Enkvist, T., Hougberg, B., Paper and Timber (Finland) 37, No. 5, (17)
201 (1955).
Gralen, iX.,J . Colloid Sci. 1, 453 (1946).
Gross, S. K., Schuerch, C., AXAL. CHEM.28, 277 (1956). Haaalund, E., Urban, H.. Cellulose-
(18) (19) (20)
Zbid., 9, 49 (1928).
’
Hess. K.. Heumann., K.., Ber. 75. 1802 (1942).
Jefferson Chemical Co., Kew York, “Ethvlene Carbonate.]’ Klages,“F., Ann. 541, 25 (1939). Loughborough, D. L., Stamm, h., J . Phys. Chem. 40, 1113 (1936). Mikam-a, H., Okada, S . , J . Chem
(21) (22) (23) (24) (25)
SOC.Japan, Ind. Chem. Sect. 54, 239 (1951). Parrette, R. L., J . Polymer Sci. 15, 447 (1955). Pauly, H., Ber. 67, 1177 (1934). Payne, J. H., Fukunaga, E., Kojima, R., J . A m . Chem. SOC.59, 1210 (1937). Pennington, D., Ritter, D. M., Zbid., 69, 665 (1947). Phillips, M., Zbid., 49, 2037 (1927). Puddington, I. E., Ibid., 72, 3840, Table I1 (1950). Roux, R. D., J . SOC.Leather Trades’ Chemists 37, 259 (1953). Sachtling, H., Zocher, H., KolloidBeih. 40, 413 (1934). Samec, M., Kolloid 2. 51, 96 (1930).
Sarkanen, K., Schuerch, C., ANAL CHEM.27, 1245 (1955). Sarkanen, K., Schuerch, C., J. Am. Chem. SOC.79, 4203 (1957).
Schuerch, C., Zbid., 72, 3838 (1950).
Ibid., 74, 5061 (1952).
Schwabe, K., Hasner, L., Cellulosechemie 20, 61 (1942).
Staudinger, H., Dreher, E., Ber. 69, 1729 (1936).
Turner, W. E. S., English, S., J. Chem. Soc. 1914, 1786.
Watanabe, J., FUOSS, R. M., J . Am. Chem. SOC.78, 527 (1956).
Wedekind, E., Katz, J. R., Ber. 62, 1172 (1929).
RECEIVEDfor review May 31, 1956. Accepted December 19, 1957.
Photometric Determination of Beryllium UNO T. HILL, Inland Steel Co., lndiana Harbor, Ind. b Existing methods for the determination of beryllium require chemical separations from interfering elements. Direct photometric methods for the determination of beryllium in aluminum, steel, copper, titanium, and mixed oxides are described. Beryllium reacts with Eriochrome Cyanine R to form a red complex having a maximum absorbance a t 512 mp a t pH 9.8. Addition of Versenate and cyanide eliminates interfering ions. The methods are accurate and rapid.
