Envlron. Sei. Technol. 7904, 18, 787-792
Derivatization of Organic and Inorganic N-Chloramines for High-Performance Liquid Chromatographic Analysis of Chlorinated Water Frank E. Scully, Jr.,* John P. Yang, and Kathryn Mazlna Alfriend Chemical Laboratories, Old Dominion University, Norfolk, Vlrginia 23508
F. Bernard Danlel Health Effects Research Laboratory, U.S. Environmental Protection Agency, Cincinnati, Ohio 45268
Organic and inorganic N-chloramines are converted to highly fluorescent dansyl derivatives by reaction with 5(dimethy1amino)naphthalene-l-sulfinicacid (DANSOZH). The synthesis and properties of this sulfinic acid are described in detail. Details of the method for derivatizing dilute aqueous solutions of N-chloramines are given along with the application of high-performance liquid chromatography to the separation of mixtures of chloramine derivatives. The derivatization method is applied to the analysis of aqueous solutions of individual amines and a mixture (2 mg/L as N in each amine component) chlorinated to different ClZ/Nlevels and incubated for 1h. The chloramine concentrations measured in this manner are correlated with residual chlorine levels determined by the DPD-titrimetric method. A sample of a chlorinated municipal wastewater effluent was analyzed and found to contain both organic and inorganic N-chloramines. The kinetics and mechanism of the derivatization reaction are discussed. Introduction Chlorine is the most widely used disinfectant of water and wastewater in the United States today and is attributed with the virtual eradication of waterborne diseases in this country. In addition, it is used to control biofouling of cooling water systems for power plants, and chlorinated water is used to cool and disinfect meat and poultry. Within the past 10 years, however, it has been recognized that chlorine reacts with natural organic compounds in these systems to produce some undesirable organic byproducts. Identification of these byproducta has been mwt successful for stable, volatile halocarbons which survive current concentration techniques and gas chromatography. Yet, a significant fraction of compounds has eluded identification. One such class of compounds is the organic N-chloramines. Organic nitrogen compounds are abundant and essential componentsof nature (1-3). However, in chlorinated water amino nitrogen compounds are converted rapidly (4) and quantitatively ( 5 , 6 )to their N-chloro derivatives (eq 1). RzNH
+ HOC1
-
R2NC1+ HzO
(1) Depending on the pH of the water and the Cl/N ratio of the mixture, ammonia can form mono-, di-, or tri-Nchlorinated compounds and organic amino compounds can form mono-, or di-N-chlorinated compounds (6, 7). Organic N-chloramines are thermally labile or readily undergo decomposition when concentrated or isolated from solution. Hence, present methods of identification of trace organics in aqueous solution are unsuitable for analysis of these labile oxidants. To facilitate future studies of the potential health and environmental effects of these compounds in disinfected water, a technique is needed that will enable the determination of the carbon backbone of organic N-chloramines actually present in chlorinated water. 0013-936X/84/0918-0787$01.50/0
For the past several years we have examined the reaction of organic and inorganic N-chloramines with arenesulfinic acids (eq 2). The sodium salt of either benzenesulfinic RzNCl ArS02- ArS02NRz+ C1(2) acid or p-toluenesulfinic acid reacts with chloramines in water to give good to high yields of the sulfonamide derivative corresponding to the amine precursor of the chloramine (8). We have adapted this derivatization to very dilute aqueous solution (9) and report here the full details of our studies.
