Table 111. Analysis of Synthetic Samples b y Procedure I
Weight
Ion
added
of nitrite
Weight, my.
found,
30 30 30 040 av. 30 32 ci, error +0 0 120 122
NO*-
0 1 0 0 5
Ca(I1) Mg(I1) Al( I I I )
c1-
NO.,-
030 6 8
pg.
0 0 2
1 33 9
Table IV. Analysis of Synthetic Samples b y Procedure II
Weight
Ion added
of nitrite
Weight, mg. 0 0 0 0 0 0 0 0 0 0
SO?
Ca(I1) JIg(I1) illlII1)
c1sop-
KO-
SO,-* (‘I K’
found, pg.
00132
16
os
004 107
av
pc error + O
00840
8
8
2h
036 16
177
1 1 1 1
8
av.
5 error
8
37 28 35 33 76 49 48 47 48
+ 0 95
CI-, ? ; 0 3 - , S04-2, K + , and S a + do not interfere in the determination. Cupric ion constitutes a serious interference. I t not only catalyzes the decomposition of diazonium salts, but also forms an insoluble complex with S-aminoquinoline ( I ) . Aimmoniareacts with nitrite to liberate nitrogen and will cause low results. Ferric ion oxidizes 8-aminoquinoline, especially at higher temperatures, to a highly colored product which absorbs a t 517 and 550 mp (1, 2 ) . This results in a serious interference in the present method. E L I M I N A T I O S O F INTERFERENCE B Y FERRIC 10s. If Fe(II1) is present in the sample, it must be removed or masked with a proper complexing agent. Trace amount? of phoslihate inhibit the oxidation of 8-aminoquinoline by ferric ions ( I , 2). This effect can be used to reduce the interference of Fe(II1) in the determination of nitrite by the present method. The data in Table I1 shox the effect of various amounts of phoslihate on the absorbance of a 10-nil. sample containing 100 pg. of SO2- and 243.5 pg. of Fe(II1). -1s the results indicate, the addition of 0.2 mmole of H 3 P 0 4 essentially eliminated all interference due to ferric ions. Care must be exercised, however, in adding
phosphate ions to the reaction misture, as the addition of too much phosphate will result in low absorbance. Analysis of Synthetic Samples. The method for the determination of nitrite was checked by the analysis of synthetic samples. Table 111 shows the results of these analyses by procedure I , while Table IT’ summarizes the results of this study by procedure 11. LITERATURE CITED
(1) Gustin, Y. K., Ph.1). dissertation, The Ohio State University, 1963. (2) Gustin, V. K., Sweet, T. R., ANAL. CHEM.3 5 , 1395 (1963). ( 3 ) Kolthoff, I. AI., Elving, P. J., “Treatise on Analytical Chemistry,” Part 11, 1‘01. 5 , p. 275, Interscience, Nex York, 1961. (4) Sawicki, E., Pfaff, J., Stanley, T. W., Rev. C-niv.Znd.Santander 5 , 337 (1963); C . A . 5 9 , 3299 (1963). ( 5 ) Sawirki, E., Stanley, T. W., Pfaff, J., D’Amico, A., Talanta 10,641 (1963). (6) Sawicki, E., Stanley, T. W., Pfaff, J., Johnson, H., ANAL. CHEM.3 5 , 3183 (1963). ( 7 ) “U. S. Pharmacopoeia,” p. 4 i , 1942. RECEIVEDfor review December 28, 1964. Arcepted February 15, 1965. Taken in part from the Ph.D. dissertation of Anthony Foris, The Ohio State University, Columbus, Ohio, 1965. Presented at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 1965.
Spectrophotometric Determination of Aluminum in the Presence of BerylIium with 5-SuIfo-4’-Diet hyl a mino - 2’, 2-Dihydroxyazo benzene T.
M. FLORENCE’
Australian Atomic Energy Commission Research Establishment, Lucas Heights, N.S. W., Australia A new reagent, 5-sulfo-4’-diethylamino 2’,2 - dihydroxyazobenzene (DDB), i s proposed for the spectrophotometric determination of aluminum in the presence of beryllium. At pH 4.7 the reagent forms a bright pink 1 to 1 complex with aluminum, which has a molar absorptivity of 41,000 at 540 mk. The beryllium complex has a molar absorptivity of less than 3 a t this wavelength, but large amounts of beryllium depress the aluminum color. Most interfering metals can be masked with (ethylenedinitri1o)tetraacetic acid (EDTA) or ferrocyanide, while gross amounts of impurities may b e removed b y a rapid triiso-octylamine extraction from 8M hydrochloric acid. The method has been successfully applied to the direct determination of aluminum in beryl and in NBL beryllium oxide spectrographic standards.
