- Email: [email protected]
Reaction of cobalt with 2-Nitroso-5-Diethylaminophenol and the solvent extraction of its cobalt complex
6%
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COMMUNICATlONS
Acknowledgement-The authors express their sincere thanks to Dr. N. A. Narasimham for his encouragement during the course of this work. Thanks are due to Dr. V. B. Kartha and Dr. Mahavir Singh for their helpful suggestions. Spectroscopy Division Atomic Research Centre Trombay, Bombay 400 085, India
N.
Bhabha
P. KARANIIKAR M. D. SAKSENA
REFERENCES 1.
V. Z. Krasil’schik and A. F. Yakovleva,
2. 1970 Annual
Book oJASTM
3. Y. Fujishiro and S. Sakai,
Zavodsk.
Lab., 1971.37, 181. Standards. Part 8. p. 350. ASTM, Philadelphia. Bunko Kenkyu. 1962.10, 141.
Summary-A spectrographic method for the determination of twenty-one trace lmpuritles in highpurity nickel oxide by the d.c. arc technique has been developed. A mixture of graphite and indium oxide in the ratio 2: I is used as buffer. The lowest determination limits for various elements lie between 1 and 10 ppm with an average relative standard deviation of f 129;. ZusaB--Ein spektrographisches Verfahren zur Bestimmung von einundzwanzig Spuren-Verunreinigungen in hochreinem Nickeloxid mit Hilfe des Gleichstromlichtbogens wurde entwikkelt. Ein Gem&h aus Graphit und Indiumoxid im Verhlltnis 2 : 1 dient als Puffer. Die niedrigsten Nachweisgrenzen mehrerer Elemente liegen zwischen I und 10 ppm mit einer relativen Standardabweichung von durchschnittlich + 12%. R&urn&-On a &labor6 une m&hode spectrographique pour le dosage de vingt et une impure& B l%tat de traces dans i’oxyde de nickel de haute puret6 par la technique de l’arc en courant continu. Un mklange de graphite et d’oxyde d’indium dans le rapport 2: I est utilid comme tampon. Les limites de dktermination les plus faibles pour divers tlements se situent entre I et IO ppm avec un &art type relatif moyen de + 12%.
T&ma,
Vol. 21. pp. 6%660
Pergamon Press. 1974. Printed m Great Britain
REACTION OF COBALT WITH 2-NITROSO-5 DIETHYLAMINOPHENOL
AND THE SOLVENT
EXTRACTION OF ITS COBALT COMPLEX (Received
S June 1973. Accepted
17 October
1973)
Nitrosonaphthols. such as I-nitroso-2-naphthol. 2-nitroso-I-naphthol and nitroso-R salt. are well-known rea. gents for the extraction and determination of cobalt. Earlier studieslW4 have shown that 2-nitroso-%dimethyl, aminophenol (nitroso-DMAP) is very useful for the determination of micro amount< of cobalt in iron and steel.’ commercial nickel salts6 and commercial chemicals.’ In general, the derivatives of naphthalene show stronger absorption than the derivatives ofbenzene, but the molar absorptivity of nitroso-DMAP is very large, comparec with that of nitrosonaphthol derivatives. This is because mtroso-DMAP possesses the strongly electron-donating dimethylamino-group in the para-position. This study concerns a nitrosocompound which possesses a morf strongly electron-donating group, viz. 2-nitroso-S-diethylaminophenol (nitroso-DEAP). By comparison with nitroso-DMAP, the cobalt complex of nitroso-DEAP has slightly greater molar absorp tivity, is much less soluble. and is much more readily extracted into 1,2-dichloroethane (DCE). Thus, the reagen is expected to be very useful for the preconcentration and determination of micro amounts of cobalt in very dilute solutions. In order to establish optimum conditions for its use the appropriate equilibrium constants have beer measured. EXPERIMENTAL
The reagents, apparatus and procedures for the determination of equilibnum constants, other than those listen below. have been described previously.4
SHORTCOMMUNlCATlONS
655
Fig 1. Absorption spectra of the complex and the reagent in aqueous solution. (1) pH = 6.3. lO-cm cell. [Reagent] 3 x IOehM; (2) [Reagent] 3 x IO-‘M, [CO] I x 10v6M.