A
RECEKT paper
from this laboratory (1) indicated Eriochrome Cyanine R as a specific reagent, for beryllium when sodium Versenate [(ethylenedinitrilo)tetraacetate] was used to mask interfering elements. The present study was made to establish more definitely the accuracy and limits of applicability of the Eriochrome Cyanine R method. Efforts were directed in particular to the development of a rapid and specific method for trace amounts of beryllium in aluminum, iron, copper, lead, titanium, and their alloys without chemical separations. ’ APPARATUS A N D REAGENTS
Beckman DU spectrophotometer. Reagents. Eriochrome Cyanine R, 0.09%, General Dyestuff Corp. Dissolve 0.90 gram of Eriochrome Cyanine R in about 250 ml. of water, add 25 grams each of sodium chloride and ammonium nitrate, add 2 ml. of nitric acid (specific gravity 1.42) and 100 ml. of 95% ethyl alcohol, dilute to 1 liter, and mix. A 0.009yo solution a t p H 6.0 should have an absorbance of 0.9 in a 1-em. cell a t 438 mp (1). Sodium Acetate buffer. Dissolve 50
grams of sodium acetate in water and dilute to 1 liter. Sodium Versenate Solution. 5%. Hach Chemical Co. Dissolve 50’ g g m s of disodium dihydrogen Versenate [(ethylenedinitri1o)tetraacetatel in water and dilute to 1 liter. Standard Beryllium Solution (1ml. = 2.0 y of beryllium). Dissolve 0.1965 gram of beryllium sulfate tetrahydrate in 25 ml. of hydrochloric acid, dilute to 1 liter, and mix. Transfer 100 ml. of this solution to a 500-ml. volumetric flask, dilute to the mark with O.lyo hydrochloric acid, and mix. I
PROCEDURES
Aluminum. T o a 1.OOOO-gram sample in a 250-ml. beaker add 20 ml. of 1 to 1 hydrochloric acid, warm on a hot plate until in solution, cool, and dilute to 100 ml. in a volumetric flask. Transfer a 1.00-ml. aliquot into a 50ml. volumetric flask and add 5 ml. of 5% sodium Versenate, 5 ml. of 5% sodium acetate, and 5 ml. of 0.09’% Eriochrome Cyanine R. Adjust the p H to 9.7 to 9.8 with lOY0 sodium hydroxide by titration from a buret. The color change of Eriochrome Cyanine R is through red, yellow, and finally dark purple. When this last end point is reached, add 5 drops of 10% hydrochloric acid to obtain a p H of 9.7 to 9.8. Dilute t o the mark and mix. Alternatively, employ a p H meter to adjust the pH. Obtain the absorbance of the sample against a blank of beryllium-free aluminum carried through all the steps of the procedure. The measurement may be carried out in a 2-em. cell a t 512-mp wave length. Obtain per cent of beryllium from a previously prepared calibration curve. Steel. Process a 1.OOOO-gram sample as for aluminum b u t adjust the p H with 10% potassium hydroxide. T h e iron must be in the reduced state.
Measure the absorbance of the sample against a blank of beryllium-free steel carried through all the steps of the procedure. Obtain per cent beryllium as for aluminum. Copper. T o a 1.0000-gram sample in a 250-ml. beaker add 20 ml. of 1 to 1 nitric acid. Warm, boil off the oxides of nitrogen, cool, and dilute t o 100 ml. in a volumetric flask. Transfer a 1.00-ml. aliquot into a 50ml. volumetric flask, and add 5 ml. of 5% sodium Versenate, 5 ml. of 5% sodium acetate, and 5 ml. of 0.09% Eriochrome Cyanine R. Add sufficient 10% potassium cyanide (2 ml. is usually sufficient) to discharge the blue coloration due to cupric complexes, and adjust the p H as for aluminum with sodium hydroxide. Dilute to the mark and mix. Obtain the absorbance against a blank of beryllium-free copper in a 2em. cell a t 512 mp. From a calibration curve obtain per cent beryllium. Titanium. T o a 1.0000-gram Sample in a 250-ml. beaker add 25 ml. of concentrated hydrochloric acid, cover, and heat on a water bath until in solution. Replenish the acid if necessary. When in solution cool and dilute to 100 ml. in a volumetric flask. To a 1-ml. aliquot in a 50-ml. flask add 4 drops of 30% hydrogen peroxide, 2.5 ml. of 5% sodium Versenate, 5 ml. of 57, sodium acetate, and 5 ml. of 0.09% Eriochrome Cyanine R, and adjust the p H to 9.7 to 9.8 as for aluminum, using 10% potassium hydroxide. Dilute to the mark and mix. Obtain the absorbance against a blank of beryllium-free titanium carried through all the steps of the procedure. From a calibration curve obtain the per cent beryllium. Oxides. T o a 1.0000-gram sample in a 250-ml. beaker add 25 ml. of concentrated hydrochloric acid, cover, and digest a t low heat. Remove cover, take to dryness, and bake to dehydrate silica. Add 10 ml. of VOL. 30, NO. 4, APRIL 1958
