Table II.
Comparison of Sensitivity of Pyrophosphate Method with Neocuproine Diethyldithiocarbamate, and Ammine Methods
Extraction required
Wavelength of Molar measurement, absorptivity, mp liters/mole-cm. 241 4, 800
Optimum concn. range,” p p.m. of Cu 2 9-9 3
Method Pyrophosphate S0 Keocuproine Yes 457 8 , 000 1 7-5 5 Diethyldithiocarbamate I-es 43i 12 34O 1 1-3 6 Ainniine (ammonia) S O 610 49 1 28t5-900 a Based on use of 20 to 6Oic transmittance range and 1-crn absorption cells. ~
(9) procedure and 4 1l.p.m. of copper, absorbance values of 0.779, 0.777, and 0.776 resulted. Nehlig’s (6) procedure was used for the ammine method. With 375 p.1j.m. of copper, absorbance values of 0.291, 0.290 and 0.290 were obtained. Although the pyrophosphate method is less sensitive than either the
neocuproine or diethyldithiocarbamate method, it has the advantage of not requiring the extraction of a metal chelate by an immiscible solvent. Even if tetraethylenepentamine were used instead of ammonia t o increase the sensitivity of the ammine by a factor of about 3.5 as huggested by Crumpler ( 2 ) ,
the pyrophosphate method is approximately 30 times as sensitive as the ammine method. LITERATURE CITED
(1) Buck, R . P., Singhadeja, S., Rogers, L. B.. i l s . 4 ~ .CHEM.26. 1240 (1964). ( 2 ) Crumpler, T. B., Ibzd., 19, 326 (1947). (3) Gahler, A. R., Ibzd., 26, 577 (1954). ( 4 ) Keattch, C. J , Talaah 3, 351 (1960). ( 5 ) Laitinen, H. A,, Onstott, E. I., J . Am. C h e m SOC.72, 4i29 (1950).
(6) Mehlig, J. P., IND.Esc. CHEM., ASAL. ED. 13, 533 (1941). ( 7 ) Sebel, &I. L., Ph.D. thesis, IVayne State University, Detroit, Rlich., 1959. (8) Rogers, L. B., Reynolds, C. .4.,J . Ana. Cheni. SOC.71, 2081 (1949). 19) Sandell, E. B., “Colorimetric Metal Analysis,” 3rd ed., p. 448, Interscience, S e w r o r k . 19.59. -I
~
(lO)-Watfers, J. T., Aaron, A , J . .4m. C‘hem. SOC.75, 611 (1953). (11) Watters, J. T., Mason, J., Aaron, A,, Ihid.,75, 542 (1963). RECEIVED for revieF December 3, 1962. Resubmitted October 14. 1063. A(>cepted October 14, 1963.
Behavior of Technetium Species with Cupferron G. B. S. SALARIA, CHARLES L. RULFS, and PHILIP J. ELVING The Universify of Michigan, Ann Arbor, Mich.
b Evidence is given for the formation of a pertechnetate adduct with cupferron in acidic media. No indication was found for significant technetium (IV) reactivity, but a technetium(lll) cupferrate does exist. Liquid-liquid extraction, supplemented by polarographic study, provides the principal evidence for these conclusions. A concentration or partial separation of pertechnetate from perrhenate is possible using cupferron and chloroform extraction.