Rengenr Nnroso-DEAP was obtained in the same way as nitroso-DMAP. The purified nitroso-DEAP hydrochloride (nitroso-DEAP.HCI) IS obtained as yellow needle-like crystals of the monohydrate (C,0H,,N202Cl~H,0). Elemental analysis gave: C 48.29;. H 6.67,. N 11.4%; C,,H,,N,03CI requires C 4&3x, H 6.9% N 11.3%. Procedure
The solubility of the cobalt nitroso-DEAP and DMAP complexes in water were determined as follows. Various amounts of cobalt were added to an aqueous solution (pH 6.2) containing nitroso-DMAP or nitroso-DEAP (1 x IO-‘M). and these solutions were shaken for about 5 hr at 25”Cand filtered; 5 ml of the filtrate were shaken with 5 ml of DCE. The orgamc phase was washed with hydrochloric acid. and the absorbance measured. Figure 2 shows the results obtained. The nitroso-DEAP complex is not as soluble as that of nitroso-DMAP, so occasionally precipitation occurred at concentrations before the break-point. With nitroso-DMAP, the absorbances before the break-point are almost in agreement with the values expected from the molar absorptivity, but with mtroso-DEAP they are somewhat smaller. Therefore the solubility of the nitroso-DEAP complex was calculated from the absorbance after the break-point.
x IO% Cobalt
(ndroso - DMAP)
x 10m6M(nltroso-DEAP)
Fig. 2. Solubility of the cobalt complex in aqueous solution. (1) nitroso-DEAP. l-cm cell. 462 nm; (2) nitroso-DMAP, 2-mm cell, 456 nm.
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Table 1. The results obtained Nitroso-DEAP
Nitroso-DMAP PKI e’(MR
X nm
nm i,;,, (MRd."m EMU,, I~mole-'.cm-' loI3 h?. log&t, log& h3aa, &I,1M A.,,_:(HR;
2.83 k 0.01 (p 0.1) 8.38 & 0.03 (p 0.2) 442 (aqueous solution pH 6.3) 408 (1,2-dichloroethane) 462 (1,2-dichloroethane) 6.2 x 10“ at 462 nm (1.2-dichloroethane) 2.35 It 0.02 (p 0.1) 24.73 f 0.16(~ @I) -0.21 + 0.20(@ 0.1) 7.3 3.6 x lO-6
269 f 0.03 840 f 0.05 445 404 456 6.0 x lo4 at 456 nm 1.42 + @02 26.17 f O-12 0.42 f 0.22 3.1 6.5 x 10-s
Dx = partition coefficient of X, K, = extraction constant, &,a, = solubility of MR,.
RESULTS
AND
DISCUSSION
The experimental results are illustrated in Figs. 1-7 and the values of the constants calculated from them are given in Table 1. The reagent and complex have similar absorption spectra (Fig. 1) but the difference in the distribution ratios of reagent and complex at pH < - 1.2 or > 12.8 can be exploited to remove the excess of reagent from the organic phase after complexation. Table 2 records the results of experiments to establish the best conditions for stripping. Nitroso-DEAP is very similar to nitroso-DMAP in its synthesis, colour, crystal form, absorption spectra of the reagent and cobalt complex, etc., but differs in some respects. such as the solubility of the cobalt complex, the extractability of the reagent and the cobalt complex, etc. (Table 1). The greater pK, , for nitroso-DEAP . HCI than for nitroso-DMAP.HCl is ascribed to the ethyl group having a stronger electron-donating effect than the methyl group. The solubility of nitroso-DEAP and its cobalt complex in DCE is larger than nitroso-DMAP. However, as nitroso-DEAP is very extractable into DCE, the extraction constant. K, , is smaller.
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16
PH
Fig. 3. Plots of absorbance 0’s.pH and of log KIMII,us. pH. (I) [Reagent] 3 x 10-6M; (2) [Reagent] 3 x IO-6M. [Co] 1 x 10-bM;(3) log K’ua, us. pH, IOcm cell. 500 nm.
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.2
PH Fig. 4. Plot of log Q vs. pH.
1 I D-Us+ &z K81 m
[Reagent] 1 x 10e3 M. 4~ =
where D,, = [HRIJHR], and subscripts o and a denote the organc and aqueous phases respectively.
0
?-
0
6-
0
H
x
5&
0 4-
L
B a
0 3-
0 2C11;;
34’ 0
360
420
460
Wovebnglh,
500
540
!
nm
Fig. 5 Absorption spectra of the complex and the reagent in the organic phase. (1) Complex (1 x lo- ‘M). 1 cm cell: (2) reagent blank, 1 cm cell. both after washing with HCl(1 + 1). (3) [Reagent] 5 x IO-“M. 1 mm cell.
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-
Fig. 6. Effect of pH on the extraction of cobalt. [Reagent] I x IO-“M; [Co] 1 x IO-“M, 462 nm, I cm cell.
