analysis capability of our system (both qualitative and quantitative) utilizing flame, dc arc, and ICP sources.
Table I. Line Wavelengths Calculated from Spectra Measured with Fourier Transform Spectrometer Experimental values, nm Literature values, nm 1 2 3 4 Mg Mg Mg A1 A1 Ca Ca
382.93 383.23 383.83 394.40 396.15 393.37 396.85
382.88 383.16 383.76 394.33 396.10 393.31 396.77
382.88 383.16 383.76 394.36 396.10 393.31 396.77
382.88 383.16 383.79 394.36 396.10 393.31 396.80
LITERATURE CITED
382.88 383.16 383.76 394.33 396.07 393.31 396.77
made with our present Fourier transform spectrometer in this spectral region. At most, only one point jitter (0.03 nm) is observed and all wavelengths are accurate to 0.07 nm or better. Further studies on the application of Fourier transform spectrochemical instrumentation to atomic spectrochemical measurements are continuing in our laboratory. These studies include the assessment of the simultaneous multielement
(1) Gary Horlick and W. K. Yuen, Anal. Chem., 47, 775A (1975). (2) H. V. Malmstadt, C. G. Enke, S. R. Crouch, and G. Horllck, “Optimization of Electronic Measurements”, W. A. Benlamln, Menlo Park, Calif., 1974, p 67. (3) J. C. Poianyl, Department of Chemistry, University of Toronto, Toronto, Ontario, private communication. (4) P. R. Griffkhs, Pittsburgh Conference on Anamlcal Chemistry and Applied Spectroscopy, Cleveland, Ohio, Paper No. 440 (1977). (5) “Nicolet 1080 System for FT-NMR”, Nicolet InsWument Corporation, 5225 Verona Road, Madison, Wisc. 5371 1. (6)J. W. Cooper, “The Minicomputer In the Laboratory”, John Wlley, New York, 1977, p 301.
W. K. Yuen Gary Horlick* Department of Chemistry University of Alberta Edmonton, Alberta, Canada T6G 2G2 RECEIVED for review March 22,1977. Accepted May 11,1977.
Stoichiometry of Nitrogen Dioxide Determination in Triethanolamine Trapping Solution Sir: Nitrogen dioxide may be determined in air by a variation of the Saltzman method (1) in which the trapping solution is 0.1 N triethanolamine (TEA) in water (2). Several workers have proposed differing stoichiometries for the formation of nitrite ion in this trapping solution (2,3) based on the results of analyses of prepared atmospheres containing NO2 in low concentrations. However, the mechanism for the reaction has not been established. The absence of mechanistic hypotheses for this important reaction renders the elucidation of a trapping mechanism at relatively high NO2 concentrations important in providing a starting point for investigation of the stoichiometry a t low NOz concentrations. The present investigation was conducted on the reaction of gram quantities of NOz with equivalent amounts of TEA. In aqueous solution, equimolar amounts of nitrite and triethanolammonium nitrate were formed. When the reaction was run in methylene chloride with the exclusion of water, a precipitate having properties consistent with formulation as a nitroso ammonium salt could be observed. On the basis of these results, the following scheme is proposed for the reaction of equivalent amounts of NOz and TEA in an aqueous solution: 2N02=
N2
O4
N204 + (HOCH2CH2)3N (HOCH2CH2)3NNO*NOi
I
+
H20
+
-
(HOCH2CH2)3NNO*
(HOCH2Cl$)3NH*NO;
NO; HN02
It
This reaction path requires a stoichiometric factor of 0.5 for the conversion of gaseous NO2 to nitrite ion.
