Ind. Eng. Chem. Res. 1999, 38, 343-351
343
On-Line Monitoring of Reactions of Epichlorohydrin in Water Using Liquid Membrane Introduction Mass Spectrometry R. C. Johnson, K. Koch, and R. G. Cooks* Purdue University Department of Chemistry, West Lafayette, Indiana 47907-1393
The industrially significant chain extender epichlorohydrin (chloromethyloxirane) can be quantified on-line at the low parts per million level in aqueous solution using membrane introduction mass spectrometry (MIMS). Solid membranes composed of microporous poly(tetrafluoroethylene) (PTFE) and nonporous silicone were used to establish this methodology using an ion trap mass spectrometer; both gave similar performance, even though they are based on different transport mechanisms. In addition, a liquid polyphenyl ether membrane reinforced with a microporous support was shown to give similar results. The predominant ions produced in an ion trap mass spectrometer using electron ionization (EI) were m/z 57 ([M - Cl]+) and 62/64 ([M - CH2O]+) while those produced under chemical ionization (CI) conditions were m/z 57 ([M + H - HCl]+), 63/65 ([M + H - CH2O]+), and 93/95 ([M + H]+). Further, the hydrochloric acid-catalyzed ring opening of epichlorohydrin to yield 3-chloro-1,2-propanediol and other products was monitored on-line using the polyphenyl ether liquid membrane. The ability to perform continuous monitoring provides access to real time kinetic data unavailable through off-line chromatographic techniques. Introduction Epichlorohydrin is a toxic and carcinogenic compound which is manufactured as a starting material for the production of glycerol, epoxy resins, and glycerol-dichlorohydrins (1,3-dichloro-2-propanol and 2,3-dichloro-1propanol).1 It is typically monitored in water using solidphase extraction (SPE)2 or solid-phase microextraction (SPME)3 followed by gas chromatography-electron capture detection (GC-ECD) or gas chromatographyflame ionization detection (GC-FID) techniques. These off-line methods offer better limits of detection than those presented here but require tens of minutes2,3 to accommodate sample preparation time and chromatographic separation prior to detection. The method presented here is of a simple on-line technique which is well suited for quantitation and kinetic modeling. Membrane introduction mass spectrometry (MIMS) is an established method of sample analysis which couples rapid introduction via a semipermeable membrane with the sensitivity and specificity of a mass spectrometer.4,5 Membranes, typically composed of crosslinked silicones, are chosen to enrich the sample stream entering the mass spectrometer in analyte while rejecting the bulk of the mobile phase. In the case of silicone membranes, method selectivity stems from the threestage partitioning process known as pervaporation, which involves (1) analyte adsorption at the membrane surface, (2) diffusion through the membrane, and (3) desorption into the gas phase of the mass spectrometer. Compounds which are suitably volatile (bp < 200 °C) as well as soluble in the membrane undergo pervaporation in tens of seconds or less. The membrane is normally heated to 50-90 °C to facilitate this process.6 MIMS using amorphous silicone membranes is ideally suited for the on-line monitoring of volatile organic7 and sometimes inorganic compounds8 in the presence of a less permeable mobile phase (i.e. water or air, which * To whom correspondence should be sent.
are discriminated against). The speed and ruggedness of this method are such that it is applied to on-line monitoring of exhaust emissions,9 environmental pollutants,10 chemical processes,11, 12 drinking water contaminants, and other aqueous-phase reactive species.13-16 High-solid-content streams containing compounds such as acrolein and acrylonitrile17 encountered in the polymer industry are well suited for analysis by MIMS. Lower limits of detection for MIMS analysis of many nonpolar, volatile organic compounds (e.g. benzene, dichloromethane, toluene) in aqueous solution are typically in the high parts per trillion to low parts per billion range.6 More polar species such as ethanol, methanol, benzaldehyde, and lactic acid are typically quantified at a level 2-3 orders of magnitude higher than that for hydrocarbons of similar molecular weight due to their lower volatility and lower solubility in the silicone polymer membrane. Silicone membranes serve as a baseline for comparison with the performance of other types of membranes.16,18 One alternative material is microporous poly(tetrafluoroethylene) (PTFE).19-21 The microporous membrane (2.0 µm pore size), however, does not utilize chemical selectivity; all components of the sample stream are passed.22 Microporous membranes necessarily have more rapid responses, as well as lower selectivities and higher fluxes of mobile phase compared to nonporous silicone membranes. This lower selectivity and shorter response time are well suited for the analysis of a polar compound such as epichlorohydrin, which does not readily permeate through a cross-linked silicone polymer.13,14 More recent developments in membrane introduction systems include ceramic zeolite membranes,23 which utilize molecular size pores to achieve selectivity, and liquid membranes composed, for example, of a polyphenyl ether diffusion pump fluid.21,24 The latter membranes have the advantage that they readily take any desired shapesincluding very thin films. They have the further advantage that their
10.1021/ie980164c CCC: $18.00 © 1999 American Chemical Society Published on Web 12/12/1998
344 Ind. Eng. Chem. Res., Vol. 38, No. 2, 1999