521
hydrochloric acid, heat briefly, add 25 ml. of water, and boil. Filter on Whatman No. 41 paper and pulp, and wash with dilute hydrochloric acid and hot water. Ignite the residue in a platinum crucible, and volatilize the silica in the usual manner by treatment with sulfuric and hydrofluoric acids. Fuse the residue with 1 or 2 grams of potassium bisulfate. Dissolve the fusion .in the filtrate, cool, and dilute to 100 ml. in a volumetric flask. Transfer a 1-ml. aliquot into a 50in). volumetric flask, add reagents, and adjust the p H to 9.7 to 9.8 with sodium hydroxide as for aluminum. Obtain the absorbance in a 2-em. cell a t 512 mp against a reagent blank carried through all the steps of the procedure. 1.4
1.2
1.0
w 0.8
u z a
m
0.6
ln
m
a
0.4
,”
021
0
3
, ’
I
I
,
1
~
5
7
9
13
II
VALUE
pH
Figure 1. Effect of pH and excess Versenate on Eriochrome Cyanine Rberyllium complex
---.-
-
Beryllium complex, 0.1 % excess Versenate, 5 12 mp Beryllium complex, no Versenote, 51 2 m p Eriochrome Cyanine R, 51 2 mp
I
l
l
I
I
I
i
Oxalic acid ~ 3 acceptably s selective but extremely sensitive to slight variations in concentrations. Saccharates (from Reading Testing Laboratories) n-ere in many respects superior to the Versenates in complexing properties. However, as Versenate a t p H 9.7 to 9.8 was a specific masking agent for the interfering elements in the photometric determination of beryllium, no alternatire method was developed using saccharates for masking. Sodium and potassium hydroxides differ in complexing properties with Versenate. K h e n analyzing steel, precipitate formation may be prevented by adjusting the p H with potassium hydroxide \Thile aluminum interference is prevented 17-ith sodium hydroxide when analyzing aluminum.
CALIBRATION CURVE
To six 1-nil. aliquots of berylliunifree aluminum, iron, titanium, or copper carried through all the steps of the procedures for each metal, add, respectively, 0, 1, 2, 3, and 5 ml. of standard beryllium solution. Complete the determination as described for each of the metals. Plot absorbance values against beryllium content to obtain a calibration curve for beryllium. EXPERIMENTAL
Choice of Masking Agents. As Eriochrome Cyanine forms colored complexes with numerous metallic ions at relatively low concentrations, a masking agent should be introduced into t h e solution t o prevent t h e formation of interfering complexes and avoid chemical separations. Although Versenate effectively blocked the formation of aluminum and iron Eriochrome Cyanine R complexes in the ratios present in iron ores while permitting the beryllium complex to forni at p H 6.0 ( I ) , this was not true when the aluminum concentration was increased by a factor of 100 or more. It was for a time erroneously believed that the upper limit for the formation of Eriochrome Cyanine R complexes was p H 7.0, because of the abrupt destruction of the aluminum complex a t this p H value. As a result of these factors, a search was made for masking agents other than Versenate.
Effect of pH. It was determined t h a t t h e abrupt destruction of the beryllium Eriochrome Cyanine R complex a t p H 7.0 was due t o coprecipitation n-ith aluminum. B y introducing Versenate or tartrate into t h e solution, hydrate formation was prevented, a n d equilibrium conditions between Eriochrome Cyanine R and other metallic ions were re-established. The beryllium-Eriochrome Cyanine R complex shows a maximum, in the absence of Versenate, a t pH about 7.2 and 512 mp (Figure 1). As most Versenate complexes increase in stability with increasing p H values, it rvas not anticipated t h a t a n Eriochrome Cyanine R method for beryllium could be developed above p H 8.3. Between p H 7.0 and 8.3 varying success was had ivith establishing equilibrium conditions betlveen beryllium and Eriochrome Cyanine R. The time for reaching equilibrium could be reduced from 24 hours to 20 minutes, if the excess of Versenate required to mask interfering ions was removed by the introduction of indifferent ions such as calcium, magnesium, cerium. or zinc, Such a method, how-
Citric acid was a nonselective masking agent for all metals forming Eriochroine %Cyaninecomplexes, including beryllium. Tartaric acid did not effectively mask iron or large amounts of aluminum. It could, however, be employed as a secondary complexing agent to keep metals in solution Iyhile adjusting the p H of the solutions. I
,
I
!