-
704
ANALYTICAL CHEMISTRY
T
most important water-soluble chromogenic reagents for aluminum are aluminon ( 6 ) , Eriochrome Cyanine R , Alizarin Red S, and Chrome Azurol S ( 4 ) . These reagents also produce strong colors with beryllium, and in most cases the reaction is actually more sensitive toward beryllium than aluminium. Since beryllium cannot be selectively masked, it must be separated comliletely before the aluminum determination is carried out. At pH 5, 8-quinolinol does not react with beryllium (6,6 ) , and aluminum quinolinate may be extracted into chloroform and the absorbance of the organic phase measured. However, a large number of other common metals also extract a t this pH, and interfere seriously with the aluminum determination. Certain di-o-hydroxyazo conipounds-e.g., Superchrome Garnet Y HE
(5-sulfo-2’,4’,2-tri hydroxyazobenzene)are known to form strong complexes with aluminum, but not with beryllium ( I ) , and have been used for the polarographic determination of aluminum in beryllium (3) and thorium (2) compounds. The weak orange color of the aluminum-Superchrome Garnet Y comples, h o w v e r , does not differ sufficiently from that of the free dye to enable aliectrol)hotonietric methods to. be used. By introducing a strongly auxochromic groui), such as the diethylamino group, into thc dye molecule, this obstacle may he overconie. l h e compound 5-sulfo-4’-diethylamino2’,2-dihydro>yaznbeiizent (DDl3) is light orange-yellow a t pH 4.7, while the aluminum com1,lex is bright 1)ink. nith a molar ahsorpti~ityof 41,000 at 540 1 Present address, Oak Ridge Sational Laboratories, Oak Ridge, Tenn.
mp. 'The molar a1jsorI)tivity of the beryllium complex is less than 3 at this wavelength. Large amounts of beryllium depress the aluminum color ( 3 ) . but the degree of deplcssion can be determined by spiking an aliquot of the sample solution with a knoivn quantity of aluminum, Several other metals produce colors with DDI3, but in most the color may be masked with cyanide or (ethylenedinitri1o)tetraGrosh amounts of . he removed by a tylamine extraction from 8.11 hydrochloric acid.
Figure 1 . Wovelengthabsorbance curves 1. 2.
Reagent blank vs. water Aluminum 16.7 pg.) plus DDB Y O . reagent blank Each solution contained 3.00 ml. of 0.030% DDB per 25 ml., pH 4 . 7 0
EXPERIMENTAL
Apparatus. -4Hilger I-vispek spectrophotometer with 1-cm matched quartz cells w a b used for all absorbance measurements Reagents. The synthesis of 5-
sulfo-4'-diethylamino-2',2-dihydroxyazobcnzene il)D13) \\as carried out b j czoupling diazotized 2-aminophenol4-sulfonic acid Rith m-diethylaminophenol.
