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Multiple element emission spectral detection gas chromatographic profiles of halogenated products from chlorination of humic acid and drinking water
Journal of’ Chromatography, 438 (1988) 3543 Elsevier Science Publishers B.V., Amsterdam CHROM.
Printed in The Netherlands
20 258
MULTIPLE ELEMENT EMISSION SPECTRAL DETECTION GAS CHROMATOGRAPHIC PROFILES OF HALOGENATED PRODUCTS FROM CHLORINATION OF HUMIC ACID AND DRINKING WATER
M. P. ITALIA*
and P. C. UDEN*
Chemistry, Lederle Graduate Research Tower, University 01003-0035 (U.S.A.) Department
of
of
Mnrsachusetts, Amherst, MA
(Received November 29th, 1987)
SUMMARY
A multi-channel microwave-induced plasma atomic spectroscopic gas chromatographic detector has been used to characterize capillary column profiles of chlorinated humic acid and drinking water for carbon, chlorine and bromine content. In addition to element selectivity and good detection limits this technique enables empirical formulae of separated compounds to be estimated with sufficient accuracy for useful peak identification. Among the compounds thus characterized are trihalomethanes, haloaliphatic acids, aldehydes and nitriles.
INTRODUCTION
Since the introduction of viable microwave-induced plasma (MIP) emission spectral cavity designs for gas chromatographic (GC) detection, these systems have been extensively explored. The first MIP systemslp* required reduced pressures and complex vacuum equipment to sustain a helium plasma. Chromatograph-plasma interface designes were also complicated. Quimby et aL3, interfaced an atmospheric pressure “Beenakker” cavity4p6 to a gas chromatograph to show the advantages of using the MIP to monitor halogenated compounds. Further studies on halogenated compounds by Quimby et aL7, and by Uden and MillerE, showed the versatility of the system. Since the MIP provides elemental spectral emission, individual halogens may be monitored separately by observing appropriate wavelengths, thus simplifying the chromatographic analysis and interpretation. A second important advantage of MIP detection is that it responds directly to the molar amount of a specific element present, and is little, if at all, influenced by the element’s molecular environment. Thus, it is an excellent element-specific detector for the determination of the halogenated products of a complex material such as humic acid. An important aspect is the possibility of monitoring two or more emission lines simultaneously (multi-channel MIP, MMIP) and subsequently determining em*
Present address: Union Carbide Corporation,
0021-9673/88/$03.50
0
Bound Brook, NJ 08805, U.S.A.
1988 Elsevier Science Publishers B.V.
M. P. ITALIA,
36
P. C. UDEN
pirical formulae. If two emissionchannels have been simultaneously monitored, and there is a known compound in the chromatogram, then the ratio of element X to element Y in any compound may ,be calculated using the following equation: X -= Y
Ht X.(unk)
Ht Y(std)
No. of X elements in std
Ht Y(unk) ’ Ht X(std) . No. of Y elements in std
(1)
where Ht = peak height of unknown (unk) and known compound (std) in a highresolution capillary chromatogram. Thus, if an element ratio can be determined an empirical formula determination is possible. The work of Uden et uI.~, Yoo’* and Perpall et al. l l, have shown that it is possible ‘to obtain accurate empirical formula data for very diverse compounds. EXPERIMENTAL
Apparatus The microwave system used was the MPD 850 (Applied Chromatography Systems, Luton, U.K.) multi-channel polychromator system with a Hewlett-Packard 5830 gas chromatograph and a Beenakker atmospheric pressure microwave-induced helium plasma cavity. The system design has been described in detail by Slatkavitz et a1.12 and the polychromator design has also been described13. The emission lines monitored included carbon (247.9 nm), chlorine (481.0 nm), and bromine (470.5 nm) wavelengths. Between the spectrometer and the chart recorders were situated three single-channel integrators, with each channel calibrated individually to give the largest number of area counts possible. Materials