0 300
340
380
1.2
I
!
!
I
IO
w
0.8
0
z
0.6 K 0 v)
0.4 0.2
420 WAVE
Figure 2. Absorption spectra of beryllium-Eriochrome Cyanine R complex, pH 9.8
522
ANALYTICAL CHEMISTRY
Figure 3.
460 500 LENGTH, Mp
540
580
620
Absorption spectra of Eriochrome cyanine R, p H
9.8, 1 -cm. cell, 0.04-mm. slit
ever, was still dependent for reproducibility upon no variations in the sample size. Such methods yield accurate results with differential spectrophotometry. B y increasing p H by addition of either sodium or potassium hydroxide, rather than ammonium hydroxide, a stable Eriochrome Cyanine R-beryllium complex could be formed at p H 9.8, which n a s proportional to the amount of berj 1lium present and independent of excess of Yemenate, within the limits of the method. Metals which usually form complexes with Eriochrome Cyanine R nere still effectively complexed m-ith the excess Versenate and the absorbance of the beryllium complex was independent of their concentration. Figurc 1 also shons the variation in absorbance with varying pH of the Eriochronie Cyanine R dye measured against water a t 512 nip. The dye has a minimum background color between p H 7.0 and 10.0. The sudden change in color of the dye a t p H 10.0 is utilized to adjust the p H of the sample without the aid of a p H meter. .4t p H 9.8 the beryllium complex has a maximum a t 512 mp (Figure 2 ) . The ma\iniuni shifts with increasing p H from the longer to the shorter wave lengths. A t p H 6.0 the maximum occurs at 550 mk, a t p H 8.3 it is 522 mk, and a t p H 9.8 it is 512 mp. Maximum negative absorbance values compared with the blank are reached at 418 nip. A stoichiometric relationship exists between Eriochronie Cyanine R, and the reacting ion ( 1 ) . Two complexes have been observed for beryllium, apparently in harmony with its two valences. Figure 3 shows the Eriochrome Cyanine spectra a t p H 9.8. The dye has a maximum a t 432 mk; a t p H 4.0 t h e maximum was 510, and a t p H 6.0 it was 438, thus duplicating the shift to the shorter wave length with increasing p H observed for the beryllium complex.
0
0.2
0.4
BERYLLIUM,
0.6 0.8 MICROGRAMS
Table I.
Analysis of Standard Samples
Sample NO.
Be Present,
Bea Found,
%
%
Difference,
%
Spec. mix. std. 1000 1.34 1.40 $0.06 0.00 0.10 0.10 Spec. mix. std. G1 0.008 -0.002 0.010 35 Spec. mix. std. G2 10.80 +o. 11 10.69 4 Cu 23%] Pb 66% 0.000 0.100 0,100 5 A1 99% 0.002 0.000 0.002 0A1 99% 0.098 -0.002 0.100 i CU 7491". A1 25% ,0.100 0.000 0.100 8 Mg 99% 0.101 +0.001 0.100 9 Fe 99% 0,098 -0.002 0,100 Ti 99% 10 Average of three determinations, none deviating from another by more than =k0.002%. b Samples 1, 2, and 3 each contained 1.34, 0.10, 0.010%, respectively, of Ag, All As, B, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, F, Fe, Ge, Hg, K, Lu, Mg, &In, N o , Na, Nb, Ni, PI Pb, Rb, Sb, Si, Sn, Sr, Ta, Th, Ti, T1, U, V, W, Zn, Zr. l b 25
DISCUSSION
Stability of Reagents. Versenate solutions deteriorate slightly on aging and tend t o form precipitates when iron is present. In this event a fresh solution must be prepared a n d care must be taken not t o exceed p H 9.8 when adding potassium hydroxide. The Eriochronie Cyanine R solution deteriorates slo~vlyin the presence of alcohol. A 0.10% Eriochrome Cyanine R solution may be made containing no alcohol and 10% of alcohol added as needed. Both potassium and sodium hydroxides should be protected from excessive carbonate formation by storing the solutions in sealed containers. Eft ect of Temperature. Increase in temperature tends t o favor t h e formation of Versenate complexes a t t h e expense of t h e Eriochrome Cyanine R complex. Deviations of more t h a n a few degrees should not be permitted from t h e room temperature employed for constructing t h e calibration curve. Order of Addition of Reagents. Versenate, acetate, and Eriochrome
