Determination of Mono-, Di-, and Trichloramine by Ultraviolet Absorption Spectrophotometry FRED W. CZECH, ROBERT J. FUCHS, and HENRY F. ANTCZAK Inorganic Research and Developmenf Deportmenf,
b The quantitative determination of monochloramine (chloramide), dichloramine (chlorimide), trichloramine (nitrogen chloride), and chlorine by ultraviolet absorption spectrophotometry is presented. The method is based on the different ultraviolet absorption characteristics of the chloramines and chlorine in anhydrous carbon tetrachloride. It has proved useful in the rapid determination of the chloramines and chlorine in gas samples or in a medium which lends itself to the selective extraction of the chloramines b y carbon tetrachloride. The optimum concentration range and the expected precision of the method are given along with the molar absorptivities of the respective chloramines and chlorine. In addition, the distribution ratios of the chloramines between carbon tetrachloride and water were determined and are reported. The chloramines are reasonably stable in anhydrous carbon tetrachloride solution. a distribution method for characterization, Chapin (8)studied the formation of chloramines from ammonia and chlorine in aqueous so1ution. Metcalf (8),in investigating the reaction between ammonia and hypochlorous acid, determined the ultraviolet absorption spectra of the chloramines in dilute aqueous solutions and used them for their identification. The findings of Metcalf (8) and those of a later study by Corbett, Metcalf, and Soper (6),who also utilized ultraviolet spectra, substantiated the earlier finding of Chapin (3)concerning the effect of p H on chloramine equilibria in aqueous solution. The above investigations showed that no more than two chloramine species are found in aqueous solution at any given pH. Meinberg, Tecotzky, and Audrieth (7)describe the determination of monochloramine in aqueous solution by ultraviolet absorption spectroscopy. Audrieth, Colton, and Jones ( I ) , in a more recent article, comment on the monochloramine determination. Coleman and Johnson (4) evaluated wet analysis methods for trichloramine, several of which were used in this study for both chloramine assay and for the SING
Food Machinery and Chemical Corp., Carteref, N. 1.
determination of the nitrogen to chlorine ratio. These methods, however, appear to be unreliable at low concentrations. Dowel and Bray (6)were unable to get quantitative recoveries of trichloramine by iodometric determination. Coleman (3)describes results obtained by the Noyes procedure (9) with respect to the nitrogen to chlorine ratio. This procedure is based on the reaction of trichloramine with hydrochloric acid to form ammonium chloride and cporine. The chlorine is determined iodometrically and the nitrogen by alkaline distillation of the ammonia. A modified Palin method for the determination of the chloramines and chlorine is described by Williams (10). The method is based on an amperometric titration and deals only with very low chloramine concentrations in water. Throughout the literature the chloramines are described as unstable compounds, extremely sensitive to light and pH changes. For problems presented to this laboratory none of the above methods proves satisfactory because of their unreliabdity at low concentrations and their nonspecificity. EXPERIMENTAL
letely by wet methods and the average R/Cl ratio was 3.17. Because of the uncertainty as to the accuracy of the nitrogen method, especially at low NCb concentrations, the subsequent standard preparations were only analyzed for total chloride by reduction of the sample with sodium sulfite as proposed by Dowel1 and Bray (6). Since most of the ultraviolet rhararteristics mere already evaluated, these could be used to establish identity. EVALUATION OF ULTRAVIOLET ABSORPTION CHARACTERISTICS. The analyzed carbon tetrachloride samples containing the NCb were diluted with dry spectro rade carbon tetrachloride and scannet in the ultraviolet range. I n carbon tetrachloride solution NC& gave two distinct absorption peaks, one at 265 and the other at 345 mp. No reference to these two analytical peaks WAS found in the literature. A typical ultraviolet absorption curve for NCls is shown in Figure 1. The maxima of the absorption