chemical properties can be manipulated by an admixture of appropriate reagents. Previous results suggest that liquid polyphenyl ether membranes should have chemical selectivity similar to that of a silicone membrane.21 Previous applications of MIMS have employed ion trap and quadrupole mass spectrometers to monitor biological and chemical reactors for long periods of time.11,25,26 Quantitation in these experiments involved the use of external standards which are conveniently alternated with plugs of sample using flow injection analysis (FIA) methods. MIMS data have also been used for feedback control27,28 and to obtain kinetic information on chemical reactions by monitoring the consumption of reactants and the formation of products.29 In contrast to the functionally simple membrane, the mass spectrometer is a highly developed instrument that is well suited to the universal and chemically specific monitoring of organic compounds such as epichlorohydrin. In more practical terms, the use of the mass spectrometer instead of a general-purpose GC detector such as an FID or ECD enables simultaneous monitoring of coeluting compounds which can be differentiated on the basis of their unique molecular fragmentation. This gives MIMS high chemical specificity as well as a rapid sample analysis time due to the absence of any chromatographic separation and associated sample preparation. Suitable mass spectrometers for MIMS are typically small, portable instruments, often ion traps18 or quadrupole mass filters.30 Data analysis in the mass spectrometer begins with analyte ionization, typically by electron impact (EI)31 or chemical ionization (CI).20,22 Each analyte produces specific fragment ions of massto-charge (m/z) ratios which allow their molecular structures to be inferred. Mass spectra can be summed over time to give a total ion chromatogram (TIC). The instrument software can manipulate the total ion chromatogram to yield analyte specific, single-ion chromatograms for quantification23 or for interpretation of reaction kinetics. The MIMS analysis can be supplemented with selective gas-phase ion/molecule reactions or complemented by collision-induced dissociation (CID).32 The capabilities of MIMS are utilized here by monitoring the hydrochloric acid (HCl)-catalyzed ring opening of epichlorohydrin in water to form 3-chloro-1,2propanediol and a dichloropropanol.1,13-15 Data supporting the chemical interpretation of the acid-catalyzed ring opening with HCl are presented through the use of standard solutions corresponding to suspected products and analogous reactions of epichlorohydrin with hydrobromic, perchloric, and periodic acids. Experimental Section Sample Preparation/Reaction Monitoring. Solutions of epichlorohydrin, 1,3-dichloro-2-propanol, 3-chloro1,2-propanediol, chloroacetaldehyde (Aldrich, Milwaukee, WI), and 2,3-dichloro-1-propanol (Fisher Scientific Company, Pittsburgh, PA) were prepared by serial dilution of the commercially available reagents using deionized (DI) water. The reactor used in these experiments was a 250 mL volumetric flask filled with 100 ppm epichlorohydrin in DI water (vol/vol) which was heated (40 °C) and continuously stirred using a Tefloncoated magnetic stir bar. The temperature was monitored using a mercury thermometer with the volumetric flask sealed with Parafilm. After steady-state analysis
by MIMS (see membrane description below), 1 mL of HCl, HBr, or HClO4 or 1 g of HIO4 (sold as HIO4‚2H2O from Aldrich Chemical Co.) was added to the reactor to initiate ring opening. Since HIO4 is a solid, 1 g of it was dissolved in 10 mL of water prior to introduction to the reactor. Periodic acid served two functions in these reactions with epichlorohydrin. In the first, the rate of its consumption in the course of formation of 3-chloro1,2-propanediol was monitored. In its second use, periodic acid was used to selectively cleave any 1,2-diols (i.e. 3-chloro-1,2-propanediol)33 formed in the reaction of HCl, HClO4, or HIO4 with epichlorohydrin. Periodic acid was added (1 g diluted in 10 mL of water) at the completion of the ring-opening reaction. By using periodic acid for the ring-opening reaction, no further periodic acid was needed to cleave 3-chloro-1,2-propanediol. Four standard solutions were examined to verify the selectivity of the periodic acid reaction with 3-chloro1,2-propandiol. These standard solutions included (1) HCl and periodic acid in water (blank, no reaction products), (2) 1,3-dichloro-2-propanol and periodic acid in water (no reaction products), (3) 3-chloro-1,2-propandiol and periodic acid in water (production of chloroacetaldehyde), and (4) epichlorohydrin and periodic acid in water (production of chloroacetaldehyde). Sample volumes in all experiments were large enough to allow steady-state fluxes to be passed across the membrane and into the mass spectrometer. The height of the steady-state response (not area), measured relative to the baseline preceding analyte response, was used for quantitation. Steady-state conditions were achieved by moving the sampling tube from the DI water mobile phase and into the sample solution until a maximum analyte response was achieved and remained constant (insets, Figure 1), after which the sampling tube was returned to the mobile phase. Reaction-monitoring experiments differed from the discrete series of injections noted in Figure 1 in that once steady state was achieved, 1.0 mL of acid was added to the sample solution, which was then continuously monitored. Silicone and PTFE Membranes. The PTFE (2.0 µm pore, 4 cm × 1.0 mm i.d. × 1.8 mm o.d.)22 and silicone (4 cm × 0.635 i.d. × 1.19 mm o.d.)22 capillary membranes were purchased from ANSPEC (Ann Arbor, MI) and Dow Corning (Midland, MI), respectively. The jet separator (Finnigan MAT, PN 10008-40010) was heated to 120 °C with a helium pressure of 133 mTorr (measured at the roughing pump). The transfer line and ion trap were heated to 120 and 25 °C, respectively, with a manifold pressure of 4 mTorr (measured at the roughing pump). Membranes were prepared by inserting stainless steel tubing in each end of the membrane capillary. The silicone capillary was initially soaked in hexane to cause it to swell, and then it was allowed to dry on the stainless steel tubing for a tight fit. The PTFE membrane did not swell and was secured to the stainless steel tubing using short lengths of stainless steel wire. These membranes were encased in a 0.25 in. (0.64 cm) stainless steel tube closed at each end with Swagelock tees (Indianapolis Valve and Fitting, Indianapolis, IN) and 0.25-0.063 in. (0.64-0.16 cm) reducing ferrules. The capillary membranes were operated in a reverse flow configuration in which the sample stream passed through the membrane counter-current to a helium