1.0 PER
1.2 1.4 MILLILITER
1.6
1.8
Figure 4. Calibration curves of beryllium based on Eriochrome Cyanine R complex, 1-cm. cell, 0.04-mm. slit
- - - pH 9.8, 5 J 2 m p , 0.20% excess Versenate - . - pH 7.3, 545 m p , 0.20% excess Versenate - pH 8.4,5 2 2 m p , 0.20% excess Versenote, 0.4%
sodium tartrate
Cyanine R form numerous metal complexes, which are not readily destroyed. T h e time interval between addition of reagents should not exceed a few minutes, so t h a t t h e complexes do not gain undue stability by aging, and t h e sequence given should be follon ed. Determination of Beryllium at pH Values below 9.8. When beryllium determinations are made at p H below 9.8, in order t o avoid precipitate formation t h e phenolphthalein end point may be employed t o adjust t h e p H t o 8.3. Addition of 5 ml. of 0.5% zinc as zinc chloride t o t h e 1-ml. aliquot prior t o addition of Versenate will aid in preventing formation of a beryllium-Versenate complex and favor the rapid formation of the Eriochrome Cyanine R-beryllium complex. Background Color. T h e beryllium content of most samples may be determined by obtaining t h e absorbance against a reagent blank carried through t h e steps of t h e procedure. Ferric iron, however, reacts with Versenate t o produce a reddish brown background coloration. For this reason most of the iron should be in the divalent state and a beryllium-free iron blank should be used to cancel out a n y differences in background color. As a n added precaution beryllium-free metal, similar to that being analyzed, when possible, is incorporated in the blank, to assure uniformity due to background absorbance. The difficulty of determining bergllium directly in mixed oxides is recognized but the feasibility of employing a reagent blank in place of a berglliumfree sample is demonstrated by determination of beryllium in a standard composition consisting of 43 elements. Concentration Range. The method is applicable t o beryllium concentrations up t o 10 y in 25 or 50 ml. of solution. A sharp change in the calibration curve at this point is due to the change in the beryllium-Eriochrome VOL. 30, NO. 4, APRIL 1958
523
Cyanine R combining ratio. Concentrations above this amount, however, may be determined by diluting the sample or by processing correspondingly less sample. If more than 10 y are made t o react a t the high dye concentration before dilution, accurate results are not obtained on dilution to larger volumes. DISCUSSION OF RESULTS
Figure 4 shows calibration curves obtained under various equilibrium conditions. The lower curve shows the complexing effect of combined Versenate and
tartrate. The sudden change in the slope of the curve is interpreted as a change in the beryllium-tartrate equilibrium caused by increasing beryllium concentration. The middle curve is obtained while maintaining a 0.20% excess of Versenate a t p H 7.3. The absorbance values were obtained 20 minutes after the addition of Eriochrome Cyanine R. Complete equilibrium was attained in 24 hours. The top curve is obtained a t p H 9.8. Equilibrium is attained within a few minutes after addition of the reagents and the complex is stable for an hour or more. The curve coincides closely with that obtained when the excess of Ver-
senate is destroyed by zinc or calcium ions a t p H 8.3. Table I compares the results obtained by the direct photometric method and known beryllium values. The method is accurate and is applicable to a wide variety of metals, alloys, and ores. LITERATURE CITED
(1) Hill, U. T., AKAL. CHEJI. 28, 1419 (1956).
RECEIVEDfor review hIarch 13, 1957. Accepted December 4, 1957. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, 1957.