Determination ofcobalt
For the determination of cobalt, nitroso-DEAP is used in a similar manner to nitroso-DMAP. Both reagents in DCE can be stripped with alkaline and acidic solutions. By treating the organic phase with hydrochloric acid the excess of reagent and other metal complexes co-extracted into the organic phase are stripped. In case of Initroso-2-naphthol and 2-nitroso-l-naphthol etc., the excess of the reagent and the other metal complexes in the organic phase must be removed with alkaline and acidic solutions, respectively. The molar absorptivity of at 462nm, which is probably larger than that of all the nitroso-DEAP complex is 62 x IO’ l.mole-‘*cm-’ other nitroso cobalt complexes used up to the present. Besides, as the partition coefficient of the cobalt complex is very large, nitroso-DEAP is especially advantageous for concentration of micro amounts of cobalt in very dilute solution by solvent extraction, and for subsequent determination of cobalt.
0
4
2 Mole
r&o,
6
c RI / cc03
Fig. 7. Mole-ratio method for organic phase. 462 nm, I cm cell, pH 6.2, [Co] 1 x IO-“M.
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COMMllNlCATlONS
Table 2. Stripping of the organic phase with HCI and KOH Absorbance of organic phase after Extraction system 1*
2t
Stripping solution 1N KOH HCl(l + 2) HCl(1 + 1) cont. HCl 1N KOH HCI (1 + 2) HCl(1 + 1) cont. HCI
1st wash 0.189 0.034 0016 0026 0.721(0.532) 0.654(@620) 0.631(0-615) 0.357(0.331)
2nd wash 0.100 0.013 0007 0.007 0.724QI.624) @636(0.623) 0*622(0.615) 0.229(0.222)
3rd wash 0.125 0.007 0004 O-005 @757(0.632) O-638(0.631) 0*625(0.621) -
Reagent solution 5 x 10-3M, cobalt solution 1 x lo- 5M. reference l,Zdichloroethane, I462 nm. * Aqueous phase-H,0 (5 ml) + buffer solution (1 ml) + reagent solution (1 ml); organic phase-5 ml. t Aqueous phase-cobalt solubon (5 ml) + buffer solution (1 ml) + reagent solution (1 ml), organic phase-S ml. The values in parentheses were obtained by subtracting the reagent blank. Acknowledgement-The advrce and drscussion.
author is greatly indebted to Professor Kyoji Tbei of Okayama University for valuable
Department of Chemisrq Faculty ofScience, Okayama Uniuerst! Tsushuna, Okayama-shi, Japan
SHOII
Moro~tzu
REFERENCES
K Toei and S. Motomizu. Nippon Kagaku Zasshi, 1971. 92,92. 2. T. Korenaga. S. Motomlzu and K. Tbet. N~ppoa Ku&u Zussh~. 1972. 93, 2445. 3. S. Motomizu. Burtsrki Kagaku, 1971, 20, 590. 4. It/ca~. Anal. Chirn. Actu. 1971. 56, 415. 5. Idem. Bunseki Kagaku. 1971,20, 1507. 6. Idem. Nippon Kagaku Zasshi, 1971, 92, 726. 7. Idem. Analyst. 1972. 97, 986. I
Summary-2-Nitroso-5-diethylaminophenol (nitroso-DEAP) is a useful reagent for cobalt, with which it forms a 1: 3 complex. Its pK,, and pK,, values are 2.83 and 8.38, and the formation constant, log K,,,, is 24.73. The reagent and complex may be extracted into 1,tdichloroethane from water. the log of the respecttve partition coefficients being 2.35 and 7.3. The extracted cobalt complex 1s not stripped by 6M hydrochloric actd, whereas excess of the reagent is. The molar absorptivity of the complex in 1.2-dichloroethane is 6.2 x 10’ 1 .mole - ’ .crn-’ at 462 run, which is larger than that of other nitroso derivatives. Zusammenfassung-2-Nitroso-5-dilthylaminophenol (Nitroso-DEAP) ist ein gutes Reagens fur Kobalt. mit dem es einen 1 :3:Komplex bildet. Seine pK,,- und pK,,,-Werte betragen 283 bzw. 8.38, die Bildungskonstante log KMR, 24,73. Reagens und Komplex kiinnen aus Wasser in 1.2-Dichlorathan extrahiert werden; die Logarithmen der betreffenden Verteilungskoefhzienten betragen 2.35 und 7.3. Der extrahierte Kobaltkomplex wird durch 6M Salzaure nicht zuriichextrahiert. dagegen das iiberschiissige Reagens. Der molare Extinktionskoetlizient des Komplexes m 1.2.Dichlorlthan betrlgt 6,2 x IO4 1 .mol-‘.cm-’ bei 462 run, ein grol3erer Wert als bei anderen Nttrosoderivaten. R&urn&-Le 2-mtroso 5-diethylaminophenol (mtroso-DEAP) est un reactif utile pour le cobalt, avec lequel il forme un complexe 1: 3. Ses valeurs pKa, et pKa2 sont 2.83 et 8.38, et la constante de formatton. log KM,, est 24.73. Le reactif et le complexe peuvent Etre extraits de l’eau en 1,2dichlorithane. le log des coefficients de partage respectifs &ant 2.35 et 7.3. Le complexe de cobalt
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extrait n’est pas reextrait en acide chlorhydrique 6M. tandis que I’excis de renctif I’est. Lr coefficient d’absorption moltculaire du complexe en 1.2-dichlorethane est 6.2 x 10J lmole- ‘. cm- ’ h 462 nm. valeur qui est plus grande que celles des autres derives nitroso.
