A N A L Y T I C A L CHEMISTRY, VOL. 51, NO. 1, JANUARY 1979
Table 111. Replication of Samples' sample sample volume, no. location L 53 54 11 12
13
OR OR recovery recovery recovery
' Same location
1 1
room room room
1.00 1.00 1.50 1.50 1.OO
N,O found, ML 27 27 7.5 7.7
N:O concn, PPm 27
6.0
6.0
lack of sample transfer step is a significant simplification. The equipment used is generally found in a reasonably equipped lahoratory. Although t h e analysis time is shorter t h a n t h e techniques which utilize sample transfer, still one analysis including the regeneration step takes approximately one hour.
LITERATURE CITED
27 5.0 5.0
15 minutes apart.
all of these were within t h e representative ranges qhonn. T h e sampling method is simple t o use a n d sequential samples can be collected if a series of columns are p r e p a r ~ d in advance. Table 111shows two sets of samples which were sequentially collected. In contrast to t h e other methods of N 2 0 field sampling and analysis reported in t h e literature, t h e technique developed here has the advantage of being uncomplicated, easy to handle. and, especially under field conditions, reasonably rugged. The
161
(1) K Schuetz, C Junge. R. Beck. and B Albrecht. J . Geophys. Res., 75, 2230 (1970). (2) C. Junge. B. Bockholt. K . Schuetz, and R . Beck, "Meteor." Forschungsergeb.. Relhe 6 , 6 , 1 (1971). (3) C. Whitcher, R., Piziali, R. Sher. and R J. Moffat. "Development and Evaluation of Methods for the Elimination of Waste Anesthetic Gases and Vapors in Hospitals." U . S H.€ W -NIOSHPubl.. 75-137. Rockville, Md., 1975. (4) R . A. Rasmussen. J Krasnec. and D. Pierotti. Geophys. Res. Lett.. 3 , 615 (1976) (5) M D La Hue M D Axelrod. and J P I-odge, Jr , Anal Chem , 43, 11 13 119711 (6) >. Hahn, Anal. Chem , 4 4 , 1889 (1972) (7) M. D. La Hue. J. E. Pate. and J. P. Lodge, Jr., J . Geophys. Res., 75, 2922 (1970). (8) R. Bock and K. Schuetz, Fresenius' Z . Anal. Chem.. 237. 321 (1968).
RECFTVEDfor review April 5 , 1978. Accepted October 2, 1978.
Extraction System for Solvent Extraction-Graphite Furnace Atomic Absorption Spectrometry Kenji Yasuda' and Shozo Toda Department of Agricultural Chemistry. University of Tokyo, Yayoi. Bunkyo-ku, Tokyo. 1 13, Japan
Chukoh Igarashi and Shohei Tamura Institute for Solid State Physics, University of Tokyo, Roppongi, Minato-ku. Tokyo, 106, Japan
Because of interferences caused by various matrix constituents, serious problems have been noticed in some applications of graphite furnace atomic absorption spectrometry (1-8). Simultaneous background correction techniques are not always effective for t h e elimination of such interferences ( 7 , 8 ) . T h e chelation-organic solvent extraction technique has therefore been employed to eliminate t h e matrix interferent (9). However, t h e use of conventional separating funnels is tedious a n d time-consuming Improvement of t h e conventional extraction system is needed to apply this technique to samples small in size or large in number. One such system, t h e primary characteristic of which lies in t h e use of Teflon porous film as a separating medium. has heen developed. I n a previous paper ( 1 0 ) t h e wlvent extraction system a n d its application to t h e determination of selenium in biological samples by graphite furnace AAS has been reported. T h e system consisted of three separate parts. Selenium extracted into CCll was transferred t o a vial after permeation through a Teflon film. Although this system wai found to be useful for small sample amounts, e.g.. less t h a n 5 mL, a more compact and much simpler one was thought to be better for routine measurement. In t h e present paper, newly developed apparatus is d e scribed a n d its practical uqe is discussed. Some of t h e advantages of our system over conventional ones are as follows, (1) easier handling a n d maintenance, ( 2 ) shorter time necessary to separate organic solvent, ( 3 ) fewer reagent5 needed. and (4)low cost per unit. T o assess the system, cadmium and lead were extracted a n d analyied by graphite furnace AAS