,OH
HO,
Suspend 7.0 grams of 2-aminophenol-4-sulfonic acid (recrystallized from 4_\1 HC1) in 40 ml. of water, and dissolve by dropwise addition of 40% S a O H (pH 8 to 9). Cool to below 5" C., and add 9 ml. of 10.U HC1. Add a solution of sodium nitrite (2.8 grams in 10 ml. of water) over a period of 15 minutes, keeping the temperature below 5' C. Allow- the solution to stand in an ice bath for 30 minutes, then add 0.5 gram of urea to remove free nitrous acid. Prepare a solution of In-diethylaminophenol by dissolving 5.3 grams in 8 nil. of ethanol, then add this, with stirring, to the diazonium salt solution. .illow to stand a t room temperature for 5 to 6 hours, then filter the azo dye on a Buchner funnel and wash well with water. Dry in a desiccator over silica Re!. Yield is 9.3 grams. r h e purity of the azo product was determined by controlled potential coulometry, and found to be 96% as the anhydrous acid. 'The free acid is only slightly s~lu1)li~ in most solvents, but dissolves readily in alkalies. The reagent solution (0.0307c) is prepared by dissolving 30 mg. of DDI3 in 30 nil. of water containing one drop of l5M SH,OH, then diluting to 100 ml. Solutions of DDI3 are not stahle, and should lie freshly prepared every 1 or 2 days. X 57c solution of triiso-octylaniine (TI0.l) in toluene was equilibrated with 8.11 HC'I before use. S1)ccl)ure 1)erylliuin sulfate tetrahydrate was ohtaiiicd from ,Johnson, 1latthr.y and C'o., Ltd., London. The aluminum content was determined by
neutron activation analysis, and found to be 5 i 2 p.p.m. Recommended Procedure. DIRECT DETERMINASPECTROPHOTOMETRIC TION. Pipet a n aliquot of the slightly acid sample solution, containing less than 15 , ~ g of . aluminum and less than 10 mg. of beryllium, into a 25-ml. volumetric flask. -1dd 2.0 ml. of 0.1% potassium ferrocyanide, 2.50 ml. of a 1JZ sodium acetate-acetic acid buffer (pH 4.70), then 3.00 ml. of 0.030% DDI3. Dilute to about 20 ml. with water. Immerse the flask in a water bath a t 40" to 55" C. for 15 minutes, then cool to room temperature. Add 2.0 ml. of 2% EDTA, and dilute to @I 0 3 8.0 L volume. .liter 15 minutes measure 1H the absorbance in 1-em. cells against a reagent blank a t 540 mk. If the Figure 2. Effect of pH sample aliquot contained more than 1 . Reagent blank vs. water 200 pg. of beryllium, correct for beryl2. Aluminum (6.7 p g . ) plus DDB vs. reagent lium absorbance and depression (see blank Discussion). Each solution contained 3.00 ml. of 0.03070 T I 0 . i SEPARATION.Evaporate the DDB per 25 ml., acetate buffer, measured a t sample almost to dryness, and dissolve 540 rn@ the residue in 5 m1. of 8 M HCI. Transfer the solution to a 50-ml. separating ever, analytical measru'emimts were funnel, using another 5 ml. of HC1. made a t 540 mp because of the high Add 10 nil. of equilibrated TIOA solublank absorbance, whirh incwa-eh tion, and extract for 1 minute. Run the aqueous phase into a 150-ml. conical rapidly a t Ion-er wavelengths. flask, and wash the organic phase with The effect of pH on sensitivity is 5 nil. of 8.11 HC1, collecting the washings shown in Figure 2. The a1)sort)imc.c in the conical flask. Add 1 ml. of 15M does not vary greatly hctwern i)H 4.0 H S 0 3 and 5 ml. of 72% HC104, and and 5.0, but drolis sharlily a h v ? I i I I evaporate almost to dryness. Dilute 5.5. .-\ pH of 4 . i \\-as cahoscn as a to a suitable volume in a volumetric convenimt value,, since it is in thc, flask, and complete the analysis as maximum buffer region of' an acetntc, described under Spectrophotometric Debuffer. .\t 1iH 4.70 and 540 m p s thr, termination. aluminum-I)Dl< comiiles has a i)racticsl molar absorlitivity of 1 1 ,000, I< complex reaches a solution. maximum at 535 mp (Figure 1). HowVOL. 37, NO. 6 , M A Y 1965
705
I8
36
!k 4
a 045 4
om t
I
I
b
B
I
12
I I8
TIME lhoursl
Figure 3.
02
."
Stability of color Figure 4. Beryllium absorbance and depression
Absence of EDTA In presence pf 2 ml. of 2% EDTA Each solution contained 6.7 pg. of AI, 3.00 ml. of 0.030% DDB, p H 4 . 7 0
1.
2.
To test the reproducibility of the method under ideal conditions, 10 repeat determinations were carried out on 6 r g . of aluminum, using the recommended procedure. The results showed a relative standard deviatiofi of I-tO.57,. Formation and Stability of Complex. I n acidic media, the reaction between aluminum and di-o-hydroxyaao compounds is usually slow ( 7 ) , and requires long standing times, or heating, to form the cornidex completely. The formation of the aluminum-DDB complex was investigated between 30' and 80" C . , using a heating time of 15 minutes. The results showed that temperatures as low as 40' C. were sufficient to develop maximum color in this time. Although
Table I.
