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ANALYTICAL CHEMISTRY, VOL. 50, NO. 13, NOVEMBER 1978
ion. To obtain well resolved reference ion mobility data, a temperature of 180 t o 220 "C should be utilized. The MNO+ ion observed in the plasma chromatography of benzene contains only a single m / e ion at any temperature and appears to be very stable. This ion may therefore be used as a characteristic product ion for benzene identification, particularly a t low temperatures. Increased sensitivity may be achieved by t h e addition of NO to the carrier gas.
LITERATURE CITED
(4) (51 (6) (7)
F. W. Karasek, Anal. Chem., 48, 710A (1974). M. J. Cohen and F. W. Karasek, J , Chromatogr. Sci., 8, 330 (1970). F. W. Karasek, M. J. Cohen, and D. I. Carroll, J . Chromafogr. Sci., 9, 390 11971). D. 1,'CarroIL 1. Dzidic, R. N. Stillwell. and E, C. Horning, Anal. Chem.. 47, 1956 (1975). F. W. Karasek, H. H. Hill, Jr., and S.H. Kim, J . Chromatoqr., 117, 327 (1976). F. W. Karasek, S. H. Kim, and H. H. Hill, Jr., Anal. Chem., 48, 1133 (1976). T. W. Carr, Anal. Chem., 49, 828 (1977).
(8) (9) (10) (1 1) (12) (13) (14) (15) (16) (17) (18) (19)
(20)
T. W. Carr, J . Chromatogr. Sci., 15, 85 (1977). D. F. Hunt and T. M. Harvey, Anal. Chem.. 47, 1965 (1975). D. F. Hunt and T. M. Harvey, Anal. Chem., 47, 2136 (1975). E. C. Horning, M. G. Horning, D. I . Carroll, I. Dzidic, and R. N. Stillwell, Anal. Chem., 45, 936 (1973). S. H. Kim, Ph.D. Thesis, Department of Chemistry, University of Waterloo, Waterloo, Ontario, 1977. E. W. McDaniel. V. Cermak, A. Dalgarno, E. E. Ferguson, and L. Friedman, "Ion-Molecule Reactions", Wiley-Interscience, New York. N.Y., 1970, p 66. E. A. Mason and H. W. Schamp, Jr., Ann. Phys.. 4, 233 (1958). H. E. Revercomb and W. E. Mason, Anal. Chem., 47, 970 (1975). A. Good. D. A. Durden. and P. Kebarle. J. Chem. Phvs., 52. 212 119701. F. H. Field and J. L. Franklin, "Electron Impact Phenomena and the Properties of Gaseous Ions", Academic Press, New York, N.Y., 1970, pp 243-482. F. W. Karasek and D. W. Denney, Anal. Chem., 46, 633 (1974). P. Kebarle, R. Yamdagni. K. Hiraoka, and T. 6. McMahome, Int. J . Mass Spectrom. Ion Phys., 19, 71 (1977). A . Good, Chem. Rev., 75, 561 (1974)
RECEIVED for review May 9, 1978. Accepted August 2,1978.
Solvent Extraction-Spectrophotometric Determination of Boron with 2,4-Dinitro- 1,8-naphthalenediol and Brilliant Green Kiyoaki Kuwada, Shoji Motomizu, and Kyoji T6ei" Depatiment of Chemistry, Faculty of Science, Okayama University, Tsushima-naka, Okayama-shi, Japan
The highly sensitive and selective spectrophotometric method for boron was newly developed. Boric acid aqueous solution was evaporated to dryness in the presence of sodium acetate and mannitol, and boron reacted with 2,4-dinitro-1,8naphthalenediol (DNNDO) in acetic acid medium to form a complex anion, which was extracted into toluene with brilliant green. The excess of brilliant green co-extracted into toluene was removed by washing the organic phase with 2 M hydrochloric acid. By measuring the absorbance of brilliant green in toluene at 637 nm, boron was determined. The calibration curve in toluene was linear in the range from 0 to 1 X M of boron, and the molar absorptivity was 10.3 X lo4 L mol-' cm-'. The absorbance of the reagent blank was 0.020 k 0.002, and the reproducibility was very good. By the recommended procedure, about 0.5 ppb of boron in an aqueous solution can be determined. This method was applied for the determination of boron in natural waters.
