T a b l e 111. Recovery of p-Hydroxyacetophenone from S p r u c e Needles Extracts
Table V. Picein and p-Hydroxyacetophenone C o n t e n t of Spruce Needlesa Wet weight, mg/g
Extract, Umoles,/ml No. of detns.
Sample
Extract Extract Extract Extract
C C C C
Found Added
2 2 2 3
Present
Av.
70
, , ,
0,636
.,.
0
0,200 0.836 0.840 0,300 0,936 0.996 0 500 1.136 1 . 1 4 0
Re1 atd dev, 70
100.5 106.5 100.5
10.5 12.0 16.0 12.5
-
Picein
0 1
3 0 17 0 52 0 Average
Picein
1st year 2nd year 3rd year 4th year
5.90 7.50 9.10 10.90
p-Hydroxyacetophenone
0,033 0.037 0.090
0,190
The needles were collected in July, and 2 grams were homogenized in 20 ml water and centrifuged. The residue was treated two times in the same manner. The combined supernatants were analyzed.
Table IV. Effect of Storage Time a t 4 "C on the Picein and p-Hydroxyacetophenone C o n t e n t in Spruce Needles Extract Storage time, hr
Age of the needles
- ~-
Extract, #moles ml
1 43 1 45 1 58 1 50 1 49
____ Av, ( c
96 97 106 100
0
4 0 5
100 0
p-Hydroxyacetophenone Extract, &moles ml
0 0 0 0
255 250 275 261
0 260
Av, 70
98 96 105 100
2 2 5 5
100 0
Recovery of known amounts of picein and p-hydroxyacetophenone from simple test solution is relatively easy. However, the adequacy of the procedure is described more accurately when added and recovered data are obtained directly from plant extracts. The results of such estimations are summarized in Tables I1 and 111. In any case, the recovery is good and compares well with the results obtained from pure test solutions. The relative standard deviation is small and ranged from 0.5 to 6.5%. In plant extracts, the possibility exists that picein is cleaved by the action of @-glucosidaseto p-hydroxyacetophenone and glucose. The results in Table IV demonstrate that in spruce needles extract even during long storage a t 4 "C, neither does the picein value decrease nor the p-
hydroxyacetophenone value increase, indicating that no measurable picein degradation occurs. An additional important factor is to be sure that extraction of picein and p-hydroxyacetophenone from spruce needles is complete so that the data of the analyzed extract actually reflect the concentration in the needles. Estimation of the yield of both compounds in different prepared extracts shows that only picein is extracted completely if 2 grams of needles are homogenized with 20 ml HzO, while the yield of p-hydroxyacetophenone is only 60-100% (yield decreasing with the age of needles) of the maximum yield obtained by repeated extraction. Soxhlet extraction of the needles with water or ethanol yielded lower values for both substances than the repeated cold extraction with water. In our experience, a complete extraction of picein and p-hydroxyacetophenone is given, if the spruce needle extract is prepared as indicated in Table V. Some data about distribution of the acetophenones in needles of picea abies are given in Table V. More detailed investigations concerning the influence of environmental factors will be published elsewhere. Received for review September 17, 1973. Accepted November 28, 1973. This work was supported by a grant (Nr. 1961) from the "Fond zur Forderung der wissenschaftlichen Forschung in Osterreich."
