Table 11. Selenium Content of Smoke Samples SeOl present, F g Hydroxylamine-oxidaCatalytic Sample No. method5 tion method Recovery, Zb 82.0 2.10 1 2.57 81 .O 3.10 2 3.86 100.0 3 3.08 3.08 2.10 100.0 4 2.10 97.0 3.78 5 3.92 95.0 2.38 6 2.52 88 .O 2.94 7 3.36 a Reference (13). * Based on results of catalytic method. River, Mass.). The solution from the sampler was made 4-5M in hydrochloric acid and boiled gently to effect the reduction of selenium(V1) to selenium(1V). Selenium was then determined by the recommended procedure. The samples were also analyzed by the catalytic method of West and Ramakrishna (13). A comparison of the results obtained by the two procedures is shown in Table 11.
SUMMARY
A new spectrophotometric method for the determination of submicrogram quantities of selenous acid has been developed. The procedure is based upon the oxidation of hydroxylamine hydrochloride to nitrous acid by selenous acid followed by the diazotization of sulfanilamide by the nitrite produced and subsequent coupling of the diazonium salt with N-(1-naphthy1)-ethylenediamine dihydrochloride. Reaction parameters such as temperature, time, and reagent concentrations have been studied in detail and optimum conditions for the system have been established. The range of determination extends from 0.01 to 0.20 milligrams of selenium(1V) per liter. The method is simple, sensitive (e = 193,000), and reproducible. There are no common interferences which cannot be easily obviated. RECEIVED for review August 7, 1970. Accepted December 1, 1970. This work was supported by the U. S. Public Health Service Grant AP 00724 from the Division of Air Pollution, Bureau of State Services. (13) P. W. West and T. V. Ramakrishna, ANAL.CHEM., 40, 966, (1968).
Automatic Monitor for Surfactants in Aviation Turbine Fuel G . P. Pilz and J. L. Manis Shell Oil Company, Research Laboratory, P. 0. Box 262, Wood River, 111. 62095 SURFACE-ACTIVE AGENTS in aviation turbine fuel have long posed a problem in the delivery of high-quality fuel to airline terminals, Contaminants in parts per million and lower concentrations can cause serious operational difficulties in fuel distribution systems as well as in gas-turbine aircraft engines. Surfactants promote the entrainment of finely-dispersed water droplets and particulate matter in the fuel, which, if not removed, may lead to abrasion of fuel pumps and plugging of fuel screens in engines by particulate matter and ice. T o assure that satisfactory turbine fuel is delivered to aircraft, filtericoalescers are commonly employed as a final defense mechanism in fuel distribution systems. These filter/ coalescers are capable of functioning effectively over extended periods provided they encounter virtually surfactant-free fuel. In order to ensure their long-term effective performance, it has become common practice to install adsorbent beds ahead of filter/coalescers in fuel distribution systems to remove surface-active components. Eventually, however, adsorbent beds become deactivated and allow the passage of surfactants which ultimately results in the disarming of filter/ coalescers. Thus, a sensitive method for monitoring surfactant concentrations in turbine fuel is needed to determine when adsorbent life has been expended. The literature contains numerous references to chemical tests for surfactant detection. These tests, however, do not lend themselves to monitoring surfactant concentrations in turbine fuels for one or more of the following reasons : Many of the tests described in the literature are applicable only to aqueous systems. Test methods are generally limited to the detection of only a specific surfactant type (i.e., anionic, cationic, or nonionic species). Most of the tests lack the sensitivity for detection of surface-active agents in the very low parts-per-million range.