M
with technetium has involved tracer-level and submilligram-level experimentation ( 2 ) . Most published information on the behavior of technetium states with reagents such as cupferron is concerned with the carrying or noncarrying of low levels of technetium by cupferron on other cupferrates ( I ) . However, little reliable information is available regarding the actual existence of cupferron adducts \T-ith technetium(VII), (IFr), or (111) states, or possible analytical applications. Although insufficient material and facilities were available for compound isolation and thermogravimetric study, the results from radiochemicallya ssayed liquid-liquid extractions, and. to a lesser extent from polarography and 146
UCH PRIOR WORK
ANALYTICAL CHEMISTRY
spectrophotometry, contribute to an understanding of those aspects of technetium chemistry n hich involve cupferron. The general analytical behavior of cupferron (4, 5 , 8 ) ha, been sufficiently well-documented that a reasonable definition of the condition3 of technetium reactiLity can indicate which separations are feasible. It was particularly interesting. however, to note the existence of a technetium(VI1) adduct, more analogous with the behavior of molybdenum(V1) than of rhenium(T’I1) (e),as subsequently dijcussed. EXPERIMENTAL
Chemicals. A solution of ammonium pertechnetate in water (pH 4) containing 46.75 mg. of T c g 9per ml. was obtained from the Oak Ridge Sational Laboratory; coulometric studies substantiate the stated concentration (10, 12). Technetium stock solution I was prepared by diluting 10 ml. of this solution to 250 ml.; 10 nil. of solution I was diluted to 100 nil. for 3tock solution 11. 811 other reagents were Nallinckrodt or J. T. Baker analytical reagent grade quality. The cupferron used (Baker RAdamson) was white in color and waa stored over ammonium carbonate. The nitrogen used for deoxygenating polarographic solutions was purified by passing
it wcccs*ively through alkaline pyrogallol solution, over heated copper uire, and through diqtilled water. Apparatus. A Sargent Model XXI Polarograph was used for polarographic measurements, which were made in a thermostated H-cell vs. a saturated calomel reference electrode. S.C.E.; all potentials are referred to the latter. The p H was measured with a Leeds R- Northrup Model 7664 pH meter; negative values of pH were not measured and only represent a formalized device for incorDoratinn the results obtained in 1 t o g-ir acid.-1Beckman Xodel 2400 DU instrument was used with 1.000-cni. quartz cells for spectrophotometric measurements. The /3-activity of technetium >ample5 was measured with a thin window Geiger tube and SuclearChicago \1odel-l51A scaler, a f l o ~ transfer-type scintillation n-ell counter (.ltomic Instrument Co. Model 162), or a 2a gas f l o ~proportional counter nith Suclear Corp. lIodel 162 scaler attached with flow transfer counter (Stomic Instrument Co. Xodel 162.1). Extraction Procedure. The test solution was usually prepared by diluting 5 ml. of stock solution I1 to 50 ml. in a volumetric flask with the desired acid to give a 0.1889mM T c solution. The pH of this solution was meaaured; a n aliquot was transferred to a 50-nil. separatory funnel and vigorously shaken Tvith a n equal yolume of diethyl ether or chloroform.
After separation of the two layers, the organic layer was dralvn off and the aqueous layer was again extracted wit’h an equal volume of soll.ent8. I n all extractions, the ether or 2hloroforni used was pre-equilibrated with aqueous acid corresponding to the pH: of the solution. One milliliter of the rwidual aqueous phase and 1 ml. of each extract n-ere t,ransferred to stainless steel planchets. ,Iny free acid was neutralized with ammonia, and the resulting mixture dried under an infrared lamp and counted. When chloroform n-as used for extraction, the 8-activity of the aqueous as well as the organic layer was measured with the scintillation n-ell count e r . The distrihution ratio, D. for all technetium specks, fo:- equal yolume contacts of the aquc’ous and organic phases, is in the organic 1)ha.e n = activity activity in the E queous phase C1o.e temperature control doe: not appear to be critical dLring the extractions, n hich mere condLcted a t ambient room teniperatureq (about 24” i 2 ” C.). Generally. equal volumes of aqueous and organic pha.es were contacted. Regardles-, rewlts expres-ed as per cent extraction ppre calculated on an equal volume ba I n anothrr set of experiments, 5 or 10 nil. of tcchnetiuni folution was treated with 1 or 2 nd., respectively, of freqhly prepared 6% cupferron solution in water and then vigorously shaken n i t h an equal i-olume of rther or chloroform. The 8-activities of the aqueous and organic lavers nere meaurrd. Similar experiments were conducted with Tc(1V) solutions obtained from ascorbic acid reduction of pertechnetate or Tc(II1) solutions from macroscale coulometric. reduction of pertechnetate (pH 1) a t -0.30 1’s.