EXPERIMENTAL Instrumentation. SpectmrnPtw. A Varian-Techtron AA 1000 atomic ahsorption spectrometer equipped with a Varian-Techtron 0003-2700/79/0351-0161$01 O O i O
--__l_.__l_..I___..____
Table I. Instrumental Conditions light source lamp current analytical line spectral bandwidth sheathing gas settings of atomization cycle dry ash atomize
Ph
Cd
Hitachi hollow cathode lamp 1 0 mA 283.3 nm 1.0 nm N: 4 L/min
Varian hollow cathode lamp 10 mA 228.8 nm 1 . 0 nm N: 4 Limin
8 0 "C, 20 s 470 "C, 40 s 2100"C, 4 s
80 'C, 2 0 s 470 ^C, 4 0 s 1800"C, 3 s
CRA 68 graphite furnace atomizer was used. The furnace used was a larger tube (dimensions: 1 2 mm in length, and 7.5 and 6 mm in a d . and i.d., respectively) than the commercially available standard tube (dimensions: 9 mm in length, and 5.2 and 2.9 mm in o.d. and i.d., respectively) for the atomizer, since improved reproducibility of measurement was achieved with the tubes in this experiment. For example, the relative standard deviations of the CC1, extract of lead corresponding to 0.02 pg/mL and 0.04 p g / m L in the aqueous phase for 1 2 firings were 3.2 and 4.4% in the larger tube, respectively, compared t.o 13.6 and 16.0% in the standard tube. Since the difference i n sensitivity was not large compared to tube dimensions. the reason for this phenomenon may be connected to the difference in the nature of graphite. The standard tube is pyrolytically coated, but the larger tube is not. When nnnpy-nlytic coated graphite tubes are used, organic solvent soaks easily into graphite and the metal extract is likely to he reduced rapidly by heating. From the viewpoint of sensitivity, thinner tubes should he hetter. Rut. as we could not obtain small and nonpyrolytic coated tubes, we adapted the above described tube. In addition, to decrease the diffusion of atomic vapor E' 1978 American Chemical Soclety
162
A N A L Y T I C A L CHEMISTRY, VOL. 51, N O . 1, JANUARY 1979
Table 11. Comparison of Extraction Systems
( a ) standards added with excess NaCl recovery, % concentration, pg/mL
proposed separating system funnel 0.1 98.9 103.9 Cd 0.04 104.2 95.6 Pb ( b ) Pb in homogenate of mussels extraction technique
INTRODUCTION TUI3E
proposed system obtained Pb content ( p g / g , wet basis) TUBE HOL3 E
0.12 0.12 0.13
av. 0 . 1 2
PVREX
a
b
Figure 1. Schematic diagram of the extraction system: separation and (b) after separation
(a) before
through the sample introduction aperture, the aperture was not made for the furnace. Background correction was not applied throughout the experiment. Settings of Graphite Furnace Atomizer. Settings of the graphite furnace atomizer were selected experimentally. as presented in Table I. The ashing temperature was very critical. because too high a temperature caused loss of the anal>te,whereas too low a temperature led to incomplete decomposition of organic materials. Temperatures given in Table I were measured by a thermoelectric thermometer (for drying and ashing stages) and an optical pyrometer (for the atomizing stage). Reagents. Cadmium and lead standards were prepared by diluting commercial 1000 pg/mL stock solution (Kanto Chemical Co. Ltd.) in 0.5 N HN03 solution. Sodium diethyl dithiocarbamate (abbreviated to SDDC below) was dissolved in slightly alkaline water. All reagents were anal>.ticalreagent grade and were purified by dithizone-CC14 extraction, if necessary. P r e p a r a t i o n of Sample. Concentrated HNO,, was added to a sample in a conical beaker or a Pyrex vial (in the case of blood) and set on a hot plate. The temperature was raised to ca. 300 "C slowly, to avoid frothing. Further small amounts of concentrated H N 0 3 were added to the boiling digest prior to disappearance of the brown fumes of nitrogen oxide. Heating was continued until the digest became clear, and then the solution was cooled and H20, added. The digest was