Anal. Chem. 1884, 56, 1737-1738
12604-63-6;Alcomax 111, 12605-51-5;silica, 7631-86-9; Hg, 7439-
LITERATURE CITED Kolthoff, I.M.; Elvlng, P. J. “Treatlse on Analytical Chemistry”; Interscience: New York, 1961; Vol. 5. Part 11, p 317. Boltz, D. F.; Howell, J. A. “Colorimetric Determination of Nonmetals”, 2nd ed.; Wiley: New York, 1978; p 337. Willlams, W. J. “Handbook of Anion Determination”; Butterworth: London, 1979; p 466. APHA-AWWA-WPCF “Standard Methods for the Examinationof Water and Wastewater”, 14th ed.; American Publlc Health Associatlon: Washington, DC, 1975; p 466. Pakalns, P. Anal. Chlm. Acta 1970, 51, 497-501. Shelton, 8. J. Natlonal Institute for Metallurgy, Report No. 1681, Johannesburg, Jan 17, 1975. British Standards Institution, Handbook No. 19, Determlrlaflon of Phosphorus, Method 3. Zettler, H.; Ensslin, F., Eds. ”Analyse der Metalle, Vol. 1, Schledsanalysen”, 3rd ed.; Springer: Berlln, 1966; p 130.
1737
(9) Elwell, N. T.; Wilson, H. N. Analyst (London) 1956, 8 1 , 136-143. (10) Speller, D. V., unpublished results, J. Roy Gordon Research Laboratorv. INCO. Ltd.. Mlsslssauoa. Ontario. Oct 1982. (11) Blair, F. A., private comnhcatlon, Huntlngton Alloys, Inc., Hungtlngton, WV, Jan 1981. (12) SiilGn, L. 0.;Martell, A. “Stablllty Constants of Metal-Ion Complexes”, 2nd ed.; Chemlcal Society: London, 1964; Special Publication No. 17. (13) Sill&, L. 0.; Martell, A. “Stability Constants of Metal-Ion Complexes”, Supplement 1; Chemical Society: London, 1971; Special Publication No. 25. (14) Hbgfeldt, E.; “Stablllty Constants of Metal-Ion Complexes”, Part A; Pergamon Press: Oxford, 1982; IUPAC Chemical Data Ser. No. 21. (15) Williams, W. J. “Handbook of Anion Determination”; Butterworth: London, 1979; p 471. (16) Stauffer, R. E. Anal. Chem. 1963, 55, 1205-1210. (17) Stoch, H.; Steele, T. W.; Rankin, R. S. National Institute for Metallurgy, Report No. 1976; Johannesburg, Sept 9, 1978.
RECEIVED for review December 23,1983. Accepted March 26, 1984.
Determinatlon of Mercury by Cold Vapor Atomfc Absorption Spectrometry Hwai-Nan Chou* and Conrad A. Naleway Council on Dental Therapeutics, American Dental Association, 211 East Chicago Avenue, Chicago, Illinois 60611 There have been many modifications and improvements in cold vapor atomic absorption spectrometry since it was first reported by Hatch and Ott (I). Several different methods have been used to measure the mercury vapor: (A) The mercury vapor was swept through the absorption cell by a carrier gas, usually air (2)or nitrogen (3),and the absorbance was recorded. (B) The carrier gas continuously circulated through the solution, and the absorbance was recorded when the partition equilibrium of mercury vapor between gas phase and liquid phase was reached (1). In both of these methods, the mercury vapor was invariably diluted by the carrier gas and the sensitivity of the measurement was reduced. (C) A stationary cold vapor technique was reported by both Tong ( 4 ) and Bourcier (5), in which the reduction was performed in the absorption cell, without the use of a carrier gas. However, Tong’s procedure requires removing the absorption cell for mixing and Bourcier’s procedure requires a long time to reach partition equilibrium. Both procedures require background correction, because of water vapor formation. This study describes a convenient method that can eliminate dilution and water vapor formation by using a custom designed syringe (Figure 1). The mercury vapor is generated in the syringe barrel and then transferred to the vacuum absorption cell through a drying tube. The advantages of this method are (a) no carrier gas is needed, which means the mercury vapor is not being diluted, and (b) the water vapor is removed since the mercury vapor is passed through a drying tube before being measured. Therefore, a background correction is not necessary. All of these contribute to a substantial enhancement of sensitivity.
