pg/ml for Hg. The linear portion of the curve for each of the elements has unity slope as predicted by theory (IO). Our detection limits are similar to those reported elsewhere for similar experimental conditions. Mansfield, Veillon, and Winefordner (11) reported detection limits for Cd and Zn of 0.0002 pg/ml and 0.0001 pg/ml, respectively, using metal vapor arc lamps as the excitation source. Using an electrodeless discharge tube as the excitation source, Mansfield, Veillon, and Winefordner (11)reported the detection limit for Hg to be 0.1 pg/ml. A detection limit of 0.000001 pg/ml for Cd by atomic fluorescence using an intense electrodeless discharge tube for excitation has been reported by Bratzel and Winefordner (12). It seems likely that the detection limit for Cd with our instrument could be greatly improved by use of a more intense excitation source. Slavin (13) has reported the detection limits of Cd, Zn, and Hg by atomic absorption spectrophotometry to be 0.01 pg/ml, 0.002 pg/ml, and 0.2 pg/ml, respectively. As noted earlier, our instrument will chiefly be useful for elements which ar? readily atomized and have their resonance lines below 3200 A. Further, because of the detector characteristics and the short source-to-burner and burner-to-detector distances, our instrument should be particularly useful for elements having short wavelength (that is, less than about 2300 A) resonance lines. (10) P. J. T. Zeegers, R. Smith, and J. D. Winefordner, ANAL. CHEM., 40 (No. 13), 26A (1968). (11) J. M. Mansfield, C . Veillon, and J. D. Winefordner, ibid., 37, 1049 (1965). (12) M. P. Bratzel and J. D. Winefordner, Anal. L e f f . 1, , 43 (1967). (13) W. Slavin, Appf. Specfry.,20, 281 (1966).
An obvious virtue of the nondispersive system is its wavelength stability. Since there is no monochromator, there is no way for the instrument to be out of wavelength adjustment. Consequences of this virtue are ruggedness and ease of operation. The nondispersive system lacks much of the flexibility of a system using a monochromator, but in many applications it may be that its virtues will far outweigh the loss of flexibility. Thus, one might anticipate that the ruggedness, ease of use, and good response at short wavelengths of the nondispersive system would lead to its use in difficult environmental situations and for routine determinations of elements such as Cd, As, Hg, Se, Bi, Zn, and Sb. ADDEDNOTE Through the kind assistance of Dr. A. Walsh we have learned that a similar nondispersive system for flame fluorescence has been suggested in two papers (14, 15) in press at the time of this writing. Larkin, Lowe, Sullivan, and Walsh (14) have measured the spectral response of the HTV R166 photomultiplier and have reported the observation of Fe flame fluorescence with a nondispersive system. RECEIVED for review April 24, 1969. Accepted July 3, 1969, Investigation supported by PHS Research Grant No. R O IGM 15996-01 from the National Institute of General Medical Sciences. (14) P. L. Larkins, R. M. Lowe, J. V. Sullivan, and A. Walsh. Specrrochim. Acta, Part B , 24, 187 (1969). (15) A. Walsh, “Physical Aspects of Atomic Absorption,” Afomic Absorption Spectroscopy, ASTM STP 443, American Society for
Testing and Materials, 1969.
3-Nitroso-2,6-~ridinediol-A New Analytical Reagent for the Spectrophotometric Determination of Osmium Curtis W. McDonald and Roosevelt Carter, Jr. Department of Chemistry, Southern University and A and M College, Baton Rouge, L a .
IN RECENT YEARS several derivatives of 2-hydroxy-3-nitrosoquinoline and 2-hydroxy-3-nitrosopyridinehave been suggested for the spectrophotometric determination of several transition metals. Ayres and Roach ( I ) reported a spectrophotometric method for the determination of iron using 2,4dihydroxy-3-nitrosoquinoline (quinisatin oxime). Ayres and Briggs ( 2 ) reported a spectrophotometric method for the determination of osmium using the same reagent. McDonald and Bedenbaugh (3) reported a spectrophotometric method for the determination of iron using ethyl 4,6-dihydroxy-3nitrosonicotinate (EDHNN), a 2-hydroxy-3-nitroso derivative of pyridine. These showed great promise as analytical reagents and prompted further investigations of related compounds. This paper introduces 3-nitroso-2,6-pyridinediol (NPD) as an analytical reagent and describes a spectrophotometric method for the determination of osmium. The method is (1) G . H. Ayres arid M. K. Roach, A n d . Chim. Acta, 26,332 (1962). (2) G. H. Ayres and T. C . Briggs, ibid., p 340. ( 3 ) C. W. McDonald and J. H. Bedenbaugh, ANAL.CHEM., 39, 1476 (1967). 1478
ANALYTICAL CHEMISTRY
based on the purple color formed when osmium is treated with NPD in slightly acidic solution. NPD was first prepared in 1916 by Gattermann and Skita (4). Titov (5) reported that NPD gave colored compounds with Ba2+, K+, Rb+, and NH4+. There was no mention of any colored species formed with the transition metals. EXPERIMENTAL
Apparatus. Spectral curves were measured with a Beckman DB recording spectrophotometer. Absorbance measurements at single wavelengths were measured with a Beckman Model D U spectrophotometer. Matched silica cells of 1.00-cmoptical path were used in the instruments. A Sargent LS pH meter was used to make pH measurements. Reagents. STANDARD OSMIUMSOLUTION.Pure osmium tetroxide, sealed in glass ampoules, was obtained from K and K Laboratories, Inc., Plainview, N. Y. The stock solution was prepared and standardized as described by Ayres and (4) L. Gattermann and A. Skita, Ber., 49,494 (1916). (5) A. I. Titov, J. Gen. Chem. (USSR), 8,1483 (1938).