Ind. Eng. Chem. Res., Vol. 38, No. 2, 1999 345
a
b
c
Figure 1. (a) Background-subtracted EI mass spectrum of epichlorohydrin employing a silicone membrane. Predominant ions are m/z 62/64 ([M - CH2O]+) and 57 ([M - Cl]+). The inset demonstrates how the silicone membrane reaches a steady-state equilibrium at various concentrations. Spikes on each peak are an artifact of the injection technique, which introduced air bubbles into the sampling membrane. (b) Background-subtracted mass spectrum using a microporous PTFE membrane under EI conditions displaying m/z 93 ([M + H]+), 62/64 ([M - CH2O]+), and 57 ([M - Cl]+) (m/z 91/92 were background ions present from previous experiments). Note the rapid response times of each sample aliquot (inset) measured in Table 1. (c) The EI mass spectrum utilizing a polyphenyl ether liquid membrane displaying the same fragmentation pattern as that for the silicone membrane. The inset displays the instrument response at concentrations between 1 and 100 ppm.
Figure 2. Water-CI mass spectrum of epichlorohydrin using a polyphenyl ether liquid membrane and water as a reagent gas. Ions noted are m/z 93/95 ([M + H]+), 63/65 ([M + H - CH2O]+), and m/z 57 ([M + H - HCl]+).
carrier gas which passed over the membrane surface and carried the analytes into the mass spectrometer via the jet separator. A Masterflex peristaltic pump equipped with Tygon tubing (Cole-Parmer, Vernon Hills, IL) pumped all solutions to the membrane introduction system through 0.063 in. (0.16 cm) Teflon tubing (Upchurch, Oak Harbor, WA). After sampling, solutions were removed from the membrane and stored in an appropriate waste container. Liquid Membranes. The polyphenyl ether liquid membrane experiments used a direct insertion probe (DIP) modified to accept a sheet membrane.21 The DIP was inserted into the ion source of the ion trap mass spectrometer via the solids probe port. The liquid membrane was prepared by sandwiching 10 µL of polyphenyl ether (Santovac 5, Monsanto, St. Louis, MO)between two layers of 0.005 cm thick microporous polypropylene (Celgard 2502, 0.05 µm pore, 37-48% porosity, Hoechst Celanese, Charlotte, NC). The resulting sandwich membrane was supported by a 50 µm thick stainless steel mesh (Spectra/Mesh, 30 µm pore size, Spectrum, Houston, TX) and mounted in the direct insertion probe (DIP).21 These liquid membranes have been found to be quite stable during continuous use21 and have a shelf life of many months. Operating conditions for this membrane were similar to those of the silicone capillary membrane, with a slightly elevated optimum temperature (Table 1). Ion Trap Experiments. A Finnigan MAT ITS-40 gas chromatograph/mass spectrometer (San Jose, CA) equipped with a solids probe port was modified by removing the gas chromatograph and adding a jet separator (SGE, Austin, TX) and a capillary membrane interface.22,34 The multiplier voltage was held at 1850 V, with a mass/charge (m/z) range of 50-200. The ionization time for each experiment was 5 ms with a filament current of 80 mA. Water-CI conditions were produced using the standard Finnigan chemical ionization software for user-defined reagent gases. During this process the water reagent gas was ionized for 1 ms to form the hydronium ion (m/z 19), which served as the reagent ion during the 31 ms reaction time.35 Tandem mass spectrometric experiments were performed using previously developed techniques, which included modifying the ITS-40 and using new magnum software instead of the standard magnum software used for EI and water-CI experiments.36 The ions of interest were isolated by the rf/dc method and fragmented at qz
346 Ind. Eng. Chem. Res., Vol. 38, No. 2, 1999
a
b
) 0.3 using an ac frequency of 118 kHz and an ac amplitude of 1.3-1.4 V. Data Analysis. Data were recorded using the commercial Finnigan software (for EI and CI spectra) or the new magnum software (for MS/MS experiments). Tables 2 and 3 list mass-to-charge ratios and relative abundances of ions occurring in the mass and MS/MS spectra. Ions greater than 1% of the base peak which are diagnostic of the molecule are listed. Examples of nondiagnostic ions which are not listed in Tables 2 and 3 may be seen in the EI mass spectra of Figure 1, which contains a high abundance of fragment ions which were not used for structural identification. These excluded ions included m/z 52-56 and m/z 58-61. Kinetic data are presented by plotting ion intensities from the EI mass spectra against time using Microsoft Excel. Results and Discussion
c
d
Figure 3. (a) EI mass spectrum of the HCl reaction products with epichlorohydrin. (b) EI reaction monitoring of predominant ions formed (m/z 79/81) from unreacted epichlorohydrin, which is monitored by m/z 62/64. (c) Water-CI mass spectrum of reaction mixture of HCl and epichlorohydrin. (d) Water-CI mass spectrum of the products of reaction between HBr and epichlorohydrin. These products are analogous to the chlorine addition products of Figure 3c.