higher temperatures did not affect the sensitivity, it is advisable to avoid heating the solutions above 55' C. in order to prevent dissociation of the ferrocyanide, and to minimize the formation of other inert D D B complexes such as those of chromium and titanium. I n the absence of EDTA, the aluminum-DDB complex is stable for a t least 19 hours (Figure 3), and showed only a 2% decrease in absorbance after 120 hours. When EDTA is used as a masking agent, it attacks the aluminum complex slowly (Figure 3). However, the per cent decrease in absorbance was found to be independent of aluminum concentration, and if an initial waiting period of 15 minutes is allowed, and the sample and standard solutions are then
Interferences in Direct DDB Method
(5.0 rg. of AI present in each case) Amount Amount Foreign added, Relativea Foreign added, pg./25 ml. error, 70 element . pg./25 ml. element 100 0 Pb 100 A@; 100 0 Pt 100 As(II1) 100 Be 0 Sb(II1) 100 HI( I I1 ) Sn(IV) 100 I00 0 Th 100 100 0 Cu. Ti(IV) Cd 50 -9 50 U(V1) Ce( 111) 100 0 100 V(5') 100 10 so 19 20 10 +?: 100 100 Cr( 111) W(T'1) 10 10 0 Zn 100 Zr 100 -5 100 Cu(I1) 10 100 -8 Fe(II1) 20 0 F50 100 100 0 WII) 100 Li 100 P04-3 0 100 SiOa--2 3Ig 100 0 hln(I1) 100 c1500 mg. 0 lIo(V1) 100 clod500 mg. +6 r\"3 100 500 mg. 0 KO3?I'd 100 SOq-' 500 mg. +2 Si 100 0 Citrate 10 mg. Ferrocvanide and EDTA masking agents used Titanium forms blue-gray complex with 1)I)B Plus 0 1 ml of 37 HZOZ Plus 1 mg of B e + 2
+
+
706 *
ANALYTICAL CHEMISTRY
Relativea error, yo 0 0 0 -2 0 Ob
+6 60 3c +8 0
++ ++292
- 25 Od
0 0 +4 +3 0 +3 - 100
0 Beryllium depression of aluminum calor cells) Each solution contained 3.00 ml. of 0.030% DDB, p H 4.70, measured a t 5 4 0 mfi
0 Beryllium absorbance ( I -cm.
measured within 30 minutes of one another, no significant error will be incurred. The composition of the aluminumD D B complex a t pH 4.70 was investigated by the method of continuous variations and the mole ratio method. Both techniques showed that the 1 to 1 complex was the predominating species. The sensitivity of the analytical method increased slowly as excess reagent was added, and the dye concentration recommended in the procedure was chosen to combine high sensitivity with a reasonably low blank absorbance. Effect of Beryllium. Figure 4 shows that beryllium in amounts greater than about 200 pg. interferes both by producing a weak color of its own with D D B and by depressing the aluminum color. The per cent depression was found to be independent of aluminum concentration, and the aluminum-DDB complex obeyed Beer's law even with beryllium concentrations as high as 15 mg. per 25 ml. If it is necessary to determine aluminum in the presence of relatively large amounts of beryllium, the measured absorbance may be corrected by reference to calibration curves such as those in Figure 4. Honever, a simpler method is to spike a separate sample aliquot with a known amount of aluminum, and measure the recovery. This procedure provides a rapid and reasonably accurate method for the direct determination of aluminum, down to the 100-1i.p.m. level, in beryllium compounds. Study of Interferences, and TIOA Separation. I n addition to aluminum, D D B forms colored complexes a t pH 4.7 with several other metals-
11). Chromium, which is not extracted Table II.
Spectrophotometric Determination of Aluminum in Diverse Materials
A1 found, p.p.m.
Sample 2,5
ue.
A1
DlUS
Direct method5
Beryllium oxide, S B L No. 72- 1
72-2 72-3 72-4 72-5 96-1 96-2 96-6
TTOA separationa
Other methods
1
by TIOA under these conditions, is volatilized during evaporation of the HC1-HC104 aqueous phase. Applications. Table I1 shows some applications of the D D B method to the determination of aluminum in beryllium-containing materials. The New Brunswick Laboratories (Nf3L) beryllium oxide samples (0.3 gram) were dissolved in HC1O4 H2F2!and sample aliquots containing about 10 mg. of beryllium used for analysis. Spectrographic intensity ratios for aluminum in these samples were in better agreement with the DDIi, results than with the XBL nominal values.
+
695 i 12 400 i 9 221 i 3 108 It 3 92 f 4 225 It 3 125 i 2 27 f 8
703 i 9 391 6 230 f 2 108 i 2 93 i 5
792c 414c 252c l05C
... ... ...