Tuisnra. Vol. 21. pp. 660-663. Pcrgamon Press 1974. Printed I” Great Brttam
TRACE
ANALYSIS BY MICROWAVE EXCITATION OF SEALED SAMPLES-III DETERMINATION OF-,0005-25 ng OF Te AND O-25-25 ng OF Se IN 0.5 ml OF AQUEOUS SOLUTION (Received
11 July
1973. Accepted
8 October
1973)
The determination of selenium and tellurium in (submanogram amounts has become more important with the increasing awareness of the importance of these elements in biological systems.‘.’ Recent methods for this include atomic-absorption spectrometry using flameless atomizing systems-’ A.5and (especially for tellurium) atomic fluorescence.” The results of these methods, however, leave room for improvement and no measurements below 1 ng/ml have been reported for these elements. The use of the electrodeless discharge lamp (EDL) as a sampleholder for the determination of (subktanogram amounts of Cd, Tl, In, Hg, Zn and Pb has already been described’s The present paper investigates its use for the determination of traces of selenium and tellurium The main problem considered is that of finding the most suitable matrix. This may consist of more than one component in order to maintain constant excitation conditions and at the same time suppress interfering band spectra. The matrix used will depend on the element concerned and thermodynamic data such as vapour pressure, solubility and stability of the element and its compounds (in our case oxides or halides). EXPERIMENTAL
Apparatus The vacuum apparatus and procedure for preparing the EDL’s, the spectrometer, the monochromator, the detector and the microwave generator are the same as before.7s The signals were corrected for a background value, measured immediately afterwards at a wavelength 0.3 nm longer than that of the line. The cavity used was the $-wave type (E.M.S. 214 L), the quartz used was “Vitreosil” (Thermal Syndicate). A nominal volume of 100 4 of matrix f sample solution was added to the EDL. Tellurium
A tellurium tube was prepared’.” containing 1mg of metallic tellurium and I mg of iodine. This tube gave an intense tellurium spectrum with the strongest lines at 238.3 and 238.6 nm; these. lines were used m further investigations In the literature it was found that tellurium tetrachloride has favourable values for its solubility. thermodynamic stability and vapour pressure. Therefore in the first experiments 100 ng of tellurium tetrachloride were used in a matrix solution (slightly acidified to prevent hydrolysis) containing 2.5 pg of sodium chloride and 2.5 pg of lithium chloride, in order to maintain constant excitation conditions, and about I mg of germanium as a getter in order to prevent interfering band spectra.’ With this matrix however, the EDL did not show any Te lines. Replacing the germanium getter by boron did not give any result either. As seen above, addition of iodine to tellurium gave an intense Taspectrum It could therefore be expected that addition of iodine to the tellurium tetrachloride introduced, would also give results, but because of its high volatility the iodine causes difficulty if used for quantitative purposes. Potassium iodide does not give such difficulties, however, and because it was found that an EDL containing potassium iodide showed exactly the same spectrum as an EDL contaming iodine, potassium iodide was used in further experiments. Moreover. in the 200-300 nm region no interfering band spectra appeared, so there was no necessity to use a getter. The optimum amount of the iodide and the optimum power (65 W, incident power minus reflected power) were determined Some filler-gases were tested: helium and hydrogen were equally good. but oxygen was useless. Different kinds of quartz were tested, “Vitreosil” was found satisfactory. Other types could also be used. Selenium The strongest selenium line from an EDL (1 mg of selenium) was at 204 nm From thermodynamic can be concluded that selenium may be determined when present as SeO,, SeF, or SeCI, in the EDL.
data it
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COMMUNICATlONS
Acknowledgement-The authors express their sincere thanks to Dr. N. A. Narasimham for his encouragement during the course of this work. Thanks are due to Dr. V. B. Kartha and Dr. Mahavir Singh for their helpful suggestions. Spectroscopy Division Atomic Research Centre Trombay, Bombay 400 085, India
N.
