Highly Accurate Continuous Recording Differential Refractometer F. A. VANDENHEUVEL' and J. C. SlPOS Fisheries Research Board o f Canada, Technological Station, Halifax, Nova Scotia, Canada
'
b A recording differential refractometer capable of 0.570 accuracy in measuring 1 X loe4 An difference in the refractive index of flowing solutions is described. Full scale deAn flection is obtained for l X a t 60y0 amplifier output with a noise level of f 5 X lo-' An. The potential range is 0.05 An. The cell compartments hold only 50 PI. The apparatus is sturdily built, and well protected against vibraiion and shock. Devices used for noise and stability control are described and discussed. Performance data are given. The apparatus is well suited to the continuous analysis and monitoring of chromatographic elulion, and should b e particularly helpful in extending the range of practical application for this technique.
A
LTHOUGH
GAS
CHROXATOGRAPHY
frequently is preferred to elution chromatography as a working tool, in many cases the latter is still the analytical and preparative method of choice. This is true, for example, when mixtures of heat-sensitive and/or high molecular weight compounds are involved. The use of refractometry as a complementary technique to this method was initiated by Tiselius and Claesson in 1942 (16). It resulted in the development of various types of automatically-recording apparatus, most of which are based on differential refractometry (1-17'). Elution chromatography is greatly assisted by these instruments which eliminate the timeconsuming eluate analysis. Unfortunately, their application is restricted by a practical sensitivity limit which, in general, is determined by noise level and instability rather than by actual lack of sensitivity. Thus none of the apparatus proposed hitherto, as judged from published performance data, is able t o measure a difference of refractive index in flowing liquids of one unit of the fourth decimal place with an accuracy better than 10%. Yet in many cases, the total change in refractivity a t the peak concentration of 1 Present address, Animal Research Institute, Research Branch, Department of Agriculture, Ottawa, Ontario, Canada.
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ANALYTICAL CHEMISTRY
bands appearing in chromatographic eluate does not exceed 3 X 10-6An for major components, and 5 X 10-6An for minor ones. This situation, which arises either from very low eluate concentration, or from the solute-solvent refractive index difference being small, will be met frequently under conditions favoring a good separation. An apparatus extending the range of usefulness of recording refractometry to such cases is, therefore, desirable. The following example \\-ill show the influence of noise upon apparatus performance. Consider, for instance, Figure 3 in a paper by Glenn et al. (8) ahere record d (50Oj, S ) shows spurious fluctuations from the ideal straight line equivalent to zk3.3 chart units. From the value of D given in Figure 4 of the same paper for the An equivalent of one chart unit, i e . , 3.4 X 10-6An a t 50% S , the value of the noise level can be deduced: it is 1.3.3 X 3.4 X 10-6An or h1.3 X 10-5~n. I n absolute value, this noise level will remain the same regardless of the refractivity difference being measured. On the measurement of 1 X lO-*An it will induce an uncertainty of 13%. A signal corresponding to 1 X 10-6An would be completely indiscernible from noise. Noise, as reflected by spurious deflections of the recorder pen is of various origins. That which is due to temperature differences between reference and unknown liquids can be partially overcome by the arrangement proposed by Glasser and Troy (7'). However, any arrangement of the analyzing cell which will increase its volume will lead to increased loss of definition in the chromatogram from eluate remixing effect. It is, therefore, imperative that the cell volume be kept as low as possible for the analysis of eluate from small laboratory columns. The arrangement proposed by Glasser and Troy derives its effectiveness from the fact that one of the solutions-the reference liquid-is kept stationary in a prismatic cell surrounded by flowing unknown. It is not nearly so effective when the technique of gradient elution is used. I n such case the continuous change in composition of the eluting solvent must be matched exactly in the reference solvent. The liquid in the
*
reference compartment cannot, therefore, remain stationary. The apparatus described below is well adapted to these techniques since both reference and unknown liquid cell compartments are of equal and very small volume (50 ~ 1 . ) . It also can be adapted to the analysis of much larger effluent output by the use of a simple sampling bypass. In spite of a very small cell aperture resulting from the reduced cell dimensions, this apparatus is capable of measuring 1 X 10-4An as a full-scale deflection. This was obtained by improving the early model proposed by Zaukelies and Frost (17): first, by using a more sensitive recorder and increasing illumination efficiency, and second, by increasing the distance between photocell cathodes and analyzing cell, and using a larger proportion of amplifier output. It was not necessary to use a complex split-beam compensating device to reduce noise level to 5 X lO-'An. This was accomplished as follows. NOISE CONTROL