Table I. Tolerance for Foreign Ions (Osmium concentration, 2.60 ppm) Tolerance, ppm at 550 mp Foreign ion Aluminum(II1) 100 Cadmium(11) 100 Chromium(II1) 20 Cobalt(I1) 9 Copper(11) 1 Gold(II1)
Iridium(1V) 1ron(111)5 Lead(II)n Manganese(I1) Palladium(II)a Plat inum(1V) Rhodium(II1) Ruthenium(II1) Forms precipitate.
1
9 0 5 100 1 2
1 0
,
400 450
506
550
WAVELENGTH
600
IN
650 700
MF
Figure 1. Spectral curve for osmium-NPD complex 4.50 ppm osnium os. reagent blank
Wells (6) and found to be 602 ppm. Working solutions were prepared as needed by dilution of the stock solution. NPD COLORREAGENT.The NPD color reagent was prepared by Dr. John Bedenbaugh of the University of Southern Mississippi. The procedure for its preparation is described by Titov (5). A 0.1 % (w/v) in 1 :1 ethanol-water was used in most investigations and is recommended in the method. BUFFER. Sodium acetate-acetic acid buffer of pH 4.7 was prepared by using equal portions of 1.OM acetic acid and 1.OM sodium acetate. Other buffers used were prepared by the method described by Robinson and Stokes (7). OTHERREAGENTS.Reagent grade chemicals were used in the interference studies. Cations were used in form of nitrates, chlorides, and acetates. Dowex 50 W-X4 cation exchange and Dowex 2-X8 anion exchange resins were used to determine the electrical nature of the complex. Procedure. In a 25-1111 volumetric flask, transfer 10 to 100 pg of osmium. Add 5 ml of pH 4.7 sodium acetateacetic acid buffer. If the pH of the resulting solution is not between 4.2 and 5 . 2 , it may be preneutralized with hydrochloric acid or sodium hydroxide. Then add 2 ml of 0.1 % (w/v) NPD and heat in a water bath at near boiling for 30 minutes. Cool the solution, dilute to volume, and measure the absorbance at 550 mp against a blank containing all the reagents except osmium. Reproducibility and Sensitivity. In the test for reproducibility (precision) of the method, 15 samples, each containing 2.40 ppm osmium, were prepared according to the recommended procedure and measured at 550 mp. The standard deviation of absorbance was found to be 0.005 absorbance unit or about 1 %. The optium concentration range is 1.5 to 6.5 ppm. The method has a molar absorptivity of 2.4 X 104 1. mole-’ cm-l. (6) G. H. Ayres and W. N. Wells, ANAL.CHEM., 22, 317 (1950). (7) R. A. Robinson and R. H. Stokes, “Handbook of Chemistry and
Physics,” The Chemical Rubber Co., Cleveland, Ohio, 1968, p D-79.
STABILITY OF NPD REAGENT SOLUTION.NPD is only slightly soluble in water. It has a higher solubility in 1 :1 ethanol-water . Solutions of the reagent changed color (from near colorless to blue) when stored in transparent bottles for 5 to 6 days. When the reagent solution was stored in brown bottles, it was stable for at least six months. Study of Variables. Tests in each study were made on solutions containing a fixed amount of osmium which was color developed by the recommended procedure except for the variable being studied. Full color development was obtained after heating the solution in a water bath at temperatures of 70 to 90 “C for 20 minutes. The color was stable for 3 days. After 3 days, there is a gradual decrease in absorbance. Full color development is obtained with a mole ratio of NPD to osmium of about 12 to 1. Higher NPD-osmium rations caused no increase in absorbance at 550 mp. The optimum pH range for color development is from 4.2 to 5.2. No color formed in highly acidic solutions. Above a pH of 5.2, there is a gradual decrease in absorbance when measured at 550 mp, A sodium acetate-acetic acid buffer of pH 4.7 was used in the recommended procedure. Varying amounts of the foreign ion were taken with a fixed amount of osmium and the color developed in the usual way. The tolerance for the foreign ion was taken as the largest amount that could be present and give an absorbance differing by no more than 0.01 from that produced by osmium alone. Tolerances of various other ions are shown in Table I. Nature of the Complex. The purple osmium-NPD complex was passed through Dowex 50 W-X4 cation exchange and Dowex 2-X8 anion exchange resins. The colored solutions passed through the cation exchange resin but the purple color was retained on the anion resin. This indicated the complex was anionic. Both the mole ratio (8, 9) and continuous variations (10) methods were used in an attempt to ascertain the reaction ratios in solution. There was excessive rounding of the curves for NPD ratios of 1 : l to 6:l. No NPD-osmium ratio could be assigned unambiguously. The very high NPDosmium ratio (12:l) required for full color formation probably accounts for the rounded curves. There may also be several NPD-osmium complexes in solution.