Bhabha
P. KARANIIKAR M. D. SAKSENA
REFERENCES 1.
V. Z. Krasil’schik and A. F. Yakovleva,
2. 1970 Annual
Book oJASTM
3. Y. Fujishiro and S. Sakai,
Zavodsk.
Lab., 1971.37, 181. Standards. Part 8. p. 350. ASTM, Philadelphia. Bunko Kenkyu. 1962.10, 141.
Summary-A spectrographic method for the determination of twenty-one trace lmpuritles in highpurity nickel oxide by the d.c. arc technique has been developed. A mixture of graphite and indium oxide in the ratio 2: I is used as buffer. The lowest determination limits for various elements lie between 1 and 10 ppm with an average relative standard deviation of f 129;. ZusaB--Ein spektrographisches Verfahren zur Bestimmung von einundzwanzig Spuren-Verunreinigungen in hochreinem Nickeloxid mit Hilfe des Gleichstromlichtbogens wurde entwikkelt. Ein Gem&h aus Graphit und Indiumoxid im Verhlltnis 2 : 1 dient als Puffer. Die niedrigsten Nachweisgrenzen mehrerer Elemente liegen zwischen I und 10 ppm mit einer relativen Standardabweichung von durchschnittlich + 12%. R&urn&-On a &labor6 une m&hode spectrographique pour le dosage de vingt et une impure& B l%tat de traces dans i’oxyde de nickel de haute puret6 par la technique de l’arc en courant continu. Un mklange de graphite et d’oxyde d’indium dans le rapport 2: I est utilid comme tampon. Les limites de dktermination les plus faibles pour divers tlements se situent entre I et IO ppm avec un &art type relatif moyen de + 12%.
T&ma,
Vol. 21. pp. 6%660
Pergamon Press. 1974. Printed m Great Britain
REACTION OF COBALT WITH 2-NITROSO-5 DIETHYLAMINOPHENOL
AND THE SOLVENT
EXTRACTION OF ITS COBALT COMPLEX (Received
S June 1973. Accepted
17 October
1973)
Nitrosonaphthols. such as I-nitroso-2-naphthol. 2-nitroso-I-naphthol and nitroso-R salt. are well-known rea. gents for the extraction and determination of cobalt. Earlier studieslW4 have shown that 2-nitroso-%dimethyl, aminophenol (nitroso-DMAP) is very useful for the determination of micro amount< of cobalt in iron and steel.’ commercial nickel salts6 and commercial chemicals.’ In general, the derivatives of naphthalene show stronger absorption than the derivatives ofbenzene, but the molar absorptivity of nitroso-DMAP is very large, comparec with that of nitrosonaphthol derivatives. This is because mtroso-DMAP possesses the strongly electron-donating dimethylamino-group in the para-position. This study concerns a nitrosocompound which possesses a morf strongly electron-donating group, viz. 2-nitroso-S-diethylaminophenol (nitroso-DEAP). By comparison with nitroso-DMAP, the cobalt complex of nitroso-DEAP has slightly greater molar absorp tivity, is much less soluble. and is much more readily extracted into 1,2-dichloroethane (DCE). Thus, the reagen is expected to be very useful for the preconcentration and determination of micro amounts of cobalt in very dilute solutions. In order to establish optimum conditions for its use the appropriate equilibrium constants have beer measured. EXPERIMENTAL
The reagents, apparatus and procedures for the determination of equilibnum constants, other than those listen below. have been described previously.4
SHORTCOMMUNlCATlONS
655
Fig 1. Absorption spectra of the complex and the reagent in aqueous solution. (1) pH = 6.3. lO-cm cell. [Reagent] 3 x IOehM; (2) [Reagent] 3 x IO-‘M, [CO] I x 10v6M.