Mechanical Noise. Displacement of parts induced by external vibrations or shock are ultimately reflected as noise component through changes in the position of the light beam. This is controlled by the sturdiness of the parts and their firm attachment t o a solid heavy base, which rests on foam rubber pads. The light source, a Monla lamp, features a very thick and tightly coiled filament connected to short sturdy supports. All connections to the apparatus are sufficiently flexible to dampen any vibration that may be transmitted through them. Optical Noise. At the same time variation in light intensity is controlled by decreasing to 5 volts the nominal 6 to 8 volts normally used with the lamp. Under such conditions the filament itself becomes a current-regulating device. I n addition, lamp life is considerably prolonged. Light intensity is controlled further by using as a source of current, a precision voltage stabilizer described below. Thermal Noise. Spurious refractive index changes of thermal origin
are prevented through the careful thermostatic control of analyzing cell temperature. Of particular importance are displacements of optical parts, resulting from mechanical distortion of apparatus components, under the influence of temperature changes. Such displacements are considerably amplified and reflected by erratic deflections of the light spot on the cathodes. To a large extent, thermostatic control of the analyzing cell assembly minimizes these effects in so far as the assembly is concerned. Thermostatic control of the lamp house is, however, just as important. The use of a low expansion heat coefficient cast iron base, and the absence of any other rigid connection between the three main parts of the apparatus, are further measures of thermal noise control. Housing the apparatus in a Fiberglas-padded box was also very helpful, provided an escape existed for excess heat from the lamp t o the outside of the box; or better, provided the lamp housing was closed by a thermostated metal lid. Careful control of the thermostated water supply is necessary. Control to =t1/5OO0 C. is obtained in the follon-ing manner. A 12-gallon glass tank is equipped with a toluene-expansion type regulator. The toluene reservoir, a coiled glass tube 150 em. in length and 12 mm. in diameter, is connected t o a mercury reservoir extending t o a capillary tube fitted Kith adjustable electrical contacts. This operates a sensitive electronic relay actuating a 100-watt immersion heater in series with a powerstat. Adjustable water cooling is also provided t o correspond to somewhat more than the heat (35 watts) removed from the apparatus. Careful balance of cooling and heat impulses induces smooth temperature control of the thermostated water which is sent to the apparatus by a centrifugal pump through heavily lagged tubing 1 inch in diameter. The latter extends along the whole length of the apparatus housing in the form of a manifold from which water is supplied to the various parts through individual rubber connections. Return to the bath is also effected through a similar manifold, both manifolds contributing to the control of temperature within the housing box. Electrical Noise. The use of high quality components in the circuits, the exclusive use of carefully filtered direct current, the excellent shielding of circuit components, the location of components in a dry atmosphere, the avoidance of the proximity of strong magnetic fields, and the filtering of the alternating current to the power supply, constitute the main measures of electrical noise control. Aside from the particular mounting of
the photocell, excellent insulation along the circuit leading to the amplifier from the photocell is necessary. Surface leakage is further reduced by application of Dow-Corning silicone dielectric compound Number 4 on and around all parts involved in this circuit. Particular attention is paid to proper grounding by selecting the most efficient ground connection available. The control measures described above have resulted in reducing the electrical noise well beyond the limit set for overall noise level, and have reduced the time required to reach equilibrium to less than 1 hour after both lamp and amplifier have been switched on. Electronic valve 5814 A, sturdiest and most reliable member of the 12ilU7 family, may have to be selected for this use. In the course of our work, one among several new tubes proved to be unsuitable although no fault could be detected by ordinary testing methods. Under the conditions of use, however, a satisfactory tube could be used almost indefinitely. Twin phototube 5584 proved t o be more efficient than the parent 920. Under the present favorable conditions (only 0.035 lumen per sq. cm.) it should last a considerable time. After several years of almost daily use, the only components needing replacement have been the dry cells, which, depending upon their quality, should