1431
V O L U M E 22, NO. 11, N O V E M B E R 1 9 5 0 Sensitivity. It is impossible to predict the effect that will be produced on a colorimetric reaction by a change in composition of the solution medium. There is an effect on the colorimetric response of phenolic material when oil is a constituent,part of the color system. Consequently, the sensitivity values listed in Table I have little significance except in an essentially aqueous
somewhat better; deviation of a single determination from the mean seldom exceeds *3%. SUMMARY
An earlier version of the phosphomolybdic acid method waa based on extraction of phenols from mineral oils with 95% ethyl alcohol. This procedure consumes considerable time in multiple extraction, centrifuging, and separation of the alcoholic extracts. Moreover, it is mandatory that the extraction be carried out in a precise manner, as the success of the determination is contingent on this step of the procedure. Consequently, the analysis is tedious and exacting to perform, and the resulting data are frequently in doubt. With the proposed procedure of simultaneous extraction and color development, complete solution of the reagent with the oil is effected, and the composition of the ammonium hydroxide solution assures an adequate concentration of ammonia in both the oil and nonoil layers for development of the molybdenum blue complex. And because the colored component is practically insoluble in oil, simplicity, sensitivity, and accuracy are achieved simultaneously. ACKNOWLEDGMENT
The authors wish to thank H. A. Ambrose for his encouragement and assistance, and especially his aid in making the presentation of this paper possible.
30
LITERATURE CITED
solvent. These values can, however, be related to the lowest practical working limit of the phosphomolybdic acid procedure if they are expressed as a concentration in terms of milligrams of phenol per milliliter of oil. While the order of magnitude of these figures is somewhat greater than for other tests that might be employed, no difficulty has been experienced because of the lack of sensitivity. Accuracy. The reliability and preoision of the method are typified by the data in Table 11. Analyses performed periodically for the purpose of checking the technique of new operators or ev.aluating the performance of different stock bases show a mean average error of +5%. The reproducibility of results is
(1) Chapin, R.M., J.Znd. Eng. C h m . , 12,771 (1920). (2) Clausen, D. F., and Shroyer, J. H., ANAL. CHEM.,20, 926 (1948). (3) Feigl, F.,“Qualitative Analysis by Spot Tests,’: .3rd ed.. New York. Elsevier Publishing Co.. 1946. Biol. Chem., 22,305 (1915). (4) Folin, O., and Denis, W . , (5) Gibba, H.D.,Zbid., 72,649(1927). (6) Graham, J. J. T., J. Assac. Ofic. Agr. C‘hernisto, 14,132 (1931). (7) Houghton, G. V., and Pelly, R. G., Analyst, 62,117 (1937). (8) Koks, M. T., Phamn. V e e k b l a d , 68,557(1931). (9)Lykken, L.,Treseder, R. S., and Zahn, V., IND.ENG.CHEM., ANAL.ED.,18, 103 (1946). (10) Miller, J. N.,and Urbain, 0. M., Zbid., 2,123 (1930). (11) Platkovskaya, V. M.,and Vatkina, S. G., J . Applied C h m . (U.S.S.R.), 10,202 (1937). (12) Snyder, R.E., and Clark, R. O., unpublished report. (13) Stoughton, W.R.,J . B i d . Chem., 115,293 (1936). RECEIVBD March 9, 1949. A portion of this paper was presented before a joint meeting of the Divisions of Analytical and Micro’Chemistry and Petroleum Chemistry, Symposium on Microchemistry and the Petroleum CHEMICAL SOCIETY, 8an Industry, at the 115th Meeting of the AMERICAN Francisco. Calif.
Seagoing Photoelectric Colorimeter WM. L. FORD’, Woods Hole Oceanographic Institution, Woods Hole, Mass.
P
HOTOELECTRIC colorimeters have come to be widely accepted in analytical work because of their objectivity and speed. However, most existing instruments are adversely affected by the vibration, motion, and high humidity of work a t sea. A successful seagoing colorimeter must be unaffected by these conditions. It must, furthermore, have greater sensitivity than visual comparative methods and a large range to accommodate wide differences of color intensity, such as are encountered between the determinations of phosphate phosphorus and nitrate nitrogen in sea water. These requirements have been met in the colorimeter herein described For convenience the instrument has been named the electric eye photometer. I Present address. Naval Research Establlshment, H.M.C.S. Stadacona, Halifax, N o \ a Scotia, Canada.