S.C.E.
Polarographic Procedure. The polarographic test solution was prepared by diluting 2.5 nil. of stock solution I1 t o 25 ml. in a volumetric flask using dilute sulfuric acid a n d t h e desired amount of cupjerron t o give a 0.1889n~11Tc(VI1) soh tion nhich wah 0.141X in HzS04. About 15 ml. was transferred to the H-ce 1, deoxygenated n i t h nitrogen for 10 to 15 minutes, and then polarographed o7.er the desired potential range (ea. 4-0.20 to -1.80 volt) Ellz and id or it were determined graphically, utilizing th: average of the recorder trace. I n another qet of eqieriments, 2 ml. of stock solution I1 \YES diluted to 25 ml. with supporting elecxtrolyte and the desired amount of cupferron to gire a 0.l5lm.11 Tc qolution, which n a s 0.231 in I&S04 (pH = 2.0 by added H2SO4) : in some i n s t a r e s , the solution mas made 10% in ethanol by volume. Fifteen niilliliters of this solution was transferred t o the H-cell, deoxygenated with nitrogen for 10 to 15 minutes, and then polarographed (0 C to -2 0 volt). I n the easr of solutions containing ethanol nitrogen equilil rated with 10%
1
2
3
4 5 _N OF A C I D
6
7
8
Figure 1. Extraction of pertechnetate from aqueous acid solutions Original TcO; concentrations in aqueous soh.,, A: from HCI tion = 0.1 89 mM; Vag, = V solution with ether. A‘: from H2SOd solution with ether. B: from H2S04 solution containing cupferron with ether. C: from HCI solution containing cupferron with ether. D: from HCI or HzS04 solution containing no cupferron with CHC13. E: from H2S04 solution containing cupferron with CHC13. F: from HCI solution containing cupferron with CHC13. A l l cupferron systems were initially about 60 mM in the aqueous phase
ethanol was used for deoxygenation. Triton X-100 (concentration of 0.00137,) \vas added to suppress maxima. Ell2 and ill or il were determined as before.
when the aqueous phase is 5n1.lL cupferron. It is evident from the preceding data. which are .summarized in Figure 1, that pertechnic acid alone is very aignificantly extracted by ether as an oxonium system; the addition of cupferrou markedly improves the extraction. Chloroform furnishes a somewhat clearer case in respect to the effect’ of cupferron in that this solvent’ alo~lc> extracts very little technetium. The increased extraction n-Mi cupferron idefinite, if not spectacular; the estraction is better from hydrochloric, than from sulfuric, acid solution. I n ether extraction from 4-11 hydrochloric acid (Table I), the optimum allparent yield is a t a cupferron concentrstion of 39m.11; however, the decrease beyond this level is undoubt’edly an artifact resulting from increaiing ,selfabsorption errors in the counting. In any ca,se,it is ei,ident from the relativeljlarge (on a stoichiometric ha&) excess of cupferron necessary for optimum extraction that a relativelj. weakly bound “adduct” rather than a “compound” may be involved.