Selection of Membrane Inlet. Nonporous silicone, microporous PTFE, and polyphenyl ether membranes, which utilize various transport mechanisms, were employed to monitor epichlorohydrin in water at the parts per million level. The suitability of each membrane for monitoring epichlorohydrin is considered here as a function of the quality of the mass spectra produced and the analyte response time. Since the main advantages of MIMS include chemical specificity and speed of analysis, an ideal membrane produces interference-free mass spectra and possesses rapid 10-90% response times. Figure 1 contains representative electron impact mass spectra for the three membranes while the insets display chromatograms created by monitoring chemically specific chlorine-containing epichlorohydrin fragment ions. The base peak of m/z 57 was not used for quantification of epichlorohydrin due to possible interferences (e.g. [C4H9]+) commonly encountered as background ions or derived from the chemical ionization reagent gas. Table 1 summarizes the response times, linear dynamic range (insets, Figure 1), and lower limits of detection of epichlorohydrin for each membrane. The nonporous silicone membrane utilizes hydrophobic interactions at the solution interface to select in favor of epichlorohydrin versus the mobile phase. The jet separator provides additional gas-phase enrichment. Figure 1a is consistent with previous electron impact mass spectra:37 predominant ions are m/z 57 ([M - Cl]+) and m/z 62/64 ([M - CH2O]+). No molecular ion was noted. The ion abundance at m/z 51 is due to the chlorine isotope of CH237Cl+, a fragment of epichlorohydrin. The choice of low mass cutoff (m/z 50) meant that the corresponding ion at m/z 49 ([CH235Cl]+), which is common to epichlorohydrin, was not monitored. In contrast to the case of the silicone membrane, the nonspecific flux of sample and mobile phase (water) through the pores of the microporous PTFE membrane precluded its use without the jet separator. In addition to removing a large portion of the carrier gas and water eluting from the PTFE membrane, the jet separator decreased the pressure difference across the membrane. This reduced the vapor pressure of the mobile phase and prevented the instrument from being vented from the membrane effluent. The microporous membrane reduced the elution time to a fifth of that of the silicone membrane but also resulted in undesired protonation of the analyte under electron impact conditions (Figure 1b). Protonation is due to H3O+, which readily donates a proton to oxygen-containing species such as epichlo-
Ind. Eng. Chem. Res., Vol. 38, No. 2, 1999 347 Table 1. Epichlorohydrin Analysis Using Various Membranes membrane
membrane temp (°C)
t10-90% (s) at 10 ppm
r coefficient (least squares)
linear dynamic rangea (ppm)
silicone capillaryb microporous PTFEb polyphenyl etherc
85 85 91
144 28 14
0.998 0.999 0.999
1-100 1-100 1-100
a The lower limit of detection (LOD) for epichlorohydrin was 0.500 ppm for each membrane. The LOD for each reaction product was measured only with the liquid membrane and was 200 ppb for 1,3-dichloro-2-propanol, 2,3-dichloro-1-propanol, and chloroacetaldehyde. The LOD for 3-chloro-1,2-propanediol was 5 ppm. b Used with the external jet separator configuration. c Used with a direct insertion probe, placed directly into the ion source of the mass spectrometer.
Table 2. EI and Water-CI Mass Spectra of Epichlorohydrin with a Polyphenyl Ether Membrane EI-MS % abundance for m/za ) 51
57
CI-MS % abundance for m/za )
62 64 75 77 79 81 51 57 62 63 64 65 75 77 79 81 93 95 111 113 129 131
compound (MW) epichlorohydrin (92) 34 100 56 18 2 100 15 1,3-dichloro-2-propanol (128) 9 100 31 22 2,3-dichloro-1-propanol (128) 14 100 31 10 4 29 6 4 3-chloro-1,2-propanediol (110)b 100 chloroacetaldehyde (78) 100
4 100 35 100 30 19
11
4
4 2 42 5 9 3 11 100 30
3 7
5 6
4 3
100 32
a
Ions greater than 1% of base peak which are diagnostic of the molecule. Examples of nondiagnostic ions, which are greater than 1% abundance, can be noted in Figure 1 with ions of m/z 52-56 and m/z 58-61. Ions which are not listed in Table 2 were not used for structural interpretation. b Low sensitivity for this compound produced a weak response.