An electric eye tube (electron-ray tube) which is unaffected by vibration and rolling is used in place of the.conventiona1 galvanometer to provide an indication of the balance point. Absorption cell lengths up to a maximum of 26 cm. may be used, thus permitting determinations over an unusually wide range of concentrations. In general, accuracy is limited by the analytical method rather than by the instrument. The sensitivity is about 0.5% of the scale range. The principle employed consists of balancing a beam of light which has been partially absorbed in passing through the colored solution against a second beam which is sent through an adjustable aperture. Each beam impinges on a phototube, the pair of which activate an electron-ray t t b e to provide an indication of balance. The balance point is attained by adjustment of the
ANALYTICAL CHEMISTRY
1432
A photoelectric colorimeter is described which has operated the past two years at seaunder conditionsofvibration, motib ity. Absorption eel1 lengths up to 26 em. are employed to aceommodate the wide variations of color intensity. enmuntered in ehemieal determinations of sea water. The sensitivity is about 0.5% of the seale range and the a-raey is in general determined by the analytical method rather than the instrument.
-._..- --.-
The color filter unit uses twofilters, each 2 X 2 inches ( 5 x 5 cm.), which do not require careful matching. The aperture and scde mechanism is shown in Figure 3. Light which passes through the left aperture is partially absorbed by t h e solution in the tuhe a b o v e , t h e remainder impinging on a phototuhe a t the top. Light w h i c h passes through the lagarithmir aperture on the right t r a v e l s through a Lurite rad directly to II second phototuhe a t the top. The a m o u n t of light passing the logarithmic aperture is adjusted by means of t,he v e r n i e r -
n
variable aperture, the position of which gives a measure of the light ahsorbed and hence of the eoneent,rstion of the solution. Because light ahmrption by a colored solution is usually governed by Beers' law, a logarithmic aperture is employed in order that the scale readines will hear a linear relationship to concentration. ECXANICAL DESIGN
conveniently described under the opucai-mecnanieal components and electrical component,s. The optical-mechanical part of the colorimeter consists of the following basic units: a source of collimated uniform light, B color filter unit, an aperture and scale-mechanism for measuring the relative amount of light being absorbed (the extinction coefficient), an absorption cell, and a phototuhe assembly. Figures 1 and 2 illustrate the relation of these components t.o one another neaaings
01
The reading of the vernier then ia n c. B. L ~ filters ~ ~ , measure ~ of the light, d. I,. Mircor a b s o r b e d by the solution, and thcrrfore t h e c o n c e i i trativn of thc suhstitnce under investigation. , . . The logarithmic apcrturc is made photographically. A largescale securately made drawing of the aperture is photogrwhed nnrl nofiit,ives of the desired sisc are nroduced on B Ianturn slidr. a.
No. 926 phototuher
e.
b.
Absorption cell Lucite md Vocnicr sos10
I.
Awclurc meohanism
Rlind
K;d& opaque, taking cart not tb overlap the edge of the ape?l.ure. The slide is cut to fit, a r e c e ~ in s tho hase plstc of the apert.uw merhmiam. If t,he lrelntin surface herames scratched or
Figure 1.
Seagoing I'hotoeleetric (:olorimeter
Piungcr Absorption dl C. Lucife md I). Spring d i p E . Aperture and SEUIF mechanism .A. H.
Mirmr G . light filters and holder if. Eleotron ray tube (elecrcie 8'.
I. J.
we)
Dark balance eonlrol Liehf source (rear)
The light system contains no prisms or lenses, ye1 provides a light h a m which is adcquztely collimated and of uniform intensity.
As show, in Figure 2, t,he light. from a 1 W w a t t projection hulh locat,ed at. t.he center of curvtLt.ure of B semicylindrical Hat-nhite surfnre iu reHeeted through a hlaek tunnel to t h e color filters and thence is directed by a mirror through the aperture mechanism to t.he xbsorpt,ion cell. Direct light from the hulh is prevented from reaching the ahsorpt,ion cell 11sit blind.
the liquid surface :LIICTRICA L COMPONENTS
.
..
tm used for the colorimeter is givenjn Figure 4,
. .
