycarbonate type
Utes. Thus, the duration of the Teff delay cycle between initial triggering and pump motor turn on is given by Teff = NT2, where N is an integer in the range of 1 I N 5 255. In this case, N is determined by the combination of switches, S5-Sl2, which are connected to the output bus of the XR2340 cascaded units. The time-base period of five minutes is determined by the external R-C network connected to pin 13 of the first XR-2340 in the cascaded timer. When the time-base is triggered by switch S2, the waveform at pin 13 of the first XR-2340 circuit is an exponential ramp with a period T i = RC. In our instruments, T1 is set to 1.176 seconds by adjusting the ten-turn 200K potentiometer connected to the 1M resistor in Figure 1, which in turn determines the total resistance of the RC network. Therefore, the time-base period T2 = 256 TI, or five minutes. The sampling time of the air pump is programmed by selectively shorting any of the switches, S13-S20, to the output of the bottom XR-2340 unit in Figure 1. The time-base period of this third XR-2340 circuit is likewise determined by an external R-C network connected to pin 13. For this K-C network, the 200K ten-turn potentiometer is adjusted to produce a T3 period of exactly one minute. Thus, the sampling time To, is given by To, = NT3, and can be programmed in the range of 1 I N I 255 by the corresponding switches.
The beginning of the timing cycle for the third XR-2340 unit is triggered by the reset pulse which occurs when the cascaded timers complete their time-delay cycle. This same reset pulse causes the Q1 output of the corresponding J K flip-flop (lh of CD4027A) to change from a low logic state to a high logic level. Whereas 81 and Q 2 were both low before this transition in Q1, the initial output of the exclusive -OR gates, G3 and G4, was low. A low a t the output of these exclusive -OR gates compels the pumping motor to be off. However, when Q1 is triggered from low to high, the output level of G3 and G4 gates also changes from a low to a high. At this moment in real time, the dc pump motor is turned on and sampling begins. When the third XR-2340 unit completes a timing cycle, its reset pulse triggers Q 2 of the corresponding J K flip-flop from a low to a high. Now Q1 and Q 2 outputs of the respective flip-flops are both high, and the output level of the exclusive -OR gates, G3 and G4, changes from a high to a low. Simultaneously, the dc pump motor is turned off. At a later time, a field technician collects the bag sample of ambient air; resets the timers via switches S3 and S4, changes the length of the timing cycles, if desired; momentarily monitors the pulse rate of the light-emitting diode, D1, by pressing switch SI in order to ensure that the timebase output of the timers is functioning; checks to ensure that the light-emitting diode, D2, is off which means the ANALYTICALCHEMISTRY, VOL. 47, NO. 8 , JULY 1975
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hours. A picture of the sampling pump and the front panel of the programmable controller is shown in Figure 2. The sample bags were made from Teflon and were approximately 30-1. capacity. The use of various plastic hags for sampling and storing atmospheric gases has been described by other researchers (9-11 ). LITERATURE C I T E D Flgure 2..The dc sampling pump and the front panel of the digital controller
(1) H. H. Westberg, R. A. Rasmussen, and M. Haldren. Aml. Chem., 46, 1852 (1974). (2) H. H. Westberg, E. Robinson, and P. Zimmennan, presented in part at the 67th Meeting of the Air Pollution Control ASSOC.,Denver, Calo., June
..