+
-
Experimental Section General. Water used for blanks in this work was chlorine-demand-free water. It was prepared from Burdick & Jackson high purity water which had been chlorinated to 2 mg/L chlorine, stoppered, and stored overnight, boiled for 2 h at a low boil, cooled, and irradiated for 8 h with ultraviolet (UV) light (Ultra-Violet Products Model 11SC-1 pen lamp). Piperidine, pyrrolidine, and dansyl chloride were obtained from Ndrich Chemical Co. Amiio acids and dansylated amino acid standards were obtained from Sigma Chemical Co. N-Chloropiperidine was prepared as described previously (IO). Acetonitrile (UV grade) used in the derivatization of N-chloramines was obtained from Burdick & Jackson Laboratories and distilled from anhydrous copper(I1) sulfate before use. All other reagents used were obtained from commercial sources and were reagent grade or better. A stock solution of sodium hypochlorite was prepared by bubbling high purity grade chlorine gas (Fisher Scientific) into chlorine-demand-free water until the solution turned dark yellow and adjusting the pH to 9.2 with sodium hydroxide. The solution was refluxed for 6 h before it was cooled and stored in an amber bottle in a refrigerator. This solution was diluted to give a working solution of 1000 f 10 mg/L hypochlorite as Clz. The working solution was standardized by the iodometric method 409A as described in ref 10. To obtain the breakpoint chlorination curves of ammonia and the mixture of ammonia and glycine, each solution was rapidly stirred while the standardized hypochlorite was added slowly over 2 min. Residual chlorine levels were measured by the DPDtitrimetric method (IO). Elemental analysis was performed by Atlantic Microlab, Inc. Chromatography. A Waters Associates Model 204 liquid chromatograph with two M-6000A pumps, a Model 720 system controller, and WISP autosampler was used to analyze derivatized samples. A Kratos Schoeffel Instruments Model FS-970 fluorescence detector with deuterium lamp was used with 250-nm excitation and a 418 nm high band-pass filter to detect elution of dansyl derivatives from a pBondapak CI8column (3.9 mm X 30 cm). The detector was routinely used on the 0.5-pA range with a 6-s time constant. With these conditions the detector response of dansylglycine was 0.68 times that of dansylamide. A variation of the gradient program of Bongiovanni
0 1984 American Chemical Society
Environ. Scl. Technol., Vol. 18, No. IO, 1984 787
and Dutton (11)was used to separate dansyl derivatives. It included isocratic elution at 18% acetonitrile/82% H20 (1% acetic acid) for the first 5 min followed by gradient elution from 18% to 54% acetonitrile over the next 45 min followed by isocratic elution at 54% acetonitrile for an additional 10 min. For the kinetic analyses a pBondapak phenyl column (3.9 mm X 30 cm) was used with isocratic elution. The eluant was 40% acetonitrile/60% water (1% acetic acid). Preparation of 5-(Dimethy1amino)naphthalene-1sulfinic Acid (DANS02H). To a vigorously stirred solution of sodium sulfite (10.7 g) in 50 mL of water warmed to 70 "C was added dansyl chloride (5 g). The reaction was kept at a temperature of 70-80 "C for 5 h. During this time all solid dissolved. After the solution was cooled, DANS02H was precipitated from the product mixture by acidifying the solution to pH 4 with sulfuric acid and filtered. The sulfinic acid was purified by dissolving it in cold, dilute, aqueous sodium hydroxide, filtering the resulting solution through a medium porosity fritted filter funnel, and reprecipitation from water or water/ethanol. The pure acid is a white solid which yellows then darkens on heating above about 150 "C. It becomes very dark before it melts with decomposition at 242-244 "C. The purity can be checked by liquid chromatography on a pBondapak amine column (3.9 mm X 30 cm, Waters Associates) with isocratic elution using 0.01 M ammonium phosphate at pH 8 as the mobile phase (2 mL/min). DGNS0,H has a retention time of 4.15 min, and its