Simple Method for the Preparation,Storage, and Use of Chromous Chloride Solutions Rodger L. Williams and Claude W. Sill Health Services Laboratory, U.S. Atomic Energy Commission, Idaho Falls, Idaho 83401
Chromous ion is one of the most powerful and fast acting reducing agents available for use in aqueous solutions, having a standard reduction potential of -0.41 volt. It is a reagent of choice for several Seductions that cannot be made conveniently with other available reducing agents. Unfortunately, chromous solutions are extremely unstable toward air, a fact amply demonstrated by their widespread use as a preferred oxygen absorbant in gas analysis. The consequent need for relatively elaborate apparatus to store and dispense the solutions under an inert atmosphere has limited the popularity and convenience of chromous salts as reagents for general laboratory use. A simple method for preparation, storage, and use of these
powerful reducing agents would materially increase their attractiveness as off-the-shelf reagents for occasional as well as more elaborate needs. Several authors have reported on the preparation, storage, and use of chromous solutions as standard reagents for use in quantitative volumetric titrations. If protected from the atmosphere, the solutions are stable over long periods of time, the chromous ion 'not being oxidized significantly by hydrogen ion a t concentrations generally used. Stone and Beeson ( I ) prepared standard volumetric (1) H. W. Stone and C. Beeson. Ind. Eng. Chem., Ana/. E d . , 8, 188 ( 1936).
ANALYTICAL CHEMISTRY, VOL. 46, NO. 6 , MAY 1974
791
Zn . H g l k
Figure 1. Container for preparation, storage, and delivery of chromous chloride solutions solutions of chromous salts by reducing solutions of violet chrome alum in a Jones reductor. Lingane and Pecsok ( 2 ) prepared chromous solutions of exactly specified concentrations determinately by reduction of appropriate quantities of pure potassium dichromate with zinc mossy amalgamated with 1% mercury. These authors also present methods for standardization of chromous solutions against copper and potassium dichromate and proved the stoichiometry of the reactions by comparison of the standardized values with the determinate ones. Stone (3) described a convenient apparatus for storage and titration with oxygen-sensitive solutions and reports the titer of dilute volumetric solutions of chromous chloride to remain unchanged for more than 10 months. In all cases, the solutions were stored and dispensed from the same all-glass apparatus in which the solutions were prepared, using either hydrogen or carbon dioxide to maintain an inert atmosphere. Somewhat simpler methods have been developed for the preparation and use of chromous ion when standard volumetric solutions are not required. Syrokomskii and Zhukova ( 4 ) prepared 0.05M chromous chloride for reduction of uranium by shaking a solution of potassium dichromate in hydrochloric acid with zinc amalgam in a separatory funnel. Cooke, Hazel, and McNabb ( 5 ) used 0.5M chromous chloride to reduce uranium prior to volumetric determination of the latter with standard potassium dichromate. The latter authors also used phenosafranine as a low-potential redox indicator to follow the reduction of the uranium and subsequent reoxidation of the excess chromous ions by air. Significantly, they prepared the chromous chloride solution in a dropping bottle by shaking chromic chloride in 1N hydrochloric acid vigorously with 15 ml of 2% zinc amalgam. Although not identified specifically, the dropping bottle used presumably required removal of the cap each time it was used, permitting free access of air, because it was necessary to regenerate the chromous ion occasionally by shaking the bottle containing the zinc amalgam. The present interest in chromous chloride in this laboratory arose out of a need to reduce uranium in 10-gram samples of dissolved soil prior to precipitation of the quadrivalent uranium with barium sulfate (6). The solutions ( 2 ) J. J. Linganeand R. L. Pecsok, Anal. Chem., 20, 425 (1948). (3) H . W. Stone. Anal. Chem., 20, 747 (1948). (4) V. W . Syrokomskii and K. S. Zhukova. Zavodskaya Lab.. 11, 373 (1945). (5) W. D. Cooke. F. Hazel, and W. M . McNabb, Ana/. Chim. Acta, 3, 656 (1949) (6) C. W. Sill, K . W. Puphal. and F. D. Hindman, "Simultaneous Determination of Alpha-Emitting Nuclides of Radium Through Californium
