Quantitative Microdetermination of Gaseous Ammonia by Its Absorption at 204.3 Mp F. A. GUNTHER, J . H. BARKLEY, M. J. KOLBEZEN, R. C. BLINN, and E. A. STAGGS Citrus Experiment Station, University of California, Riverside, Calif.
calibrated in the usual manner by maximum instrument response to the emission spectrum of mercury vapor from 185 mp to 302 mp and to minimum instrument response to the six strong oxygen absorption bands between 184 mp and 195 mp (Table 11). From these calibration data a smoothed correction curve of apparent us. actual readings was prepared. In all subsequent discussions reported, wave length values are the corrected ones unless otherwise indicated.
A direct spectrophotometric method for the quantitative determination of ammonia gas at atmospheric pressure utilizes the absorption maximum of ammonia at 204.3 mp (E, 3127) which allows determinations from 7 p.p.m. (5 y per liter) to 1000 p.p.m. of ammonia in air. Data are presented to indicate sensitivities achievable at 10 other absorption maxima of ammonia within the region from 190.3 to 224.4 m p . Comparisons of fused silica and crystal quartz spectrophotometers in this application are reported in detail.
Rates of Introduction of Dry Nitrogen"into Spectrophotometer Approximate Flow Rate, Liter /Minute Position Initialb Stabilized Resistor box 0.30 0.10 Lamp house 0.15 0.05 Nonochromator 1.20 0.40
Table 1.
A
MONG the many recorded micromethods for the deter-
mination of gaseous ammonia, some require collection of the ammonia in a scrubbing solution followed by colorimetric assay (4, 5, 7), while others are capable of more direct determination, ss by the ordinary thermal diffusion process (1, 8, 12) and by changes in electrical resistance of very hot (l20Oo to 1300' C.) platinum wires immersed in the gas mixture ( 3 ) . Quantitative utilizations of the striking and ideally suited absorption maxima of ammonia in the ultraviolet region from 226 mp to about 190 nip have not appeared in the literature. The present report is concerned with the analytical exploitation of the electronic absorption of the ammonia molecule; details of the utilization of this method with automatic recording in evaluating sorption of ammonia by citrus fruits and by fiberboard will be reported elsewhere. In 1935, Llulliken (6) proposed electron configurations for some of the possible transition assignments of one of the electrons of the absorbing electron pair in ammonia, and in 1946 Thompson and Duncan (IO) reported oscillator strengths and positions of hands for the ultraviolet spectrum of ammonia in the range from 45,000 cm.-l (222 mp) to 120,000 em.-' (83 mp). Recently, Tannenbaum and con-orkers (9) published their detailed ammonia spectrum from 45,000 cm.-] (222 mp) to 60,000 cm.-' (167 mp) as obtained with a vacuum. spectrograph and the flowing vapor technique. Their spectrum exhibited doublets a t about 217 nip, 213 mp] and 209 mp, as estimated from their spectral plot. In the present study ammonia was determined in an especially rcbuilt Beckman Model DU spectrophotometer. EXPERIMENTAL
Instrument. A Beckman Model DU spectrophotometer was modified by the manufacturer by replacing the 30' crystal quartz prism by a 33" fused silica prism. This instrument is now available as a Beckman Model DUS spectrophotometer. To gam detection sensitivity and to improve resolution in the region ot interest, the instrument was equipped with the standard Beckman photomultiplier attachment. Because of possible interferences in the low ultraviolet region fiom chemicals in the laboratory atmosphere, the following changes were made by this laboratory. The instrument was drilled and tapped, and l/s-inch tubing fittings were inserted for continuously urging the resistor box (back side), the lamp house (bottom; theyamp house cover was replaced vith a gasketed solid pl:rte), and the cast monochromator housing (1 inch away from the prism baffle plate) with the quantities of dry nitrogen shown in Table I. Also, the standard DU four-turn wave length paper scale was replaced with the lower wave length portion of the sixturn paper scale from a Beckman DK-2 spectrophotometer. Because both scales and the D U scroll were made for crystal quartz instruments, the wave length scale had to be recalibrated for the present purpose. The new scale was positioned and
a
itc.
