species had decayed to negligible levels. The precision of the determination within each set of specimens bombarded simultaneously is a few per cent. It is believed that much of the scatter could be reduced if identical deuteron energies within each specimen were ensured by using bombardment capsules machined with high precision. I n general, this technique can be extended to any nonvolatile matrix, and for many materials analyses may be performed by counting induced radioactivity without chemical processing. A detailed description of the present work is given by Winchester (3).
Table 1. Relative Counting Rates of 157-Minute Si3I to 112-Minute F1* /3* in Deuteron Bombarded S i 0 2
Bom-
0.93, 1.03, 1.03 1.03, 1.01, 1.02, 0.94, (0.69)” 3 1.09, 1.11,0.94, 1.00,0.85 4 1.03. 1.02, 1.02, 1.01. 0.92 5 0.98; 0.94; 1.06’ 6 0.99, 1.01 a Quartz sample from different source than the other four samples. Not included in average. 1 2
‘
F.
I30
/
-
LITERATURE CITED
curve, measured from 20 minutes to
4 hours after bombardment, shows only the 10.0-minute NI3 and 112-minute FIE components which are resolved graphically. Owing to the higher relative isotopic abundance of C12 over 0’’ and OlS, the XI3 component is prominent even for low carbon contentse.g., in the analysis of SiOz containing 0.2% C the counting rate of N1s exceeds that of F*8up to 1 hour after bombardment. The relation between the C/O and X13/F18 ratios is linear. These data also shon- a small activity of N13 where no S i c has been added; this may be due in part to impurity of C initially present in the SiOz and in part to failure to eliminate completely interference from the nuclear reaction 016(d,n~)X13. the threshold of which is 8.4 m.e.v.
SIR: Because of cross interference in analysis for nitrite (6) and 2-nitropropane (6) preliminary separation of the components in an appropriate solvent is required. I n part this cross interference might be expected since the coupling of Znitroalkanes to form azo compounds is known (4). However, consideration of i t is not apparent in the determination of either nitrite formation by extracts of pea plants from 2nitropropane (6) or of nitrite formation for the determination of nitroethane oxidase actimty ( 3 ) . PROCEDURE
Aqueous solutions (1.5 ml.) containing nitrite and the 2-nitropropane were extracted with 1 to 5 ml. of heptane or benzene. Nitrite ion was determined on an appropriate aliquot (2.0 to 35.0
J ~.
~~
IC
3-
20
~
C Y
~
52
Corbo‘ &I
Figure 1. tures
3r)qen
lox
Analysis of S i O r S i C mix-
Table I gives the relative counting rates of p- from Si3I and 0.51-m.e.v. annihilation y from F18,induced by short deuteron bombardments in SiOZ, compared to the ratio Si/O and normalized to the average value. A thin A1 absorber was used to eliminate interference of Fl8 p + in the measurement of the more energetic 0- of Si31 by an endwindon proportional counter, and counting was performed a few hours after bombardment when shorter lived
mpmoles of nitrite) of the aqueous layer by the sulfanilamide method ( 5 ) . For the work reported here readings mere made in a Klett-Summerson colorimeter with the green (No. 54) filter, and sodium nitrite was used as a primary standard. For determination of 2-nitropropane, the hydrolysis method of Sweet et al. (6) was applied to the organic extract. Adaption of this method to the lower concentrations of nitro compounds required reduction of volume and modification of procedure. Thus: to an aliquot of the organic layer containing 2-nitropropane (0.2 to 22.0 pmoles), 5 ml. of water and 1.0 ml. of 6.3M NaOH were added. The well shaken mixture was allowed to stand for 10 minutes, after which 0.5 ml. of 30% hydrogen peroxide was added. The mixture was heated in a loosely stoppered tube for 1 to 1.5 hours in a
(1) Koch, R. C., “Activation Analysis Handbook,” Academic Press, New York, _ 1960. _ (2’1 Strominner. D.. Hollander. J. M.. Seaborg, 6. T., Rev. Mod. Phis. 30, 585 (1958). “Table of Isotopes.” (3) Winchester, J. W., “The Use of 15 h1.e.v. Deuterons for the Determination of Carbon, Oxygen, and Silicon in Solid Materials by Radioactivation Analysis,” Technical Rept., Dept. of Geology and Geophysics, M.I.T., Cambridge, Mass., October 26, 1960. JOHNW. WINCHESTER MICHAEL L. BOTTINO \-I
Department of Geology and Geophysics Massachusetts Institute of Technology Cambridge 39, Mass. RECEIVED for review November 17, 1960. Accepted January 3, 1961. Work supported in part by a contract with the AVCO Corp. and by a grant from the National Science Foundation.