RESULTS AND DISCUSSION Reaction of a slight excess of TEA in distilled water with a measured amount of NO2 yielded 96% of the theoretical amount of nitrite based on the proposed reaction scheme. In addition, 83% of the theoretical amount of recrystalized I1 could be recovered from the aqueous solution. Since no characterization of I1 could be found in the literature, its 1448
ANALYTICAL CHEMISTRY, VOL. 49, NO. 9, AUGUST 1977
structure was established by satisfactory elemental analysis, molecular weight determination by freezing point depression, NMR (Figure l),IR (Figure 2), and UV (Figure 3). When TEA was reacted with NO2 at -5 “C in CH2Clzunder nitrogen with the exclusion of water, a white precipitate I, different from 11, formed immediately on addition of NOz. Compound I melted over a range (60-67 “C) with decomposition and vigorous evolution of gas. The qualitative UV spectrum obtained in methanol from freshly isolated I was different from the spectra of 11, NO2, or NaNOz in methanol (Figure 3). Gradual decomposition with evolution of gas occurred during warming to room temperature under both vacuum and a nitrogen atmosphere. Attempts to isolate I for elemental analysis were unsuccessful; however, its behavior is consistent with formulation as a nitroso ammonium salt. Under neutral or alkaline conditions the nitroso salt would be expected to yield nitrite on hydrolysis ( 4 , 5). Although isolation of I followed by reaction with water gave a nitrite yield of only 54%, immediate reaction with water in situ resulted in a nitrite yield of 86% based on the proposed reaction scheme. Formation of I1 and appearance of nitrogen dioxide above the solid when I was exposed to moist air can be accounted for by hydrolysis of I to yield nitrous acid which subsequently decomposes to nitric oxide and nitrogen dioxide. Also, in accordance with the results expected -for a nitroso ammonium intermediate, compound I1 could be recovered without recrystallization in 97% yield when the NO2 addition was run in methylene chloride in the presence of one equivalent of water. The formation of I from NOz is in accord with a number of observations in the literature. Spectroscopic evidence indicates that nitrogen dioxide in equilibrium with dinitrogen tetroxide may exist to some extent as a tautomer that can be formulated as nitrosyl nitrate (6). Consistent with this Tiding, dinitrogen tetroxide appears to heterolyze in solution to NO’ and NO3- (7, 81, which in the presence of TEA would be expected to lead to I. Reactions of primary and secondary amines with potential NO’ donors appear from kinetic considerations to proceed
Table I. Results of Analyses of Dynamically Prepared Concentrations of Nitrogen Dioxide Based on Data from Ref. 3 Av . No. of stoichiodetermetric Nominal NO, minafactor concn, ppm tions found iff 3.3-3.5 6.6-6.7 10.6-10.8
Grand total
Figure 1.
9 3 4
0.73 0.61 0.56
0.05 0.03 0.06
16
0.67
0.10
Likewise, there is at this time no evidence to support an explanation for the trend in the stoichiometric factor observed in Table I for the TEA reaction. However, the proposed reaction scheme with the stoichiometric factor 0.5 appears to hold for air concentrations of NOz >10 ppm.
60-MHz NMR of compound I1
EXPERIMENTAL
i.0
i.0
0.0
6.0
7.0"8.0l0.0IZ014.0 WClVELENOTn (mlcronl)
Figure 2. IR of compound 11. Range 2.5-7 pm, fluorolube mull; range 8-14 pm, Nujol mull
spectra in methanol. (-) compound I, nitrogen dioxide, and (+++) compound I1
Figure 3. UV
(---)
(-e-)
nitrite ion,
via nitroso ammonium salts analogous to I (9-11). Additionally, reaction of several tertiary amines with NOBFI ( 5 ) and NO2 (12) at low temperature yielded precipitates with properties similar to I and consistent with nitroso ammonium salts. The proposed scheme for the trapping of high concentrations of NO2by aqueous TEA solution is supported by data (3) on the analysis of dynamically prepared concentrations of NO2 in air. Data from Ref. 3, regrouped and presented in Table I, show that for NO2concentrations above 10 ppm the stoichiometric factor is -0.5. However, the factor appears to increase with decreasing NO2 concentration. A number of investigators have examined the question of a similar concentration effect for the stoichiometric factor of the Saltzman reaction (13-15) and have arrived at conflicting conclusions. In the case of the Saltzman determination the question of predominance among competing mechanisms has been raised (15),but evidence to support specific hypotheses is lacking.