again heated until colorless and the volume was reduced to 1 to 2 mL. The digest was finally transferred to a volumetric flask and made up to volume with deionized water. The blood sample was not transferred, but determined by direct extraction from the digest. Extraction System. Materials. The Teflon porous film disk of about 40-pm pore diameter allows organic solvents to permeate but not water. Two Pyrex vials with Teflon-lined screw caps were used for one system. Other glassware was also made of Pyrex. Construction. The new extraction system was constructed as shown in Figure 1. In Figure l a , Teflon porous film was set below the lower Teflon-lined packing and supported at the center by two Teflon tube holders. The aeration capillary was charged with
separating funnel 0.14 0.14 0.15 av. 0 . 1 4
a Teflon porous film chip a t the bottom t o prevent aqueous solution from entering. The length of the capillary should be adjusted accordingly as the volume of organic solvent is varied, because once organic solvent is absorbed into the Teflon chip, aeration is hindered. Handling. After shaking a tightly screw-capped vial which contains aqueous solution and organic solvent, the extraction system was built up as shown in Figure l a . When the whole system was inverted as in Figure l b , only organic solvent permeated the Teflon porous film disk and entered the lower vial. The aqueous solution remained completely above the disk. The amount of organic solvent retained in the disk was negligible. The time necessary to separate 1 mL of CC1, from an equal volume of water is about 5 s. Less quantity of solvent takes less time. It is possible to separate as little as 0.1 mL. Extraction Procedure. C a d m i u m . Sample solution, 1 mL, containing cadmium was transferred to the vial and 1mL of citrate buffer was added. The pH was adjusted to about 7 using dilute ammonia solution and then 0.1 mL of 0.01 7' SDDC solution and 1 mL of CCI, were added. The system was shaken vigorously for 2 niin and then separated into two layers. When extractability of the new system was compared with that of a separating funnel, reagents were added in the same proportion, but quantities in the new sb-stem were one tenth of those in the separating funnel. Lead. Sample solution, 1 to 2 mL, containing lead a t less than 0.1 ug were transferred to the Pyrex vial. Then 2 mL of 1 M citrate buffer (pH 4.5) and 0.2 mL of 0.1 M EDTA disodium salt solution were added. The pH was adjusted to between 4 and 5, since EDTA suppressed the extraction of lead above pH 5 and lead is extractable over a pH range 4 to 11 ( 2 1 ) . After shaking, 1 mL of carbon tetrachloride was added to the vial. The vial sealed with a screw cap was then shaken for 2 min. After removal of the screw cap, the extraction system was joined and the organic solvent was separated as described above. Aliquots of the extract, 20 pL.were introduced into a graphite furnace with a micropipet (Finn pipet).
RESULTS AND DISCUSSION Comparison w i t h Conventional S e p a r a t i n g Funnel. Cd a n d Pb S t a n d a r d s A d d e d with E x c e s s i v e A m o u n t of N a C l . Cd (0.1 pg/mL) and P b (0.04 pg/mL) standard solutions with and without addition of NaCl (10000 pg/mL) were extracted by t h e SDDC-CC1, method, using two extraction systems. Contamination from NaCl was corrected for both elements. Results were shown in Table II(a). Two separate runs were tried and t h e averages are indicated. From t h e recoveries of Cd and P b , it was found that t h e proposed system was comparable in performance to t h e conventional one. Pb in t h e H o m o g e n a t e of Mussels. Comparison was also made with a real sample. From t h e homogenate of mussels ( M y t i l u s e d u l i s ) from Tokyo Bay, a portion weighing ca. 10 g was taken, digested, and made u p t o 100 m L . -4liquots of t h e digest were extracted as stated in t h e preceding section. Results are given in triplicate in Table II(b).