T h e analytical chemistry of boron is very important in the fields of nuclear-reactor materials, industrial metallurgy materials, pharmacy, and agriculture. Furthermore, boron is one of a few common elements whose spectrophotometric determination must be developed. Several spectrophotometric methods for boron were reported u p to date. Of these, the methods using t h e extraction of tetrafluoroborate with methylene blue (1-3) and t h e curcumin (4-10) are very sensitive and have been used for the determination of micro amounts of boron. In the former, though the reaction can be carried out in an aqueous solution, the hydrofluoric acid is necessary and a long time is consumed for the complete formation of tetrafluoroborate. Besides, the absorbance of the reagent blank is relatively large. The latter is probably 0003-2700/78/0350-1788$01 .OO/O
the most sensitive of the reagent~sreported up to date and has often been used for the determination of boron since 1903 ( 1 1 ) . In general, the methods using curcumin are 1Yei-y troublesome, involve many practical difficulties, and often require many precautions, though many improvements have been made. For such reasons, the sensitive, selective, and moreover simple method for determining micro amounts of boron is now expect,ed to be developed. The studies of the solvent extraction of the ion pairs formed between complex anions and large cations are very important in analytical chemistry. Of these extractions, the one with a cationic dye possessing a large molar absorptivity can he applied to the spectrophotometric determination of metals. Such a method possesses the possibility for development of a highly sensitive and selective method, in which the chelate reagent takes charge of the high selectivity and the cationic dye takes charge of the high sensitivity. The authors reported such extraction systems for the determination of neodymium with 5,7-dinitrooxine and Rhodamine B (121, iron with 1chloro-2-nitrosophenol and Rhodamine I3 (13 ~1.51,and arsenic with 4-nitrocatechol and brilliant green (16). I n this paper, the authors report the very useful method for boron, in which boron reacts with 2,1-dinitro-1,8naphthalenediol in acetic acid medium to form a complex anion, and subsequently this anion is extracted into toluene with brilliant green and the absorbance of the hilliant green in toluene is measured. The proposed method is very sensitive, selective, reproducible, and not troublesome, and the absorbance of the reagent blank is very small.
EXPERIMENTAL Apparatus. The absorptiometric measurements were made on a Hitachi-Perkin-Elmer model 139 spectrophotometer and a Hitachi EPS-X'I' recording spectrophotometer in a glass cell o f 10-mm path length. An Iwaki, Model V-S Type KM, shaker was c_ 1978 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 50, NO. 13, NOVEMBER 1978
used to shake the separatory funnel. Reagents. 1,8-Naphthalenediol, This was synthesized according to literature (17, 18). A mixture of 4 g of l-naphthol8-sulfonic acid sodium salt (Tokyo Kasei Co.), 18 g of potassium hydroxide, and 8 mL of water was fused slowly, with vigorous stirring, to 200-230 "C in a zirconium crucible. After fusion and cooling, the mixture was dissolved in 100 mL of 13% hydrochloric acid solution, and a few milliliters of concentrated hydrochloric acid was added to it, and it was diluted with water to 300 mL. After being boiled and filtered hot, it was cooled. The product precipitated was recrystallized from a mixture of benzene and ligroin (mp 143-145 "C, lit. (17) mp 140 "C). 2,4-Dinitro-l,8-naphthalenediol. This was synthesized according to the literatdre (19). To 4 g of l&naphthalenediol, 10 mL of acetic anhydride and about 0.5 mL of pyridine were added. After warming on the water-bath for 10 min, water was added and the excess of acetic anhydride was hydrolyzed. The product precipitated (1,8-diacetoxynaphthalene)was recrystallized from acetic anhydride (crystalline: mp 152-154 "C). Six grams of the diacetoxynaphthalene recrystallized was slowly added to 30 mL of concentrated nitric acid, kept at 25-30 "C. The product was washed with water, dried on the steam-bath, and recrystallized from acetic acid (crystalline: mp 200 "C). A solution of 4 g of potassium hydroxide in 100 mL of methyl alcohol was boiled with 2 g of 2,4-dinitro-l-hydroxy-8-acetoxynaphthalene for 1 h. The alcohol was driven off and the dark red product was dissolved in boiling water and excess of hydrochloric acid was added. The product precipitated was recrystallized from dilute hydrochloric acid (crystalline: mp 180-182 "C, lit. (19): 180-182 "C). 