corresponding sulfonic acid (DANS0,H) has a retention time of 3.5 min. Contamination by small amounts of the sulfonic acid (DANS0,H; mp 315 "C) (12)does not affect the derivatization of chloramines as described below. The compound reacts with N-chloropiperidine to produce dansylpiperidine, mp 111.5-112 "C (lit. mp 110 "C) (12); IR 3700,1620,810,775, 745,1470,1380,1170,1000,920 cm-'; 'H NMR (DMSO-d6) 8.3-8.0 (m, aromatic, 3 H), 7.7-7.5 (m, aromatic, 3 H), 3.6 (8, H20),3.1 ppm [s, N(CH3)2, 6 HI. Anal. Calcd. for Cl2Hl3NO2S-H2O:C, 56.89; H, 5.97; N, 5.53; S, 12.66. Found C, 56.85; H, 5.97; N, 5.53; S, 12.64. Preparation of DANS0,H Reagent Solution. Sodium bicarbonate (1.05 g, 12.5 mmol) was dissolved in about 10-15 mL of chlorine-demand-free water. DANS02H (0.0633 g, 0.25 mmol) was added and dissolved. The resulting solution was diluted to 25 mL in a volumetric flask. Derivatization of N-Chloramines. Ten milliliters of a chlorinated sample to be derivatized was placed in a 50-mL conical flask along with NaHCO, (200 mg). The solid was dissolved before the following were added and dissolved in the order listed freshly distilled acetonitrile (10 mL), 10 N aqueous NaOH (2 drops), and DANSOzH reagent solution (1 mL). The sample was mixed thoroughly to homogeneity, glass stoppered, and stored overnight in the dark. Solutions of chloramines with concentrations greater than M were analyzed by high-performance liquid chromatography (HPLC) without concentration. Solutions less than lo4 M were concentrated 10-fold. To do this, the sample was concentrated on a rotary evaporator to remove the acetonitrile. Throughout most of these studies samples were recovered from this concentrate by using an extraction procedure. In this procedure the pH of the concentrate was adjusted with concentrated phosphoric acid by using a standardized pH electrode to pH 3.0 for recovery of dansyl amino acids or pH 7.0 for recovery of dansyl amines. The concentrate was then decanted into a 60-mL separatory funnel and ex788
Envlron. Sci. Technoi., Vol. 18, No. 10, 1984
tracted with either methylene chloride or ethyl acetate (4 X 5 mL). The extracts were combined and dried over 2 g of anhydrous Na2S04. The extract was then concentrated to dryness on a rotary evaporator. Exactly 1.00 mL of acetonitrile was pipetted into the flask to dissolve the residue. The resulting solution was transferred to a 1-mL vial and sealed with a PTFE-lined cap. If samples were not analyzed immediately by HPLC, they were stored in a freezer. In the latest studies to determine concentrations of chloramines along a breakpoint curve, it was found that recovery was much higher, easier, and more reproducible, if after removal of the acetonitrile from the freshly derivatized solution the pH of the concentrate was adjusted to three before it was passed through an equilibrated CI8 SEP-PAK cartridge (Waters Associates). The reaction flask was washed with 4 mL of water which was also passed through the SEP-PAK cartridge. Dansyl derivatives could then be recovered by elution with 2.0 mL of acetonitrile and either concentrated or diluted to the desired volume. Kinetic Studies. The relative initial rates of reaction of methylamine, piperidine, and pyrrolidine with dansyl chloride were measured in the following manner. Two solutions were prepared each of which contained 5.0 X lo4 M concentrations of two amines: (1)piperidine and pyrrolidine and (2) piperidine and methylamine. One milliliter of each solution was mixed with the following reagents in a small test tube: NaHCO, (42 mg), 1mL of a 0.2 M solution of dansyl chloride in acetonitrile, and 2 drops of 1M NaOH. The reagents were mixed thoroughly. Two minutes after mixing, an aliquot of the solution was injected into the liquid chromatograph and analyzed for the relative amounts of dansylpiperidine and dansylpyrrolidine or dansylpiperidine and dansylmethylamine. The ratio of the peak areas was corrected for the different detector responses of the dansyl amines. Results and