RESULTS AND DISCUSSION
Extraction of Technetium(VI1). Radiometric away for Tc99 indicates t h a t 1.4 t o $77, of technetium(VI1) can be extracted from aqueous solution by equal volumes of ether in the p H range 5.5 to -0.78 1%-ithrespect to HCI. I n 9J1 HCl the extraction falls to 15% because of the reduction of Tc(VI1) by hydrochloric acid giving in sequence Tc(V1) and (V) states including a binuclear species ( 1 ) . When an aqueous mixture of 1 ml. of 6% cupferron solution and 5 ml. of 0.1889mJ1 Tc(VI1) solution is contacted with ether, 1.8 to 95% of the Tc (1‘11) can be extracted in the p H range 5.5 to -0.95 (HCl). V i t h cupferron and 6-11 HCI, 99% of the Tc(VI1) can be extracted by tn-o equilibration. with ether. K i t h sulfuric acid, 1.4 to 59% of Tc(VII) can be extracted into an equal volume of ether in the pH range of 5.5 to -0.90. The presence of cupferron increases the level of extraction to 2 to 88% in the same p H range. Using 411 or 6-11 sulfuric acid, 99% of the Tc(VI1) can be iqolated by two ether extractions. Chloroform alone is essentially incapable of extracting the pertechnetate ion; the observed 0.6 to 1.9% extraction can be ascribed to the solubility of water in chloroform. The addition of cupferron increases the extraction to 2.8 to 75y0 in the p H range of 5.5 to -0.95 (HC1). and 2.8 to 307, in the pH range of 5.5 to -0.90 (H2S04). Using evaporated aliquots and conventional Geiger-Xuller counting, apparently only 0.057, of pertechnetate extracts from 0.19mX solution, ivhich is 0.1411 in HzSO,; this is increased to only O.llyo
Table I. Ether Extraction of Pertechnetate with Cupferron
(0.189niL1fTc04-; 4 J f HCI; TYaq. = 17,,, ) cupcupferron ferron concn., Extracted, concn., Extracted, mM 0 8
16 23 31
cic
13 .59 - .,
65 66 T3
niJl 39 47 -.
54
--
62 ii
70
8d
--
77 .. iD
65 66
Kliile other cayes of cupferron reactivity with oxygenated anionic species of elements-e.g., W,NO,V-are well known, the posbibility way considered of the occurrence of pertechnetate reduction by the cupferron, followed by extraction of a Tc(VI), (V),or (IV) cupferrate. Lower states than (IV) are not probable without a btronger reducing agent. Subsequent study in&cated that the (IV) state does not extract n ell with cupferron. Khile the (VI) state is not generally stable, the existence of Tc(V) in complexed or chelated form is possible (3). Polarographic and spectrophotometric study of the pertechnetate remaining unextracted in the aqueous phase and of technetium re-equilibrated into fre-h aqueous acid, after cupferron extraction, gave no evidence of the occurrence of any significant reduction. Extraction of Technetium(1V). Tc(IT’), formed by ascorbic acid reduction ( I S ) , extracts n i t h ether to an extent of 3.2% at pH 2.0. In the preaence of HC1 (pH 2.0 to -0.78), VOL. 3 6 , NO. 1, JANUARY 1964
147
Table 11. Polarographic Behavior of W a v e I of Technetium(VI1) in the Presence of Cupferron (0.15llm44 TCOi-’ 0.2M &SO4 +H,SO, (pH 2.0); 0.0015% Triton X-100; 10% ethanol) Cupferron concn., mM ic, pa. Em, volt 0.0 3.8 -0.13 0.10 3.8 -0.12 0.20 3.8 -0.11 0.30 3.8 -0.11 0.40 3.9 -0.10 0.50 3.8 -0.09 0.60 3.8 -0.10 0.70 3.8 -0.12 0.so 3.8 -0.13 0.90 4.3 -0.12
when cupferron is added, only 3 to 9% of the technetium extracts with ether. This indicates that Tc(1V) does not complex with cupferron. The slight increase in the technetium extraction is due to the air oxidation of Tc(1V) while shaking with ether. I n the presence of sulfuric acid (pH 0.0 to -0.90), 2.5 to 5.5% of the teclinetium extracts n-ith chloroform; the addition of cupferron does not produce any change. Technetium(1V) solutions vvere also prepared by coulometric reduction (‘7, 10) in phosphate-pyrophosphate and phosphate-citrate buffers. Deaerated hydrochloric or sulfuric acid was added to the