in Soil," U.S.Atomic Energy Commission, Idaho Falls, Idaho, in
preparation 792
ANALYTICAL CHEMISTRY, VOL. 46, NO. 6, MAY 1974
contained as much as 0.5 gram of iron in strong hydrochloric acid solutions containing high concentrations of calcium and potassium sulfates. Common reducing agents such as sulfite, hydroxylamine, hydrazine, etc. do not reduce either iron or uranium significantly under these conditions. Titanium trichloride reduces both elements rapidly and quantitatively but the quadrivalent titanium produced during reduction of such large quantities of iron forms an insoluble double salt with the potassium sulfate required for efficient precipitation on barium sulfate. Even with 5 to 10% mercury present, a Jones reductor reacts so vigorously with the strong hydrochloric acid solutions required to prevent precipitation of calcium sulfate that the flow of solution through the column is seriously impeded by the evolution of hydrogen gas, and so much acid is consumed that calcium sulfate is frequently precipitated. Opportunity for contamination between samples is considerable unless the column is replaced each time it is used. Also, polonium-210 is reduced and retained incompletely in the column, interfering with the use of uranium-232 tracer in the alpha spectrometric determination of the other uranium nuclides. In the present application, volumetric solutions were not required, but a much more concentrated reagent than that used by Cooke et al. was desired to provide the necessary large reducing capacity without requiring excessive volumes of solution. Also, because of the inherently dark color of the chromic ion, a method was desired by which the chromous ion could be added to the solution without significant additional oxidation by air to keep the resulting solutions as light-colored and transparent as possible. When a chromous solution is allowed to drop even a few inches through air from a conventional dropping bottle, undesirably dark solutions generally result, even with little or no oxidant being present in the solution. The simple container described permits a 3M solution of chromous chloride to be prepared and stored for months without significant reoxidation, and to be added to solutions with almost quantitative efficiency.
EXPERIMENTAL Apparatus. The container used for preparation, storage, and delivery of the chromous chloride solution is shown in Figure 1. The container is a conventional 250-ml polyethylene wash bottle having a fine thin-walled polyethylene delivery tube extending through a tight-fitting hole in the cap (Ansell-Plax washbottle, S. H. Ansell and Son, Inc., Boston, Mass.) but which is not sealed or of one-piece molded construction. Pull the delivery tube through the cap from the outside until only about 0.5 inch of the lower end remains below the underside of the cap. Bend the delivery tube downward so that it runs vertically down the side of the bottle with a sharp crease in the tube where it comes through the cap and with the normal delivery tip sticking out at nearly right angles tu the bottle. Slip a rubber band around the bottle to hold the tube firmly against the side. Because pressurization by hydrogen and/or the weight of the solution itself are both sufficient t o cause a flow of liquid under normal conditions of use. a squeeze bottle is not necessary. A glass bottle with the correct threads to fit the polyethylene dispensing cap is preferred and appears to make the solution somewhat more stable over long periods of time. Reagents. Amalgamated Zinc, 14% Hg. Dissolve 4 grams of HgC1, in 15 ml of 6 M HC1 in a 30-ml beaker. Place 20 grams of 20-mesh zinc shot in a 250-ml beaker. add 50 ml of water. and place the beaker in a bath of cold water. Add 5 ml of concentrated HCI. stir for 10 seconds to clean the surface of the zinc, and add the mercuric chloride solution slowly over a period of 1 or 2 minutes while stirring the zinc shot rapidly and continuously. Leave the beaker in the cold water bath for at least 5 minutes with occasional stirring to obtain complete reduction of the mercury. Wash the 22 grams of amalgamated zinc thoroughly with water and transfer t o the 250-ml bottle to be used for storage and dispensing. Drain the zinc thoroughly, tapping t h e bottle sharply several times to free as much of the excess water as possible.