2,4-Dinitro-1,8-naphthalenediol (DA'NDO) Acetic Acid Solution. Recrystallized DNNDO, 0.064 g, was dissolved in glacial acetic acid to give a 100-mL of solution (2.5 X M). This solution was used for at least 10 days. Cationic Dye Solution. Cationic dye was dissolved in deionized water to give a 1 x 10 M solution. Standard Boron Solution. Boric acid (H3B03),0.618 g, was dissolved in deionized water to give a 100-mL solution (1.000 X IO-' M). This solution was stocked in a polyethylene bottle and used after accurate dilution. Sodium Acetate Solution. Sodium acetate (CH,COONa.3H20), 0.136 g, was dissolved in deionized water or glacial acetic acid to give a 100-mL solution (1 x lo-' M). This solution was stocked in a polyethylene bottle. Mannitol Solution. Mannitol, 0.016 g, was dissolved in deionized water to give a 100-mL solution (1 X M). This solution was stocked in a polyethylene bottle. Commercially available acetic acid contains less than 0.570 of water and was used without further purification. All reagents used were of analytical-reagent grade. Procedure. From the results examined in this work, the following procedure is most recommended as the standard procedure. Standard Procedure. Transfer the sample solution containing boron up to 0.5 pg into a porcelain or platinum evaporating dish, and add 1 mL each of mannitol (1 X M)and sodium acetate (1 X M) solutions and, if necessary, adjust the pH with sodium hydroxide or hydrochloric acid to 3-11. Evaporate to dryness on the water-bath. Add 3 mL of glacial acetic acid and 1.5 mL of DNNDO acetic acid solution (2.5 x 10-~3 M) and allow it to stand for more than 1 h. Transfer this acetic acid solution into a separatory funnel, wash the dish with water. and pour into the separatory funnel. Add 1 mL of 1 N sodium hydroxide solution and dilute it to about 30 mL with water (the pH is adjusted to 2.5 to 3.5). Add 0.5 mL of a brilliant green solution (1 X M) and 5 mL of toluene. After shaking it for 10 min, discard the aqueous phase. Add 10 mL of 2 N hydrochloric acid solution and shake for 10 min. Measure the absorbance in toluene at 637 nm in a glass cell of 10-mm path length. Pre-experiments. Reaction of Boric Acid with Some Reagents. In general, boric acid reacts with anthraquinones possessing hydroxyl group in the peri position (20,P I ) , aliphatic 1,3-diols (221,and catechols (23)to form six- or five-membered rings. Boric acid also reacts with chromotropic acid (l,&dihydroxynaphthalene-3,6-disulfonic acid) (24-26) in aqueous solution at pH 3-5. l&Dihydroxynaphthalene and DNNDO, though these are very similar to chromotropic acid, did not react with boric acid
1789
in aqueous solution at room temperature or even at higher temperature. When the mixture of boric acid and DNNDO solutions was evaporated to dryness at pH 3.5 to ,4.5 (initial pH), the boron complex was formed and extracted into toluene with brilliant green. The absorbance of the reagent blank, however, was large and what is worse, the reproducibility was very low. This is because the reagent and the complex formed are unstable at the higher temperature. The other nine reagents such as 1,8dihydroxynaphthalene, 2,6-dihydroxybenzoic acid, 5-nitrosalicylic acid, 3,5-dinitrocatechol,4,5-dichlorocatechol, 3,5.dinitrosalicylic acid, 5-chlorosalicylic acid, saligenine, and pyrocatechol were examined at room and higher tempmature. Of these reagents, 2,6-dihydroxybenzoic acid reacted with boric acid a t room temperature and the ion-pair was extracted into toluene, and the reproducibility was the highest of the reagents examined. The molar absorptivity was smaller than that expected and was 4.3 X lo4 L mol-' cm-' and the absorbance of the reagent blank was relatively large (about 0.3) with malachite green. Even when the mixture of boric acid and 2,6-dihydroxybenzoic acid was evaporated to dryness and the complex formed was extracted into toluene with malachite green, the molar absorptivity was about 8 X lo4 L mol-' cm-'. It was found that boric acid reacted1 with DNNDO in glacial acetic acid and less than 2% (vjv) of water did not interfere with the complex formation, and the salt such as sodium acetate was necessary to complete the reaction with DNh'DO. Thus, boric acid aqueous solution (1 X M) was diluted with glacial acetic acid to give a 1 X lo-' M or less solution. To 3 mL of this boric acid-acetic acid solution, 1.5 mL of DNNDO acetic acid solution and 1 mL of sodium acetate acetic acid solution (lo-' M) were added. After standing for 1 h, the boron complex was extracted into toluene according to the standard procedure. The calibration curve was linear at the range of 0-1 X M boric acid and the molar absorptivity calculated from the slope was 10.6 X lo4 L mol-' cm-'. When the sodium acetate was not added, about 8070 of the boron was reacted with DNNDO. Of the other nine reagents, 1.8-dihydroxynaphthalenereacts with boric acid. In this reagent, however, the reproducibility was very low because a substance insoluble both in aqueous and organic phase was produced on extraction. For these reasons, the compl'ex formation of boric acid with DNNDO was carried out in an acetic acid medium in the presence of a salt such as acetate.