rcduced solution and ether or chloroform extraction was tried with and without cupferron addition. Since significant reoxidation to (VII) occurred during these operations, the amount of Tc(VI1) was estimated polarographically. The modest enhancement of extraction found with cupferron in these experiments seems to be ascribable to the amount of Tc(VI1) present. Extraction of Technetium(II1). Aliquots of Tc(II1) solution, prepared by coulometric reduction (10) of pertechnetate in p H 1.3 solution (KCl HC1) at a potential of -0.30 volt were adjusted to various p H with HCl and were extracted with ether or chloroform. Extraction with chloroform varied from 3.7 to 6.0% over the p H range of 2.7 to -0.95. Extraction with ether varied from 0.2 to 6.1% over the p H range of 2.4 to -0.78. Polarographic examination of the Tc(II1) solution kept under nitrogen showed the presence of 3.7% Tc(VI1). With cupferron present, extraction with ether increased from 2.1 to 26.2% and with chloroform from 3.7 to 20.1%, indicating the formation of a Tc(II1) cupferrate (Figure 2). Polarography a n d Spectrophotometry. T h e information obtainable by these two techniques is limited by experimental difficulties. For ex-
+
148
ANALYTICAL CHEMISTRY
ample, t h e most pertinent region for study would involve strongly acidic solutions, in which t h e anodic dissolution of mercury prevents reading a true E ~ /for z the first polarographic wave of pertechnetate (10). The wave shifts on the addition of cupferron, in any case, seem to be rather complex and difficult to reproduce. Under conditions where polarographic wave I involves the reduction (VII) -P (111)-e.g., at p H 2-addition of cupferron gives no substantial shift in E I ~ z . The polarographic results were quite erratic due to the formation of a film on the dropping mercury electrode. Some improvement in reproducibility resulted from the addition of 10% ethanol, probably by lessening the tendency for film formation as a result of increased solubility of the film formed in the ethanolic solution (Table 11). The absence of a shift in EliP confirms the liquid-liquid extraction results, in that no substantial interaction of technetium and cupferron should occur at so high a pH. With 0.08mM Tc04- in 1.6111 H&04 the ratio of waves 1:II was 2.23:0.76 pa.-Le., 3 : 1-indicating a separation of the (VII) -+ (IV) and (IV) + (111) steps. The addition of about 70mM cupferron shifts El,* of wave I1 about 0.4 volt more positive, which implies the existence of a tightly bound Tc(II1) cupferrate. The principal utility of polarography was to confirm the lack of m y significant chemical reduction of pertechnetate by cupferron. Unextracted aqueous pertechnetate, or pertechnetate re-equilibrated into aqueous acid from cupferron-organic phaLes, seemed to retain the expected height of polarographic wave I and the appropriate ratio of waves 1 : I I (10). I n work with the (IV) and (111) states, the extent of any air reoxidation to (VII) could be determined polarographically. The presence of (VII) in (111) or (IV) states could also be detected spectrophotometrically. Cupferron apparently fluoresces, resulting in negative absorbance readings below about 350 mp, and obscuring many of the phenomena of likely spectrophotometric interest. However, the absence of absorption above 350 mp, which would occur if lower Tc states were present, also indicates the nonreduction of (VII) by cupferron. Separation of Pertechnetate a n d Perrhenate. Prior work involving a cupferron extraction of molybdate from perrhenate (6) indicates that perrhenate begins to extract, when hydrochloric acid or too high a concentration of sulfuric acid is used in the aqueous phase. Therefore, only moderately favorable conditions for separation by the extraction of pertechnetate are usable.