Chromous Chloride, 3M.Dissolve 80 grams of CrC134H20 ir ml of water and 10 ml of concentrated HC1 by heating the s( tion briefly to near boiling. Cool the solution to about 40°C i transfer without rinsing to the battle containing the amalgama zinc. Tighte? the cap securely and hold the delivery tube tigl against the side of the bottle with a rubber hand. Swirl the SI tion vigorously by hand for 1minute and loosen the cap to relr the pressure that will have built up because of heating the SI tion hy the initial reaction. Keep the solution ont of the neck much as possible while swirling to prevent some leakage while bottle is pressurized. Retighten the cap and shake the bottle orously on a mechanical shaker until the deep green solul changes to a brilliant indigo color that does not change on furl shaking. Subsequent pressurization due to formation of hydra gas is very slight and is released harmlessly around the cap hale through which the delivery tube passes. At the tempera1 generated, only shout 15 minutes of vigorous shaking is requi for complete reduction. The entire preparation including tha the amalgamated zinc requires only 45 minutes. Safranin 0, 1%. Dissolve 0.5 gram of Safranin 0 (National I line Division, Allied Chemical and Dye Corp., New York, N Color Index 841) in 50 ml of water. Procedure. Hold the bottle in an inverted position in the left hand with the fingers holding the delivery tube securely against &IL.. -lr -:Am A &hn *I.r L-+rla T%+L +La *.,- -:ght hand, remove the rubber re. taining band and take hold of tht5 end of the delivery tube, keeping the tube creased sharply wht?re it comes through the cap to prevent premature flow of liquicI. Place the tip of the delivery tube wherever the chromous chloride is to be delivered and start the flow of liquid by gently raisi ng the bottle while holding the delivery tube in position so that the crease begins to open. The method of dispensing the solutior1 is shown in Figure 2. Stop the flow by lowering the bottle untilI the crease closes the opening. The flow rate can be regulated and controlled with almost micrameter precision. After use, rincse the end of the delivery tube :+L ...O+n- *"A Go. -..,Js of. the .solution .. . . . . to . the sink to eliminate any chance of contamination ot erther the reagent c,I subsequent samples. For storage, fold the delivery tube hack alon'g the side of the bottle. redace the rubber band around the hottli and set the bottle right-side-up hack on the shelf until the ne]rt use. "L
... nlbl.
nab=L
L.L.y
- .-..
-1
1 !
The long thin delivery tube permits the solution to he introduced very near or even underneath the surface of the solution to which it is being added, thus reducing markedly the loss of reducing capacity and buildup of chromic ion due to air oxidation, Particularly, when the solution is to he added to boiling solutions, the delivery tube can be inserted between the watch glass and the pouring lip of a beaker or down the neck of an Erlenmeyer flask into the steam, making it a virtually closed inert system. Lingane and Pecsok (7) showed that chromous ion reduces nitrate ion quantitatively to ammonium ion and used this fact as the basis for the volumetric determination of nitrate. Because its equivalent weight is only 7.75 in this reaction, nitrate ion should he rieorouslv excluded from solutions to he reduced by c hromous ion. The samf? authors also demonstrated the mrirked catalytic effect o t titanium on the reduction of nitr;ite due to rapid reduc tion of titanic ion by chromous io.. y..yuyy_.-., "_.." idation of titanous ion by nitrate. Consequently, nitrate is particularly detrimental to efficient reduction of iron or uranium in soil samples with chromous solutions without producing large quantities of chromic ion because of the 0.5% titanium that is present in an average soil. However, it is fortunate that titanium is reduced by chromous ion because tervalent titanium is much more stable in air than chromous ion and makes a superior holding reductant for quadrivalent uranium even in boiling solutions which are required for precipitation of quadrivalent uranium on where such a holding reductant is ..hariwm -w1fnt.e -..-.. .. partitcularlv necessarv. Saltranine 0 is a highly colored phenazine dye,. simila:r ..-..A I-. n"..,." AI-"L :" :A"",,. to the- _p L~ u w c--..:-a a ~ ~ uscu a ~ ~ u~y ~U r Vn U ~r~~Y L . , C I I ~ L .I) iurairi suited for use as an internal oxidation-reduction indicator with chromous solutions. Its color changes from red in water through magenta, purple, and blue with increasing concentrations of sulfuric or hydrochloric acids. The indicator is reduced to its colorless leuco form a t a reduction potential of about -0.24 volt by both chromous and titanous ions. Because the reduced form of the indicator is itself powerful enough to reduce he, ax .rl.ent uranium, the absence of indicator color is visual e\ ience that the uranium is in the quadrivalent state. However, the indicator is slowly destroyed on boiling so that an extra drop or two should be added periodically during prolonged boiling to ensure that indicator is still present before such a concluD