water bath. After cooling, the sample was brought to 10 ml. and the nitrite ion formed mas determined as above on a 1.0- or 0.1-ml. aliquot for the range of 0.2 to 2.2, and 2.2 to 22.0 pmoles, respectively. For these concentrations the care in increasing the temperature of hydrolysis has not been as essential as the original method indicates. RESULTS
Indication that %nitropropane interferes with the sulfanilamide determination of nitrite is shown in Figure 1. For any one concentration of nitrite ion the amount of interference is not a function of Znitropropane concentration. Interference was also observed when the ratio of concentration of nitrite and 2nitropropane was 1:1 or 1000:1 as well as 1:1000 as shown in the figure. VOL. 33, NO. 3, MARCH 1961
473
r
'601 70
50
3
20
IO
mpmoles
30
N o NO2
Figure 1 . Effects of 2-nitropropane on determination of nitrite ion by sulfanilamide method
Evidence that 2-nitropropane wili react with the test reagents is shown in Figure 2. Honever the absorbance in the 540-mp range was not a function of concentration and examination of the spectrum indicated no other usable peak. There is, however, indication that less than 1 pmole of 2-nitropropane, in the absence of nitrite ion, might be determined by direct diazotization and coupling. This in effect has been used by Cohen and Altshuller ( I ) for determination of primary nitroparaffins by coupling with p-diazobenzenesulfonic acid, which is formed in the test solution from potassium nitrite and sulfanilic acid. For 2-nitropropane they reported a product with weak absorption a t 365 mp; this they attributed to impurities. Our examination of this procedure suggests that i t is not applicable to 2-nitropropane, thus in effect confirming their observations. Khen the original hydrolysis treatment for the determination of aliphatic nitro compounds (6) was applied to a known sample of 2-nitropropane, the amount of nitrite ion formed accounted for the concentration of 2-nitropropane originally added. Likewise, determinations of known samples of sodium nitrite indicated that the nitrite ion was unchanged by hydrolysis treatment. However, n hen mixtures of known concentrations of nitrite and 2-nitropropane were used, the amount of nitrite ion subsequently determined did not account for the total 2-nitropropane and nitrite in the sample. This suggests the possi-
I
2
3
7 8 m a l e a 2 . N8froprapane 4
,a
5
6
9
I0
11
Figure 2. Effect of 2-nitropropane on reagents for nitrite determination in presence and absence of nitrite ion
474
ANALYTICAL CHEMISTRY
bility of interaction of nitrite and 2nitropropane under these conditions. Variations of the conditions of the nitrite determination, such as pH, time, and buffer, gave equivocal results for the mixtures. Removal of one of the components by oxidizing or reducing agents gave interference with the test reagents or color. Attempts to destroy the nitrite with sulfamic acid were unsuccessful since any excess subsequently destroyed the nitrite formed from the nitro compound. Initially the thioglycolic acid method of Ziegler and Glemser (7') for nitrite shon ed promise since i t effectively measured nitrite ion in the micromole range without interference from the nitro compounds. However, this method is not effective in the millimicromole range and in the presence of buffers, especially phosphate, the results are not reproducible. Since chemical methods would not directly differentiate these compounds, physical separation was explored. specifically the extraction of the nitropropane by organic solvents. Unfortunately a number of these extractants removed the nitrite ion along with the nitro compound. These include petroleum ether, n-amJ1 alcohol, ethyl acetate, and a mixture of isobutyl alcohol and benzene. Heptane nil1 remove 2-nitropropane and nitroethane from an acidificd buffered aqueous solution without removing the nitrite ion. 1-Kitropropane. honever, is not completely removed. Figure 3 shows the curve obtained from determining the nitrite ion recovered from buffered