Humic acid was obtained from Dr. B. Matvienko, Universidad do Sao Paula, Sao Carlos, Brazil, and contained 35.08% C, 7.33% N and 4.51% H. Two samples were then prepared by adding 0.100 g to 160 ml of pH 7 phosphate buffer in a crimp-top vial. To this was added 3.5 ml of chlorinating reagent, sodium hypochlorite, to give a 5:l chlorine:carbon mole ratio. The sample was then allowed to react for 24 h, after which it was quenched with sodium thiosdfate. A neutral extraction of one sample was performed using 2 x 100 ml of ether, after which it was concentrated to approximately 100 ~1 in a Kuderna-Danish concentrating apparatus with a three-ball Snyder column. The second sample was acidified to a pH of 1 (to litmus) with sulfuric acid and derivatized with boron trifluoride-methanol, according to the procedure reported by Young14 and Italials. After extraction with diethyl ether-hexane (1: I), v/v), the sample was concentrated to approximately 100 pl* Water samples were prepared by extracting 1.5 1of tap water with 1 1of diethyl ether (after initial quenching with thiosulfate), followed by concentration to 100 ~1. Gas chromatography GC conditions used were: initial temperature, 40°C; initial hold, 2 min; temperature increase, S”C/min to lXO”C, followed by a 1 min final hold. All of the conditions were the same for acid or neutral analysis with the exception of the initial
GC-MMIP
OF HALOGENATED
PRODUCTS
37
temperature, which in the acid analysis was 50°C. The injection port temperature was 225°C and the transfer line temperature was 300°C. The microwave plasma was operated with a helium flow of 60 ml/min and a 75-W forward power reading. All injections for humic acid work were 0.2 ~1 with a GC split ratio of 2O:l. For tap water it was necessary to inject 3 pl to obtain a large, integratable signal on the halogen channels. The column was a J&W Scientific (Folsom, CA, U.S.A.) 25 m x 0.2 mm I.D. DB-5 fused-silica capillary column, with a 2O:l split ratio. The attenuation for each output was 32 x for carbon emission, 2 x for chlorine emission and 4 x for bromine. RESULTS
Standard compound analysis
To determine that the system was functioning properly a standard solution of chloroform, bromodichloromethane, chlorodibromomethane and bromoform was injected into the chromatograph to obtain the chromatograms in Fig. 1. It had been reported previously1 * that the choice of standard compound may influence the empirical formula determinations significantly. To investigate what effect the choice of internal standard would have upon this analysis, the empirical formula caicuiations were performed using both chlorodibromomethane and bromodichloromethane as reference compounds. After applying eqn. 1 and dividing through all the ratios by the smallest mole ratio available, empirical formulae were determined as shown in Table I. As is shown, the calculated empirical formulae are the same within expected error limits, and correspond well to the actual formula. It was decided to use chlorodibromomethane as the internal standard, as this compound eluted later in the chromatogram and was easily resolved. Analysis of halogenated humic acid
The MMIP traces of each emission line of the humic acid “neutral” fraction are shown in Fig. 2 and as expected there are more peaks present in the carbon emission channel than for the halogen channels. Calculating empirical formulae for the halogen containing compounds gave results corresponding to: dichloroacetonitrile, trichloroacetaldehyde, trichloroacetone, bromodichloromethane, chlorodibromomethane, bromodichloroacetaldehyde, chlorodibromoacetaldehyde, bromoform and tribromoacetaldehyde (Table II). It may be noted from the table that there are a number of cases in which an exact whole number is not obtained for the empirical formula. This is attributable to a variety of integration problems. When this situation is encountered a set of decision-making parameters must be adhered to. In this analysis any ratio that had a mole fraction above 0.85 and below 1.15 was considered to constitute a mole fraction of one and any compound between 0.40 and below 0.60 was considered to have a mole fraction of 0.50. In this manner some of the calculations were simplified with the additional justification that these molecules were short chained and the empirical formula would presumably also be the molecular formula. However, when the ratios appeared to be in the areas between these two ranges, the policy was to determine what was chemically and chromatographically possible and make logical assignments based on that knowledge. It is noted that chloroform, the most abundant product formed in the halogenation of humic acid,
38
M. P. ITALIA, P. C. UDEN B
D
BROMINE C
CHLORINE
Fig. 1. Multi-channel MIP analysis of a standard mixture of (A) chloroform, (B) bromodichloromethane, (C) chlorodibromomethane and (D) bromoform monitored on the carbon (247.9 nm), chlorine (481.0 nm) and bromine (470.5 nm) emission wavelengths. Chromatograms are offset for clarity.