EXPERIMENTAL SECTION Apparatus. All mercury measurements were performed with a Pekin-Elmer Model 306 atomic absorption spectrophotometer equipped with a mercury electrodeless discharge lamp. The absorbance was measured at 253.7 nm and read directly from the digital readout. The absorption cell was made of a acrylic plastic tubing. It is 15 cm long with outside and inside diameters of 13 mm and 9.5 mm, respectively. Quartz windows were attached to both ends of the tube (Figure 1). The cell was mounted on the burner head with tape. A 30-mL glass syringe barrel with the tip closed off by a Teflon insert was used as the reduction cell. The plunger which was used to transfer the mercury vapor to the absorption cell was specially designed and made of Teflon.
Drying tube was made of a 3-mL disposable plastic syringe barrel. Reagents. A stock 1000 ppm of Hg solution was prepared by dissolving HgClz in 5% (v/v) “0% Working standards were prepared weekly by appropriate dilution from stock solution with 5% HN03-0.01% K2Crz07solution as recommended by Feldman (6). Potassium permanganate was 5% (w/v) in deionized water. Hydroxylamine hydrochloride was 25% (w/v) in deionized water. Stannous chloride was 10% (w/v) in 5% (v/v) H2S04.
Procedure. Measurement of the Available Volume of the Absorption Cell. The available volume of the absorption cell is the amount of mercury vapor which can be transferred to the absorption cell for measurement after the absorption cell is evacuated. It is dependent on the power of vacuum pump as well as the geometric volume of the absorption cell, but it is not necessarily equal to the geometric volume of the cell. With valve 11 (Figure 1)closed, valve 14 was opened whereby connecting the absorption cell to the vacuum pump. In the meantime, the plunger was inserted into the syringe barrel until 20 mL of space was left, valve 7 was then closed, and the needle was inserted into the septum of the drying tube. To start the measurement, valve 14 was closed followed by the opening of valve 7. Since the absorption cell was evacuated, the plunger was pushed into the barrel by the atmospheric pressure until equilibrium was reached. The volume remaining in the barrel was then recorded. The available volume of the absorption cell was the difference between the initial and the final volume. Then the stopper of the plunger was adjusted to stop the plunger at the position where the space left in the barrel was equal to the volume of the reaction mixture plus 0.5 mL of safety space. Sampling. One milliliter of liquid sample or standard solution, which will be called original sample and original standard hereafter, was pipetted into a glass test tube (1.5 cm x 14.7 cm) and 2.5 mL of 5% KMn04 was added, followed by 1 mL of concentrated HzSOb The solution was mixed with a vortex mixer and then cooled to room temperature. An aliquot of 0.2 mL of 25% NH,OH.HCl was added and the solution was vortexed until it became colorless. The total volume of the solution is about 4.5 mL and this will be defined as the digested solution. Analysis. Four milliliters of the digested solution was pipetted into the syringe barrel, 0.1 mL of 10% SnCl, was added, and the plunger was promptly inserted into the barrel. Valve 7 was closed when the plunger reached the mark where the space left between the plunger and the solution equaled the available volume of the absorption cell plus 0.5 mL of safety space (this was 14 mL in our setup). With the plunger in position, the reaction mixture was vortexed for 15 s and then the needle was inserted into the septum of the drying tube. In the meantime, valve 14 was opened to the vacuum pump. After the needle was inserted into the
0003-2700/84/0358-1737$0 1.50/0 . . 0 1984 American Chemical Soclety
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Figure 1. Schematic diagram of experimental arrangement: (1)Teflon insert: (2)glass syringe barrel; (3)Teflon plunger; (4)screw; (5) stopper: (6) polyethylene tubing (0.11 c m Ld.); (7)two way valve; (8) rubber (11)two way septum: (9) needle: (10) drylng tube filled with Mg(CIO,),; valve: (12)absorption cell: (13)burnner head: (14)three way valve: (15)to vacuum pump; (16) to laboratory vacuum line.
septum of the drying tube, valve 14 was closed and then valve 7 opened. The plunger was pushed into the barrel by atmospheric pressure and the mercury vapor was driven into the absorption cell. The maximum absorbance which was reached in a few seconds was recorded. After the measurement, the needle was pulled out from the septum and valve 14 was switched to the laboratory vacuum line. Valve 11was opened for a few seconds to let in room air to flush the inside of the absorption cell. Then valve 14 was switched to connect the absorption cell with the vacuum pump again. The plunger was removed from the barrel, and the barrel was rinsed thoroughly with deionized water and shaken dry. With this procedure, 20 determinations can be made in an hour.