rohydrin. Note the signals due to protonated epichlorohydrin (m/z 93 and 95). While problems attributed to the large flux of sample across the microporous membrane can be troublesome under EI conditions with a parts per million level of sample, they can be reduced by decreasing analyte concentrations or by using the coeluting mobile phase as a chemical ionization reagent gas.22,38,39 The use of water as a CI reagent increases the specificity of the method for an analyte which may suffer from mass spectral interferences using electron impact. The third membrane evaluated was a polyphenyl ether liquid membrane, recently found to produce mass spectra and response times comparable to those of a silicone membrane of a similar thickness.21 The transport mechanism of the liquid membrane is based on permeation through the low-vapor-pressure, high-molecular-weight liquid polymer. These experimental results are the first application of these liquid membranes with MIMS. They produced interference-free EI and water-CI (Figures 1c and 2)22 mass spectra with rise times 50% of those of the microporous membrane (rise times are similar when comparing EI and CI techniques). These characteristics were used to select the liquid membrane for use in the study of epichlorohydrin with hydrochloric acid. Reaction Monitoring and Product Identification. In water, epichlorohydrin is known to protonate readily in the presence of hydrochloric acid13,15 and ring open to form three possible products (Scheme 1). These include a diol formed from the addition of water or two isomeric halide addition products.13 An EI mass spectrum of this reaction mixture (Figure 3a, compare Figure 1c) shows the base peak of m/z 79/81, which might be diagnostic of chloride addition to epichlorohydrin and corresponds to the neutral loss of CH3Cl from ClCH2CH(OH)CH2Cl. 2,3-Dichloro-1-propanol did not produce any significant abundance of m/z 79/81, only a base peak of m/z 62/64 (Table 2). The other anticipated ring-opening product was 3-chloro-1,2-propanediol, which was difficult to monitor due to its poor sensitivity with MIMS and efficient fragmentation to form m/z 49/51 (common to the reactant). Hydrophilic, high-boilingpoint diols, in general, give poor responses using MIMS
because they do not readily pass across membranes as compared to lower boiling point compounds such as epichlorohydrin (115-116 °C), 1,3-dichloro-2-propanol (174.3 °C), and chloroacetaldehyde (85 °C at 748 mmHg). The limit of detection (LOD) for 2,3-dichloro-1-propanol, 1,3-dichloro-2-propanol, and chloroacetaldehyde was 200 ppb while the LOD for 3-chloro-1,2-propanediol was 5 ppm. The ability of MIMS to monitor the reaction of epichlorohydrin and hydrochloric acid on-line is demonstrated in Figure 3b, which plots the selected ion chromatograms of m/z 79/81 (products of reaction) in contrast to ions characteristic of the reactant (m/z 62/ 64).1,13,14 This ability to monitor reactions on-line is a key advantage of the MIMS introduction system and allows one to gather kinetic data and quantitate reaction progress. However, with the use of electron impact there was very little information gained regarding the molecular weights of the products (Table 2). Chemical ionization produced a great number of protonated molecular ions and was more informative about the nature of the hydrochloric acid reaction products (Figure 3c, compare Figure 2). Dichloropropanol formed by halide addition is suggested from the protonated molecular ions at m/z 129 and 131.1,13,15 Ions of m/z 111 and 113 may be derived from the fragmentation of the halide addition product, or they could be the molecular ions of the expected diol product, 3-chloro1,2-propanediol (Scheme 1). To confirm the source of m/z 129, hydrobromic acid (HBr) was reacted with epichlorohydrin, producing an analogous halide addition product at higher mass. The ions formed were consistent with the bromide addition to epichlorohydrin (m/z 173, 175, and 177, C3H6ClBrO) and the rapid dehydration to form m/z 155, 157, and 159 (Figure 3d). Note the absence of m/z 111 in the product of epichlorohydrin and HBr, which indicates that the corresponding ion (m/z 111) in Figure 3c is most likely produced by the dehydration of the halogen addition product (m/z 129). Since m/z 129 and 111 are derived from halide addition processes, perchloric acid (HClO4) treatment of epichlorohydrin was used in order to eliminate competition from halide reactions in solution and produce only 3-chloro-1,2-propanediol.13,14 In monitoring
5 3 15 14
2 6 100 31 2
2
2
a Ions greater than 1% of base peak which are diagnostic of the molecule. Examples of nondiagnostic ions, which are greater than 1% abundance, can be noted in Figure 1 with ions of m/z 52-56 and m/z 58-61. Ions which are not listed in Table 3 were not used for structural interpretation. b The addition of a halogen to epichlorohydrin is directly monitored using m/z 75/77 and 129/131 contrasted to m/z 63/65. c Confirms halogen addition to oxirane. d Does not readily confirm source of ion. e These data reflect the cleavage of 3-chloro-1,2-propanediol formed competitively with the addition of chlorine to epichlorohydrin. Periodic acid was added at completion of epichlorohydrin reaction with either HCl or HClO4. f Analogous mass spectrum to chlorine addition with HCl, with rapid dehydration when ionized. g No reaction products noted with perchloric acid reaction; overall decrease of total ion current with some formation of m/z 75, indicating the formation of a less volatile product (e.g. diol). h Chloroacetaldehyde is a product from the oxidation of 3-chloro-1,2-propanediol. i As expected with periodic acid. j Diol readily cleaved to form chloroacetaldehyde. k In this case, periodic acid protonated epichlorohydrin, formed a 1,2-diol, and then oxidized the diol to form chloroacetaldehyde.