Rengenr Nnroso-DEAP was obtained in the same way as nitroso-DMAP. The purified nitroso-DEAP hydrochloride (nitroso-DEAP.HCI) IS obtained as yellow needle-like crystals of the monohydrate (C,0H,,N202Cl~H,0). Elemental analysis gave: C 48.29;. H 6.67,. N 11.4%; C,,H,,N,03CI requires C 4&3x, H 6.9% N 11.3%. Procedure
The solubility of the cobalt nitroso-DEAP and DMAP complexes in water were determined as follows. Various amounts of cobalt were added to an aqueous solution (pH 6.2) containing nitroso-DMAP or nitroso-DEAP (1 x IO-‘M). and these solutions were shaken for about 5 hr at 25”Cand filtered; 5 ml of the filtrate were shaken with 5 ml of DCE. The orgamc phase was washed with hydrochloric acid. and the absorbance measured. Figure 2 shows the results obtained. The nitroso-DEAP complex is not as soluble as that of nitroso-DMAP, so occasionally precipitation occurred at concentrations before the break-point. With nitroso-DMAP, the absorbances before the break-point are almost in agreement with the values expected from the molar absorptivity, but with mtroso-DEAP they are somewhat smaller. Therefore the solubility of the nitroso-DEAP complex was calculated from the absorbance after the break-point.
x IO% Cobalt
(ndroso - DMAP)
x 10m6M(nltroso-DEAP)
Fig. 2. Solubility of the cobalt complex in aqueous solution. (1) nitroso-DEAP. l-cm cell. 462 nm; (2) nitroso-DMAP, 2-mm cell, 456 nm.
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Table 1. The results obtained Nitroso-DEAP
Nitroso-DMAP PKI e’(MR
X nm
nm i,;,, (MRd."m EMU,, I~mole-'.cm-' loI3 h?. log&t, log& h3aa, &I,1M A.,,_:(HR;
2.83 k 0.01 (p 0.1) 8.38 & 0.03 (p 0.2) 442 (aqueous solution pH 6.3) 408 (1,2-dichloroethane) 462 (1,2-dichloroethane) 6.2 x 10“ at 462 nm (1.2-dichloroethane) 2.35 It 0.02 (p 0.1) 24.73 f 0.16(~ @I) -0.21 + 0.20(@ 0.1) 7.3 3.6 x lO-6
269 f 0.03 840 f 0.05 445 404 456 6.0 x lo4 at 456 nm 1.42 + @02 26.17 f O-12 0.42 f 0.22 3.1 6.5 x 10-s
Dx = partition coefficient of X, K, = extraction constant, &,a, = solubility of MR,.
RESULTS
AND
DISCUSSION
The experimental results are illustrated in Figs. 1-7 and the values of the constants calculated from them are given in Table 1. The reagent and complex have similar absorption spectra (Fig. 1) but the difference in the distribution ratios of reagent and complex at pH < - 1.2 or > 12.8 can be exploited to remove the excess of reagent from the organic phase after complexation. Table 2 records the results of experiments to establish the best conditions for stripping. Nitroso-DEAP is very similar to nitroso-DMAP in its synthesis, colour, crystal form, absorption spectra of the reagent and cobalt complex, etc., but differs in some respects. such as the solubility of the cobalt complex, the extractability of the reagent and the cobalt complex, etc. (Table 1). The greater pK, , for nitroso-DEAP . HCI than for nitroso-DMAP.HCl is ascribed to the ethyl group having a stronger electron-donating effect than the methyl group. The solubility of nitroso-DEAP and its cobalt complex in DCE is larger than nitroso-DMAP. However, as nitroso-DEAP is very extractable into DCE, the extraction constant. K, , is smaller.
-
16
PH
Fig. 3. Plots of absorbance 0’s.pH and of log KIMII,us. pH. (I) [Reagent] 3 x 10-6M; (2) [Reagent] 3 x IO-6M. [Co] 1 x 10-bM;(3) log K’ua, us. pH, IOcm cell. 500 nm.
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.2
PH Fig. 4. Plot of log Q vs. pH.
1 I D-Us+ &z K81 m
[Reagent] 1 x 10e3 M. 4~ =
where D,, = [HRIJHR], and subscripts o and a denote the organc and aqueous phases respectively.
0
?-
0
6-
0
H
x
5&
0 4-
L
B a
0 3-
0 2C11;;
34’ 0
360
420
460
Wovebnglh,
500
540
!
nm
Fig. 5 Absorption spectra of the complex and the reagent in the organic phase. (1) Complex (1 x lo- ‘M). 1 cm cell: (2) reagent blank, 1 cm cell. both after washing with HCl(1 + 1). (3) [Reagent] 5 x IO-“M. 1 mm cell.
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Fig. 6. Effect of pH on the extraction of cobalt. [Reagent] I x IO-“M; [Co] 1 x IO-“M, 462 nm, I cm cell.