RESULTS AND DISCUSSION Contamination f r o m W a t e r , Reagents, a n d Vessels. Contamination from water was examined by using five kinds of waters: (1) type 2 water was treated with anion-exchange resin (Dowex 21K(SBR-P), -OH type), by passing through a glass column (20 cm in length and 2 cm in diameter), (2) water deionized with ordinary apparatus and distilled with distilling apparatus of Pyrex glass commercially available, (3) water deionized and distilled with distilling apparatus of copper, (4) type 5 was treated with anion-exchange resin, and ( 5 ) deionized water. The contamination from these waters was checked according to the standard procedure. Water type 2 showed relatively large absorbance increase as the sample taken increased. When 0: 10, and 30 mL of water 2 were used, the absorbances were 0.020, 0.068, and 0.142, respectively. When 10 and 30 mL of water 3 were used, the absorbances were 0.027 and 0.036, respectively, and when 10 and 30 mL of water 4 were used, the absorbance's were 0.034 and 0.039, respectively, and when 10 and 30 mI, of water 5 were used, the absorbances were 0.036 and 0.040, respectively. When 10 and 40 mL of water 1 were used, the libsorbances were 0.020 and 0.026, respectively: that is, the absorbance is the smallest of the five. From these results, water which is deionized, distilled, and treated with anion-exchange resin is the best of all,and must be used when the calibration curve is prepared. Contamination from vessels of gla:;s and of polyethylene was examined. In the same kinds of vessel which are made of the same material and by the same manufacturer. the solutions which pHs are various from 6.5 to 11.5 were transferred and a 5-mL portion of the solution was pipetted
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ANALYTICAL CHEMISTRY, VOL. 50, NO. 13, NOVEMBER 1978
into a platinum dish and the contamination was checked according to the standard procedure. The contamination from glass vessels was very large and the more alkaline the solution was and the longer the solution stayed in the vessel, the larger the contamination was. For example, when the aqueous solutions of p H 8.5 and 11.5 remained in a new volumetric flask for three days, the absorbance increases were 0.028 and 1.423, respectively. Contamination from the polyethylene bottle was very small even when the solution was strongly alkaline. For example, even when the solution of p H 11.5 remained in a new 100-mL polyethylene bottle for 13 days, the absorbance increase was 0.010. Contamination from the evaporating vessel was examined on evaporating to dryness. As evaporating vessels, porcelain and platinum dishes, glass beakers (Pyrex and standard glass beakers, 50 mL), Teflon beakers (50 mL), zirconium crucible (50 mL) and nickel crucible (50 mL) were checked. Deionized water, 10 mL, was transferred into each vessel and contamination from the evaporating vessels was examined according to the standard procedure. As a result of the examination, it was concluded that platinum and porcelain dishes showed the smallest absorbance, their dispersion was very small, and there was no difference between porcelain and platinum dishes: that is, the absorbance was 0.020 f 0.002 (five determinations). Teflon beakers and zirconium crucibles also showed small absorbances (0.024 f 0.004 and 0.028, respectively). The former, however, is not recommended because of more time consumed for evaporation and it is more expensive than porcelain dishes. Other vessels (glass beakers and nickel crucibles) showed large absorbances and, what is worse, the reproducibility was very bad. For these reasons, the porcelain dish is the most useful of the vessels examined, because it is very cheap and has large thermal conduction. In this work, the authors used the porcelain dish with diameter and volume of about 80 mm and 80 mL, respectively. Though the porcelain dish is very useful, never use it when the solution is very alkaline: the absorbance was too large to be measured when about 0.1 N sodium hydroxide solution was evaporated to dryness in a new porcelain dish. Contamination from reagents used in this procedure seems t o be very small: that is, the absorbance of the reagent blank is 0.02 to 0.03 and only small parts of the absorbance of the reagent blank seem to be caused by reagents. In this work. the reagents were used without purification. Evaporation of the Sample Solution to Dryness. In the curcumin method ( I O ) , evaporation is carried out in the presence of sodium hydroxide, and the reaction with curcumin is carried out in the mixture of acetic acid and sulfuric acid. The authors also examined evaporation in the presence of sodium hydroxide in place of mannitol and sodium acetate in platinum dishes, and the boron was reacted in the mixture of acetic