Conductometric Determination of Small Amounts of Oxygen in Titanium MAURICE CODELL and GEORGE NORWITZ Pitman-Dunn laboratories, Frankford Arsenal, Philadelphia, Pa.
b In a proposed method for the conductometric determination of small amounts of oxygen in titanium, the sample reacts with bromine and carbon in an improved bromination apparatus. The carbon monoxide thus produced is oxidized to carbon dioxide with hot copper oxide. The carbon dioxide is then absorbed in a barium hydroxide solution and the change in conductance is measured.
(11).
T
bromination-carbon reduction method for the determination of oxygen in titanium cannot be readily applied to samples containing small amounts of oxygen ( 5 , 6). By determining the carbon dioxide conductometrically instead of gravimetrically the range of the method may be extended t o small percentages. The conductometric method for determining carbon dioxide by absorption of the carbon dioxide in barium or sodium hydroxide solutions and measurement of the conductance was proposed by Cain and Maxwell in 1919 (4). Much work has been done since, particularly in the development of absorption cells and resistance bridges of high precision for conductivity measurements (2,s. 7-13, 15, 16). HE
APPARATUS
The apparatus is shown in Figure 1. The absorption cell, conductivity cells, measuring bridges, and electronic circuits are essentially the Leco conductometric carbon determinator (Laboratory Equipment Corp., Saint Joseph, 524
Mich.) for the determination of carbon in steels. However, the heated catalyst for oxidizing the carbon monoxide and hydrocarbons in oxygen was not effective in oxidizing the carbon monoxide and hydrocarbons in argon or helium. As it was not feasible to pump the barium hydroxide solution by gas pressure, a pressure bulb m s used. The gas storage bottle for oxygen and the purification train of manganese dioxide are not necessary in the proposed method, The electronic circuit has been described
ANALYTICAL CHEMISTRY
The bromination part vias improved and simplified. A conical dry ice trap that can be cleaned in 1 minute replaced the three traps previously recommended. Because this trap did not freeze shut even after running the bromine for several hours, the mercury safety valve was no longer necessary. Also omitted vere the sulfuric acid bubbler from the middle of the system and the copper sulfate reagent. The latter substance seemed to have no effect on the blank or result obtained with the new system conductometrically or gravimetrically. The Anhydrone after the copper oxide tube was not necessary, as small amounts of water had no effect on conductometric measurements. All purification tubes (and their heaters) were vertical to prevent the coppel, copper oxide, Ascarite, and Anhydrone from sagging and thus leaving a space oTer which the gas could flow. A 1-inch layer of glass wool, preceding the Ascarite column that followed the dry ice trap, absorbed practically all the bromine and volatile bromides t h a t were not frozen out. This permitted the Ascarite to be kept indefinitely FT-ithout caking or discoloring. The bromine and volatile bromides
evaporated from the glass vi001 on exposure to the atmosphere overnight. SPECIAL REAGENTS
Barium Hydroxide Solution ( 2 1 ) . Bubble carbon dioxide-free air for 45 minutes thSough 16 liters of distilled r a t e r in a n 18-liter bottle. Dissolve 18 grams of barium hydroxide octahydrate in 500 ml. of carbon dioxidefree water and filter into t h e treated water. Dissolve 2 grams of gelatin in 500 ml. of warm carbon dioxidefree u-ater, add 5 ml. of octyl alcohol, and pour the solution into t h e above. Dilute t o 18 liters with carbon dioxide-free water. Stopper, shake thoroughly, and allow to stand 1 week before using. Purified Bromine ( 6 ) . PROCEDURE
Fill the mater jackets with distilled water, and fill the standard cell and tempering coil with barium hydroxide solution. Turn on the switch for t h e constant temperature bath (40' C.), and heat the copper oxide tube to 500" C. and the copper oxide in the Ascaritecopper oxide tube to 400" C. Place purified bromine and sulfuric acid in the bromine bottle and flush (6). Place 0.2 gram of the sample, prepared as previously described (6), in a platinum boat, the bottom of which has been covered with a thin layer of spectrographic graphite powder. Cover the sample with about 0.5 gram of the graphite. Push the boat to the center of the reaction tube and flush the system for a few minutes with a rapid flow of argon. Heat the reaction tube to 925" C., and fill the dry ice box.