Discussion Derivatization and Handling. To enhance the sensitivity and selectivity of detection of the sulfonamide products, a sulfinic acid was synthesized that gives highly fluorescent sulfonamide products (9). Dansyl chloride (5-dimethy1amino)naphthalene-1-sulfonylchloride) is a well-characterized fluorescent derivatizing reagent for amines (13), amino acids (14, 15), and proteins (16). It forms stable, highly fluorescent sulfonamides which are detectable at nanomolar concentrations and can be separated by thin-layer chromatography (TLC) or HPLC. Dansyl chloride reacts with sodium sulfite to give a stable sulfiiic acid, 5-(dimethylamino)naphthalene-l-sulfinic acid (DANS02H). The compound is an amino acid and hence exists in a zwitterionic form at its isoelectric point (approximately pH 4). In dilute base aqueous solutions of DANSOzHreact with chloramines to give the same dansyl derivatives (Scheme I) formed by the reaction of dansyl chloride with the unchlorinated amine. These sulfonamides can be chromatographed and quantitated by fluorescence analysis. Several important steps in the method of handling dilute solutions of chloraminesare worthy of specific note for the successful utilization of this technique. These include using a cosolvent, controlling the pH, and allowing sufficient time for completion of the reaction. For instance, unless a volume of a polar aprotic solvent is used, which is equivalent to the volume of solution to be derivatized, no sulfonamide product is formed. Acetonitrile has been found to be a better cosolvent than tetrahydrofuran (THF) or acetone because it gives higher yields of derivatives, To remove traces of amines which may interfere with the analysis, the acetonitrile is distilled
Scheme I @FIRST EXPERIMENT
S0,Cl
0 SECOND
EXPERIMENT
I
H,C/~-CH,
H3C0NXH3
a
L3
s 3L
L
TIME DEPENDENCE OF DERlVATlZATlON
100%
80 .
1
U’
--/
2
L
6
8 1 0 TIME [HOURS)
23 2L
6
7
Figure 2. Linearity of calibration factor of HPLC fluorescence detector after chromatographyof solutions of Nchloropiperldine (concentrations in water ranging from lo4 to IO-’ M) which had been derhratlzed wlth DANS02H. Results of two separate experiments are plotted.
I
n
5
NEGATIVE LOG CONCENTRATION
LB
Figure 1. Percent of the maximum yield obtainable from solutions of M (- -) N-chloropiperkline (NCP) as either 1 X (-) or 1 X a function of time.
-
from anhydrous copper(I1) sulfate before use. The significance of the use of a cosolvent is discussed later. Another important aspect of the method is the proper adjustment of pH during the derivatization. When three separate solutions of N-chloropiperidine in a phosphate buffer are adjusted to different pHs (pH 5,7, and 9) and then derivatized, only the pH 9 solution gives a product. Typically, a sodium bicarbonate solution buffered to about pH 9.5-10 is used for all derivatizations. The effect derivatization time has on the yield of dansyl piperidine has been examined also. Seven aliquots (1 mL) of a lo4 M solution of N-chloropiperidinewere derivatized in the standard manner. At various time intervals the reactions were analyzed for the amount of dansylpiperidine formed. As Figure 1showB, the reaction is greater than 95% complete in 2.5 h and is essentially complete overnight. Typically, derivatizations of dilute solutions of chloramines have been carried out overnight with good reproducibility. There are no known interferences to the method from the type of organic compounds which have been identified in chlorinated drinking water, specifically the halocarbons. Thus, chloroform, methyl iodide, dichloroacetonitrile, dibromoacetonitrile, and a-chloroacetone (all active substrates for nucleophilic displacement reactions) fail to yield a chromatographically distinguishable product under the conditions described here. Although sulfinate salts have been shown to react with alkyl halides to form sulfones, the reaction requires high temperature, long reaction times, and organic solvents to produce even fair yields of sulfones (17).