and sulfuric acids with DNNDO. Though the reaction of boron with DNNDO proceeded almost to completion. the amounts of sulfuric acid must be controlled very severely according to the amounts of sodium hydroxide used and, what is worse, the reproducibility was bad. Thus, another method for prevention of volatilization of boron was examined. In general, boron does not volatize more in the alkaline solution than in the neutral or acidic solutions, and boric acid reacts in the aqueous solution easily with mannitol. So, the effects of mannitol and alkalies which are not so strong as sodium hydroxide were examined. When, in the absence of mannitol and sodium acetate, 10 mL of boric acid aqueous solution (boron: 0.324 fig) was evaporated to dryness, only about 8% boron remained in the dish. When in the presence of 1mL M) 10 mL of the solution was evaporated, of mannitol 88% boron remained in the dish, and when in the presence of 1 mL of sodium acetate (lo-' M) 10 mL of solution was
evaporated, 90% of the boron remained in the dish. When in the presence of 1 mL of mannitol and sodium acetate, 10 mL of the solution was evaporated, the loss of boron was very small and constant. As a result of this examination, both mannitol and sodium acetate must be added to the sample solution before evaporation. It must be noted that sodium acetate is necessary not only to prevent the boron from volatilization, but also to complete the reaction with DNNDO. The effect of alkaline substances as well as neutral and acidic substances (Na2C03,NaHC03, KH2P04, Na2HP04, NaC1, NaHS04,Na2S04,NH4C1)was examined. Of these salts, the salts of weak acids such as carbonate and phosphate are very effective, and when 1 mL of lo-* M solution of CH3COONa, Na2C03,NaHC03, and Na2HP04 was used, the absorbances obtained according to the standard procedure (boron: 0.324 fig) were 0.638, 0.629, 0.629, and 0.638, respectively, and the absorbances of the reagent blank were 0.016 to 0.020. Unexpectedly, the salts of strong acids such as chloride and sulfate are also effective, though their effect is smaller than acetate: that is, when 1 mL of M solution of NaC1, NaHS04, Na2S04,and NH4Cl were used in place of sodium acetate, the absorbances obtained according to the standard procedure (boron: 0.324 fig) were 0.506,0.272,0.588, and 0.547, respectively. When only the amounts of sodium acetate were varied in the standard procedure, the largest and most constant absorbances were obtained in the range of 0.2 to 6.0 mL of sodium acetate (1 X lo-* M) added to 10 mL of sample solution. In the case of disodium hydrogen phosphate, the optimal amounts added to 10 mL of sample solution were 0.2 to 1.0 mL of 1 x M solution. The effect of pH on the evaporation of the sample solution was examined for sodium acetate and disodium hydrogen phosphate. The pHs were adjusted with hydrochloric acid and sodium hydroxide solutions after adding 1 mL of sodium acetate (1 x M) or 0.6 mL of disodium hydrogen M) to 10 mL of sample solution. The phosphate (1 X optimal pH regions both in acetate and phosphate were very wide and were pH 3 to 12 and 4 to 10, respectively. Phosphate reacts easily with metal ions such as iron and alkaline earth metal ions to give a complex or precipitate. In fact, calcium ions which amount was one hundred-fold of boron interfered with the boron determination. In these results, acetate is the most useful in the practical analysis and the most effective of all salts examined. The effect of the amounts of mannitol was examined by varying only the amounts of mannitol added in the standard procedure. When 0.6 to 2.0 mL of mannitol solution (1X M) was added to 10 mL of sample solution, the absorbances obtained were maximum and constant. When mannitol solution below 0.6 mL or above 2.0 mL was added, the absorbances decreased gradually. The effect of the volume of sample solution was examined by varying the volume from 5 to 45 mL according to the standard procedure. But no effect of the volume was observed. The volatilization of boron in evaporation was examined in detail. Fifteen milliliters of boric acid solution were transferred into a porcelain dish. When the sample solution was evaporated and concentrated to 10,5,3,and 1mL, 1 mL of mannitol solution and 1 mL of sodium acetate solution were added to the concentrated sample solution, and again the solution was heated and evaporated to dryness. It was found that volatilization of boron did not occur until the volume reached about 5 mL. Reaction of Boron with DNNDO in Acetic Acid Medium, Boron reacts with DNNDO in acetic acid medium even in the presence of mannitol. Mannitol is very effective not only in prevention of loss of boron on evaporation, but
ANALYTICAL CHEMISTRY, VOL. 50, NO. 13, NOVEMBER 1978
1791
07r
a O.=0.6
g0.4 -
n U
0.30.2 -
/
d 0.1 .