Paa Ez 0 . 4
a[ if?, [r
=;- 0.1
,
, 1
2
3
4
,
5 6 OF i i C l
,
,
, 7
8
9
Figure 2. Extraction of Tc(ll1) from hydrochloric acid solution Vag, = V,,,. A: 0.04 m M TC(III) with chloroform. A : same with 1% cupferron present. B: 0.1 m M Tc(lll) with ether. B‘: same with 0.5% cupferron present
Ten milIiliters of an aqueous phase, which was 4M in H2SO4, lOmM in Re(T711), and 0.189mM in Tc(VII), was twice extracted with 55-ml. portions of chloroform containing cupferron (120 ml. CHC13 was pre-equilibrated with 10 ml. 1% cupferron in 4M acid) and then washed with 10 ml. of pure chloroform. Counting showed that 74% of the pertechnetate had been extracted. Spectrophotometric examination of the aqueous phase indicated that 89% of the rhenium remained unextracted-Le., 11% had apparently been extracted with the teclinetium. CONCLUSIONS
There is good evidence for the formation of a technetium(VI1) adduct with cupferron although information on its composition and water solubility is lacking. Its existence in strongly acidic media suggests a [(Cupf.)+(TcOJ-] species (11). Equally plausible would be association of cupferron with undissociated pertechnic acid (9), which might explain both the need for high acidity for efficient extraction and the difference in behavior from that of perrhenic acid. Indeed, such an association may be involved in the formation of cupferrates. such as those of hlo or W(V1). KO evidence of an ether- or chloroform-extractable Tc(1V) cupferrate was found. However, competitively complexing anions were usually present. A technetium(II1) cupferrate evidently exists on the basis of both extraction and polarographic evidence. The latter suggests that the species may be a rather tightly bound cupferrate of the normal type-Le., Tc(Cupf.)J. A concentration separation of pertechnetate from perrhenate by cupferron extraction of the former is possible. However, only minimal conditions for satisfactory technetium recovery using aqueous sulfuric acid and chloroform solvent, can be used to reduce coextraction of rhenium.
LITERATURE CITED
(1) AndeW E
“The Radiochemistry of Technetium>’”ICAS-NS 30217 OfficeOf Technical Services, Washington, D.C., 1960. (2) Boyd, G. E., J . Chem. Educ. 36, 3 (1959). (3) Crouthamel, C. E., ANAL. CHEM.29, 1766 (1957). (4) Furman, K. H. Mason, W. B., Pekola, J. S., ANAL. CHEM.21, 1325 (1949). ( 5 ) Lundell, G. E. IF., Hoffman, J. I., “Outlines of Methods of Chemical Analysis,” Wiley, Xew York, 1938.
(6) Meyer, R. J., Rulfs, C. L., ANAL. CHEM.27, 1387 (1955). (7) Miller, H. H., Kelley, M. T., Thornson, P. F., “Advances in Polarography,” I. S. Longmuir, ed., Vol. 2, pp. 716-26, Pergamon Press, London, 1960. (8) Morrison, G. H., Freiser, H., ltSolvent Extraction in Analytica1 Chemistry,” R’iley, New York, 1957. (9) Rdfs, c. L., Hirsch9 R.F., Pacer, A., Nature lg9, 66 (1963). (10) Salaria, G. B. s.9 Rulf@, c. L.8 Elving, P. J., ANAL. CHEM. 35, 979 (1963). (11) Zbid., p. 983.
(12) Salaria, G. B. S., Rulfs, C. L., Elving, P. J., J . Chem. SOC. 1963, p. 2479.
(13) Salaria, G. B. s., Rulfs, C. L., Elving, P. J., Talanta, in press.
RECEIVEDfor review June 17, 1963. Accepted September 23, 1963. One of the authors (GBSS) thanks the National Academy of Sciences for an appointment supported by the International Cooperation Administration under the Visiting Research Scientist Program. This study was assisted by an equipment grant from the Michigan Memorial Phoenix Project of The University of Michigan.
Spectrophotometric Determination of Titanium Using Salicylic Acid in H 2 S 0 4 Medium A.
E. HULTQUIST
lockheed Missiles & Space
Co., A
Group Division o f lockheed Aircraff Corp., Sunnyvale, Calif.
b Discrepancies between the behavior of the complex of salicylic acid with titanium in concentrated HzS04 reported in the literature and that observed in some preliminary testing at Lockheed suggested that some additional investigation of this procedure should be performed. A stable 1 : 1 complex was formed in this medium by a modification of the sainple preparation. The molar absorptikity was calculated to be 2.5 X l o 3 c.nd the equilibrium constant for the complex formation was found to be 220. The use of the spectrophotometer eliminated interferences from several metal ions, and the spectra of the vanadium complex were determined.