Reagents. Sodium nitrite, Mallinckrodt reagent grade, was assayed by adding excess KMn04 and back-titrating with ferrous ammonium sulfate (16) and found to be 99.3% pure. Methylene chloride, Fisher reagent grade, was distilled from CaClz for dry reactions. TEA, Fisher reagent grade, was used as received for reactions run in water. For water-free reactions, the TEA was mm evacuated in a desiccator containing P2O5 for 48 h at and then vacuum distilled (bp 135-140 "C, 10-2mm). Nitrogen dioxide, Matheson Gas Products 99.5% pure, was passed through P2O5 before use. Nitrite Determinations. Nitrite yields were determined colorimetrically by the diazo coupling of N-(1-naphthyl) ethylene diamine and sulfanilamide (2) using solutions of assayed sodium nitrite as standards. Reaction of TEA and NO2 in Aqueous Solution. (a) A 500-mL round bottom flask with stopcock adaptor having a total mm and filled to atvolume of 527 mL, was evacuated to mospheric pressure with NO2. At room temperature (23 "C) and atmospheric pressure with 82% dimerization of NOz, this volume corresponds to 19.6 mmol NzO4. With the stopcock closed, the N02/Nz04was condensed to a white solid by placing the bottom of the reaction flask in crushed dry ice and a solution of 5 g TEA (33.5 mmol) in 150 mL distilled water added through the stopcock by suction resulting from the vacuum created on condensation of the NOn. The reaction mixture was rinsed into a 500-mL volumetric flask and made up to volume with additional distilled water. This stock solution was further diluted 500:l for nitrite determination. Average yield of four runs: 96%. (b) This reaction was also run at room temperature by adding 500 mL of N02/Nz04gas by syringe to a stirred solution of 4.5 g TEA in 250 mL distilled water, resulting in a nitrite yield of 86%. Repetition of the reaction with the removal of the water on a rotary evaporator, followed by two recrystallizations from MeOH-CHC13yielded 3.29 g (83%) of 11, mp 78-80 OC. Compound I1 was recrystallized from MeOH-CHC13five times and evacuated at mm overnight for elemental analysis. Calculated for CsHl6NzOs;c, 33.96%; H, 7.55%; 0,45.28%;N, 13.21%. Found: C, 33.93%; H, 7.52%;0, 45.19%;N, 13.06%. The molecular weight determined by freezing point depression in water was 210 f 3 compared to the expected value of 212. The NMR (DzO)consisted of two AzBzmultiplets in 1:l ratio centered at 83 Hz and 111Hz downfield from CH3CN (Figure 1). The IR (fluorolube) showed bands at 3.00, 3.20, 3.45,6.45, and 6.80 pm. In Nujol, additional bands occurred at 9.30,9.40,9.85, 10.1, and 12.2 pm (Figure 2). The UV (MeOH) had A,-(€) at 297 mm (9.5). Yield of Nitrate Salt i n CH2C12. Reaction (a) was carried out with a solution of 5 g TEA in 150 mL CH2C12to which 0.4 mL distilled water (1 equiv) had been added. The precipitate was collected on a fritted filter, rinsed with CHzClzand evacuated at mm to constant weight, yielding 4.03 g (97%) of the crystalline nitrate, mp 73-76 OC undepressed by 11. Nitrite Yield from I i n Situ. Reaction (a) was run with the exclusion of water, adding via syringe a solution of 5 g dry TEA ANALYTICAL CHEMISTRY, VOL.
49, NO. 9,
AUGUST
1977
1449
in 30 mL CHzClz distilled from CaClz under nitrogen. The precipitate was allowed to warm to 0 “C and then quenched with 100 mL distilled water. After decanting the water from the CHPClz into a 500-mL volumetric flask, 100 mL 0.1N NaOH was added to the reaction flask, and the CHzClzevaporated at room temperature on a rotary evaporator. The NaOH solution was added to the volumetric flask and the nitrite determination performed as described above, giving a yield of 86%. Attempted Isolation of Nitrosoammonium Salt. Five grams of dried TEA were distilled into a 500-mL 3-neck flask equipped with a Teflon stir bar and a three-way stopcock adaptor. After distilling in 100 mL CHzClzfrom CaClz under nitrogen, an inlet for NOz was fitted to one neck and the reaction flask cooled to -5 “C in an ice-brine bath under positive nitrogen pressure. Approximately 500 mL NOz/NZO4passed through P z 0 5 was metered via a rotameter into the stirred reaction mixture. After the addition had been completed, the reaction mixture was held at -5 “ C for 10 min and then the CHzClzwas filtered off with nitrogen pressure through a frit placed on one neck. At this point, the formation of bubbles in the precipitate indicated some decomposition. No attempt was made to characterize decomposition products. The reaction flask was briefly evacuated to remove traces of CHzClzand transferred to a glove box under nitrogen where an aliquot was weighed out for determination of nitrite (best yield of three reactions, 54%). A qualitative UV in dry methanol was also taken at this juncture.
Occupational Health Program Harvard School of Public Health 665 Huntington Avenue Boston, Massachusetts 02115
ACKNOWLEDGMENT The author thanks 0. Grubner and G. Dudek for helpful discussions and the Chemistry Department of Harvard University for use of their NMR spectrometer.
RECEIVED for review December 22, 1976. Accepted May 4, 1977. Supported by NIOSH Grant OH00369-05 and Center Grant (ES 00002) from the National Institute of Environmental Health Sciences.