2 . . 02
04
06
08
~
10
1 2 '1520253035
2.4-Dt nitro-1 6-naphthalenedl 01 ( 2 5 x 1 0 - 3 M ) added(rnL)
Figure 1. Effect of DNNDO on the complex formation in acetic acid medium. Boron(II1): 0.324 pg. ( l ) ,(2), and (3): in the presence of mannitol, (4): in the absence of mannitol, (1) and (4): sample (ref: toluene), (2): reagent blank (ref: toluene), (3): net (ref: reagent blank)
Table I . Molar Absorptivities ( E ) of Ion Pairs Extracted into Toluene washing solution, € ( x 104 L cationic dye HC1, N , , A mol-' cm-'1 2.0 636 9.5 malachite green 2.0 637 10.3 brilliant green 1.5 605 9.5 crystal violet 4.0 569 9.5 Rhodamine B 8.3 Rhodamine 6G 5.0 536 ~
also in the formation of the boron complex with DNNDO as shown in Figure 1, which was obtained by mixing the boron, sodium acetate, and DNNDO acetic acid solutions in the absence of mannitol, and by evaporating the sample solution in the presence of mannitol and sodium acetate and reacting with DNNDO. In the presence of mannitol, the amounts of DNNDO necessary to complete the reaction were smaller than the amounts in the absence of mannitol. This is probably because mannitol is an auxiliary complexing agent and helps t h e formation of the boron-DNNDO complex. The effect of time on the complex formation in acetic acid medium was examined. The constant and maximum absorbance was obtained 50 min after adding DNNDO solution a t 20 "C, and the complex formed was stable at least one day. When the solution was heated on the water bath for only 5 min, the complex formation was almost completed. The absorbances, however, varied a little widely. This is probably because a part of DNNDO or complex will decompose. In this work, t h e mixture stood for more than 60 min a t room temperature. T h e effect of amounts of total glacial acetic acid on the formation of the boron complex was examined by varying the volume from 1 to 6 mL. The constant and maximum absorbance was obtained in a volume above 3 mL. E x t r a c t i o n of Boron-DNNDO Complex w i t h Cationic Dye and W a s h i n g the O r g a n i c P h a s e . Four kinds of cationic dye as well as brilliant green were examined. As shown in Table I, brilliant green shows the largest molar absorptivity of the five. Brilliant green shows the maximum and constant absorbance a t the amounts from 0.1 mL to 1 mL of 1 X M aqueous solution. The optimal p H region in the extraction was 1 to 4, but the emulsion sometimes forms in shaking near p H 2. Therefore, the extraction was carried out a t p H 2.5-3.5. Washing the organic phase after extracting the ion pair and discarding the aqueous phase is necessary to remove the large excess of dye co-extracted into toluene. This removal was
15
20
25
30
35
4.0
Concentrat ion of HCI (mol I L )
Figure 2. Effect of acid concentration on the back-washing. Boron(II1): 0.324 pg. (1): sample (ref: toluene), (2): reagent blank (ref: toluene), (3): net (ref: reagent blank)
Table 11. Effect of Co-existing added, m$ ion none 11= Na' K' 2c 2 x lo-] Ca" Mg2+ 1.2 x 10-1 Ba '+ 6.8 X lo-' cuz+ 3.2 X Zn2' 1.6 X lo-' Cd2+ 5.6 X Mn'+ 2.7 x lo-*' co2+ 2.9 X lo-' Ni *+ 2.9 X lo-' Pb2+ 1 x lo-' 1 x 10-l Hgz+ 8.4 X Fe3+ ~ 1 3 + 1.4 X l o v 2 3.8 X As(I11 ) 3.8 x lo-' As(V) Sb3+ 6.1 x lo-" 1BC c14c Br6.3 x lo-' 1F4 x 10-3 NO,3.1 X IO-" 4. BC SO,'1.1c PO,,1.9 x 10-1 S i 0 ,*-
Ionsd added as absorbanceb 0.638 NaC!1 0.638 0.638 KC1 0.638 CaCI, 0.629 MgC1, 0.635 BaC1, 0.638 cuso, 0.638 ZnSO, 0.648 Cd(N03 12 0.648 MnCl, 0.642 Co(NO,), 0.638 Ni(NO,), 0.648 PbCI, 0.648 HgCX, 0.635 F e w 031 3 0.642 AVO,), 0.635 AS'O, Na,.HAsO, 0.635 0.633 SbC1, NaCl 0.638 NaBr 0.652 KI 0.646 KF 0.623 NaNO, 0.638 0.638 Na,SO, 0.642 Na,HP04 Na2Si0, 0.638
(I Maximum tolerance concentration. Reference: toluene. Maximum tested. d Boron: 0.324 pg. Total initial volume of aqueous solution: 1 2 mL.