Several surfactant test methods, devised for specific application to aviation turbine fuels and responsive to various surfactant types, have been published. These methods are based on the responses to secondary effects induced in turbine fuel by surface-active agents. ASTM Method D1094-67 ( 1 ) determines the effect of water-miscible components in aviation turbine fuel on the appearance of the fuel-water interface. A gravimetric procedure, ASTM Method D2276-67T ( I ) , determines particulate contamination in turbine fuel, which relates to surfactant concentration. ASTM Method D255066T ( I ) , intended to simulate filter/coalescer performance on a small scale, determines the ease with which entrained or emulsified water is released from a fuel on passage through a coalescer-type water separator. Although the latter test provides a reliable measure of surfactant concentration, operation of the equipment is rather laborious and the sensitivity of the method is somewhat limited. The automatic Constant-Volume Drop Time (CVDT) monitor described in this paper measures the total contribution of all surfactant species which may be present in aviation turbine fuel and possesses the sensitivity required for detection of surface-active agents at extremely low concentration levels. The test is based on a modification of the drop-volume interfacial tension (IFT) method (2). In the latter method, water drops of varying size are dispensed to the tip of a capillary immersed in the nonaqueous phase and the IFT is calculated from the volume of the drop, the densities of the two phases, the radius of the capillary, an empirical correction factor, and known physical constants. In the CVDT test, constant-volume drops of aqueous 1N NaOH are delivered to the tip of (1) ASTM Standards, Part 17 (1968). (2) W. D. Harkins and E. C . Humphrey, J . Amer. Chem. SOC.,38, 228 (1916). ANALYTICAL CHEMISTRY, VOL. 43, NO. 4, APRIL 1971
e
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tants (cationic, anionic, and nonionic), which may be introduced as contaminants in aviation turbine fuel during pipeline transmission, show essentially the same response as that obtained with sulfonic acids. The CVDT test has been in field use since October 1969 with favorable results. EXPERIMENTAL
Figure 1. Photograph of aut the capillary and the elapsed time from drop delivery to drop detachment is measured, The surfactant concentration in turbine fuel has a profound effect on drop time values. Drop detachment time is inversely proportional t o concentration and varies from intervals of 1000 to greater than 2000 seconds for essentially surfactant-free turbine fuel to values as low as 5 seconds when only a few parts per million of surfactant (such as dodecyl benzene sulfonic acid) is incorporated in the same fuel. In addition to sulfonic acids, naphthenic acids are also frequently encountered as surfactants in aviation turbine fuel. Naphthenic acids exhibit somewhat lower sensitivity than sulfonic acids; nevertheless, they are readily detected at the 5-ppm level in the CVDT test. Other surfac-
Apparatus. A photograph of the complete, automatic CVDT apparatus is shown in Figure 1. Basically, the equipment consists of a control box, a syringe pump, a 1-ml syringe, a stainless steel capillary, a timer, and a conductivity detector cell. Formation of the constant-volume drop is achieved in the following manner: depressing a switch mounted on the control box starts an electronic timer and actuates a Sage Model 234 syringe pump which contains a synchronous motor. The drive unit advances the syringe plunger at a constant rate. Since the rate of drive is constant, the drop size is controlled by the time interval during which the pump is driven. This time interval is set by the electronic timing circuit and its associated power supply. The electronic timer design utilizes a silicon controlled switch (SCS) and a unijunction transistor. Figure 2 shows the schematic diagram of the timer. Cl is initially charged to the V, potential of 30 volts. When SW, is closed, the SCS conducts, which energizes RT. This relay controls the syringe pump and the secondary control relay in the drop detachment time measuring circuit. When the SCS conducts, the voltage across Cldecreases from 30 volts to a few volts. As C, discharges through R4,Ra, Rs,and R1,the emitter of the unijunction transistor rises above the intrinsic standoff voltage causing the unijunction to conduct. Current flowing through the emitter of the unijunction, Cl and RI turns
r Figure 2. Schematic diagram of CVDT timer
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ANALYTICAL CHEMISTRY, VOL. 43, NO. 4, APRIL 1971
Figure 4. Photograph of CVDT elmhode assemhly
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off the SCS and charges C1 back to 30 volts for the next timing cycle. Rsprovides variable control of the R C time constant and is used to set the time interval of the timer. The circuit used to measure drop detachment times is composed of a sample cell, a conductivity detector relay, and a control relay. A schematic diagram of this circuit is shown in Figure 3. The electrode assemhly for the sample cell is illustrated in Figure 4. The sample cell, consisting of a Teflon (Du Pont) frame into which platinum lead wires have been incorporated, is positioned under the syringe needle tip. Depressing the start switch actuates relays RT and R,. R, turns on the conductivity circuit and starts the digital timer. When the 80-pl drop of 1N NaOH becomes detached from the capillary tip and bridges the platinum electrodes, the conductivity increase energizes R, and deactivates R,. R,, in turn, inhibits the conductivity detector and stops the digital timer. Drop detachment times are held on the timer until the timer is reset. Power requirements for the timer and the conductivity detector are provided by the regulated power supply shown in Figure 5 . The circuit uses the Fairchild pA723C integrated circuit regulator. A 30-volt variation in ac line voltage produced a maximum variance of only 0.029 V in the regulated output voltage. The excellent regulation provided by the pA723C regulator thus should compensate for any ac line fluctuationsand assure good reproducibility. A 1.0-ml Hamilton Gas-Tight Syringe (No. 1001 LT) with a Teflon-coated plunger and tip is used with the automated CVDT apparatus. Syringes of larger capacity (2.5, 5.0, and 10.0 ml) were also considered for use with the test, for these would offer the advantage of requiring less frequent filling.