DISCUSSION After reduction of 80 grams of CrCls.GH20 by the 22 grams of 14% amalgamated zinc, approximately 12 grams of 25% amalgamated zinc remains which is sufficient to keep the chromium reduced for extended periods of time while keeping formation of hydrogen gas in the acid solution at an adequately low level. However, the continuous production of hydrogen from the acid-zinc reaction is sufficient to keep the contents under slight internal pressure and prevent diffusion of air into the air-sensitive solution. The excess pressure escapes harmlessly around the cap and where the delivery tube comes through the hole in the cap. Obviously, pressure-tight caps or those of molded one-piece construction must not be used. Under normal conditions of use, there is little or no oxidation of the chromium over a period of several months. Even if the rate of withdrawal of solution is greater than the replacement rate of hydrogen gas, the quantity of air admitted can never be greater than the volume of the solution withdrawn if a glass bottle is used or if the polyethylene bottle is not squeezed more than necessary. The oxidizing capacity of such a small quantity of air is quickly offset by reaction with the zinc present. However, after a month or so, depending on the rate a t which the solution is used up, most of the acid will have been consumed by reaction with the excess amalgamated zinc, and a bluish white precipitate forms, presumably of chromous hydroxide. Addition of 10 ml of concentrated hydrochloric acid per 100 ml of solution with as little admission of air as possible and shaking vigorously for a few seconds will quickly restore both the clarity and the indigo blue color of the solution. The solution is then stable for another several weeks.
-__
^_^^^
^'
(7) J. J. Linganeand R. L. Pecsok. Anal. Chem.. 21, 622 (19491.
ANALYTICAL CHEMISTRY, VOL. 46, NO. 6 . MAY 1974
* 793
sion is valid. The red to purple colors provide sufficient contrast to the green of the chromic ion to make the color change very pronounced, although as much as 1 ml of 1% indicator might be necessary when large quantities of chromous ion are used. The reddish cast of the indicator
shows u p best through the green color of chromic ion if the solutions are examined in light from a tungsten source. Received for review October 31, 1973. Accepted December 26, 1973.
Rapid and Convenient Laboratory Method for Extraction and Subsequent Spectrophotometric Determination of Bitumen Content of Bituminous Sands Mahendra S. Patel Product Research and Development Division, Research Council of Alberta, 7 7375-87
Currently, solvent extractions by toluene or carbon tetrachloride using standard Soxhlet apparatus, and a density method are the three analytical procedures described in the literature for the determination of bitumen content of bituminous sands ( I ) . The toluene-extraction method yields the most accurate results and is widely used in laboratory determinations. In the toluene-extraction procedure, the water and bitumen are simultaneously extracted with toluene. The amount of silt that passes through the extraction thimble is determined by ashing, and applied as a correction to the bitumen. Bitumen content is calculated on a dry weight basis from loss in weight. The procedure requires four to six hours for extraction and several extra hours for residual solids determination; for routine analyses, this is very time-consuming and laborious. The purpose of this present investigation was to develop a rapid and simple analytical procedure for determining bitumen content of bituminous sands. In the present method, extracting solvent (toluene) is pumped through a column of bituminous sand of known moisture content. Bitumen content of the extract is then determined by absorbance measurement and calculation from a per cent bitumen us. absorbance plot of a standard bitumen.