In addition, there is no interference from hypochlorite which is usually present in real chlorinated systems. Sulfinate salts have been shown to be oxidized rapidly by hypochlorite in basic solution to sulfonate salts (18). Chromatography and Detection. Fluorescenceis one of the most highly sensitive methods of detection in liquid chromatography. Solutions (1 mL) of N-chloropiperidine M) can be derivatized and analyzed by HPLC quite simply without need of further concentration. Solutions of lo-’ M N-chloropiperidine as small as 10 mL require only slight concentration. The separation of dansyl derivatives of amino acids by HPLC has been described (11,15).A reverse-phase column was found to be most convenient for the separation of dansylated amines and amino acids. The lower limit of detectability of N-chloropiperidine by this derivatization method and the chromatographic analysis just described is approximately 10 ng. Since concentrations of individual N-chloramines in chlorinated aqueous solutions are expected to be about lo-’ M, a protocol was developed for handling concentrations at this level. Dansylated amines are neutral molecules at pH 7, but dansylated amino acids are negatively charged in aqueous solution above pH 4. Therefore, following derivatization of 10 mL of a chloraminesolution and removal of the cosolvent under vacuum, the pH of the solution is adjusted with phosphoric acid to either pH 7 or pH 3 and extracted with methylene chloride or ethyl acetate. At pH 7 dansyl amines are extracted, and at pH 3 dansyl amino acids are extracted. The extraction solvent can then be dried and concentrated to the desired volume. Throughout much of the work described here liquid-liquid extraction and concentration was used. However, this technique was subject to variations in recovery as well as operator error. The operation was considerablysimplified and made more reproducible by adsorbing the derivatives onto octadecyl-silica (SEP-PAK cartridges) and recovering them by elution with acetonitrile. By use of fluorescence detection coupled with liquid chromatography, the amount of dansyl amine formed is directly proportional to the concentration of chloramine in the underivatized solution, This is illustrated in Figure 2 for concentrations of N-chloropiperidine in the range from lo-’ to lo4 M. Chloramines in Breakpoint Chlorination. For a solution containing ammonia and organic amines, a Environ. Scl. Technol., Vol. 18,No. 10, 1984 780
160
CHLORINE DOSE irng/L)
CHLORINE DOSE h g / L I
Flgure 3. Dansylamide (H-D) recovered after derivatization wlth DANSOpHof aqueous solutions of ammonium sulfate (1.8 mg/L as N) in 0.01 M phosphate buffer (pH 7.2) which had been chlorlnated to dlfferent levels. After chlorlnatlon each solution was Incubated In the dark at room temperature for 1 h before a portion was analyzed for total residual chlorine (0- -0)and then derlvatlzed.
Figure 4. Dansylglyclne (H) and dansylamide (A)recovered after derivatization with DANS0,H of aqueous solutions of glycine (2 mg/L as N) and ammonium sulfate (2 mg/L as N) in 0.01 M phosphate buffer (pH 7.2) which had been chlorinated to different levels. After chlorination, each solution was Incubated in the dark for 1 h at room temperature before a portion was analyzed for total residual chlorine (0) and then derivatized.