202c 102c
+
65. 1.F
15d
Each figure is mean and standard deviation of four results using two sample weights. Gravimetric. c Nominal value (New Brunswick Laboratories). d Spectrographic.
ACKNOWLEDGMENT
0
viz., Fe, Cr. Co, C u , Ti, V , IT-, U, and Th-although, with the exception of cobalt and vanadium, the color reactions are far less sensitive t h a n that of aluminum. Advantage may be taken of the inert nature of the aluminum-DDR and E D T A complexes to use EDT.4 as a masking agent for some interfering metals, since the aluminum-dye complex, once formed, is attacked only slowly by E D T A (Figure 3 ) . Some difficulty was experienced in overcoming the interference of iron and cobalt. The brown-colored iron-DDB comp1e.c is destroyed by EDT.4, but even small amounts of iron cause low
aluminum recoveries. Cobalt produces a cherry-red color ( e = 31,000 a t 540 mp) which is unaffected by EDTA. Ferrocyanide proved to be the only masking agent capable of minimizing the iron and cobalt interference, without affecting the aluminum color. Table I is a comprehensive study of interferences in the D D B metkod, using ferrocyanide and E D T A masking agents as described in the Recommended Procedure. Small quantities ot vanadium can be complex with hydrogen peroxide. Many of the interfering elements may be separated from aluminum by a rapid TIO,1 extraction from 8-11 HCI (Table
I t is a pleasure to acknowledge the assistance of Y. J. Farrar and 13. 11. Ryan in obtaining the experimental results. Spectrographic analyses were carried out by L. S. Dale. LITERATURE CITED
(1) Coates, E., Rigg, B., Trans. Farads!!
Soc. 5 8 , 2058 (1962). ( 2 ) Florence, T. AI,, AKAL. CHEM.34. 496 (i962j. (3) Florence, T. AI., Izard, D. B., Anal. Chim. Acta 2 5 , 386 (1961). (4) Pakalns, P., Ibid., in press. ( 5 ) Pollock, E. N., Zopatti, L. P., Ibid., 2 8 , 68 (1963). ( 6 ) Sandell:, E. B., “Colorimetric AIetal Analysis, 3rd ed., Interscience, Yew York, 1959. ( 7 ) Willard, H. H., Dean, J. A4., ANAL. CHEY.2 5 , 249 (1963).
RECEIVED for review December 18, 1964. Accepted February 15, 1965.
Anion Exchange Separations in Hydrobromic Acid-Organic Solvent Media JOHANN KORKISCH and ISIDOR HAZAN Analytical Institute, University of Vienna, IX. Wahringerstrasse 38, Ausfria
b The anion exchange behavior of several metal ions, including gallium, iron, uranium, and cobalt, toward the strongly basic anion exchanger Dowex 1, X 8 has been investigated, in mixtures consisting of 90% organic solvent-1 0% 4.5N hydrobromic acid. Measurements of the distribution coefficients in these media show that for analytical separations, methanol i s the most suitable organic component of such a mixture. Under this condition gallium, indium, zinc, cadmium, lead, bismuth, and copper are retained b y the resin, whereas all other investigated elements-e.g., iron, alu-
minum, uranium, cobalt, the alkaline earth metals, etc.-pass into the effluent. Subsequent elution with water-1 0% 4.5N hydrobromic acid removes gallium, indium, and zinc, thus separating these metals from cadmium, lead, bismuth, and copper, which are further adsorbed on the resin. To avoid formation of bromine and ensure that all iron i s in the divalent oxidation state, an excess of ascorbic acid i s a d d e d to all solvent-hydrobromic acid mixtures. This separation principle i s applied to the determination of gallium in bauxite samples.
T
ion exhange behavior of copper, cobalt, zinc, and gallium in aqueous hydrobromic acid solutions has been investigated by Herber and Irvine who showed that anion exchange seliarations in such media offer no advantages over those in hydrochloric acid solutions under comparable experimental conditions. Vsing 0.3 to 0.5S hydrobromic acid as eluent Fritz and Garralda ( 1 ) separated mercury(II), bismuth (111), and cadmium(I1) from most othpr metal ions on the cation exchanger Dowex 50 W X8. I n 0.1 to 0.6.V acid these elements can be separated from each ot’her and from other metal ions. HE
(@j
VOL. 37, NO. 6, M A Y 1965
707