is not one of the identified peaks. This is due to the inability to resolve the chloroform peak on the carbon emission channel, and this subsequently gives a false integration signal. The humic acid “acidic” fraction shows a large number of peaks that appear in all three channels (Fig. 31, making the analysis complex. However, once the neutral
GC-MMIP
OF HALOGENATED
PRODUCTS
39
TABLE I EMPIRICAL FORMULA DETERMINATIONS FOR A STANDARD MIXTURE OF CHLOROFORM, BROMODICHLOROMETHANE, CHLORODIBROMOMETHANE AND BROMOFORM RUN ON THE MMIP MONITORING THE CARBON (247.9 nm), CHLORINE (481.0 nm) AND BROMINE (470.5 nm) EMISSION WAVELENGTHS Ratios are calculated on two “internal standard” compounds, bromodichloromethane momethane. crw?lpoli?ld
CHC13 CHClzBr CHClBr, CHBr3
CHBrG (std. peak)
CHBrzCI (std. peak)
clc12.8
GC13
-
C1Cl1.sBr0.9 -
ClCIlBrl.8
CHBr2.9
CHBr3.2
and chlorodibro-
Emviricai formula
-
-
cc13 CCl*Br CCIBrl CBr3
_
E
-L
I
B
B
ILL
CHrnINE
Fig. 2. The GC-MMIP traces of the neutral fraction of halogenated humic acid monitored on the carbon (247.9 nm), chlorine (481.0 nm) and bromine (470.5 nm) emission wavelengths. Identifications are: A = bromodichloromethane, B = dichloroacetonitrile, C = trichloroacetaldehyde, D = chlorodibromomethane, E = bromodichloroacetaldehyde, F = trichloroacetone, G = bromoform, H = chlorodibromoacetaldehyde and I = tribromoacetaldehyde.
M. P. ITALIA,
P. C. UDEN
-_I_ BROMINE
CRLORINE
CARBON Fig. 3. The GC-MMIP traces of the “acidic” fraction of halogenated humic acid monitored on the carbon (247.9 nm), chlorine (481.0 nm) and bromine (470.5 nm) emission wavelengths simultaneously. Compound identifications are as methyl esters: A = chloroacetic acid, B = dichloroacetic acid, C = trichloroacetic acid, D = dibromoacetic acid, E = bromodichloroacetic acid, F = chlorodibromoacetic acid and G = tribromoacetic acid.
fraction peaks that pass through the acidic preparation scheme are removed. the analysis is simplified. For this set of calculations, chlorodibromomethane, one of the neutral remnants, was chosen as the standard. This was possible because ratioing requires only a compound for which a good signal is obtained, and concentration is not a factor. The data for seven of these compounds is shown in Table III, and they have been identified as the methyl esters of chloroacetic acid, dichloroacetic acid, trichloroacetic acid, dibromoacetic acid, bromodichloroacetic acid, chlorodibromo-
GC-MMIP
OF HALOGENATED
PRODUCTS
B
F
E
i
BKtlINE
Fig. 4. GC-MMIP trace of the neutral fraction of South Deerfield drinking water monitoring the carbon (247.9 nm), chlorine (481 .O nm) and bromine (470.5 m-n) emission wavelengths. Identifications are: A = chloroform, B = bromodichloromethane, C = dichloroacetonitrile, D = trichloroacetaldehyde, E = chlorodibromethane and F = bromoform.
acetic acid and tribromoacetic acid. While these may comprise a high proportion of the halogenated products, there are still more unidentified, higher order acids to be found and characterized. In making the above identification from GC-MIP response ratio data, much
M. P. lTALlA,
42
P. C. UDEN
TABLE II MMIP EMPIRICAL FORMULA DETERMINATIONS OF THE NEUTRAL FRACTION OF HALOGENATED HUMIC ACID FROM THE CHROMATOGRAPHIC ANALYSIS IN FIG. 2 IdentiJication in Fig. 2
Gcl1.4r1.0 GClI.2 GCl1.4 ClCliBrl.9
ClCllBr0.6 CIC10.75 CIBr3.Z GCIO.&I C&2.6
Empirical formula (hydrogens removed)
IdentiJication
CClzBr CCL C*C13 CClBr2 C,C12Br cc1 CBr3 CZClBr2
Bromodichloromethane Dichloroacetonitrile Trichloroacetaldehyde Chlorodibromomethane Bromodichloroacetaldehyde Trichloroacetone Bromoform Chlorodibromoacetaldehyde Tribromoacetaldehyde
C&3
reference was made to the prior knowledge of the products of humic acid halogenation, and thus an internal standard was not needed or used. If such a standard were necessary, it would have to contain all the elements that were to be measured. Tap water analysis A drinking water sample was obtained from South Deerfield, MA, U.S.A., and concentrated according to the protocol reported previously. Fig. 4 shows the analysis of that sample and the subsequent peak identification. The increased complexity of the carbon trace, coupled with the greater simplicity of the halogen responses, reflect an appropriate assessment of tap water analysis. From peak ratioing and empirical formula determinations, six contaminants of this water sample were identified as chloroform, bromodichloromethane, dichloroacetonitrile, trichloroacetaldehyde, chlorodibromomethane and bromoform. Due to chromatographic interference, chloroform was identified only From retention time knowledge and its correct wavelength response. However, with a different sample concentration protocol and under different chromatographic conditions, chloroform could be readily confirmed.