-
breakpoint chlorination curve is a measure of the residual oxidant for a particular chlorine dose at a specified time after dosing. Although some N-chloro compounds may present problems (191,conventional analytical methods distinguish between residual hypochlorite (free residual) and the sum of all the N-chlorinated amino nitrogen compounds present (combined residual). While ammonia is generally the single most abundant amino nitrogen compound in natural waters and wastewaters, organic amino compounds present can contribute to the overall pool of compounds which are measured as “combined residual chlorine”. In order to characterize the contribution different types of chloramines can have on a composite breakpoint curve, the chlorination and derivatization of model compounds and mixtures were examined. Figure 3 is a plot of the dansylamide recovered from solutions of ammonium sulfate in 0.01 M phosphate buffer at pH 7.2 chlorinated to various points along a breakpoint curve and derivatized 1 h after chlorination. Plotted on the same graph are chlorine residuals. In this and in all subsequent breakpoint plots the curves are plotted so as to give the best visual fit for the recorded data, and the scales of the two plots are adjusted so that their maxima have identical peak heights. There is reasonably good correlation between recovered dansylamideand the measured residual chlorine. It is clear that NH2Cl, as measured by the dansylamide recovered, reaches a maximum at about the same point as the measured oxidant level. However, it should be noted that, because of the mechanism of derivatization as discussed below, dichloramines would probably not be distinguishable from monochloramines. In addition, under the conditions of the derivatization (pH 9.5-10) NHC12is not very stable (6,20)and so would either be converted back to NHzCl or decompose to a non-chloramino product. In any case, a unique derivative of dichloramine such as a di-dansylated amine is not observed. The dansylamide measured is probably derived from both mono- and dichloramines. Piperidine reacts with hypochlorous acid to form a monochloramine which is stable even in the presence of excess hypochlorous acid. When aqueous solutions of piperidine (2 mg/L as N in 0.01 M phosphate buffer at pH 7.2) are chlorinated to varying levels, the amount of dansylpiperidine recovered after a 1-h incubation is directly proportional to the hypochlorite added. At a C12/N mole 780
Environ. Sci. Technol., Vol. 18, No. 10, 1984
ratio of 1/1the dansyl piperidine formed reaches a maximum. Beyond this point it remains constant and a free chlorine residual is observed. Glycine (2 mg/L as N) gives a breakpoint curve similar to that of ammonia. While there is reasonably good correlation of measured N-chloroglycine (as dansylglycine) at the beginning of the curve, there is a reproducible deviation from the measured oxidant level at the end of the curve. At a chlorine dosage of 18mg/L there is a 1.6 mg/L chlorine residual after 1h. However, there is considerably less dansylglycine formed than anticipated for this residual, and the DPD test suggests there is no NJV-dichloroglycine present at the time the solution was derivatized. A similar result was obtained with chlorinated solutions of alanine. Recently, Le Cloirec and Martin (21) have discussed the intermediacy of an N-chlorimine in the decomposition of N-chloralanine in the presence of excess hypochlorite. If the N-chlorimine of formaldehyde (the corresponding intermediate in the breakdown of N-chloroglycine in excess hypochlorite) is present, it may give a DPD residual but no dansyl derivative. This may account for the discrepancy between the measured residual and the corresponding amount of N-chloroglycine measured at C12/N mole ratios greater than 1. To demonstrate the power of the derivatization technique in sorting out the components of a conventionally determined breakpoint curve, equimolar solutions of glycine and ammonia were chlorinated to different levels and derivatized after 1 h. The dansyl derivatives were then isolated and analyzed by HPLC. The areas of the chromatographic peaks were corrected for the relative detector response of the dansyl derivatives. Figure 4 is a plot of the relative amounts of the chloramine derivatives recovered. It shows that glycine is chlorinated before ammonia on the front edge of the breakpoint curve and that N-chloroglycinereaches a maximum before NH2C1. This is consistent with the relative rates of reaction of glycine and ammonia with hypochlorite. Interestingly, if the meas of the chromatographic peaks for the two chloramine derivatives are summed for each dosage point, the new points generate a curve almost identical with the breakpoint curve as determined by the chlorine residual measurement. This demonstrates not only that the measurement of chloramine concentrations by the derivatization method follows predicted concentrations but also that the measurement is
Scheme I1 R,NCI +DANSO,H
DANSO,NR,
A
R,NH + DANS0,CI
k3
DANS0,NR;
1
k4 4 0
r
DANS03H +HCI
10
20
30
LO
50
RETENTION TIME (Minutes)
.Figure 5. High-performance liquid chromatogram of 300 pL of a concentrate of unchiorlnated municipal wastewater effluent which had been chlorinated to 140 mg/L and incubated in the dark at room temperature for 24 h before belng derivatired with DANS02H. Water was sampled on Nov 15, 1983.