1 3 3 23 100 78 3 6 4
6
5
6
6
6 11 69 6
8 14 100 6 4
59 26 10 8 5 100 10 13 23 78 24 100 31 3 89 27 5 2 7 3 100 30 4 3 12
81 93 95 111 113 119 121 123 125 129 131 155 157 159 173 175 177 79 77 75 62 63 64 65 57 51
Table 3. On-Line Reaction Monitoringa
reactions monitored (1) epichlorohydrin + HClb 100 CID of m/z 129c CID of m/z 111d rxn 1 + HIO4e 18 (2) epichlorohydrin + HBrf 38 (3) epichlorohydrin + HClO4g 2 100 rxn 3 + HIO4h 4 (4) 1,3-dichloro-2-propanol + HIO4i no reaction (5) 3-chloro-1,2-propanediol + HIO4j (6) epichlorohydrin + HIO4k same as rxn 1 + HIO4
CI-MS % abundance for m/z )
348 Ind. Eng. Chem. Res., Vol. 38, No. 2, 1999 Scheme 1
the products of this reaction, the overall concentration of epichlorohydrin decreased with very little formation of products (m/z 75 was noted under CI conditions). This is consistent with the formation of a higher boiling point compound (possibly a diol) which does not readily pass through the membrane. The decrease of m/z 93/95 noted during the reaction of perchloric acid most likely was a result of the consumption of epichlorohydrin to form 3-chloro-1,2-propanediol. The diol produced m/z 93/95, but its much lower response than that of epichlorohydrin leads to an overall decrease in the abundance of m/z 93/95. To confirm these interpretations, standard solutions of the expected products were examined under both water-CI and EI conditions (Table 2). The water-CI mass spectra of three 100 ppm standard solutions containing either 1,3-dichloro-2-propanol, 2,3-dichloro1-propanol, or 3-chloro-1,2-propanediol are presented in Figure 4a-c. One immediately notices the common high-mass ions at m/z 129/131 (Figure 4a and b) compared to the reaction mixture in Figure 3c, which corresponds to the halide addition to the protonated oxirane. Further insight into the structure of m/z 129 was gained through collision-induced dissociation (CID), which produced expected fragments of a halide addition product (Figure 5). The only ions which differentiated the halide addition products were m/z 62/64 (unique for 2,3-dichloro-1-propanol under water-CI conditions). The fact that the interrogation of m/z 129 did not produce these diagnostic ions can only indicate either that 2,3dichloro-1-propanol is not present in the reaction mixture or that its concentration is not large enough to produce a measurable quantity of these diagnostic ions. The CID of m/z 129 from a standard solution of 1,3dichloro-2-propanol (Figure 5b) shows fragmentation to give m/z 111 ([M + H - 18]+). Since it was difficult to monitor low levels of 3-chloro1,2-propanediol directly using MIMS, a method of reacting the 1,2-diol to form a more volatile product was devised. Periodic acid is known to selectively oxidize 1,2diols (Scheme 1)33 and was first added to a 100 ppm standard solution of 3-chloro-1,2-propanediol, which immediately produced a base peak of m/z 79/81 (Figure 6, compare Figure 4d). The oxidation products of 3-chloro1,2-propanediol from the reaction of periodic acid are chloroacetaldehyde and formaldehyde. Chloroacetaldehyde was observed as m/z 79/81, but the low mass cutoff
Ind. Eng. Chem. Res., Vol. 38, No. 2, 1999 349
a
b
c
Figure 5. (a) CID of m/z 129 from a reaction solution of HCl and epichlorohydrin. (b) CID of m/z 129 from a standard solution of ClCH2CH(OH)CH2Cl. Product ions from the CID of m/z 129 are consistent with halogen addition products but cannot differentiate isomers (1,3-dichloro-2-propanol and 2,3-dichloro-1-propanol).
d Figure 6. Reaction of periodic acid with 3-chloro-1,2-propanediol to form chloroacetaldehyde using water-CI conditions.