bands, which were taken from a number of samples, are shown in Table I. No ultraviolet evaluation of the chloramines wm possible below 245 to 250 mp because of the high absorption of carbon tetrachloride. Since this method was intended for routine identification as well as quantitative evaluation of samples, it was helpful to develop identification ratios, the ratio of the absorbances a t different wave lengths. In this way an unknown sample can be identified with as few as three readings. The identification ratios are listed in Table 11. The molar absorptivities a t the wave lengths of the main absorption peaks, and also at the wave lengths of the absorption peaks of all the other chloramines were determined and are listed in Table 111. They were obtained from the standard curves b graphic evaluation of the general agsorption curves. They were determined with the goal in mind of setting up simultaneous equations for
Apparatus and Reagents. The ultraviolet absorbances were determined with a Beckman DU spectrophotometer with ultraviolet attachment and using 10-mm. rectangular quartz cells. A simple pressure pipet device consisted of a double bore rubber stopper through which were inserted a pipet and an air pressure bulb. Spectrograde carbon tetrachloride was used throughout the investigation for extraction and dilution of standard and unknown samples. Other grades of carbon tetrachloride contained substances which reacted with chlorine or chloramines. All other reagents used in the preparation of chloramines were of reagent quality Table 1. Maximum Absorption W a v e with exception of the chlorine and length of Chloramines and Chlorine in sodium hypochlorite, which were comCCl, mercial quality. Trichloramine (NClr). PREPARACompound A m . , Mp TION. Trichloramine w w prepared according to a method described by "IC1 262 NHClr 257,300 Noyes (9). Aliquots of NCb in carbon NClr 265,345 tetrachloride were taken for the de335 c1* termination of total nitrogen and total chloride. Five runs were analyzed comVOL 33,
NO. 4, M A Y 1961
705
r
the quantitative determination of complex chloramine mixtures. The distribution ratio was dctermined a t room temperature (26' C.) between equal volumes of carbon tetrachloride and distilled water, and is ahown in Table IV. This value was determined by available chlorine titrations with the identity of the dissolved species confirmed by ultraviolet absorption. The conformity to Beer's law a t the maximum absorption bands was confirmed and the calculated absorbance factors to be used for quantitative dekrmination of the NCla are shown in Table V. Mono- and Dichloramine ("$1, The monoNHClr). PREPARATION. and dichloramines were prepared by reacting 15 ml. of 5% sodium hypo-
0.8
o, 0.1 U
0
e3
0.4
n U 0.7.
Wave
Figure 1. Ultraviolet absorption of the chloramines and chlorine in CCI, Left.
Table II. ldentiflcation Ratios of Chloramines in Ultraviolet Absorption Spectrophotometry
Compound NHzCI NHClz
Ratios None
300f257 300/268 257/268
1.94 f 0.21 2.35 i 0.27 1.21 Az 0.05
NCla
265/345 265/315 345/315
1.87 f 0.09 3.13 i 0.27 1.68 0.10
*
Ch
Table 111.
None
Length, MJJ
Right.
---.----Okhloramlne
chlorite solution, 150 ml. of water, and 10 ml. of 1 to 10 aqueous ammonium hydroxide. The pH was adjusted only for the dichloramine with HCl. Chapin (9) found only monochloramine a t pH values above 8.5. At pH 4.5 to 5.0 dichloramine was the sole product, with mixtures of the two at intermediate pH values; a sharp transition point between dichloramine and trichloramine was reported at pH 4.4. These findings were substantiated later by Metcalf (8). The solutions were extracted with carbon tetra-
Molar Absorptivities of Chloramines and Chlorine at Analytical Wave Lengths
Wave Length, M M 257
NHiCl NHCI, NClr
262 423 112 450
400 135 415
...
c1z
...
Table IV. Distribution Ratios between CC14 and Water for Chloramines
Distrib. Ratio, D
Compound "$21 NHCIt NCI,
0.058
0.88
32.0
Table V. Absorbance Factors of Chloramines and Chlorine in CCl,
Compound NHiCl NHCli NCL
MP
ReciDrocal Absorptivit l - c m . Setells
262 257 300 265 345 335
0.13 0.64 0.30 0.28 0.58 0.96
Wave Length,
Clr (Concn., mg./ml., = reciprocal absorptivity x absorbance)
706
ANALYTICAL CHEMISTRY
265 414 110 462
...
300 25 293 165 31
335
345
...
...