However, the repeatability of drop size (nominal volume = 80 p l ) was appreciably poorer with the larger volume syringes. Reagents. The 1.ON sodium hydroxide solution is prepared fresh, as required, in a 100-ml volumetric flask with reagent grade sodium hydroxide and distilled water. Solutions of lower normality (0.1N and 0.5N NaOH) fail to produce the response required for detection of surfactants in the low ppm range. The use of plastic containers or containers with plastic caps should be avoided. Surface-active agents (e.g., plasticizers) are leached from plastics in contact with the caustic solution. Procedure. The Constant-Volume Drop Time apparatus must be installed and operated in a location free of air currents and vibration. The 1.0-ml syringe is cleaned thoroughly with distilled water and acetone, followed again by distilled water in this exact sequence and is then filled, after several rinsings, with 1.ON sodium hydroxide solution. The stainless steel capillary (0,054-inch i.d., 0.072-inch 0.d. with a squared, polished tip) is also cleaned with distilled watei, acetone, and distilled water before attachment to the syringe. Approximately 40 ml of the aviation turbine fuel sample is poured into a 5 0 4 beaker which is cleaned witb distilled water and acetone, and air-dried immediately preceding its use. The conductivity detector is immersed in the sample, and leads from the control box are connected to the conductivity detector terminals. The capillary is immersed in the fuel sample to a depth such that the tip is 10 mm below the meniscus. The capillary tip also should be no closer than 10 mm from the platinum electrodes. Drops delivered to the capillary tip are timed. A total of 10 drop time measurements can be made with the contents of the 1.0-ml syringe. The turbine fuel sample is agitated after each drop time measurement to minimize the possibility of localized depletion of surfactant in the proximity of the capillary tip. The following drop is not formed for 30 seconds after agitation to ensure that the sample has again reached a quiescent state. ANALYTICAL CHEMISTRY, VOL. 43. NO. 4, APRIL 1971
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Table I. Precision of CVDT Measurements Average Rel. drop Std std time,a dev, dev, sec sec 6 h0.48 8.0 11 10.73 6.6 40 14.2 10.5 51 zk5.1 10.0 198 +21 10.6 +27 9.4 287 300 1 28 9.3 1080 &113 10.5 Mean = 9.4 Based on 10 drop time determinations on each sample.
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RESULTS AND DISCUSSION Figure 6 illustrates the effect of surfactant concentration on interfacial tension and on drop detachment time. Since surfactants in levels as low as 1 ppm have a very deleterious effect on fuel quality, it is readily apparent from this plot that
the interfacial tension method lacks the sensitivity for differentiation between high quality and unsatisfactory turbine fuel. The drop time data, on the other hand, demonstrate that the CVDT method fulfills this requirement. Precision data for CVDT measurements are presented in Table I. These results are based on 10 successive measurements of drop time made on each of a series of turbine fuel samples into which dodecyl benzene sulfonic acid had been incorporated over a concentration range of 0-10 parts per million. Relative standard deviations average 9.4 over the range of 10-1100 seconds. Aviation turbine fuel samples to which naphthenic acids were added yielded precision data which were in very close agreement with these results. ACKNOWLEDGMENT The authors acknowledge the assistance of D. W. Williams of this laboratory who constructed the conductivity detector cell. RECEIVED for review July 27, 1970. Accepted November 30, 1970.