A N A L Y T I C A L CHEMISTRY, VOL. 51, NO. 1, JANUARY 1979
Table 111. Determination of Pb in Biological Samples obtained valuea certificate value kind of sample NBS SRM 1 5 7 1 Orchard Leaves 1 5 7 7 Bovine Liver
rat whole bloodb a b C
44.3p g / g , dry basis 0.30pg/g, dry basis
45 t 3 p g / g , dry basis 0.34 + 0.08 pg/g, dry basis
0.05 pg/mL < 0 . 0 2 pg/mL < 0 . 0 2 gg/mL
These values are the mean of triplicate (Orchard Leaves) and duplicate (Bovine Liver and rat whole blood) determinations. Three rats were used: a, b, and c. Sample volume for Pb determination was 0.5 mL. a
From these results shown in Table II(a) and (b), it is concluded that in regard to extractability the proposed system is similar to the conventional one, but the former is more convenient and requires a small amount of sample and reagent. Sensitivity a n d Calibration C u r v e for Lead. Differences in sensitivity were not observed between the new extraction system and the conventional one. T h e concentration corresponding to 1 7 6 absorption (absorbance = 0.0044) for routine calibration was 1 2 n g / m L in aqueous solution. T h e linear calibration curve for P b was obtained over the range of 0 t o 0.4 p g / m L . Standards were prepared according to the procedure for sample solutions. A p p l i c a t i o n t o Biological Samples. N B S SRMs. N B S Standard Reference Materials, 1571 Orchard Leaves and 1577 Bovine Liver, were used to assess the accuracy of the proposed apparatus and method. Results are given in Table 111. T h e
163
values obtained were in good accord with those in the N B S certificates. Rut Blood. Mature female Wistar rat (6-nlonth old) blood was collected into Pyrex vials containing EDTA dipotassium salt as an anticoagulant and digested with H N 0 3 and H,Oz by using an aluminum heating block on a hot plate. Results are shown in Table 111. Since the lead concentration in rat blood was low, P b was detected in only one sample. From the results presented in Table 111, the newly-developed extraction system was demonstrated to be an effective microextraction procedure. At present, only solvents heavier than water can be applied to this !system, but studies are to be performed for lighter solvents. ACKNOWLEDGMENT T h e authors express their gratitude to S. Tarumi for his advice for rat keeping and treatment. LITERATURE CITED (1) C. HendrikxJongerius and L DeGalan, .4nal. Chim. Acta, 87, 259 (1976). (2) E. J. Czobik and J. P. Matousek, Anal. Chem.. 5 0 , 2 (1978). (3) W. Oelschlager and W. Lautenschlager, Fresenius Z. Anal. Chem.,287, 28 (1977). (4) W. Weascheider. G. KnaDD. and H. SDitzv. , . .~ Fresenius Z . Anal. Chem.. 283, 163 (1977). (5) D. J. Hodges, Analyst (London),102, 66(1977). (6) J. W. McLaren and R . C. Wheeler, Anaiyst(London), 102, 542 (1977). 17) N. M.Morris. M. A. Clarke. V . W . Trim. and F. G. Caroenter, J . Agric. Food Chem , 24. 45 (19761 (8) F. J. Fernandez, C/in.'Chem.( Winston-Salem, N.C.),21, 558 (1975). (9) M. T. Volosin, N. P. Kubasik. and H. E. Sine, Cin. Chem: ( Winston-Salem, N.C.),21, 1986 (1975). (10) K. Yasuda, M. Taguchi, S.Tamura, and S. Toda, BunsekiKagaku, 26, 442 (19771. ( 1 1 ) H. Bode, Fresenius Z . Anal. Chem., 144, 165 (1954)
RECEIVED for review April 11. 1978. Accepted September 12, 1978.
Analytical Applications of a Recording Interference Refractometer P. N. Yi" Department of Physics, DePaul University, Chicago, Illinois 606 14
R. C. MacDonald" Department of Biological Sciences, North western University, Evanston, Illinois 60202
Interferometers have been used for accurate measurements of changes in length ( I ) , volume ( Z) , refractive indices of gases and liquids (31,and plasma electron density ( 4 ) . These uses of interferometers exploit the shift of the interference pattern. generated by a relative alteration in the optical paths of interferometer arms. If a translator nulls an optical path change automatically. the amount of the compensation may be calibrated t o give the path change. A piezoelectric transducer holding one mirror of a Michelson interferometer would serve such a purpose. Kupper and Mastop ( 4 ) have already used such a n arrangement to null the effect of low frequency noise in the measurement of electron densities of a plasma. Only a single light probe was needed for the purpose. However, a t least two independent measurements are necessary to determine both the magnitude and direction of the refractive index change. Although a high-power, high-voltage amplifier is needed to deliver a large current to t h e piezoelectric crystal, t h e resulting rapid compensation permits continuous recording of the index change produced 0003-2700/79/0351-0163$01.00/0
by wavelength scan, by temperature variation, or by titration. T h e apparatus described in the present article was developed to measure small changes in the refractive index and, with minor modification, the optical rotatory power of aqueous suspensions of biological material. Biological materials are often available only in small quanti1 ies, and they often form turbid suspensions. Given these factors, interferometry is the refractometric method of choice. A similar apparatus, but based upon the Michelson design. has been used to measure the temperature dependence of a supramolecular conformational change of membranes (.SI. T h e present apparatus overcomes the difficulty of the superposed multiple interference patterns associated with the cell surface reflections in a Michelson interferometer. An additional advantage of the Jamin interferometer used here is the side-by-side location of sample and reference cells. This arrangement facilitates temperature control of the two solutions and permits dual beam titration a t any chosen temperature. In addition to detecting conformational changes of biological C 1978 American Chemical Societv