carried out effectively by washing the organic phase with hydrochloric acid solution as shown in Figure 2. The optimal concentration of the hydrochloric acid is 2 to 2.5 N, a t which the reagent blank is very small and constant and the absorbance of the complex is maximum and constant. Both in extraction and washing, shaking for 5 min was enough to complete the extraction and removal. The ion pair extracted into toluene was very stable and the absorbance of the organic phase did not vary for at least 4 days. A b s o r p t i o n Spectra a n d C a l i b r a t i o n Curve. The absorption spectra of the ion pair formed between boron complex and brilliant green in toluene obtained by the standard procedure are shown in Figure 3. The maximum absorbance of the ion pair is a t 637 nm, where the absorbance of the reagent blank is very small. The calibration curve obtained by the standard procedure was linear in the range from 0 to 0.5 pg of boron and the molar absorptivity calculated from the slope of the curve was 10.3 X lo4L mol-' cm-'. The curve obtained by using the boric acid-acetic acid solution without evaporation also was linear and the molar absorptivity was
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ANALYTICAL CHEMISTRY, VOL. 50, NO. 13, NOVEMBER 1978
Table 111. Determination of Boron in River and Seawater and Recovery of Boron recovery test sample'
boron, ppb
River waterb River waterC River waterd River watere Seawaterf Seawaterg
8.7 11.6
boron in sample s o h . boron added, taken, ng ng 87 116
found, ng
recovery, ng
boron added, %
216 216 21 6 21 6
289 20 2 95.4 327 21 1 98.5 8.8 88 305 21 7 100.3 10.2 102 317 21 5 99.7 4300 215 108 325 110 100.6 4400 220 108 324 104 98.8 ' 10 m L of river water was taken and seawater was diluted to one hundred-fold, and 5 mL of the diluted sea water was taken. Asahi River, Okayama Prefecture, Japan. Asahi River. Samples b and c were sampled at different places. Takahashi River, Okayama Prefecture. e Yoshii River, Okayama Prefecture. f Seashore at Tanohama, Ehime Prefecture, Japan. Seashore a t Uno, Okayama Prefecture. Table IV. Comparison of Some Spectrophotometric Methods wavelength, nm
lo4L method mol-' cm-l) chromotropic acid (extraction) 351 1.4 BF;-methylene blue (extraction) 660 8.3 curcumin-oxalic acid (in ethanol soln) 550 9.6 curcumin (extraction) 555 17.0 curcumin (in ethanol soln) 550 16.2 this method 637 10.3 These were calculated from absorbance data obtained by each method.