be renewed every 6 to 12 months. Noise Induced by Flowing Liquids. It is necessary to protect liquids flowing to the analyzing cell against temperature changes. A difference of l/loooo C. is enough to produce a change in refractive index of the order of 4 x lO-'An equivalent to the upper limit set for noise level. Thus, not only must the narrow, preferably metal, ducts leading the liquids to the cell be made to pass through a simple tubular jacket where thermostated water is circulated, but as little temperature difference as possible should exist a t their point of origin because of the limitations of the system as a heat exchanger. Impurities such as dust and lint are easily removed by filtration. Bubbles are avoided by using liquids degassed by boiling and subsequently cooled in stoppered containers, and also by ensuring perfect tightness of all connections. Improved performance results from flow control, and the use of moderate flow rates. DESCRIPTION OF APPARATUS
The apparatus (Figure 1) consists of lamp housing A , photocell compartment B, analyzing cell assembly C, and amplifier H . The latter is connected to a IO-mv. full-scale Brown recorder and a 5-volt direct current regulated power supply not shown. Elements
A , B, C, and H , are firmly attached by screws to D, a thick slab of cast iron. The thermostated water circulation system described above completes the equipment. LamD Housing. A. Inner housing 1, entikly surro;nded by jacket 2, i'; 0.025 inch wider than bulb 3 (Leitz Universal Monla bulb) which is screwed tightly in threaded Teflon receptable 4. The latter is held in the collar of lamp 5 by three setscrews of which one, 6, is shown. Lamp holder 5 is fitting exactly in housing 1 and is held in position by a setscrew passing through base D as shown. The end of this screw fits in a vertical groove (not shown) in the side of lamp holder 5. Thus only vertical movement is allowed to the lamp holder when the setscrew is loosened. Jacket 2 is connected to a source of thermostated ~ a t e through r inlet 7 and outlet 8. Centered on the optical axis of the apparatus and passing through the jacket is a cylindrical opening in which collimator lens holder 9 fits snugly. Details of 9 are given in Figure 2. Photocell Compartment B. Figure 1, center, shows a top view of B with top panel and photocell arrangement removed. Below is shown a vertical section through B. Photocell compartment B consists of an airtight box, obtained by assembling several panels fastened by screws to fixed front bracket 10 and base plate 11. The front bracket is fitted with flanged window 12 sealed by plane glass 13. The '/d-inch thick base plate bears photocell carriage 15, a 1/8-inch thick rectangular plate screwed to sliding undercarriage 16. One of the 45' slanted sides of 16 slides against the 45 undercut in the apex of bracket 10, the other 45" slanted side sliding against guide 17, which is screwed to 11 and is adjustable for optimum efficiency in sliding motion. Part of a standard micrometer, '/z to inch, is attached as shown in E to base plate 11. Alicrometer rod 18, reduced to inch diameter, engages into 3/ls-inch diameter hole 14, drilled part way through the middle of undercarriage 15. A a/16-inch diameter steel ball 19 is lodged a t the bottom of this hole to ensure smooth contact with the micrometer rod end. I n F , shoning a back view of the under carriage, are seen the openings of two holes 20 drilled part way through and on each side of the undercarriage. Each contains a tube 21, closed a t one end. In both tubes is lodged a coiled spring pressing against the bottom of holes 20 and against the closed bottom of tubes 21 which are themselves leaning against the back panel of the compartment. A continuous pressure is thereby exerted upon the undercarriage, and backlash is eliminated. I n the middle of carriage 15 is screwed collar 22 over which photocell shield 23 fits tightly. The latter, a cylinder opened a t the base and covered by lid 24, contains photocell 25. The cell is made to fit the shield tightly by winding a few turns of very thin Teflon tape O
VOL. 33,
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FEBRUARY 1961
287
around the cell, above and below the electrode area. No socket is used, and the lead wires, which are soldered directly to the photocell prongs, are led out of the shield through three '/?-inch diameter Teflon disks wedged in holes drilled through the lower end of the 26, shield. Rectangular opening
t i l
centered on the optical axis allows the light beam to reach the cathodes. Three 30-volt hearing aid dry cells 27, part of the photocell circuit, are pinched between the sides of holder 28 which is screwed to the carriage. Completing the photocell compartment is drying agent holder 29, consisting of tube 30
with one open threaded end screwed over the threaded collar of a flange fastened to the top left corner of the panel. Tube 30 contains a gauze cartridge filled with silica gel. Analyzing Cell Arrangement C. (See also front view G.) The cell block holder consists of two support-
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I 288
ANALYTICAL CHEMISTRY
1
Figure 2.