Determination ofcobalt
For the determination of cobalt, nitroso-DEAP is used in a similar manner to nitroso-DMAP. Both reagents in DCE can be stripped with alkaline and acidic solutions. By treating the organic phase with hydrochloric acid the excess of reagent and other metal complexes co-extracted into the organic phase are stripped. In case of Initroso-2-naphthol and 2-nitroso-l-naphthol etc., the excess of the reagent and the other metal complexes in the organic phase must be removed with alkaline and acidic solutions, respectively. The molar absorptivity of at 462nm, which is probably larger than that of all the nitroso-DEAP complex is 62 x IO’ l.mole-‘*cm-’ other nitroso cobalt complexes used up to the present. Besides, as the partition coefficient of the cobalt complex is very large, nitroso-DEAP is especially advantageous for concentration of micro amounts of cobalt in very dilute solution by solvent extraction, and for subsequent determination of cobalt.
0
4
2 Mole
r&o,
6
c RI / cc03
Fig. 7. Mole-ratio method for organic phase. 462 nm, I cm cell, pH 6.2, [Co] 1 x IO-“M.
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659
COMMllNlCATlONS
Table 2. Stripping of the organic phase with HCI and KOH Absorbance of organic phase after Extraction system 1*
2t
Stripping solution 1N KOH HCl(l + 2) HCl(1 + 1) cont. HCl 1N KOH HCI (1 + 2) HCl(1 + 1) cont. HCI
1st wash 0.189 0.034 0016 0026 0.721(0.532) 0.654(@620) 0.631(0-615) 0.357(0.331)
2nd wash 0.100 0.013 0007 0.007 0.724QI.624) @636(0.623) 0*622(0.615) 0.229(0.222)
3rd wash 0.125 0.007 0004 O-005 @757(0.632) O-638(0.631) 0*625(0.621) -
Reagent solution 5 x 10-3M, cobalt solution 1 x lo- 5M. reference l,Zdichloroethane, I462 nm. * Aqueous phase-H,0 (5 ml) + buffer solution (1 ml) + reagent solution (1 ml); organic phase-5 ml. t Aqueous phase-cobalt solubon (5 ml) + buffer solution (1 ml) + reagent solution (1 ml), organic phase-S ml. The values in parentheses were obtained by subtracting the reagent blank. Acknowledgement-The advrce and drscussion.
author is greatly indebted to Professor Kyoji Tbei of Okayama University for valuable
Department of Chemisrq Faculty ofScience, Okayama Uniuerst! Tsushuna, Okayama-shi, Japan
SHOII
Moro~tzu
REFERENCES
K Toei and S. Motomizu. Nippon Kagaku Zasshi, 1971. 92,92. 2. T. Korenaga. S. Motomlzu and K. Tbet. N~ppoa Ku&u Zussh~. 1972. 93, 2445. 3. S. Motomizu. Burtsrki Kagaku, 1971, 20, 590. 4. It/ca~. Anal. Chirn. Actu. 1971. 56, 415. 5. Idem. Bunseki Kagaku. 1971,20, 1507. 6. Idem. Nippon Kagaku Zasshi, 1971, 92, 726. 7. Idem. Analyst. 1972. 97, 986. I
Summary-2-Nitroso-5-diethylaminophenol (nitroso-DEAP) is a useful reagent for cobalt, with which it forms a 1: 3 complex. Its pK,, and pK,, values are 2.83 and 8.38, and the formation constant, log K,,,, is 24.73. The reagent and complex may be extracted into 1,tdichloroethane from water. the log of the respecttve partition coefficients being 2.35 and 7.3. The extracted cobalt complex 1s not stripped by 6M hydrochloric actd, whereas excess of the reagent is. The molar absorptivity of the complex in 1.2-dichloroethane is 6.2 x 10’ 1 .mole - ’ .crn-’ at 462 run, which is larger than that of other nitroso derivatives. Zusammenfassung-2-Nitroso-5-dilthylaminophenol (Nitroso-DEAP) ist ein gutes Reagens fur Kobalt. mit dem es einen 1 :3:Komplex bildet. Seine pK,,- und pK,,,-Werte betragen 283 bzw. 8.38, die Bildungskonstante log KMR, 24,73. Reagens und Komplex kiinnen aus Wasser in 1.2-Dichlorathan extrahiert werden; die Logarithmen der betreffenden Verteilungskoefhzienten betragen 2.35 und 7.3. Der extrahierte Kobaltkomplex wird durch 6M Salzaure nicht zuriichextrahiert. dagegen das iiberschiissige Reagens. Der molare Extinktionskoetlizient des Komplexes m 1.2.Dichlorlthan betrlgt 6,2 x IO4 1 .mol-‘.cm-’ bei 462 run, ein grol3erer Wert als bei anderen Nttrosoderivaten. R&urn&-Le 2-mtroso 5-diethylaminophenol (mtroso-DEAP) est un reactif utile pour le cobalt, avec lequel il forme un complexe 1: 3. Ses valeurs pKa, et pKa2 sont 2.83 et 8.38, et la constante de formatton. log KM,, est 24.73. Le reactif et le complexe peuvent Etre extraits de l’eau en 1,2dichlorithane. le log des coefficients de partage respectifs &ant 2.35 et 7.3. Le complexe de cobalt
SHORT
660
COMMUNICATIONS
extrait n’est pas reextrait en acide chlorhydrique 6M. tandis que I’excis de renctif I’est. Lr coefficient d’absorption moltculaire du complexe en 1.2-dichlorethane est 6.2 x 10J lmole- ‘. cm- ’ h 462 nm. valeur qui est plus grande que celles des autres derives nitroso.