solutions containing knon n amounts of 2-nitropropane (0.22 to 22.0 pmoles) and nitrite ion (3 to 30 mpmoles) in nliich the trichloroacetic acid treated solution n as extracted with heptane and the nitrite ion determined on the aqueous phase. Because of the volumes involved and the position of the v i n d o ~in the KlettSummerson instrument, removal of the heptane wab not required. Over a range of 3 to 30 mpmoles of nitrile ion the reproducibility was nithin 3 mpmoles after removal of 0.22 to 22.0 pmoles of 2-nitropropane. If the samples were prepaied in water, the addition of trichloroacetic acid n as not required but in the presence of phosphate buffer i t n a s essential to the extraction. Benzene extraction was comparable to that of heptane but the aqueous phase must be removed since on standing some of the nitrite is also taken up (Figure 3). For concentrations of nitrite in the micromole range, benzene extraction previous t o dilution for nitrite determination removed some of the nitrite ion. With the demonstration of separation of the nitrite and 2-nitropropane, the hydrolysis method of Sweet et nl. (6) was applied to the organic extract. Figure 4 shows the curves for 2-nitro-
0700-
Figure 3. Variation in nitrite determination b y sulfanilamide method (5) in test solution including buffer and trichloroacetic acid after extraction Ranges of readings for 3, 21, and 30 pmoles of nitrite represent 31 separate determinations Extraction from 1.4 ml. with 1 .O ml. of heptone of 0.2, 2.2, and 22.0 pmoles of 2-nitropropane Extraction from 1.5 ml. with 5.0 ml. of benzene of 22.0 pmoles of 2-nitropropane
-
----
propane in the 0.22- to 2.2- and 2.2- t o 22.0-fimole range. These curves were prepared from benzene extracts of acidified buffered solutions of 2-nitropropane in the indicated concentrations. For a series of 13 sets of determinations in which each set included all of the concentrations indicated, the absorbance was linear with concentration within each set. but the slope of such plotted data varied from set to set. Eighteen further determinations were made in an effort to check specific concentrations, especially 2.2 and 22.0 pmoles. Including the additional individual determinations a 10% difference in readings was observed for these concentrations examined and is shown in the range of values included in Figure 4. The broader ranges have been included to emphasize that replicate determinations give agreement which cannot beobtained from consecutive determinations. These variations have not been related to the rate of hydrolysis or the method of extraction but may be related to the age of the 2-nitropropane solution. This approach for recovery and determination of aliphatic nitro compounds appears to be limited by the extractant. Thus, heptane nil1 remove up to 10 pmoles of nitroethane without inter1
0*3
2 275 50 hl C l C r n O , < $
2 - Nllrcoroosne
Figure 4. Determination of 2-nitropropane from nitrite ion formed after extraction in 5.0 ml. of benzene and hydrolysis of 1 .O-ml. aliquot
- - _0.0 to
2.2 pmoles Mmoles
-- 2.2 to 22.0
fering with subsequent treatment but is ineffective for removing nitromethane or 1-nitropropane. Benzene will remcwe both 1- and 2-nitropropane but is no more effective for nitroethane or nitromethane. LITERATURE CITED
(1) Cohen, I. R., Altshuller, A. P., XSAL. CHEX 31,1638 (1959). (2) Little, H. N., J . Biol. C‘hein. 229, 231 (1957).
(3) Little, H. N., in “hlethods in Enzymology,” Colowick, S. P., Kaplan, S . O., eds., 1‘01. 11, p. 400, iicadernic Press, Yew York. 1955. (4) Parmerter. S. I f . . in ‘,Organic Reactions,” Adams, R., ed., Vor 10, p. 19, Wiley, Kern York, 1959. (5) Snell, F. D., Snell, C. T., “Colorimetric Methods of Analysis,” 3rd ed., p. 804, I-an Sostrand, Sen. York, 1949. (6) Sm-eet, R. L., Spindt, R . S., hleyer, 1‘. D., Division of Petroleum Chemistry, 128th Meeting, .1CS, General Papers S o . 34, 3-9, September 1955; personal communication. ~
( 7 ) Ziegler, AI., Glemser, O., Z. Anal. Chem. 144, 187-91 (1955).
FRAXCES L. ESTES I