73 208 73
0.28 X
-Trlchloramine 0.28 X ------..Chlorine 0.68 X -Monochlorornine 0.92 X
39 232 70
chloride, and after drying with anhydrous NaBO,, the extracts were scanned in the ultraviolet range. EVALUATION OF ULTRAVIOLET ABBORFTION CHARACTERISTICS. Typical absorption curves are shown in Figure 1. All attempts to eliminate selectively the 265 peak from the dichloramine pattern failed. The distribution ratios for the two chloramines between carbon tetrachloride and water are shown in Table IV. It is interesting to note the close a reement of the distribution ratio for dichoramine found by Chapin (8), 0.85, with the value of 0.88 found by this laboratory. The identification ratios for the maximum and minimum absorption points for dichloramine are shown in Table 11. The conformity of the observed absorbances to Beer's law was proved to be valid, and the calculated absorbance factors are shown in Table V. The molar absorptivities are given in Table 111. Chlorine. PREPARATION. A solution of chlorine in carbon tetrachloride
IO-* g./ml. lo-'
g./rnl.
10-8 g,/ml. 10 -3 g./ml.
was prepared from cylinder chlorine and analyzed for available chlorine by the potassium iodide-thiosulfate volumetric method. EVALUATION OF ULTRAVIOLET ABSORPTION CHARACTERISTICS. A diluted sample was scanned in the ultraviolet range givin an absorption curve as shown in f'igure 1. The calculated molar absorptivities are given in Table
111.
DiSCUSSlON AND RESULTS
Analysis of Mixtures by Simultaneous Equations. The method of
simultaneous equations was never used to the full extent, and the necessity for using it is questionable in view of the statement by Corbett (6),that there are never more than two species of chloramines present at any one pH in aqueous solution. HOWever, it is possible that the different species might be stable in the vapor phase and be absorbed in carbon tetrachloride. In this case the method might prove of value tzj a tool for kinetic studies. Practical Applications, Determina-
tion of NCls. The quantitative determination of NCL in gas samples or in aqueous solution has been carried out on a routine basis in this laboratory using the ultraviolet method developed in this investigation. For the analysis of gas samples (usually a measure of NCla evolved from solids, slurries, or solutions), the gas is simply passed through a gas-absorbing bottle containing cold carbon tetrachloride. Absorption of NCla is essentially quantitative at about -10' C., but losses are small enough at 0' C. for most work. The carbon tet(rach1oridesolution is simply warmed to room temperature, diluted to known volume, dried with anhydrous Na$O+ and analyzed by the ultraviolet method. For the analysis of aqueous solutions,
Table VI. Ultraviolet Analysis of Known Chloramine and Chlorine Mixtures
Mixture NCh C18
+ Clr + NCli
Concn., lo-’ % G./MI. Present Found Recovery 0.06 0.048 96 0.45 0.43 95.6 95.6 0,110 0,106 0.205 0.207 100.9
c1*+
:;;!:::;!:‘ti:
NCls
+ c12 + NCla c11
NCI,
NH&l NCI,
+
0.133 0.149
0.135 0.152
101.5 102
0.067 0.037
0.068 101.5 0.040 108.1
0.040 0.089
0.038 0.088
95.0 98.9
a n aliquot of the solution is extracted with several successive portions of carbon tetrachloride and the combined extracts are dried, diluted to known volume, and analyzed by the ultraviolet method. Analysis of Mixtures of NCls and Clz. A common mixture encountered is a mixture of NCls and chlorine,
since chlorine is a product of decomposition of NCls. The chlorine absorption peak at 335 mh does not interfere with the 265 NCls peak so that the NCla content can be determined directly from the 265 absorbance. It is then a simple matter to correct for NCla and determine the chlorine by difference from the reading a t either 336 or 345 mh. Mixtures were prepared from standard solutions of chlorine and NCls in carbon tetrachloride and analyzed by ultraviolet. All solutions used in these mixtures were dried and assayed prior to mixing. Some quantitative results are shown in Table VI. The results were arrived at by graphic solution rather than by calculation using simultaneous equations. The recoveries range from 95 t o 108%. Other Mixtures. Carbon tetrachloride solutions containing various chloramines were mixed and ultraviolet scans were taken of t h e mixtures. No quantitative analyses were attempted. A mixture of monochloramine and chlorine showed dichloramine formation. The pattern changed with time. A mixture of mono- and trichloramine also showed dichloramine formation and the reaction appeared to progress with time. A mixture of