TABLE III MMIP EMPIRICAL FORMULA DETERMINATION OF THE ACIDIC FRACTION OF HALOGENATED HUMIC ACID FROM THE CHROMATOGRAPHIC ANALYSIS IN FIG. 3 Identfication in Fig. 3
Ratio
Empirical formula (hvdrogens removed)
Identification (as methyl esters)
C1Cl0.3 CICl0.7 C1Clo.92 ClBr0.78 CiClo.sBro.3 CiClo.sBro.7 W3ri.i
C3CI CJCll cc1 C3Br2 C3C12Br C3ClBrz CBrJ
Chloroacetic acid Dichloroacetic acid Trichloroacetic acid Dibromoacetic acid Bromodichloroacetic acid Chlorodibromoacetic acid Tribromoacetic acid
GC-MMIP
OF HALOGENATED
PRODUCTS
43
CONCLUSION
While there are many detectors which are selective, none, save perhaps mass spectrometry, offers the selectivity capabilities of multi-channel microwave-induced plasma. When the acquisition and maintenance costs are compared, MMIP has distinct advantages. This technique offers the element selectivity of an emission procedure and detection limits which are often better than mass spectrometry. The analysis of a chromatographically complex mixture can be simplified by removal of extraneous compounds through selective emission spectroscopic detection. Most importantly, the ability for empirical formula determination from chromatographic separations and emission channel responses creates useful analytical opportunities. The possibility of using a chromatograph to separate compounds and obtain the empirical formula almost instantly (through computer manipulation) is an attractive one. ACKNOWLEDGEMENTS
This research was supported in part by the Geological Survey, U.S. Department of the Interior through the Massachusetts Water Research Institute and by the 3M Corporation and the Dow Chemical Company. REFERENCES I C. A. Bathe and D. J. Lisk, Anal. Chem., 39 (1967) 786. 2 W. R. McLean, D. L. Stanton and G. E. Penketh, Analyst (London), 98 (1973) 432. 3 B. D. Quimby, P. C. Uden and R. M. Barnes, Anal. Chem., 50 (1978) 2112. 4 C. I. M. Beenakker, Spectrochim. Acru, 31B (1976) 483. 5 C. I. M. Beenakker, Spectra&m. Actu, 32B (1977) 173. 6 C. I. M. Beenakker and P. W. J. M. Boumans, Spectrochim. Acta, 33B (1978) 53. 7 B. D. Quimby, M. F. Delaney, P. C. Uden and R. M. Barnes, Anal. Chem., 52 (1980) 259. 8 P. C. Uden and J. W. Miller, J. Am. Water Works Assoc., 75 (1983) 524. 9 P. C. Uden. K. J. Slatkavitz and R. M. Barnes, Anal. Chim. Acta, 180 (1986) 401. IO Y. J. Yoo. Ph.D. Dissertation, University of Massachusetts, Amherst, MA, 1987. 11 H. J. Perpall, P. C. Uden and R. L. Deming, Spectrochim. Acta, 42B (1987) 243. 12 K. J. Slatkavitz. P. C. Uden. L. D. Hoey and R. M. Barnes. .I. Chromafogr.. 302 (1984) 277. 13 MPD 850 AG Organic Analyzer Instruction Manual, Applied Chromatography Systems Limited, ton, Sect. 3, 1979, pp. l-10. 14 M. S. Young. Ph.D. Disserfation. University of Massachusetts, Amherst, MA, 1988. 15 M. P. It&a, Ph.D. Dissertutiun, University of Massachusetts, Amherst, MA, 1987.