Horizontal section through lamp housing and analyzing cell arrangement showing details of optical system and cell
ing elements screwed to base D. Each consists of a strong ring 31, mounted on legs 32 welded to 1/2-inch thick base bar 33. The rings are split by a vertical saw cut leaving a gap l/a2 inch wide at the top and bottom. Tightening screws 34 brings the two halves of the rings together for a very firm hold on the thermostated cell block. The latter consists of tm.0 hollow halves 35 and 36, each of which is fitted with a water inlet 37 and outlet 38. Tightening of rings 31 will bring the two halves of the cell block together, thus forming a cylinder the inside diameter of which is exactly that of the analyzing cell. The latter is positioned in the middle by two threaded knobs 39 fitting in the threaded ends of the cell block. For further details see Figure 2. 4 Figure 1 .
Diagram of apparatus
Top right, optical system Top left, circuits of amplifier and photocell Middle right, top view of apparatus Middle left, front view of analyzing cell arrangement Bottom right, vertical section through apparatus Bottom left, amplifier
Amplifier H. (Also see circuit diagram top left of Figure l.) The amplifier is housed in a completely airtight box immediately following the photocell compartment and connected to the latter by a Jones plug and receptacle (P-2404-SBJ S-2404-SB) arrangement (on diagram K1, K2). The vacuum tube is surrounded by thermostated water jacket 41 fastened to the top panel of the amplifier by flange 42 fitted with 0 ring 43. Drying agent holder 44 is screwed to the front panel by flange 45 fitted with 0 ring 46. The 1-inch diameter gauze tube (not shown), containing silica gel, fits over a collar on the inside face of the flange. The amplifier circuit and photocell circuit parts are given below. R1 = R2 = 20megohm; R3 = 20 kiloohm; R4 = 50 kiloohm; R5 = 9 kiloohm; R6 = 400 kiloohm; R7 = 100 kiloohm. All are precision metal film Nobleloy resistors (Bayly Engineering, Ajax, Ontario) type KR-25, 1 W, tolerance 1%. CI, 0.1 pf; C2, 0.01 pf., high quality condensers. P1, P2, high quality rotary decade stud switch KO. D-904-B/4 (Nuirhead Instruments Ltd.). P1, sensitivity control, 10 X 400
ohms; P2, coarse zero adjust, 10 X 500 ohms; P3, fine zero adjust., 1 kiloohm, 10-turn Helipot, A series fitted with counter. K3, Amphenol 91-lIC3AI and 91PC3F connected to recorder by Belden No. 8422 two-conductor microphone cable. E l , 3 X 30-volt hearing aid cells. E2, 90-volt dry cell. R1, R2, and E, are housed in 13. Constant Voltage Power Supply. The current for the filaments of both amplifier tube and RIonla lamp is 5-volt direct current obtained from a precision, + O . O 1 ~ o regulation, voltage stabilizer. ( S o . 80710, Xylab, Xew York). Optical System. .I diagram of this system is shown at the top right of Figure 1. For clarity, the scale of the vertical dimensions has been made ten times that of the horizontal ones. Filament T of the Monla lamp is approximately 2.5 mm. wide and 2 mm. high, Collimator lens L1, a planoconvex achromatic lens of 15-mni. focal length, projects a slightly enlarged image (3.4 mm. diagonal) of this filament on the plane face of plano-convex achromatic lens L2. The latter (focal length, 32 mm.) is also the front window of analyzing cell S (cell diameter 4 VOL. 33, NO. 2, FEBRUARY 1961
289
mm.). The diagram shows a geometrical construction of the filament image (dotted lines). On the other hand, lens L2 is focused on square diaphragm V (1.78 X 1.78 mm.) located against the plane face of lens L1. The diagram shows the construction of MINI, the 18-mm. image of MN, which is the 2 . 5 mm. diagonal of diaphragm V. An image, (0.5 X 0.5 inch), of the diaphragm is being projected on the cathodes. It is immediately apparent from the diagram that no light is intercepted by the cell. Diaphragm V is both the field stop and limiting aperture of the system. The arrangement is similar to the Kohler illumination used in photomicrography for the purpose of increasing illumination efficiency. At the same time it produces a sharp, square light spot on the cathodes, a desirable feature from the point of view of linearity of response, and results in a very compact arrangement of optical parts ahead of the analyzing cell. Details of this arrangement are shown in Figure 2. Diaphragm 1 is made of four straight edged strim of metal foil cemented one b y o n e on' a thin ('/sp-inch) metal disk which has a l/s-inch hole in its center. The diaphragm is cemented on threaded mount 3. Cementing operations are conducted under a traveling microscope for accuracy in dimensions and centering. The diaphragm is brought in contact with plane face of lens L1 cemented in mount 4. Mount 5, holding the lens-diaphragm assembly, is held in position in lens holder 6 by threaded set ring 7. Heat absorbing glass disk 8 protects the assembly which furthermore, is surrounded by thermostated water jacket 9 of lamp house 10. Positioning of tightly fitting holder 6 is effected