1974
DumD . . motor is also off: and finally attaches a new samDle
hag for collection of the next air sample. In some field monitorine situations where it was necessary to place the dc sampling pump within three feet of the cycle controller, we found that either a miniature DIP relay or an opto-isolater should he used to couple the controller outDuts with the inductive motor. This additional isolation inrreasea sampling reliability. Noo-Reactive Pumo and Samolr Raes. The Kamhvr sampling pumps employed in our monitoring studies were selected for use in this system because all of their gas-contacting parts are Teflon (8). The current drain for each pump is less than 200 mA and they have proved to he quite reliable for field sampling. Their motor life is about 750
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I
(3) "XR-2240l2340 Application Note". Exar Integrated systems. In=., SunnyyaIe. Calif.. November 1973. (4) "555 and 556 Timers", Signetin. 811 E. Arques Awe.. Sunnyvale, ,.^'il vo
,,,.. *O?.,
(5) G. Karisson. Anal. Chem.. 46, 1618 (1974). (6) C. Crook. Electronics. 47, 132 (1974). (7) 'DOS/MOS Digital integrated Circuits", RCA Solid State Databaak Se ries, Sommervilie. N.J.. 1973. 18) . . Komhn Teflon Gas SamDiino . . Pumw, . M d e i &ZOO. Science Pump Corp.,.Camden, N.J. (9) A. P. Altshuller, A. F. Wartburg, I. R. Cohen, and S . F. Sieva, ht. J. Air WaterPoilut. 6, 75 (1962). (IO) C. A. Clemons and A. P. Alishdler, J. Air Polia. ConWiAssm.. 14,407 (1964). (11) H. Drasche, L. Funk, and R. Herbabheimer, StaubSleinhaL Luff, 32, 20 (1972).
RECEIVEDfor review November 18, 1974. Accepted April 16,1975.
Technique of Preparing Powder Samples for AES and/or ESCA Analysis G. E. Theriault, T. L. Barry, and M. J. B. Thomas Technical Assistance Laboratory, GTE Sylvanis hcorporat~,Sylvania Lighting Center, 100 Endicon Street, Danvers. Mass. 07923
A clean, rapid, and simple technique for mounting powder samples for Auger Electron Spectroscopy (AES) and Electron Spectroscopy for Chemical Analysis (ESCA), where depths analyzed are about 10 to 20 A, offers distinct advantages in obtaining an uncontaminated representative sample over techniques previously employed. Some prior techniques and their major drawbacks are listed below. 1) Utilization of Double Backed Sticky Tape for Powder Retention. Decomposition of tape by interaction with the excitation source (if electron beam encounters any exposed area) and redeposition of organics on the powder sample being analyzed. Also, a significant vapor pressure which limits the level of vacuum attainahle. 2) Pressing Powder into a Mesh Screen. Contamination of and mechanical work on the powder surface from the mesh material plus the possihility of the irradiating beam hitting the mesh material. 3) Entrap Larger Particles in a Mesh Material Which Will Not Peratit Passage of the Powder Granules. Same as in (2) above except for the mechanical action. 4) Pressed Pellets of the Powder Material. Potential contamination of the surface to be analyzed by the pellet mold or any confining surfaces used and potential structural changes due to the pressure applied. 5) Powder Placed in a Depression in the Sample Holder (Carousel). Potential loss of sample material in obtaining a level of vacuum suitable for analysis (-2.0 X Torr). Because of its drawbacks, this technique is seldom used. 1492 * ANALYTICAL CHEMISTRY, VOL. 47. NO. 8, JULY 1975
6 ) Place Powder Inside a Container and Tilt Container toward the Analyzer. Spilling of sample in vacuum chamher aligning sample with analyzer. This, as is (5) above, is a loose powder technique of little utility. The present technique consists of embedding the powder in a suitable metal foil. An excess of powder is placed in a folded indium strip and hand pressed to embed the powder in the very soft, malleable, and ductile metal. When the fold is open, the excess powder not embedded in the indium can be discarded, and a fresh powder surface which has had only contact with other powder, and not even with the indium substrate, may he presented to the instrument for analysis. Advantages of This Technique. A clean, mechanically unworked, surface which has only had contact with itself can be presented for analysis. The indium metal "sample holder" is less susceptible to charging than any technique utilizing a nonmetallic substrate for mounting. Coverage of the indium surface by powder is usually complete and indium lines do not appear in the resulting spectra. In the event indiun is excited, its spectra are quite simple (would not significantly complicate the sample spectrum) and easily distinguishable. If, for some reason, indium cannot he used with a parhicular sample, tin may be used as an alternative. Physical properties of indium which contribute to its utility are a low melting point (156.17') and a high boiling point (ZOO0 "C). These properties contribute to its soft,