.
ions to he met: 1. The equipment u m t.o be operat,ed at sea with inhererlt rihrat.ion and movement, of i~ ship, which dictated the use of . ~ indicator n unaffected hg motion. 2. Camrmnents would have to withst.and high humidity and salt-carrying air. 3. The equipment had to be unaffected by line voltage variatmns in the order of 10 to 20%. To satisfy the first condition, an electron-ray tuhe u-as chosen as being most adaptable. This tuhe is capaI)Ie of showing
V O L U M E 22, NO. 11, N O V E M B E R 1 9 S O
1433
voltage changes (hence light unbalance) in the order of a few millivolts by utilizing a ray of electrons striking B target situated within the glass envelope. The angle of shadow provides a balance indicator using no moving parts and hence is unaffected by vibration and rolling. The second factor (the most troublesome) was overcome by the use of well constructed and sealed parts, careful placement of parts, and spraying the wiring and componmts with 8 fungusand moisturepraofing compound such as General Electric Company Glyptal No. 1202 gray. The third condition was solved by the use of voltageregulating glow tubes which place B fixed voltage on the sensitive circuit elements. Tests indicate that supply voltages varying from 105 to 130 volts produce no appreciable errors in the operation of the instrument. No. ,926 phototubes are used because of their satisfactory response to the visible light spectrum. The pair of phototubes must he selected so that they will have similar cathode emission characteristics. The Type 38 tube should have low grid current characteristics. The elect.ronic assembly is divided in two convenient partsa phototube head mounted on top of the optical-mechanical asneml,ly (see Figure I ) and a power unit nhich also contains the deetron-my tub?.
T a b l e 1. Calibration Phosphate Phosphorus (Usins 9-om. absorption cell and red filter u,ith transmittance Dealt at 645
conen. Of P, (~p Atom Distilled water Blank 1 0.50 0.75 1.00 1.50 2.00 2.50 Blank 2
Distilled water
Deviation front ,Me&n,
Direct Reading
R'
Fb
%
470 478 558 595 622 686 772 856 480 470
79 116 143 207 293 378
0.00633 0.00646 0.00700 (0.04725) 0.00684 O.OOC65
5.0 3.0 0.6
MW."
(8.9) 2.7 0.2
0.oocI66
(omitting 1.50)
Corrected reading, direct reading minus average reading for blanka. b Faecor for converting R to conon. oi phnaphmus.
OPERATION OP INSTRUMEI
...
The power unit Is turned on some 10 mir.=.-.., LY.Y...I attain warm-up stability. With the light source off and the door' of the colorimeter closed tiehtlv so that no lieht. reaches t,ha .~~. phototubes, tbn adjustment &llid the "dark balance" is made by adjusting the control, I in Figure 1 (Z%kv.-ohm potentiometer in Figure 3), to obtain an arbitrary balance of the phototubes, indicated bv a narrow slit on the electron-ray tube. In the next step a reading with distilled water is obtained. The appropriate light filters for the ~
yy
~
~~
~
Figure 3.
Aperture and Scale \Ieehanisrn
I
~
~~~~~~~~~
PHOTO H E A D
from time to time a t h n e Or two concentratio&
I
POWER S U P P L Y - I N D I C A T O R
Figure 4.
~
and the light source is turned on. The vernie; is adjustid until the electrun-ray tube ret,urns to the Same narrow slit obtained in the dark balance, and the reading is noted. The light is bhon turned off to cheek the dark balance reading, which should remain unchanged. From t,ime to time during a series of measurements the distilled water reading is repeated to determine the rresence or absence of drift in the halanee poi&. The third step is to run a reagent blank to measure the color originating from the reagents. This is usurtlly done both a t the beginning m d md of a serics of an+lyses. The procedure is identical to that in step 2. In the fourth &p, t,he unknown solut,ion t u which reagents have becn added is placed in t,he absorption ecll and a reading is obtained as described above. I n calibrating the inst,rument the same proce
S c h e m a t i c Circuit Diagram of Photoelectric Colorimeter
Because, in nearly all cases, the calibration curve is a straight line over a wide range, the concentration of the unknown is obtained directly by multiplying the corrected reading by a factor which is the reciprocal of the slope of the curve. The corrected reading is obtained by subtracting the value for the reagent h l w k from the direct reading. These operations me illustrated in Table I, which is a typical set of calibration data for the phosphate phosphorus determination. Certain precautions are to be observed. The outside of the absorption cell must he dry and clean, especially the bottom. Its orientation in the colorimet.er must always be the same, to avoid errors from inequality of light transmittance through the different parts of the bottom. It is essential that the level of solution in the cell he high enough to cover the end of the plunger, which must also be free of air bubbles that sometimes tend to collect.