di- and trichloramine showed no ultraviolet pattern change. A mixture of mono- and dichloramine appeared to form a stable system, initially, but one which appears to be time limited. LITERATURE CtTED
(1) Audrieth, I,. F., Colton, E., Jonea M. M., J. Am. Chem. boc. 76, 1428-31 (1954). (2) Chapin, R. M., Ibid., 51, 2112-17 (1929). (3) Coleman G. H.,Nitrogen Trichloride Studies, Ofhe of Scientific Research and Development, -I, .^.^ RePt- No. 858, August lY4L. (4) Coleman, G. H., Johnson, H. L., “Inorganic Syntheses,” Vol. 1, p. 69, McGraw-Hill, New York, 1939. (5) Corbett, R. E.,Metcalf, W. S., Soper, F. G., J. Chent. SOC.1953, 1927-9. (6) Dowell, C. T., Bray, W. C., J. Am. Chem. SOC.39,896(1917). (7) Kleinberg, J., Tecotzky, M., Audrieth, L. F., ANAL.CHEW26, 1388-9 (1954). (8) Metcalf, W. S., J. Chem. SOC.1942, 148-50. (9) Noyes, W..A., “Inorganic Syntheses ’’ Vol. 1,. *D. 65, . McGraw-Hill, New York, 1939. (10) Williams, D. B., Water and Sewage Works 1951,475-7. RECEIVED for review November 16, 1960. Accepted February 23, 1961. Pittsburgh Conference on Analytical Chemistry & Applied Spectroscopy, Philadelphia, Pa., February-March 1960
Mass Spectra of Aliphatic Thiols and Sulfides E. J. LEVY, The Atlantic Refining Co., Philadelphia, Pa. W. A. STAHL,’ U . S. Quartermaster Research and Engineering Center, Natick, Mass.
b Mass spectra molecular structure correlations for thiols and sulfides were developed during an investigation of the components responsible for odor changes in irradiated beef. By using these correlations a compound can b e identified as a thiol or a sulfide. The thiols can b e further classified as primary, secondary, or tertiary, and the sulfides can b e identified as to the carbon number of the alkyl substituents and the degree of cy branching. The major fragmentation ions of the thiols can b e classified into four types: the molecular ion less CnHgn+l and the molecular ion less each of the groups, SH(CH2),, SH*(CH2),, and SH3(CH2),. The sulfides show similar fragment ion series plus two additional types, R-SHf, and R-SHzf, formed by the loss of C,H*, and C,,H~,-I, respectively, from the molecular ion. Cleavage of the /3 carbon-carbon bond to
Present address, McCormick & Co., Baltimore, Md.
yield sulfur-containing fragment ions is most prevalent in the thiols and lower molecular weight - sulfides, but a-bond cleavage becomes important in the symmetrical sulfides of higher molecular weight.
results of an investieation into components of irradiated beef demonstrated the importance of sulfur-containing compounds as odor constituents (16). To aid in the identification of thiols (mercaptans) and sulfides for which calibration compounds may not be available, mass spectra molecular structure correlation rules were sought. The correlations resulting from this study enable a compound to be identified as either a thiol or a sulfide and then assigned to a structural class within each sulfur compound type. Previous correlation studies have been made for many classes of compounds. These include alcohols (4,II), aliphatic acids ( 7 ) ,acetals (S),ald-hydes -HE
1 the off-odor
(6), ethers (9), esters (Id),thiophenes ( 8 ) , lactones (6), ketones (IS),halides (IO), and hydrocarbons (1, 12). It
has been shown that a molecular ion aftcr formation will dissociate into fragment ions in a random statistical manner whm no weak bonds or directing functional groups arc present. For thiols and sulfides, dissociations are very strongly influenced by the sulfur atom and generally occur a t bonds a,8, and y to the functional group, often with rearrangement. EXPERIMENTAL
The mass spectra of 29 mercaptans and 31 sulfides were examined. The spectra of compounds containing up to eight carbon atoms were either from API Project 44 or obtained from samples run a t the Quartermaster Research and Engineering Center using a Consolidated 21-103B mass spectrometer. These samples included compounds purchased from Eastman and purified by gas chromatography or API standard VOL. 33, NO. 6, MAY 1961
707