by manipulation of flange 11. Both this operation and thermal contact are helped by lubrication. The analyzing cell consists of two truncated cylindrical halves, 12 and 13, identical in size. When pressed together in thermostated cell block 14 by threaded knobs 15 and 16, the two halves join by their 45"-slanted faces. Note that a vertical shallow groove (not shown) in the middle of both top and bottom jaws of thermostated cell block 14 leaves space for l/le-diameter stainless steel solution inlet and outlet tubes 17 cemented in the cell walls. Solution compartment 18 is fitted with cemented lens L2 while the solvent compartment is fitted with cemented 1-mm. thick plane glass 19. Both compartments have been fitted with inside windows 20, 21. These are made of square sections of microscope cover glass cemented to the 45O-slanted face in a 8/1000-inch deep square depression machined around the center. Care is taken in cementing all part: with epoxy resin cement curing a t 90 C., to prevent excess cement from invading the lumen of the cell channel. In cementing 20 and 21 the cover glasses are brought level with the plane of the metal faces by pressing gently against a plane surface before curing. Mounting the assembly is accomplished by first 290
ANALYTICAL CHEMISTRY
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7
Figure 3. Record obtained at 60% output (S = 6),lamp on, showing extent of noise and total pen deflection for 1 /lOOO-inch movement of photocell
heating the two half-cells, and all other parts such as cell blocks, knobs, and holders, in an oven a t 110' C. Then a small drop of molten Canada balsam is placed in the center of one of the cover glasses, and the two half-cells are pressed together, avoiding any air bubbles between the glasses. All parts are then assembled while hot. The completed assembly is left to cool to room temperature before it is mounted on the apparatus base. All inside surfaces except the cell walls, are painted with black optical finish.
Thus, r
0.01584
= -~ 156 = 1.01
x
10-4 A%
Reversing the positions of the two solutions obtained a displacement in the other direction corresponding to 0.150 inch, indicating a nonlinearity of response over a 0.0300An range of only 2%. Full advantage of the total range, which is about 5 X 10-2An, could be taken by replacing the 400-ohm resistor in the first step of the sensitivity control by a 400-ohm Helipot potentiometer. PERFORMANCE DATA The number of chart units U S corresponding to 1 x 10-4An, or one 10+ From the simple theory of this type inch displacement of the photocell, of instrument (8), the change in reconstitutes an important value t o be fractive index corresponding to l/l~ooredetermined from time to time since inch lateral movement of the photoit slowly decreases with aging of the cell is expressed by dry cells. The most convenient way is 10-8 A~ to determine the number of chart units r =tga--(1) D inch a corresponding to a 5 X movement of the photocell when the where cy is the boundary angle of the sensitivity is set a t lOyo (S = 1). analyzing cell compartments and D If S is the position number on senthe distance in inches between this sitivity decade P1, boundary and the photocell cathodes along the optical axis. V S = aS/5 (3 1 I n our case a = 45O, D = 10. ThereThen, fore, t =
1 X lO-'An
(2)
(4)
A difference in refractive index of one unit of the fourth decimal place corresponds, therefore, to 1 X 10-3 inch displacement of the photocell carriage. Measurement of T was made by filling the cell compartments with aqueous ethyl alcohol solutions of known refractive indices determined with a precision Abbe refractometer. As an example, two solutions A(ng = 1.34518) and B ( n g = 1.36104) differing by An = 0.01584 caused, when placed in the solvent and solution compartments, respectively, a deflection of the recorder pen corresponding to 0.156 inch. This was the distance the carriage had to be moved to bring back the recorder pen to a position obtained when both compartments contained solution A .
represents the change in refractivity corresponding to full-scale deflection a t a given sensitivity setting S. With a = 83, and S = 6, F s = 1 X 10-4~n The An value corresponding to any deflection of the recorder pen observed a t sensitivity S is calculated from the corresponding number of chart divisions and the value Fs. The relative error on F s is about 2oj, when obtained from a single value of a. With an average a value obtained through repeated determinations, the error is naturally decreased in proportion to the number of values involved. Figure 3 shows the recording obtained a t sensitivity position 6 (6OY0 output)
chromatogram in Figure 4 (no = 1.36055; 125 = 1.4292; A = 1.13; F~ = 1.5 x 10-4; j = 200 x 108 fil.), Equation 5 yields us = 24.8 pl. (25 theoretical) ACKNOWLEDGMENT
The authors are indebted t o Russell E. Heffler, Physics Department, Dalhousie University, Halifax, Nova Scotia, Canada, for building important parts of the instrument. LITERATURE CITED
c
c
Figure 4.