Rapid Separation of Berkelium from Rare Earth Fission Products and Trivalent Actinides R. F. Overman Sacannah River Laboratory, E . I . du Pont de Nemours and Company, Aiken, S. C. 29801
NUMEROUS METHODS for the analytical separation of berkelium from other actinides and lanthanides have been given in the literature. The adaptation by Farrar, Cooper, and Moore ( I ) of the classic isobutyrate cation exchange method of Choppin, Harvey, and Thompson (2) is rapid and gives good separations, but requires rather elaborate equipment and very close control to achieve good separation of berkelium from californium and curium. Moore and Jurriaanse (3) have published a procedure that can be used for separating berkelium from curium by liquid-liquid column extraction with di(2ethylhexy1)orthophosphoric acid (HDEHP) coated on Teflon (Du Pont) powder as the stationary phase. This method does not give good separation of berkelium from californium and europium, because the distribution coefficients are similar. Additional data on HDEHP distribution coefficients have been provided by Horwitz and coworkers ( 4 ) . Peppard (5) has reported an extraction of Bk(1V) into HDEHP. A method for the separation of berkelium and cerium by anion exchange was published by Moore (6). The method described here combines the anion exchange NaBrOa from separation of Bk(1V) in 8M "O3-0.2M (1) L. G. Farrar, J. H. Cooper, and F. L. Moore, ANAL.CHEM., 40,
1602(1968). (2) G. R. Choppin, B. G. Harvey, and S. G. Thompson, J. Znorg. Nucl. Chem. 2,66 (1956). (3) F. L. Moore and A. Jurriaanse, ANAL.CHEM., 39,733 (1967). (4) E. P. Horwitz, C. A. A. Bloomquist, D. J. Henderson, and D. E. Nelson, J. Itzorg. Nucl. Chem., 31, 3255 (1969). (5) D. F. Peppard, S. W. Moline, and G . W. Mason, ibid., 4, 344 (1957). (6) F. L. Moore, ANAL.CHEM.,39, 1874 (1967). 600
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Ce(1V) with the extraction of Bk(1V) on an HDEHP column. After all of the nuclides with a I11 valence are eluted from the HDEHP column, the Bk(1V) is reduced and eluted with 4 M H N 0 3 . The berkelium is sufficiently decontaminated from other actinides to permit radioassay of Z49Bk by beta counting. The method has been successfully applied to solutions originally containing activities of lO8(244Cm), 107(144Ce), and 105(lj4Eu)times that of 249Bkactivity, and is readily performed in contained facilities with relatively simple equipment and reagents. EXPERIMENTAL Equipment. A glass tube, 5 mm inside diameter and 90 mm long, was drawn to a tip at one end and was fastened to a glass reservoir, 10 mm in diameter and 80 mm long, at the other end. Glass wool was placed in the bottom of the tube. The appropriate filler was added to the tube with a medicine dropper in the form of a slurry in 8 M H N 0 3 . Anion Exchange. REAGENTS.The 8M "O3-0.2M NaB r 0 3 solution was made fresh daily from analytical grade reagents. Dowex 1-X4 (100-200 mesh) was obtained as analytical grade. PROCEDURE. After the glass tube was filled with resin, about 5 ml of a solution of 8M HN03-0.2M NaBr03 was passed through the column immediately prior to adding the sample solution. To prepare the sample solution, the sample was added to about 10 ml of 8M "O3-0.2M NaBr03, and allowed to stand for 20-30 minutes to ensure complete oxidation of the Ce(II1) and Bk(II1). The sample was introduced into the column and eluted with 3 to 5 ml of 8M "Os0.2M NaBr03 solution. The nitrate-complexed Ce(1V) remained on the column, and the Bk(IV), Eu, Cm, Cf, and