~
1434
ANALYTICAL CHEMISTRY
8m
It has been indicated that any length of absorption cell up t o a m a x i m u m of 26 cm. may be used. I n practice, the three lengths, 26, 9, and 1.5 cm., have accommodated all analyses so far encountered. The 2 6 cm. cell is made from a Nessler tube of a b o u t 1-inch (2.5cm.)outside diameter cut to a length of 28 cm.; 26 cm. is the W length of the light E absorption path b e o c / / tween the bottom of 4 w the tube and the a p l u n g e r when t h e tube is in place. The tube need not have a n optically flat bottom (but must be oriented in the same way for all readings). The 9-cm. cell is also m a d e from a Neasler tube as described above, but I I I I 0 Figure 5. Photoelectric Colorimeter cut to an o v e r - a l l 3 6 9 12 9c1 length of about 11 cm. I I I I A . Front view 0 1 a. 9-Cm.abao tioncall. 10 20 30 40 50 1.5 When this cell is used, b. Supporting%eite rod IRON CONCENTRATION LIG -ATOMS/LITECR a sparer of Lucite B . Plan view showing colorimeter in position rod is fitted into thp for use with 1.5-cm. ebnorption cell Figure 6. Calibration Curves for Determination of c. 1.5-Cm.abaorption cell lower part of the leftd. Cell holder Reducible Iron in Sea Water h a n d c h a m b e r as e. Lucitc rod illustrated in Figure f . C l a ~ splunger 5, A . It conducts the light beam upThe data for the 26-cm. cell are the result of two runs 7 days ward to the 9-cm. cell located between the Lucite rod and apart. Beers’ law is obeyed up to a concentration of 3.5 microthe plunger. The rod has protective brass rings a t each end. The 1.5-cm. cell is square in crow section and 3 cm. high. gram-atoms per liter, but the usable range extends to 5.5 microWith the colorimeter in a horizontal position (see Figure 5, B ) , gram-atoms per liter. For the 9-cm. cell, results of three runs the 1.5cm. cell in a suitable holder is placed between the glass extending over 10 days are given. The curve is linear up to plunger and a Lucite rod which conducts the light beam from the aperture mechanism. Access to the 1.5cm. cell is through a small sliding hatch in the door of the colorimeter. The 3-cm. height of the cell provides sufficient depth of solution to avoid interference of the light path by the surface.
t
/
B
Color filters are used which have a narrow spectral band and a transmittance peak a t the same wave length as the absorption peak of the solution. For this purpose the so-called monochromatic filter glass combinations are useful. The importance of these considerations is seen in the case of the colorimetric determinations of phosphate in sea water. It has been pointed out by Harvey (1945) and others (1-3) that in this analysis a greenish tinge sometimes develops in what is normally a blue solution. If a color filter is used which has a narrow spectral band covering the absorption peak for the phosphomolybdic complex a t 645 mp, the danger of interference by other. absorption bands is greatly reduced.
0
E200 U w
a
-
SOME EXPERIMENTAL RESULTS ’ The instrument has been used on a routine bask a t sea for the colorimetric determination of the following constituents of sea water: phosphate phosphorus, nitrate nitrogen, silicate silicon, and reducible iron. Calibration data for phosphate and reducible iron are presented, as illustrative of experimental results. The iron was determined by a method ( 2 ) in which ferrous iron combines with 1,l’-bipyridine to give a stable red coordination compound. Because of the reproducibility of the method, the calibration data give an indication of the accuracy to be expected from routine operation of the cdlorimeter. Results of rum using absorption cells 26, 9, and 1.5 cm. in length are given in Figure 6.