c
Chromatogram record
Obtained from reversed phase partition chromatography of mixture of methyl laurate and methyl myristate showing peak deflection corresponding to less than 5 X 1 O-6An for these major components
by moving the photocell 1 X inch after adjusting the pen position to the zero mark. the same solvent flowing through both compartments of the cell. The noise level is reflected by deviations ( i 5 X lO+An) from a straight horizontal course indicative of high stability. The micrometer was used in this instance to set approximately a deflection of l X 10-4An. I t s normal use is in calibrating the instrument. When the latter is used in analyzing effluent from a chromatographic column, recalibration is required once before each complete operation and only Then the highest accuracy is desired. A typical example of the use of the instrument in reversed phase chromatography is given in Figure 4 showing the chromatogram obtained a t S = 4 from a 50y0mixture (by volume) of methyl laurate and methyl myristate.
Fifty microliters of this mixture were placed on a silicone-coated, 100- to 200-mesh crushed firebrick column moistened with iso-octane. Develop ment with 82% (v./v.) iso-octane equilibrated aqueous ethyl alcohol a t a rate of 300 ml. per hour resulted in complete separation. When the solute involved is a liquid of known refractive index, the volume us of this liquid dissolved in a chromatographic band is given by (5)
Where A is the area under the curve in square inches, F E the quantity defined in Equation 4,f the rate of flow per hour, n g the refractive index of the solute, and no, that of the solvent. Recorder chart speed: 2 inches per hour. Applied to the first band in the
(1) Ashman, L. E., Schwartz, W. S., Jones, H. E., ANAL. CHEM.24, 191 (1952). (2) Barnes Engineering Co., Stanford, Conn., Model Re. -46. (3) Claesson, S., Ann. N . Y . Acad. Sci. ’ 49,183 (1948). (4) Claesson, S., Arkiv Kemi Mineral. Geol. 23A, No. 1 (1946). (5) Evans, C. D., Ferguson, hl. J., Hilger J . 5, No. 4, 51 (1959). (6) Forrest, J. W., Ytraat, H. W., Shurkus, A. A,. Control Enq. 2, No. 11, 103 (1955)’. (7) Glasser, L. G., Troy, D. J., Ind. Eng. Chem. 50, 1149 (1958). (8) Glenn, R. A., Wolfarth, J. S., DeWalt, C. W., Jr., AXAL. CHEM.24, 1138 (1952): (9) Hagdahl, L., Holman, R. T., J . Am. Chem. SOC.72, 701 (1950). (10) Hiird. C . D.. Thomas, G. R.,’ Frost, ---A. A,, 16’id:, 72,3733 (1950). (11) Jones, H. E., Ashman, L. E., Stahly, E. E., AXAL.CHEBI. 21,1470 (1949). (12) Keaeles, G., J . Am. Chem. Sac. 69, ’ 1302 (3947). . (13) Miller, E. C., Crawford, F. LT-., Simmons, B. J., AXAL.CHEM.24, 1087 (1952). (14) Muller, R. H., Frachtman, H. E., Intern. Conqr. Pure and Appl. Chem. p. 33 (1951): (15) Thomas, G. R., O’Konski, C. T., Hurd, C. D., ANAL. CHEM.22, 1221 (1950). (16) Tiselius, .4.,Claesson, S., Arkiu Kemi Mineral. Geo2. 15B, No. 18, 1 (1942). (17) Zaukelies, D., Frost, A. A., ANAL. CHEW2 1,743 (1949). ’
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RECEIVED for review July 5, 1960. Accepted September 23, 1960.
Method for Determining Total Hydrocarbons Dissolved in Water A. H. WEHE’ and J. J. McKETTA Department of Chemical Engineering, University o f Texas, Austin, Tex.
b There is no rapid accurate method for the determination of the amount of hydrocarbons dissolved in water. A method is discussed which can b e applied to the measuremenf of a gas dissolved in water. The results are
within &s% of the true value which is considered satisfactory for these low concentrations. The method may be applied to any gas dissolved in water,
I
N A STUDY of
phase equilibrium in the n-butane-1-butene-water system a t
1 Present address, Esso Research & Engineering, Baton Rouge, La.
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