LITERATURE C I T E D (1) B. E. Saltzman, Anal. Chern., 26, 1949 (1954). (2) D. A. Levaggi, W. Siu, and M. Feldstein, J. Air follut. Control Assoc., 23, 30 (1973). (3) J. H. Blacker, Am. Ind. Hyg. Assoc. J., 34, 390 (1973). (4) W. Lijlnsky, L. Keefer, E. Conrad and R. Van de Bogart, J. Natl. Cancer Inst., 48, 1239 (1972). (5) P.A. S. Smith and R. N. Loeppky, J. Am. Chem. SOC.,88, 1147 (1967). (6) H. A. Bent, Inorg. Chern., 2, 747 (1963). (7) C. C. Addison, W. Karcher and H. Hecht, “Chemistry in Nonaqueous Ionizing Solvents,” Vol. 111, PergamFon Press, New York, 1967, pp 3-75. (8) F. A. Cotton and G. Wllklnson Advanced Inorganic Chemistry, a Comprehensive Text,’’ 3rd ed.,Interscbnce, New Ywk, 1972, pp 357-359. (9) S. Patai, “The Chemistry of the Amino Group,” Interscience, New York, 1968, pp 305-320. (10) B. C. Challis and J. H. Ridd, R o c . Chem. SOC.(London), 245 (1960). (11) E. D. Hughes and J. H. Ridd, J. Chem. SOC.,82 (1958). (12) A. E. Comyns, J. Chem. SOC.,1557 (1955). (13) F. P. Scarlngelli, E. Rosenberg, and K. A. Rehme, Envlron. Scl. Techno/., 4, 924 (1970). (14) H. J. Crecelius and W. Forweg, Staub-Reinholt. Luft, 30, 23 (1970). (15) H. Hartkamp and G. Nltz, Staub-Relnhofi Luft, 34, 340 (1974). (16) J. Rosin, “Reagent Chemicals and Standards,” 5th ed., 0. Van Nostrand Co., Inc., Princeton, N.J., 1967, p 471.
Avram Gold
AIDS FOR ANALYTICAL GHEMISTS Modified Inductively Coupled Plasma Arrangement for Easy Ignition and Low Gas Consumption John L. Genna and Ramon M. Barnes* Department of Chemistty, University of Massachusetts, Amherst, Massachusetts 0 1003
Charly D. Allemand Jarrell-Ash Division, Fisher Scientific Company, Wakham, Massachusetts 02 154
Since the initial description by Reed ( I ) of a practical inductively coupled plasma (ICP) discharge and the independent realization of its potential as an analytical tool by Greenfield et al. (2), and Wendt and Fassel (3),developments of the ICP discharge as a spectrochemical source have intensified (4,5). Design of an ICP arrangement specifically for totally automated, unmanned operation with low coolant gas consumption and ease of ignition emphasized optimization of plasma tube geometry in the region near the induction coil (6). The resulting successful configuration required precise machined dimensions obtainable with material like boron nitride but not with quartz. This note describes a simple modification of the gas flow injection region which is readily achieved with conventional materiak such as quartz and which promotes the formation of closed loops of ionized gas to ease discharge ignition. This modification also provides reduced coolant gas consumption. In popular ICP arrangements ( 7 - I I ) , total argon flows reach approximately 11 to 30 L/min with the major portion used in the outer tube (Figure 1) annulus to prevent the outer quartz confinement walls from overheating. In high-power 1450
ANALYTICAL CHEMISTRY, VOL. 49, NO. 9, AUGUST 1977
level ICP discharges, high nitrogen flows in the outer annulus provides effective cooling and low background levels ( I I , I 2 ) . Reed recognized the importance of tangential coolant gas introduction for vortex stabilization ( I ) . Although laminar (3)and other arrangements have been explored (131,tangential gas introduction is popular and effective. Stabilization is attributed t o production of a low pressure region along the central axis of the tubes by the swirling gas flow near the confinement wall (I). This low pressure allows increased amounts of countercurrent gas flow. The low pressure produced by the tangential introduction of gas is a function of the mass flow rates, but, more importantly, the gas velocity. In cylindrical coordinates, the gas velocity comprises the following three components (Figure 1): a radial (V?),an axial (V&, and angular or swirl (V,) component. The swirl velocity travels parallel to the circular torch walls and is critical in the stabilization of the discharge. Control of the swirl component is essential in the improvements described here. T o increase the argon flow countercurrent to the main flow, the low-pressure regions in the discharge must be increased. These low-pressure regions may be created, in turn, by the