Lu-
Printed in The Netherlands
20 258
MULTIPLE ELEMENT EMISSION SPECTRAL DETECTION GAS CHROMATOGRAPHIC PROFILES OF HALOGENATED PRODUCTS FROM CHLORINATION OF HUMIC ACID AND DRINKING WATER
M. P. ITALIA*
and P. C. UDEN*
Chemistry, Lederle Graduate Research Tower, University 01003-0035 (U.S.A.) Department
of
of
Mnrsachusetts, Amherst, MA
(Received November 29th, 1987)
SUMMARY
A multi-channel microwave-induced plasma atomic spectroscopic gas chromatographic detector has been used to characterize capillary column profiles of chlorinated humic acid and drinking water for carbon, chlorine and bromine content. In addition to element selectivity and good detection limits this technique enables empirical formulae of separated compounds to be estimated with sufficient accuracy for useful peak identification. Among the compounds thus characterized are trihalomethanes, haloaliphatic acids, aldehydes and nitriles.
INTRODUCTION
Since the introduction of viable microwave-induced plasma (MIP) emission spectral cavity designs for gas chromatographic (GC) detection, these systems have been extensively explored. The first MIP systemslp* required reduced pressures and complex vacuum equipment to sustain a helium plasma. Chromatograph-plasma interface designes were also complicated. Quimby et aL3, interfaced an atmospheric pressure “Beenakker” cavity4p6 to a gas chromatograph to show the advantages of using the MIP to monitor halogenated compounds. Further studies on halogenated compounds by Quimby et aL7, and by Uden and MillerE, showed the versatility of the system. Since the MIP provides elemental spectral emission, individual halogens may be monitored separately by observing appropriate wavelengths, thus simplifying the chromatographic analysis and interpretation. A second important advantage of MIP detection is that it responds directly to the molar amount of a specific element present, and is little, if at all, influenced by the element’s molecular environment. Thus, it is an excellent element-specific detector for the determination of the halogenated products of a complex material such as humic acid. An important aspect is the possibility of monitoring two or more emission lines simultaneously (multi-channel MIP, MMIP) and subsequently determining em*
Present address: Union Carbide Corporation,
0021-9673/88/$03.50
0
Bound Brook, NJ 08805, U.S.A.
1988 Elsevier Science Publishers B.V.
M. P. ITALIA,
36
P. C. UDEN
pirical formulae. If two emissionchannels have been simultaneously monitored, and there is a known compound in the chromatogram, then the ratio of element X to element Y in any compound may ,be calculated using the following equation: X -= Y
Ht X.(unk)
Ht Y(std)
No. of X elements in std
Ht Y(unk) ’ Ht X(std) . No. of Y elements in std
(1)
where Ht = peak height of unknown (unk) and known compound (std) in a highresolution capillary chromatogram. Thus, if an element ratio can be determined an empirical formula determination is possible. The work of Uden et uI.~, Yoo’* and Perpall et al. l l, have shown that it is possible ‘to obtain accurate empirical formula data for very diverse compounds. EXPERIMENTAL
Apparatus The microwave system used was the MPD 850 (Applied Chromatography Systems, Luton, U.K.) multi-channel polychromator system with a Hewlett-Packard 5830 gas chromatograph and a Beenakker atmospheric pressure microwave-induced helium plasma cavity. The system design has been described in detail by Slatkavitz et a1.12 and the polychromator design has also been described13. The emission lines monitored included carbon (247.9 nm), chlorine (481.0 nm), and bromine (470.5 nm) wavelengths. Between the spectrometer and the chart recorders were situated three single-channel integrators, with each channel calibrated individually to give the largest number of area counts possible. Materials