truly proportional to the contribution of each individual chloramine to the composite breakpoint curve measured by other techniques. Recently, unchlorinated secondary municipal wastewater effluent from the Army Base Wastewater Treatment Plant in Norfolk, VA, was obtained. Samples of this water, which required 220 mg/L chlorine to reach breakpoint, were chlorinated to 140 (the chloramine maximum) and 240 mg/L and incubated in the dark at 20 OC for either 15 rnin or 24 h before being derivatized. Figure 5 is the liquid chromatogram obtained from one of these samples after workup. The peak with a retention time of 2 min is due to unreacted DANS02H and any DANSOsH present. The 11-min peak is due to the derivative of NH2Cl and the peaks at 21 and 34 min are due to oxidative degradation of the dimethylamino unit of DANS02H by high concentrations of either hypochlorite or chloramines. The mass spectrum of the compound having the retention time of 34 min matches that of dansyldimethylamine, and the 21-min peak has the same retention time as dansylmethylamine. The remaining peaks appear to be due to dansyl derivatives of organic N-chloramines in the sample. As expected, the concentration of organic N-chloramines is considerably lower when a sample is chlorinated past the breakpoint than at the chloramine maximum. In addition, the profile of organic N-chloramines changes between samples chlorinated for 15 min and those chlorinated for 24 h. Most of the compounds have retention times similar to dansyl derivatives of amino acids and small polypeptides. Any large hydrophilic polypeptide chloramine derivatives would have been eliminated in the workup of the samples. Identification of these compounds is currently under investigation. Kinetics and Mechanism. DANS02H does not itself react with amines to form sulfonamides. However, when solutions of chloramines containing unchlorinated amines are derivatized, the sulfonamide products of both the chloramine and the amine are found. The product ratios reflect the relative reactivities of the amine or the parent amine of the chloramine toward dansyl chloride. Thus, when a dilute solution equimolar in both the chloramine, N-chloropiperidine, and the unchlorinated amine, methylamine, is derivatized with DANS02H in the standard manner, both dansylpiperidine and dansylmethylamineare recovered in a 1.6/1 ratio. Competition studies between N-chloropiperidine and pyrrolidine also give dansyl products of each compound in a ratio of l.l/l,respectively. In our initial report of the reaction of chloramines with sulfinic acids (8) it was pointed out that, when a M solution of N-chloropiperidine is mixed with a lo9 M solution of sodium benzenesulfinate, benzenesulfonyl
chloride can be isolated. This suggests the mechanistic scheme outlined in Scheme I1 where the rate of the formation of DANS02Cl is much greater than its reaction with RzNH or R2*NH and the product ratio is equal to k2[&NH]/(k3[&*NH]). This is supported by the fact that when aqueous solutions equimolar in piperidine and pyrrolidine or equimolar in piperidine and methylamine are mixed with solutions of dansyl chloride in acetonitrile, the kinetic product ratios (from initial rates) are identical (1.6/1 and 1,1/1,respectively) with the sulfonamide ratios listed above for the reaction of mixtures of the corresponding chloramines and amines with DANS02H. These data and observations have the greatest implication for the analysis of chloramines in water which has been chlorinated to a level below a chlorine to amino nitrogen mole ratio of l. Under such conditions both amines and chloramines are present. At f i t glance the above data suggest that dansyl sulfinic acid would not distinguish between amines which are chlorinated and those which are not. However, two facts support the proposal that the concentrations of dansyl derivatives in the derivatized sample are proportional to the chloramines present prior to derivatization. First, Morris and Margerum have shown that the rate constant for the reaction of amines with hypochlorite to form chloramines increases with the basicity of the amine (7, 22). Consequently, in a solution which is chlorinated below its chloramine maximum, the concentration of each chloramine present is proportional to both the concentration and basicity of each parent amine (7,221 (see eq 3 and 4). Thus, [R2NC1]/[R2*NC1] R2NH + HOCl