(8) J. H. Yoe and A. L. Jones, IND.ENG.CHEM., ANAL.ED., 16, 111 (1944). (9) J. H. Yoe and A. E. Harvey, . I . Amer. Chem. Soc., 70, 648
(1948). (10) P. Job, Ann. Chim. (Paris), 9 (lo), 13 (1928). VOL. 41, NO. 11, SEPTEMBER 1969
0
1479
DISCUSSION
oE;o- ‘N
The molar absorptivity of osmium, measured as the NPD complex, is 2.4 X lo4. This compares favorably with other methods suggested for the spectrophotometric determination of osmium. There are several ions which must be absent when osmium is determined by this method. Well established methods for separating osmium based on the volatility of osmium tetroxide have been described (ZI, 12). The structural formula of NPD may be shown as
It forms colored complexes with ruthenium(II1) (purple), gold(II1) (blue), rhodium(II1) (yellow), and palladium(I1) yellow. These observations indicate a need for further investigation of the reaction of NPD with these and other ions. ACKNOWLEDGMENT
The authors thank Dr. J. H. Jefferson for valuable consultations during the investigation. ( 1 1) F. E. Beamish and W. J. Allen, ibid., 24, 1608 (1952). (12) F. E. Beamish and A. D. Westland, ibid., 26, 739 (1954).
RECEIVED for review May 14, 1969. Accepted June 23, 1969.
Application of Column Bleed Absorption in High Sensitivity Gas Chromatography and in Gas Chromatography-Mass Spectrometry R. L. Levy,’ H. Gesser, T. S. Herman,2 and F. W. Hougen Department of Chemistry and Department of Plant Science, The University of Manitoba, Winnipeg, Canada
HIGH-SENSITIVITY IONIZATION detectors and combined gas chromatography-mass spectrometry (GC-MS) have proved to be powerful tools for detection and identification of minute quantities of organic material ( I , 2). However, the evaporation of the liquid phase from a column, the so-called “column bleed,” seriously interferes in both high-sensitivity gas chromatography and GC-MS (3, 4), particularly in programmed temperature operation. The dual-column tech1 Present address, McDonnell Research Labs, St. Louis, Mo. 63166. 2 Midwest Research Institute, Kansas City, Mo. 64110.
(1) V. Svojanovsky,K. Krejci, K. Tesarik, and J. Janak, Chromatog. Rev., 8, 90 (1966). (2) W. H. McFadden, Separation Sci., 1, 723 (1966). (3) S. Dal Nogare and R. S . Juvet, “Gas-Liquid Chromatography,” Interscience, New York, 1962, p 120. (4) R. Teranishi, R. G. Buttery, W. H. McFadden, R. T. Mon, and J. Wasserman, ANAL.CHEM.,36, 1509 (1964).
1 85
I
I
105
I
I
125
nique (5) (which is not applicable in GC-MS) was introduced to alleviate the problem. However, it can be used only in cases of low or moderate sensitivities. For dual-column temperature programming a t high sensitivities, the two columns and all the associated components of the dual system must be perfectly matched in their behavior. This ideal condition could not be achieved in our laboratory when the sensitivity, in terms of the minimum detectable quantity, was 10-10 to lo-‘* gram/sec. In GC-MS the sensitivity is limited by the extent of column bleeding (4), and only liquid phases that do not mask the mass spectral patterns of the sample compounds can be used. This situation greatly restricts the selection of liquid phases, and limits the maximum operating temperature of the gas (5) W. E. Harris and H. W. Habgood, “Programmed Temperature Gas Chromatography,” John Wiley & Sons, New York, 1966, p 228.
1
I ’
140
,#,..
I
180
I
190
1
195 “C
Figure 1. Recorder base line obtained by single column temperature programming a t relatively high sensitivity A . Analytical column only B. Bleed absorbing column attached, 1st run C. Bleed absorbing column attached, 2nd run 1480
0
ANALYTICAL CHEMISTRY