Humic acid was obtained from Dr. B. Matvienko, Universidad do Sao Paula, Sao Carlos, Brazil, and contained 35.08% C, 7.33% N and 4.51% H. Two samples were then prepared by adding 0.100 g to 160 ml of pH 7 phosphate buffer in a crimp-top vial. To this was added 3.5 ml of chlorinating reagent, sodium hypochlorite, to give a 5:l chlorine:carbon mole ratio. The sample was then allowed to react for 24 h, after which it was quenched with sodium thiosdfate. A neutral extraction of one sample was performed using 2 x 100 ml of ether, after which it was concentrated to approximately 100 ~1 in a Kuderna-Danish concentrating apparatus with a three-ball Snyder column. The second sample was acidified to a pH of 1 (to litmus) with sulfuric acid and derivatized with boron trifluoride-methanol, according to the procedure reported by Young14 and Italials. After extraction with diethyl ether-hexane (1: I), v/v), the sample was concentrated to approximately 100 pl* Water samples were prepared by extracting 1.5 1of tap water with 1 1of diethyl ether (after initial quenching with thiosulfate), followed by concentration to 100 ~1. Gas chromatography GC conditions used were: initial temperature, 40°C; initial hold, 2 min; temperature increase, S”C/min to lXO”C, followed by a 1 min final hold. All of the conditions were the same for acid or neutral analysis with the exception of the initial
GC-MMIP
OF HALOGENATED
PRODUCTS
37
temperature, which in the acid analysis was 50°C. The injection port temperature was 225°C and the transfer line temperature was 300°C. The microwave plasma was operated with a helium flow of 60 ml/min and a 75-W forward power reading. All injections for humic acid work were 0.2 ~1 with a GC split ratio of 2O:l. For tap water it was necessary to inject 3 pl to obtain a large, integratable signal on the halogen channels. The column was a J&W Scientific (Folsom, CA, U.S.A.) 25 m x 0.2 mm I.D. DB-5 fused-silica capillary column, with a 2O:l split ratio. The attenuation for each output was 32 x for carbon emission, 2 x for chlorine emission and 4 x for bromine. RESULTS
Standard compound analysis
To determine that the system was functioning properly a standard solution of chloroform, bromodichloromethane, chlorodibromomethane and bromoform was injected into the chromatograph to obtain the chromatograms in Fig. 1. It had been reported previously1 * that the choice of standard compound may influence the empirical formula determinations significantly. To investigate what effect the choice of internal standard would have upon this analysis, the empirical formula caicuiations were performed using both chlorodibromomethane and bromodichloromethane as reference compounds. After applying eqn. 1 and dividing through all the ratios by the smallest mole ratio available, empirical formulae were determined as shown in Table I. As is shown, the calculated empirical formulae are the same within expected error limits, and correspond well to the actual formula. It was decided to use chlorodibromomethane as the internal standard, as this compound eluted later in the chromatogram and was easily resolved. Analysis of halogenated humic acid
The MMIP traces of each emission line of the humic acid “neutral” fraction are shown in Fig. 2 and as expected there are more peaks present in the carbon emission channel than for the halogen channels. Calculating empirical formulae for the halogen containing compounds gave results corresponding to: dichloroacetonitrile, trichloroacetaldehyde, trichloroacetone, bromodichloromethane, chlorodibromomethane, bromodichloroacetaldehyde, chlorodibromoacetaldehyde, bromoform and tribromoacetaldehyde (Table II). It may be noted from the table that there are a number of cases in which an exact whole number is not obtained for the empirical formula. This is attributable to a variety of integration problems. When this situation is encountered a set of decision-making parameters must be adhered to. In this analysis any ratio that had a mole fraction above 0.85 and below 1.15 was considered to constitute a mole fraction of one and any compound between 0.40 and below 0.60 was considered to have a mole fraction of 0.50. In this manner some of the calculations were simplified with the additional justification that these molecules were short chained and the empirical formula would presumably also be the molecular formula. However, when the ratios appeared to be in the areas between these two ranges, the policy was to determine what was chemically and chromatographically possible and make logical assignments based on that knowledge. It is noted that chloroform, the most abundant product formed in the halogenation of humic acid,
38
M. P. ITALIA, P. C. UDEN B
D
BROMINE C
CHLORINE
Fig. 1. Multi-channel MIP analysis of a standard mixture of (A) chloroform, (B) bromodichloromethane, (C) chlorodibromomethane and (D) bromoform monitored on the carbon (247.9 nm), chlorine (481.0 nm) and bromine (470.5 nm) emission wavelengths. Chromatograms are offset for clarity.