Water-pumped nitrogen passed over calcium chloride and Ascar-
* For approximately 1.5 minutes, or until instrument readings stabilized. Table 11. Calibration in Millimicrons of Wave Length Scale Using LMercuryEmission Lines and Atmospheric Oxygen Absorption Bands Hg or 02 Scale Hg or 02 Scale Line Reading Line Reading 1 8 4 . 6 (02) Off-scale 225.3 225.0 184.9 1 8 6 . 3 (02) 1 8 8 . 2 fOzi 190 2 io,, 192 35 (02) 194 2 194 7 ( 0 2 ) 202 7 205 3 222 5
185.0 186,3 188.2 190 3 192 3 194 2 194 6 202 5 204 9 221 6
226.0 239.9 248.3 253 7 265 2 275 3 289 4 296 7 302 2
225.5 238,3 246.3 251 3 262 1 271 3 284 2 290 8 295 7
Subsequently, a Beckman DK-2 spectrophotometer was utilized, for some of the routine analytical work with gaseous ammonia. This spectrophotometer was equipped with the standard Beckman dry nitrogen purge kit for this model instrument. Calibration of the DK-2 against the modified manual DU through the range of interest (202 mp to 206 mp) indicated scale agreement within *0.2 mp. For quantitative applications both instruments were carefully preset to fixed wave length via optimum instrument response corresponding to the absorption maximum of ammonia at 2043 mp. This broad intense band \vas chosen to have minimum effect when slit width was changed, as n-ell as to avoid interference from absorption by water vapor. Cells. Both 1-cm. and 10-em. scaled silica cells xere used, with a high-vacuum, silicone-type lubricant as sealant. All cells were cross calibrated with dry air. In all subsequent discussions the corrected cell values are used. Calibration with Ammonia. Initial semiquantitative measurements to ascertain the expected sensitivity and precision of the analytical method a t different absorption maxima were made by mixing known volumes of anhydrous ammonia gas and dry nitrogen in a calibrated 100-cc. syringe. For example, ammonia gas in a continuous, rapid stream was introduced a t the bottom of n 1-liter beaker until the beaker was overflowing, then 10 cc. was drawn into the syringe from near the bottom of the beaker; similarly, dry nitrogen was then drawn into the syringe to make 100 cr. total volume. This mixture was alloxed to stand briefly, then was flushed through the cells through a hypodermic needle.
1985
ANALYTICAL CHEMISTRY
1986 Mare precise estahlishment of t.he sensitivity and precision of this method for ammonia. was accomplished with the aid of the apparatus shown schematicnlly in Figure 1. All pertinent glassware was immersed in B wstter bath held a t 26.0" + 0.2' C. Allglass conneotions were used, mzith the only nongless portions of the system occurring within the pulsing diaphragm Dynapump. The 10-em. cell arrangement, adopted from a previous use ( d ) , is shown in Figure 2. This device permits shifting either the reference cell or the sample cell into the energy beam without interrupting gas flow through the sample cell. All spherioitl and standard taper connections wwe generously lubricated with a high-vacuum, silicone-type lubricant. The system urns maintained at atmospheric pressure.
Figure 1.
Schematic drawing of a p p a r a t u s u s e d in preparing standard curyes
The gas introduction pipet,(shown in detail in Figure 1) when calibrated with mercury in the usual manner was found to have a reproducible volume of 1.544 f 0.003 cc. a t 26.0' C., including the bores of both stopcocks. The pipet was connected to a cylinder of ammonia. gas by %lubricated spherica.1 joint, and the gas was passed through i t a t 2 pounds pressure for 30 seconds. The stopcock remote from the cylinder was closed first. then the
the h&g slit width. a €
5
rng. / liter
Figure 6.
Absorbance-concentration curves for ammonia gas vs. dry nitrogen
___ I a n u a l instrument _ _ _ - IRecording instrument
Figure 5. Log molar absorptivity-wave length curve for ammonia gas US. dry nitrogen in 1-cm. cells
V O L U M E 2 8 , NO. 1 2 , D E C E M B E R 1 9 5 6 however. For example, in Figure 5 there are clean maxima both at 190.3 mp and a t 187.0 mp, with apparent e values of 3715 liters per mole-cm. (Table V) and 2370 liters per mole-cm., respectively. The DK-2 instrument recorded the maximum a t 190.3 mp with an apparent e value of 1106 liters per mole-cm. but failed to record the maximum a t 187.0 mp. At 204.3 mp both instruments are capable of detecting about 5 y (7 p.p.m.) of ammonia per liter of air or nitrogen under optimum instrument conditions with IO-cm. cells Mulliken (6) states that, in regard to the electronic configuration of ammonia, the structure, [sall2[~el4 [zal] (3saJ, 'AI, indicates that the XHa + core per ee should be stable because the electron removal is essentially nonbonding, but that the possibility of predissociation of excited NH, exists. Thus, the excited electron may interact with the core as follows:
KH,+
+e
-+ Ir;Ha
+H
but predissociation should in general tend to diminish with increase in the principal quantum number of the excited electron. To test the effect of prolonged radiation a t 204.3 mp upon ammonia gas, two 1-cm. cells carefully matched a t this wave length Rere filled a t i24 mm. with a mixture of ammonia gas (3 mg. per liter) and dry nitrogen. One cell was exposed continriously to the ultraviolet energy, whereas the companion cell v a s exposed only for the few seconds necessary to make readings. Typical results against dry nitrogen are shown in Table VI. At the end of this period the two cells were quickly scanned from 200 to 206 mp, with essentially parallel absorption curves resulting. These data and curves indicate that prolonged irradiation of ammonia gas in this region does decrease the effective concentration of the absorbing species of interest, unless this predissociation is reversible in that concentration varies with elapsed time b e k e e n exposure and concentration measurement.