100-
0 PHOSPHATE PHOSPHORUS CONCENTRATIONUGAT
3 VLITER
Figure 7. Calibration Curve for Determination of Phosphate Phosphorus in Sea Water 9-cm. mbwrptien 4
1435
V O L U M E 22, NO. 11, N O V E M B E R 1 9 5 0 9 microgram-atoms per liter. A single series of data is given for the 1.5-cm. cell. Its curve is linear to 30 micro*-atoms per liter, but has a usable range to at least 60 microgram-atoms per liter. These figures indicate the wide range of concentration that may be mearmred by the instrument. The absolute accuracy decreases with decreasing length of cell, but the percentage error for y y given concentration is about the same for all three cases-for e?uunp!e, a t a scale reading of about 300 the percentage error is approximately *3%. The phosphates were run by the ceruleomolybdate method of Denigb as applied to sea water by Atkins (I), with the modifice tion that samples w e d analyzed in the colorimeter within 5 t o 10 minutes after the stannous chloride had been added. It has been found that the maximum color is developed in that time. The results of a typical calibration are presented in.Table I. The corresponding calibration curve is given in Figure 7. The curve is linear to 2.5 microgram-atpms per liter. The points are distributed within t0.05 microgram-atoms per liter of the curve with the exception of one a t concentration 1.5 microgram-atoms per liter. This figure for the margin of error is substantiated by numerous other calibration runs. The electric eye photometer, in common with other photoelectric colorimeters, has certain advantages over visual comparators. Errors due to eye fatigue and color blindness are elimi-
d.Eye fatigue becotnes especially important a3 a wurce of error when visual colorimeters, which employ an eyepiece, are used at sea. In such analyses as that for phasphate in sea water where the color is t d t o r y , it is important to determjne the optimum time after the addition of reagents to take the reading. Thie m a y be done with the present instrument, as the rate of fsding of the color may be measured. ACKNOWLEDGMENT
The author wishes to express his appreciation for the many helpful suggestions from members of the staff of the Woods Hole Oceanographic Institution and in particular for the contributions of Robert Walden, who designed and built the electronic assembly. LITERATURE U T D
(1) Atkins, W. R. G., J. Marine Eiol. Assoc. United Kingdon, 13, 119; 14,447; 15,191; 16,821 (1923-30). (2) Cooper, k,. H. N., PTOC. Rou. SOC.London, 118B,419 (1935). (3) Harvey, H. W., “Recent Advances in the Chemistry and Biology of Sea Water,” London, Cambridge University Press, 1945.
RECEIVED November
14, 1949.
Contribution 492 from the Wooda Hole
Oceanographic Institution.
Apparatus for Turbidimetric Study of Polymerization Activators T. W. SARGE, Suran Development Laboratory, The Dow Chemical Company, Midland, Mich.
T
H E principal object of the present esposition is to describe a simplified turbidimeter and to present experimental dits relating particularly to the polyinerization of monomer-insoluble polymers, as those of vinylidene chloride. Obviously, the prinviple upon which the study is founded is not new: the developnierit of haze, and eventually of opacity, produced by the formation of colloidal particles which first scatter and then eventually, :tlmost completely, obstruct the path of transmitted light The instrument first devised by Jackson for measurement of water turbidity was later converted to a turbidimeter for sulfur analysis ( 3 ) and more recently modifications of technique and apparatus permit the study of solids showing haze, such as plastic films (1, 2). Polymer chemistry presents an intermediate field for the application of turbidimetry, or viewed somewhat differently,
A simple turbidimeter for the measurement of dynamic polymerization phenomena is described. By graphical analysis of the direct data, i t is possible to obtain Pi, the induction time of polymerization, as well as dZ/dt, the slope or change of intensity which is proportional to the rate of polymerization a t the interval examined. By an extension of the data, a simple but workable equation relates the over-all rate of polymerization as determined by actual bottle or semiplant polymerizations to the turbidimetric data as follows: Rate of polymerization (observed) = k X 1/P1 X dZ/dt (T,catalyst)
polymerization processes may be studied by dynamic turbidimetry, whereas the applications previously mentioned involve static concentration (in liquid) or static form (in solid). Expressed more specifically, it appears possible to obtain in situ relative quantitative data on polymerization phenomena, such as polymerization induction time, polymerization rates, influence of inhibitors and catalysts (by effect on induction time and rate polymerization), and the effect of concentration of reagents, inhibitors, catalysts, and other additaments. DESCRIPTION OF APPARATUS
An extremely simple apparatus was designed to enable assembly from readily available parts. Figure 1 shows all the essential cooperative parts, while Figure 2’indicates the over-all size.
Data are presented for the vinylidene and vinyl-type monomer which form monomer insoluble polymers, but i t is also shown that if a precipitant is added to the original monomer, polymers that are normally soluble in monomer may likewise be examined. Direct application to problems of monomer purity, catalyst concentration, effect of inhibitors, influence of comonomers on polymerization rate, etc., are discussed, and i t is suggested that the apparatus may generally be used to study emulsion stability, and reactions where concentration, time, temperature, and cloudiness are factors.