Figure 4. Water-CI spectra of 100 ppm standard solutions of (a) 1,3-dichloro-2-propanol, (b) 2,3-dichloro-1-propanol, (c) 3-chloro1,2-propanediol, and (d) chloroacetaldehyde.
value of m/z 50 precluded measurement of the abundance of formaldehyde. To ensure the specificity of this additional reaction, periodic acid was then added to a 100 ppm solution of 1,3-dichloro-2-propanol containing 1 mL of HCl and also to a blank solution of water and HCl (no reaction was noted in either case). A solution of epichlorohydrin (without HCl) did react with periodic acid over a period of 1 h to form m/z 79/81, which indicated that a diol was present in the acidic epichlorohydrin solution. The periodic acid reaction with epichlorohydrin was reasoned to be a result of the cleavage of 3-chloro-1,2-propanediol formed from the ring opening
350 Ind. Eng. Chem. Res., Vol. 38, No. 2, 1999
reaction between 40 and 50 °C. The kinetics of the halogen addition does not follow simple first- or secondorder kinetics, as may be noted in the curve-fitted equations for each slope in Figure 8. While this study does not focus on interpreting this kinetic data, the ability to gain access to these data opens an avenue for further research which may be used to further explore reaction mechanisms of epichlorohydrin in aqueous solution. Conclusions
Figure 7. Water-CI mass spectrum of the reaction mixture containing HCl and epichlorohydrin with periodic acid added at the end of the HCl-epichlorohydrin reaction. Note the high abundance of m/z 79/81 (compared to Figure 3c), indicative of the oxidation of a 1,2-diol.
Figure 8. Kinetics data from the epichlorohydrin and HCl reaction. Note that the consumption of epichlorohydrin and the formation of products are not first- or second-order reactions. Nonlinear regression was performed on the sum of the intensities from m/z 62 to 64: y ) 0.0007x3 - 0.2124x2 + 0.0715x + 3432.6; R2 ) 0.9995.
of the oxirane under acidic conditions (acidic conditions created by the addition of periodic acid). The procedure to confirm the presence of the diol and halogen addition products from the reaction of HCl and epichlorohydrin included adding periodic acid to the reaction mixture upon completion of reaction (Scheme 1). The resulting mass spectrum (Figure 7, compare Figure 3c) indicated the presence of 3-chloro-1,2-propanediol in the reaction mixture by the increase in m/z 79/81 as compared to m/z 75/77. The increase in abundance of m/z 79/81 is consistent with the oxidation of 3-chloro-1,2-propanediol to form chloroacetaldehyde. Kinetic data for the reaction of epichlorohydrin with hydrochloric acid may be gathered by quantitating epichlorohydrin in solution with respect to time. The data gathered by monitoring the reaction of epichlorohydrin with HCl are included in Figure 3b and can readily be transferred to a spreadsheet or other appropriate program for curve fitting. Figure 8 presents the data from Figure 3b after being input into Microsoft Excel and being curve fitted. The three curves in Figure 8 were produced by separately plotting the intensities of m/z 62 + m/z 64, m/z 62, and m/z 64, respectively. The slope of each curve has been fitted with Excel and showed no significant changes when doubling the volume of HCl added or increasing the temperature of
MIMS is appropriately applied for the rapid monitoring of samples for key components which are indicative of either the progress of a reaction (epichlorohydrin in acidic solution) or the presence of an unwanted contaminant (epichlorohydrin in drinking water). Positive responses measured with MIMS are typically supplemented by slower chromatographic techniques which can analyze less volatile components of sample streams (e.g. diols) or further identify structurally similar contaminants (e.g. methylene chloride, trihalomethanes, and carbon tetrachloride) which may suffer from mass spectral interferences when simultaneously introduced into a mass spectrometer. MIMS has been used in the past to monitor the kinetics of reactions in water,29 and the chemistry of epichlorohydrin and other oxiranes has previously been established. The coupling of this technique with the base of chemical knowledge on oxiranes has directed the interpretation of the reaction monitored here. This study demonstrates the applicability of this technique for monitoring industrially significant compounds in water, but improvement is needed in the limits of detection of this method for epichlorohydrin. Decreasing the LOD may be achieved by front-end sampling with a liquidnitrogen-cooled coldfinger inserted between the membrane inlet and the ion source of the mass spectrometer to rapidly trap and concentrate organic compounds.40 In addition, ion-trapping techniques employing stored waveform inverse Fourier transforms (SWIFTs) should produce improvements.35 Optimal limits of detection for epichlorohydrin could then be combined with matrix operations41 to identify components in complex mixtures such as those monitored here in the reaction of epichlorohydrin and hydrochloric acid. Acknowledgment Financial support for this project was sponsored by the Office of Naval Research and a fellowship from the Phillips Petroleum Company. Literature Cited (1) Riesser, G. H. In Encyclopedia of Chemical Technology; Mark, H. F., Othmer, D. F., Overberger, C. G., Seaborg, G. T., Eds.; John Wiley and Sons: New York, 1979; Vol. 5, pp 848-864. (2) Neu, H.-J.; Springer, R. Fresenius J. Anal. Chem. 1997, 359, 285-287. (3) Santos, F. J.; Galceran, M. T.; Fraisse, D. J. Chromatogr. A 1996, 742, 181-189. (4) Srinivasan, N.; Johnson, R. C.; Kasthurikrishnan, N.; Wong, P. W.; Cooks, R. G. Anal. Chim. Acta 1997, 350, 257-271. (5) Lauritsen, F. R.; Katiaho, T. Rev. Anal. Chem. 1996, 15, 237-263. (6) LaPack, M. A.; Tou, J. C.; McGuggin, V. L.; Enke, C. G. J. Membr. Sci. 1994, 86, 263-280. (7) Bauer, S.; Solyom, D. Anal. Chem. 1994, 66, 4422-4431. (8) Cisper, M. E.; Hemberger, P. H. Rapid Commun. Mass Spectrom. 1997, 11, 1454-1456.