EXPERIMENTAL The extraction column consisted of a stainless steel tube (4-in. X 5b-in. i.d.) with threaded caps at each end for inlet and outlet of the extraction fluid. The caps were fitted with metal filter disks (Yg-in. coarse-grade porous bronze) and rubber O-rings (Buna-N or Viton A). .4 Milton Roy Minipump, Model 196-47. with 240 ml per hour volume capacity and discharge pressure of 1000 psi, was used to pump the extraction solvent. Absorbance measurements were made at 530 nm. using toluene (ACS grade) as the solvent and blank, on a Bauch and Lomb Spectronic-20 colorimeter with a square silica cell of 10-mm path length. A gas chromatograph equipped with a flame ionization detector was used for toluene determination. A stainless steel column (6-in. X Yg-in. i.d.) packed with 5% SE-30 on Chromosorb G (AW 100-120 mesh) was used a t a helium flow rate of 40 ml/minute and column and injection port temperatures of 60 and 75 "C, respectively. The samples used for this study were collected at the Great Canadian Oil Sands mining site in the Fort Mcxlurray, Alberta, area of t h e Athabasca bituminous sand deposit. Draper, A . Yates, and H. McD. Chantler, Canadian Dept. Mines & Tech. Surveys, Mines Branch, Rep. FRL-211, Fueis Division, December 1955.
(1) R. G .
794
ANALYTICAL CHEMISTRY, VOL. 46, NO. 6, MAY 1974
Avenue, Edmonton, Alberta, Canada T6G 2C2
Procedure. The extraction column was assembled as shown in Figure 1. A cap was placed a t the bottom end of the extraction tube. A bed of clean sand 5 - to 10-mm thick was deposited on top of the metal filter and the tube was weighed accurately t o the nearest 0.01 gram. A representative sample (20-25 grams) of bituminous sand was added to the tube with light packing and the tube was reweighed. A second cap was then placed at the top end of the tube and connected to the solvent line. The extracting solvent was introduced a t the top of t h e column and the extract was collected directly into a tared centrifuge tube. Overhead pressure was maintained a t 10-20 psi by adjusting the solvent flow through t h e column. Complete extraction of bitumen was achieved within 10-20 minutes, with a total extract volume of 75-100 ml. Water content of the bituminous sand was simultaneously determined on another independently weighed sample (ea. 100 grams) by t h e Dean and Stark method. using toluene as solvent. After centrifugation of the toluene extract to remove silt, its absorbance was determined upon suitable dilution to read between 0.40 and 0.60 absorbance unit on the photometric scale. Bitumen content of the sample was then determined from a calibration curve and is reported on a dry weight basis. For calculation of bitumen content by difference, the amount of dry solids, including silt, were determined by drying the extracted column in a vacuum oven a t 120 "C for 1-2 hours. Calibration Curve. A standard sample of bitumen required for the curve was prepared as follows. A bituminous sand sample (20.90 grams) of known moisture content (0.3% H20) was extracted with toluene by the extraction procedure described herein. The extract was evaporated in the cold (water bath temperature 25-30 "C) under reduced pressure on a rotary evaporator to remove the solvent. yielding crude bitumen (2.86 grams). The bitumen sample so obtained contained no detectable amount of water (IR, Karl-Fischer titration). The amount of residual toluene was quantitatively determined (15.26% w/w) by gas-liquid chromatography. using chloroform as solvent and toluene as external standard, and applied as a correction to the bitumen content. A stock solution of bitumen in toluene (0.80070 w/v) was prepared from standard bitumen accurately weighed to the nearest 0.0001 gram. Serial dilutions of bitumen in toluene, ranging in concentrations from 0.019-0.064%, were prepared and their absorbances determined. A plot of per cent bitumen rs. absorbance produced a straight line passing through the origin, corresponding to a n apparent absorptivity of 6.81 f 0.02. Calculation: % bitumen = % concentration bitumen (found) x (initial volume of extract) x (final volume of diluted solution/ vol. of extract aliquot x wt. of bituminous sand sample ( d r y ) )
RESULTS AND DISCUSSION Direct determination of bitumen by the spectrophotometric method is based on the following observations. First, when measured at 530 nm in a spectrophotometer, absorbances of the color of solutions of bitumen in toluene