500
550
600
650
700
Wavelength (nrn)
Figure 3. Absorption spectra in toluene. Boron(II1): 0.324 Fg. (1): sample (ref: toluene), (2): reagent blank (ref: toluene)
10.6 X lo4 L mol-' cm-', which is a little larger than that obtained by t h e standard procedure. Effect of Co-existing Ions. The effect of co-existing ions was examined by the standard procedure and the results obtained are shown in Table 11, from which it can be seen that alkali and alkaline earth metals, and transition metals, arsenic, and antimony do not interfere with the determination of boron even at the amounts of one thousand-fold, and one hundred-fold of boron, respectively. Of the common anions, fluoride ion a t amounts more than tenfold of boron gives rise to negative errors because fluoride reacts with boron to form tetrafluoroborate. Application to the Determination of Boron i n N a t u r a l W a t e r s . The amounts of co-existing ions generally existing in river and seawaters are much smaller than those listed in Table 11. Ten milliliters of river water, and 5 mL of seawater which was diluted with water to one hundred-fold were transferred into a porcelain dish and the boron was determined by the standard procedure. The results obtained are shown in Table 111. The recovery tests of the boron were also carried out by adding known amounts of boron (as the boric acid) and determining the boron according to the standard procedure. T h e results are also shown in Table 111. The recoveries of boron are good and are 95.4 to 100.6%.
E(X
absorbance of reagent blank 0.098
0.124 0.040
0.750 0.060 0.020
absorbance' (per 0 . 1 wg B) 0.026 0.077 0.044 0.157 0.059 0.187
lit. (26)
(3) (9) (10)
(7) -
CONCLUSION I n Table IV, this new method is compared with other methods, particularly in point of actual sensitivity calculated from the absorbance data obtained according to the procedure. Of these, the method proposed in this work shows the largest absorbance per 0.1 Fg of boron. This new method seems to be much more useful and general in a practical analysis for boron than other spectrophotometric methods reported u p to date in the following advantages: (1) high sensitivity and high selectivity for boron, (2) relatively more simple and less time-consuming procedure, (3) procedure using common apparatus and vessels, especially evaporation of the sample solution is carried out in the cheap porcelain dish, (4) good reproducibility of determination of boron, and (5) very small absorbance of the reagent blank. LITERATURE CITED (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26)
L. Ducret, Anal. Chim. Acta, 17, 213 (1957). L. Pasztor and J. D. Bode, Anal. Chem., 32, 277 (1960). S. Uisumi, S. Ito, and A. Isozaki, Nippon Kagaku Zasshi. 86, 921 (1965). J. A . Naftel, Ind. Eng. Chem., Anal. Ed., 11, 407 (1939). L. Siiverman and K. Trego, Anal. Chem., 25, 1264 (1953). G. S. Spicer and J. D. H. Strickland, Anal. Chim. Acta, 18, 231 (1958). M . R . Hayes and J. Metcalfe, Ana/yst(London), 87, 956 (1962). L . R . Uppstrom, Anal. Chim. Acta. 43, 475 (1968). M . Miyamoto, Bunseki Kagaku, 11, 635 (1962). H.Got6. Y. Kakita, and K. Takada, Bunseki Kagaku, 18, 52 (1969). C. E. Cassal and H. Gerrans, Chem. News, 87, 27 (1903). K. TBei and K. Nakato. Nippon Kagaku Zasshi, 92, 731 (1971). T. Korenaga, S. Motomizu, and K . T k i , Anal. Chim. Acta, 65, 335 (1973). T. Korenaga, S. Motomizu, and K . TBei, Jalanta. 21, 645 (1974). K. TSei. S.Motomizu, and T. Korenaga, Analyst(Lom%n), 101, 974(1976). K. Kuwada, S. Moiomizu, and K. TBei, BunsekiKagaku, 26, 609 (1977). H. Erdrnann, Ann., 247, 356 (1888). A. P. Lurie, G. H. Brown, J. R. Thirtie, and A. Weissberger, J . A m . Chem. Soc., 83, 5015 (1961). F. Calvet and M. C. Carnero. J , Chem. Soc., 1936, 556. I . M. Korenman, Zh. Anal. Khim., 2, 135 (1947). K. Emi, K. TBei, and K. Harada, Nippon Kagaku Zasshi, 78, 1299 (1957). 6.Egneus and L. Uppstrom, Anal. Chim. Acta, 66, 211 (1973). E. J. Hakoila, J. J. Kankare, and T. Skarp, Anal. Chem., 44, 1857 (1972). D. F. Kuemmel and M. G. Mellon, Anal. Chem., 29, 378 (1957). J. Lapid, S. Farhi, and Y. Koresh, Anal. Lett., 9, 355 (1976). T. Korenaga, S.Motomizu, and K. T k i , Analyst(Lom%n), 103, 745 (1978).
RECEIVED for review June 14, 1978. Accepted August 7, 1978.