is not one of the identified peaks. This is due to the inability to resolve the chloroform peak on the carbon emission channel, and this subsequently gives a false integration signal. The humic acid “acidic” fraction shows a large number of peaks that appear in all three channels (Fig. 31, making the analysis complex. However, once the neutral
GC-MMIP
OF HALOGENATED
PRODUCTS
39
TABLE I EMPIRICAL FORMULA DETERMINATIONS FOR A STANDARD MIXTURE OF CHLOROFORM, BROMODICHLOROMETHANE, CHLORODIBROMOMETHANE AND BROMOFORM RUN ON THE MMIP MONITORING THE CARBON (247.9 nm), CHLORINE (481.0 nm) AND BROMINE (470.5 nm) EMISSION WAVELENGTHS Ratios are calculated on two “internal standard” compounds, bromodichloromethane momethane. crw?lpoli?ld
CHC13 CHClzBr CHClBr, CHBr3
CHBrG (std. peak)
CHBrzCI (std. peak)
clc12.8
GC13
-
C1Cl1.sBr0.9 -
ClCIlBrl.8
CHBr2.9
CHBr3.2
and chlorodibro-
Emviricai formula
-
-
cc13 CCl*Br CCIBrl CBr3
_
E
-L
I
B
B
ILL
CHrnINE
Fig. 2. The GC-MMIP traces of the neutral fraction of halogenated humic acid monitored on the carbon (247.9 nm), chlorine (481.0 nm) and bromine (470.5 nm) emission wavelengths. Identifications are: A = bromodichloromethane, B = dichloroacetonitrile, C = trichloroacetaldehyde, D = chlorodibromomethane, E = bromodichloroacetaldehyde, F = trichloroacetone, G = bromoform, H = chlorodibromoacetaldehyde and I = tribromoacetaldehyde.
M. P. ITALIA,
P. C. UDEN
-_I_ BROMINE
CRLORINE
CARBON Fig. 3. The GC-MMIP traces of the “acidic” fraction of halogenated humic acid monitored on the carbon (247.9 nm), chlorine (481.0 nm) and bromine (470.5 nm) emission wavelengths simultaneously. Compound identifications are as methyl esters: A = chloroacetic acid, B = dichloroacetic acid, C = trichloroacetic acid, D = dibromoacetic acid, E = bromodichloroacetic acid, F = chlorodibromoacetic acid and G = tribromoacetic acid.
fraction peaks that pass through the acidic preparation scheme are removed. the analysis is simplified. For this set of calculations, chlorodibromomethane, one of the neutral remnants, was chosen as the standard. This was possible because ratioing requires only a compound for which a good signal is obtained, and concentration is not a factor. The data for seven of these compounds is shown in Table III, and they have been identified as the methyl esters of chloroacetic acid, dichloroacetic acid, trichloroacetic acid, dibromoacetic acid, bromodichloroacetic acid, chlorodibromo-
GC-MMIP
OF HALOGENATED
PRODUCTS
B
F
E
i
BKtlINE
Fig. 4. GC-MMIP trace of the neutral fraction of South Deerfield drinking water monitoring the carbon (247.9 nm), chlorine (481 .O nm) and bromine (470.5 m-n) emission wavelengths. Identifications are: A = chloroform, B = bromodichloromethane, C = dichloroacetonitrile, D = trichloroacetaldehyde, E = chlorodibromethane and F = bromoform.
acetic acid and tribromoacetic acid. While these may comprise a high proportion of the halogenated products, there are still more unidentified, higher order acids to be found and characterized. In making the above identification from GC-MIP response ratio data, much
M. P. lTALlA,
42
P. C. UDEN
TABLE II MMIP EMPIRICAL FORMULA DETERMINATIONS OF THE NEUTRAL FRACTION OF HALOGENATED HUMIC ACID FROM THE CHROMATOGRAPHIC ANALYSIS IN FIG. 2 IdentiJication in Fig. 2
Gcl1.4r1.0 GClI.2 GCl1.4 ClCliBrl.9
ClCllBr0.6 CIC10.75 CIBr3.Z GCIO.&I C&2.6
Empirical formula (hydrogens removed)
IdentiJication
CClzBr CCL C*C13 CClBr2 C,C12Br cc1 CBr3 CZClBr2
Bromodichloromethane Dichloroacetonitrile Trichloroacetaldehyde Chlorodibromomethane Bromodichloroacetaldehyde Trichloroacetone Bromoform Chlorodibromoacetaldehyde Tribromoacetaldehyde
C&3
reference was made to the prior knowledge of the products of humic acid halogenation, and thus an internal standard was not needed or used. If such a standard were necessary, it would have to contain all the elements that were to be measured. Tap water analysis A drinking water sample was obtained from South Deerfield, MA, U.S.A., and concentrated according to the protocol reported previously. Fig. 4 shows the analysis of that sample and the subsequent peak identification. The increased complexity of the carbon trace, coupled with the greater simplicity of the halogen responses, reflect an appropriate assessment of tap water analysis. From peak ratioing and empirical formula determinations, six contaminants of this water sample were identified as chloroform, bromodichloromethane, dichloroacetonitrile, trichloroacetaldehyde, chlorodibromomethane and bromoform. Due to chromatographic interference, chloroform was identified only From retention time knowledge and its correct wavelength response. However, with a different sample concentration protocol and under different chromatographic conditions, chloroform could be readily confirmed.