Tuisnra. Vol. 21. pp. 660-663. Pcrgamon Press 1974. Printed I” Great Brttam
TRACE
ANALYSIS BY MICROWAVE EXCITATION OF SEALED SAMPLES-III DETERMINATION OF-,0005-25 ng OF Te AND O-25-25 ng OF Se IN 0.5 ml OF AQUEOUS SOLUTION (Received
11 July
1973. Accepted
8 October
1973)
The determination of selenium and tellurium in (submanogram amounts has become more important with the increasing awareness of the importance of these elements in biological systems.‘.’ Recent methods for this include atomic-absorption spectrometry using flameless atomizing systems-’ A.5and (especially for tellurium) atomic fluorescence.” The results of these methods, however, leave room for improvement and no measurements below 1 ng/ml have been reported for these elements. The use of the electrodeless discharge lamp (EDL) as a sampleholder for the determination of (subktanogram amounts of Cd, Tl, In, Hg, Zn and Pb has already been described’s The present paper investigates its use for the determination of traces of selenium and tellurium The main problem considered is that of finding the most suitable matrix. This may consist of more than one component in order to maintain constant excitation conditions and at the same time suppress interfering band spectra. The matrix used will depend on the element concerned and thermodynamic data such as vapour pressure, solubility and stability of the element and its compounds (in our case oxides or halides). EXPERIMENTAL
Apparatus The vacuum apparatus and procedure for preparing the EDL’s, the spectrometer, the monochromator, the detector and the microwave generator are the same as before.7s The signals were corrected for a background value, measured immediately afterwards at a wavelength 0.3 nm longer than that of the line. The cavity used was the $-wave type (E.M.S. 214 L), the quartz used was “Vitreosil” (Thermal Syndicate). A nominal volume of 100 4 of matrix f sample solution was added to the EDL. Tellurium
A tellurium tube was prepared’.” containing 1mg of metallic tellurium and I mg of iodine. This tube gave an intense tellurium spectrum with the strongest lines at 238.3 and 238.6 nm; these. lines were used m further investigations In the literature it was found that tellurium tetrachloride has favourable values for its solubility. thermodynamic stability and vapour pressure. Therefore in the first experiments 100 ng of tellurium tetrachloride were used in a matrix solution (slightly acidified to prevent hydrolysis) containing 2.5 pg of sodium chloride and 2.5 pg of lithium chloride, in order to maintain constant excitation conditions, and about I mg of germanium as a getter in order to prevent interfering band spectra.’ With this matrix however, the EDL did not show any Te lines. Replacing the germanium getter by boron did not give any result either. As seen above, addition of iodine to tellurium gave an intense Taspectrum It could therefore be expected that addition of iodine to the tellurium tetrachloride introduced, would also give results, but because of its high volatility the iodine causes difficulty if used for quantitative purposes. Potassium iodide does not give such difficulties, however, and because it was found that an EDL containing potassium iodide showed exactly the same spectrum as an EDL contaming iodine, potassium iodide was used in further experiments. Moreover. in the 200-300 nm region no interfering band spectra appeared, so there was no necessity to use a getter. The optimum amount of the iodide and the optimum power (65 W, incident power minus reflected power) were determined Some filler-gases were tested: helium and hydrogen were equally good. but oxygen was useless. Different kinds of quartz were tested, “Vitreosil” was found satisfactory. Other types could also be used. Selenium The strongest selenium line from an EDL (1 mg of selenium) was at 204 nm From thermodynamic can be concluded that selenium may be determined when present as SeO,, SeF, or SeCI, in the EDL.
data it