D
URINQ THE PRICLIMINARY TESTINQ
of the specti~ophotometric procedure for the determination of titanium using salicylic acid JI HzSOd, some discrepancies in the data obtained by M. Schenk (4) and tholse produced by the Lockheed method bere noted. Schenk indicated that the complex was not stable and t h a t 86% HzSOd was the best medium for analytic a1 purposes. Data obtained in this laboratory have shown that the complex when formed by the Lockheed procedure is very stable and that a concentrated HzS04medium can be used very conveniently. The molar absorptivity and equilibrium constant were determined and confirm Schenk’s conclusion concerning the nature of the complex. The modified procedure indicated that, although Co+2, Cu+z, Mn+2, and MoS6 discolored the solutions, they did not seriously affect the titanium detern-ination a t the concentrations tested. The simultaneous
determination of titanium and vanadium appears to be possible, provided the vanadium complex can be stabilized. EXPERIMENTAL
Reagents. The salicylic acid solution was made by dissolving 1.00 gram of technical-grade salicylic acid in 75 ml. of concentrated H2S04 and diluting to 100 ml. with additional concentrated HzS04. Good reproducibility was achieved with this reagent. It was quite stable, but developed a yellow tinge on standing for 2 to 3 weeks. However, discolored reagent has been used without apparent interference. The use of a better grade of salicylic acid might improve the reagent in this respect. A standard solution of titanium was prepared by weighing accurately approximately 100 mg. of clean titanium sheet, 99.95% Ti, and dissolving in 25 ml. of 30% by volume H2SOc solution. When dissolution of the metal was complete, the blue violet, Ti+*, was oxidized to Ti+’ by adding 1 ml. of concentrated HNOI. This solution was transferred quantitatively to a 100-ml. volumetric flask and diluted with I&O to mark. The vanadium stock solution was made by accurately weighing and dissolving about 100 mg. of 99.9% vanadium metal in a 50% by volume HzSOl solution. This solution was transferred to a 100-ml. volumetric flask and diluted to volume with HzO. Less concentrated solutions were prepared by appropriate dilution. Apparatus. Beckman spectrophotometer Models DU or DK-2 recording units were used for all measurements. Method. The sample containing more than 7.5 ug. of titanium was placed in a small beaker. If the sample is not in solution, it can be dissolved by any convenient acid except those containing
phosphate, chromate, or manganate ions
as they are not expelled in the fuming procedure and interfere with the color reaction. When the sample was in solution, the total concentrated HzSOc added was brought to 5 ml. The solution was heated until fumes of SO, evolved, then cooled and transferred to a 25-ml. volumetric flask. The salicylic acid was pipetted to the beaker, swirled, and transferred to the volumetric flask. Concentrated II,SO‘ was used t o rinse the beaker several times, and these washings were added to the flask. The solution was diluted to volume with concentrated H2SOd. The absorbance of the sample was measured a t 410 mp against a reagent blank consisting of the identical amount of salicylic acid diluted to 25 ml. with concentrated H2SOI. The titanium content can be determined from a previously prepared calibration curve. The procedure used with the vanadium samples and with all other metal ions was the same. RESULTS AND DISCUSSION
The Complex Spectra. Absorption spectra of the salicylic acid-titanium complexes in concentrated and 86% H&O, are shown by curve B of Figure 1. These data were obtained on a Beckman DK-2 recording spectrophotometer within 2 hours of sample preparation. The absorption spectrum of salicylic acid in H2SOc using HzSOdas the reference solution (curve A ) was determined on a Beckman DU spectrophotometer. The data show that the spectra of the complexes are identical, even though the solvent media are different. The Complex Stability. The stability of the complexes with time is shown in Table I. Between readings, VOL. 36,
NO. 1, JANUARY 1964
149