2R2NCl + H 2 0 +
R2*NH + HOCl -kR2*NC1 H 2 0
(3)
(4)
= k6[R2NH]/(k6[R2*NH]).While this ratio holds true in the study of the mixture of glycine and ammonia, Isaac has noted that this ratio is influenced by pH at some point, since it is the unprotonated form of the amine that reacts with hypochlorous acid to produce a chloramine. For instance, Isaac points out that chlorination of equimolar mixtures of dimethylamine and glycylglycine at pH 7 would give faster initial reaction of the less basic amine because of the relative concentrations of the unprotonated forms of the amines (23). Whether the derivatization with DANSO2H is able to reflect this phenomenon is under current investigation. Second, several workers have shown that the rate of reaction of aromatic sulfonyl chlorides with amines is also proportional to the basicity and concentration of the amine ( 2 4 , s ) . Thus, on partial chlorination of an equimolar solution of two amines, not only will the reaction of the more basic amine with hypochlorite be more rapid, thus forming more chloramine, but also, when the solution is derivatized with dansyl sulfinic acid, the more basic amine will react faster with the dansyl chloride intermediate (see Scheme 11)to form proportionally more sulfonamide derivative (k, vs. k3 in Scheme 11). The results Envlron. Sci. Technol., Voi. 18, No. 10, 1984
791
of the breakpoint curve of the mixture of glycine and ammonia shown above (Figure 4) support this. A dichloramine probably undergoes two successive displacements of its chlorines on reaction with DANS02H to form its parent amine and two dansyl chloride molecules. Subsequent reaction would yield the same derivative as the corresponding monochloramine. Figure 3 supports this since there is good correlation between the amount of recovered dansylamide and the residual oxidant in the region of the curve where dichloramine formation becomes significant. The use of a cosolvent inhibits the hydrolysis of the intermediate sulfonyl chloride. However, even in the presence of a cosolvent k4 is still significant. When concentrations of chloramines are very low, the absolute yields of dansylpiperidine formed by derivatization of and lo4 M solutions of N-chloropiperidine are low (20% and 7%, respectively). Nevertheless, as demonstrated above, detection levels are more than sufficient to be of importance both in model studies and in studies of waters containing significant quantities of organic N-chloramines.
Acknowledgments We thank John Van Norman for suggesting the use of anhydrous copper(I1) sulfate for the removal of trace amines from solvents and Dennis Seeger, U.S.Environmental Protection Agency, Drinking Water Research Division, Metropolitan Environmental Research Laboratory, Cincinnati, OH, for obtaining mass spectra for us. Registry No. DANS02H,71288-39-6;DANS02C1,605-65-2; NH2Cl,10599-90-3;H20,7732-185; N-chloropiperidine,2156-71-0; N-chloroglycine,35065-59-9;N-chlorodimethylamine,1585-74-6; N-chloromethylamine, 6154-14-9.
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Scully, F. E., Jr.; Bempong, M. A. EHP, Environ. Health Perspect. 1982, 46, 111-116. Ram, N. M.; Morris, J. C. Environ. Znt. 1980,4, 397-405. Weil, I.; Morris, J. C. J. Am. Chem. SOC.1949,71,1664-1671. Higuchi, T.; Hussain, A.; Pitman, I. J. Chem. SOC.B 1969, 626-63 1. Gray, E. T., Jr.; Margerum, D. W.; Huffman, R. P. In
“Organometalsand Organometalloids,Occurrence and Fate in the Environment”;Brinkman,F. E.; Bellama, J. M., Eds.; American Chemical Society: Washington,DC, 1978; ACS Symp. Ser. No. 82, pp 264-277. Morris, J. C. In “Principles and Applications of Water Chemistry”;Faust, S. D.; Hunter, J. V., Eds.; Wiley: New York, 1967; pp 23-53.
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(8) Scully, F. E., Jr.; Bowdring, K. J . Org. Chem. 1981, 46, 5077-5081. (9) Scully, F. E., Jr.; Yang, J. P.; Bempong, M. A.; Daniel, F.
(10)
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