TABLE III MMIP EMPIRICAL FORMULA DETERMINATION OF THE ACIDIC FRACTION OF HALOGENATED HUMIC ACID FROM THE CHROMATOGRAPHIC ANALYSIS IN FIG. 3 Identfication in Fig. 3
Ratio
Empirical formula (hvdrogens removed)
Identification (as methyl esters)
C1Cl0.3 CICl0.7 C1Clo.92 ClBr0.78 CiClo.sBro.3 CiClo.sBro.7 W3ri.i
C3CI CJCll cc1 C3Br2 C3C12Br C3ClBrz CBrJ
Chloroacetic acid Dichloroacetic acid Trichloroacetic acid Dibromoacetic acid Bromodichloroacetic acid Chlorodibromoacetic acid Tribromoacetic acid
GC-MMIP
OF HALOGENATED
PRODUCTS
43
CONCLUSION
While there are many detectors which are selective, none, save perhaps mass spectrometry, offers the selectivity capabilities of multi-channel microwave-induced plasma. When the acquisition and maintenance costs are compared, MMIP has distinct advantages. This technique offers the element selectivity of an emission procedure and detection limits which are often better than mass spectrometry. The analysis of a chromatographically complex mixture can be simplified by removal of extraneous compounds through selective emission spectroscopic detection. Most importantly, the ability for empirical formula determination from chromatographic separations and emission channel responses creates useful analytical opportunities. The possibility of using a chromatograph to separate compounds and obtain the empirical formula almost instantly (through computer manipulation) is an attractive one. ACKNOWLEDGEMENTS
This research was supported in part by the Geological Survey, U.S. Department of the Interior through the Massachusetts Water Research Institute and by the 3M Corporation and the Dow Chemical Company. REFERENCES I C. A. Bathe and D. J. Lisk, Anal. Chem., 39 (1967) 786. 2 W. R. McLean, D. L. Stanton and G. E. Penketh, Analyst (London), 98 (1973) 432. 3 B. D. Quimby, P. C. Uden and R. M. Barnes, Anal. Chem., 50 (1978) 2112. 4 C. I. M. Beenakker, Spectrochim. Acru, 31B (1976) 483. 5 C. I. M. Beenakker, Spectra&m. Actu, 32B (1977) 173. 6 C. I. M. Beenakker and P. W. J. M. Boumans, Spectrochim. Acta, 33B (1978) 53. 7 B. D. Quimby, M. F. Delaney, P. C. Uden and R. M. Barnes, Anal. Chem., 52 (1980) 259. 8 P. C. Uden and J. W. Miller, J. Am. Water Works Assoc., 75 (1983) 524. 9 P. C. Uden. K. J. Slatkavitz and R. M. Barnes, Anal. Chim. Acta, 180 (1986) 401. IO Y. J. Yoo. Ph.D. Dissertation, University of Massachusetts, Amherst, MA, 1987. 11 H. J. Perpall, P. C. Uden and R. L. Deming, Spectrochim. Acta, 42B (1987) 243. 12 K. J. Slatkavitz. P. C. Uden. L. D. Hoey and R. M. Barnes. .I. Chromafogr.. 302 (1984) 277. 13 MPD 850 AG Organic Analyzer Instruction Manual, Applied Chromatography Systems Limited, ton, Sect. 3, 1979, pp. l-10. 14 M. S. Young. Ph.D. Disserfation. University of Massachusetts, Amherst, MA, 1988. 15 M. P. It&a, Ph.D. Dissertutiun, University of Massachusetts, Amherst, MA, 1987.
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