1989 Table VI.
Photodecomposition of Ammonia Gas at 204.3 M p and 26" C. Elapsed Transmittance Time, Minutes Unexposed Exposed 0 31.2.31.1 31.1.31.3 20 31.3;31.4 38.2i38.2 80 31.4,31.5 40 .O,40.1 110 31.8.31.9 42.6.42.5 130 31.9;31.9 43.8;44.0
ACKNOWLEDGMENT
The authors wish gratefully to acknowledge technical and other assistance extended by many members of Beckman Instruments, Inc., especially Lee Cahn, R. Pat Connor, George Kincaid, J. G. Myers, and Henry Noebels. LITERATURE
(1) Bahner, F.,Chem.-Ing.-Tech. 25, 89 (1953). (2) Carman, G. E., Gunther, F. A., Blinn, R. C., Garmus, R. D., J . Econ. Entomol. 45, 771 (1952). (3) Huguenard, M. E.,Compt. rend. 213,21 (1941). (4) Kruse, J. SI.,Rlellon, AI. G., ANAL.CHEM.25, 1188 (1953). (5) hlagill, P.L.,Am. I n d . Hyg. Assoc. Quart. 11, 55 (1950). (6) Mulliken, R. S ,J. Chem. Phys. 3, 506 (1935). (7) Scheurer, P.G., Smith, F., ANAL.CHEM.27, 1616 (1955). (8) Schwarz, N., A p p l . Sca. Research Al, 47 (1947). (9) Tannenbaum, E.,Coffin, E. AI., Harrison, a.J., J . Chem. Phys. 21, 311 (1953). (10) Thompson, R.J., Duncan, -1.B. F., Ibid., 14,573 (1946). (11) Ususovskaya, L. G.,Frank-Kamenetskii, D. A , Zuvodskaya Lab. 14, 12 (1948). R E C E I V E for D review M a y 14, 1956. Accepted September 6, 1956. Paper No. 918, University of California Citrus Experimental Station, Riverside,. Calif.
Determination of Thorium in Urine R. W. PERKINS
and D. R. K A L K W A R F
General Electric Co., Richland, Wash.
A bioassay procedure can be used to determine thorium in submicrogram amounts in urine. Thorium is separated from interfering materials by coprecipitation with lanthanum fluoride, followed by an extraction using 2thenoyltrifluoroacetone in benzene. The amount of thorium is determined colorimetrically as the thoriumniorin complex.
I
N ORDER to determine the relationship between urinary excretion of thorium and the amount of thorium present in the body, a procedure must be available to detect the small amount of thorium that can be expected in the urine. A maximum permissible limit of 89 mg. (0.01 pc.) of thorium in the body has been recommended by the International Commission on Radiological Protection (9). The available information on the rate of excretion of thorium has been recently summarized (8); however, it is not sufficient to define the sensitivity required of a bioassay procedure for determining a given body burden of thorium. ;In estimate based on the biochemical similarity of thorium and plutonium (7) indicated that a sensitivity of 0.27 of thorium would be sufficient to detect any significant thorium content in an individual and thus be suitable for future studies of the relationship between urinary excretion and body burden of thorium.
Several possible analytical techniques for estimating the thorium content of urine samples were considered. An alphaparticle counting procedure sensitive to 0.05 disintegration per minute (0.2 y of thorium-232) can be realized; however, complicating factors in the case of thorium make this approach undesirable. One of the thorium-232 decay products is thorium228, which is also an alpha emitter. The relative amounts of the two isotopes present are a function of the time since the decay chain between them had been broken. The alpha emissions of thorium might be counted immediately on separation and then again 1 to 4 weeks later, when the amount of thorium-228 could be determined by the build-up of alpha-particle-emitting daughters of thorium-228. However, this would be difficult to evaluate a t present because only nuclear track counting has the required sensitivity and 1 week or more of exposure would be required for each count, further confusing the analysis. The direct determination of as little as 0.3 y of thorium in animal tissue samples with an emission spectrograph has been reported (6). Because urine contains the same inorganic salts as tissue but in a higher concentration (by a factor of about loa), a spectrographic analysis might be performed after a preliminary separation of the thorium from the bulk of the urine salts. A recently reported mass spectrometric determination of thorium indicated (19) that 0.1 y of thorium could be detected; hon-ever, a preliminary separation would again be required.