RESULTS AND DISCUSSION When 4 mL of digested solution was used, the detection limit was 0.013 ppb or 0.05 ng of Hg and the calibration curve was linear to 3.5 ppb with a- slope-of 0.080 ppb-l for the digested solution and linear to 15 ppb with a slope of 0.0177 ppb-l for the original standard. When 2 mL of digested so-
lution was used, the slope of calibration curve was 0.045 ppb-l for the digested solution or 0.0101 ppb-' for the original sample; the linear range is up to 7 ppb and 30 ppb for digested solution and original standard, respectively. The precision of this method is very good. For original standards, the RSD was 1.0% a t 2 ppb, 0.5% a t both 10 ppb and 20 ppb when 4 mL of digested solution was used for analysis. The amount of space in the syringe barrel should be as close to the available volume of the absorption cell as possible. If the amount of space in the syringe barrel is greater than the available volume of the absorption cell, some of the mercury vapor which exists in the air phase will not be transferred into the cell for measurement. If the amount of space in the syringe barrel is less than the available volume of the absorption cell, the maximum available amount of mercury will not be distributed in the air phase for measurement. In both cases, the sensitivity will be reduced. The study presented here provides an AAS method for measuring mercury in liquid samples. This method is sensitive, accurate, precise, and easy to perform. Preconcentration, scale expansion, and background correction are not necessary. Because of its sensitivity, the concentration of mercury can be measured at the 0.1 ppb level in an original sample even with a sample size of 1mL. It is believed that this method can be applied to other kinds of samples which are properly digested.
ACKNOWLEDGMENT The authors wish to thank William Gasparac for making the syringe, the plunger, and the absorption cell. LITERATURE CITED (1) Hatch, W. Ronald; Ott, Welland L. Anal. Chem. 1968, 40, 2085-2087. (2) Hawley, J. E.: Ingle, J. D., Jr. Anal. Chem. 1975, 47, 719-723. (3) Velghe, N.; Campe, A.; Claey, A. A t . Absurpt. News/. 1978, 17, 37-40. (4) Tong, Soo-Loong Anal. Chern. 1978, 50, 412-414. (5) Bourcler, D. R.; Sharma, R. P. J. Anal. Toxicol. 1981, 5, 65-68. (6) Feldman, Cyrus Anal. Chem. 1974, 46, 99-102.
RECEIVEDfor review September 26,1983. Resubmitted March 19, 1984. Accepted March 21, 1984.
Colorirnetrlc Determination of y-Cyclodextrin Takashi Kato* and Koki Horikoshi
The Institute of Physical and Chemical Research, Wako-shi, Saitama 351, Japan Analysis of cyclodextrin (CD) with high-performance liquid chromatography (HPLC) on a silica derivative containing amino groups, with acetonitrile-water mixtures as the eluent, has been described ( I , @ . However, maltooligosaccharides, such as maltotetraose, maltopentaose, maltohexaose, maltoheptaose, and maltooctaose, interfere with the analysis. To avoid this interference, oligosaccharides which were not converted to C D s should be digested with glucoamylase (3),but this method is somewhat complicated. No simple and specific quantitative analysis for -y-CD has yet been reported. The inclusion of a compound in a CD mixture may cause a change in the absorption spectrum. Such a characteristic spectral change has been reported for the inclusion complex of a dye molecule such as Congo red, methyl orange, and crystal violet with a-CD, (3-CD, and y-CD (4). We found that bromocresol green (BCG) also made a inclusion complex with 0003-2700/84/0356-1738$0 1.5010
y C D having a stronger absorption spectrum than those of other CD's. This paper deals with a rapid and simple colorimetric analysis of y C D by using BCG.
EXPERIMENTAL SECTION Enzymes. The cyclomaltcdextringlucanotransferase (CGTase) (5)of alkalophilic Bacillus sp. No. 38-2 (ATCC 21783) was kindly supplied by Meito Sangyo Co., Ltd. The CGTase of Bacillus macerans (IAM 1243) was prepared according to the method of Kitahata et al. (6). Reagent. a-, p-, and y-CD and CH-30, which is a mixture of a-,p-, 7-CD and maltooligosaccharides, were kindly supplied by Nihon Shokuhin Kako Co., Ltd. (Tokyo). BCG was purchased from Tokyo Kasei Kogyo Co., Ltd. (Tokyo). Analytical Method. A Hitachi spectrophotometer, Model 200-10, was used. The analysis by HPLC was done with a Shi0 1984 American Chemlcai Society