Ind. Eng. Chem. Res., Vol. 38, No. 2, 1999 351 (9) Matz, G.; Walte, A.; Munchmeyer, W.; Rikeit, H.-E. Soc. Automot. Eng., [Spec. Publ.] SP 1996, SP-1161, 175-179. (10) Wise, M. B.; Guerin, M. R. Anal. Chem. 1997, 69, 26A32A. (11) Johnson, R. C.; Srinivasan, N.; Cooks, R. G.; Schell, D. Rapid Commun. Mass Spectrom. 1997, 11, 363-367. (12) Blaser, W. W.; Bredeweg, R. A.; Harner, R. S.; LaPack, M. A.; Leugers, A.; Martin, D. P.; Pell, R. J.; Workman, J.; Wright, L. G. Anal. Chem. 1995, 67, 47R-70R. (13) Pritchard, J. G.; Siddiqui, I. A. J. Chem. Soc., Perkin Trans. 2 1973, 452-457. (14) Lamaty, G.; Maloq, R.; Selve, C.; Sivade, A.; Wylde, J. J. Chem. Soc., Perkin Trans. 2 1975, 1119-1124. (15) Kwart, H.; Goodman, A. L. J. Am. Chem. Soc. 1960, 82, 1947-1949. (16) Bauer, S. J.; Cooks, R. G. Talanta 1993, 40, 1031-1039. (17) Choudhury, T. K.; Kotiaho, T.; Cooks, R. G. Talanta 1992, 39, 1113-1120. (18) Overney, F. L.; Enke, C. G. J. Am. Soc. Mass Spectrom. 1996, 7, 93. (19) Maden, A. J.; Hayward, M. J. Anal. Chem. 1996, 68, 18051811. (20) Kasthurikrishnan, N.; Cooks, R. G.; Bauer, S. Rapid Commun. Mass Spectrom. 1996, 10, 751-756. (21) Johnson, R. C.; Koch, K.; Kasthurikrishnan, N.; Plass, W.; Patrick, J. S.; Cooks, R. G. J. Mass Spectrom. 1997, 32, 12991304. (22) Wong, P. S. H.; Cooks, R. G. Anal. Chim. Acta 1995, 310, 387-398. (23) Cook, K.; Falconer, J.; Bennett, K. 45th ASMS Conference on Mass Spectrometry and Allied Topics, Palm Springs, California, 1997. (24) Johnson, R.; Kasthurikrishnan, N.; Koch, K.; Hardy, J.; Cooks, G. 45th ASMS Conference on Mass Spectrometry and Allied Topics, Palm Springs, California, 1997. (25) Cox, R. P. In Mass Spectrometry in Biotechnology Process Analysis and Control; Heinzle, E., Reuss, M., Eds.; Plenum Press: New York, 1987; pp 63-74. (26) Hayward, M. J.; Riederer, D. E.; Kotiaho, T.; Cooks, R. G.; Austin, G. D.; Syu, M.-J.; Tsao, G. T. Proc. Contr. Qual. 1991, 1, 105-116.
(27) Srinivasan, N. M. S., Purdue, May 1994. (28) Srinivasan, N.; Kasthurikrishnan, N.; Cooks, R. G.; Krishnan, M. S.; Tsao, G. T. Anal. Chim. Acta 1995, 316, 269-276. (29) Wong, P. S. H.; Srinivasan, N.; Kasthurikrishnan, N.; Cooks, R. G.; Pincock, J. A.; Grossert, J. S. J. Org. Chem. 1996, 61, 6627-6632. (30) Bauer, S.; Griffin, T.; Bauer, J. Int. J. Mass Spectrom. Ion Processes 1996, 155, 107-121. (31) Hansen, K. F.; Gylling, S.; Lauritsen, F. R. Int. J. Mass Spectrom. Ion Processes 1995, 152, 143-155. (32) Whittle, C. E.; Farrar, J.; Henrickson, C.; Wilson, D. S.; Hollis, J.; Holman, R. W.; Gross, M. L. Int. J. Mass Spectrom. Ion Processes 1997, 171, 1-6. (33) Dryhurst, G. Periodate Oxidation of Diols and Other Functional Groups; Analytical and Structural Applications, 1st ed.; Pergamon Press: Oxford, 1970. (34) Slivon, L. E.; Bauer, M. R.; Ho, J. S.; Budde, W. L. Anal. Chem. 1991, 63, 1335-1340. (35) Soni, M.; Bauer, S.; Amy, J. W.; Wong, P.; Cooks, R. G. Anal. Chem. 1995, 67, 1409-1412. (36) Soni, M.; Amy, J.; Frankevich, V.; Cooks, R. G.; Taylor, D.; McKewan, A.; Schwartz, J. C. Rapid Commun. Mass Spectrom. 1995, 9, 911. (37) Munson, M. S. B.; Field, F. H. J. Am. Chem. Soc. 1966, 88, 2621-2630. (38) Lauritsen, F. R.; Choudhury, T. K.; Dejarme, L. E.; Cooks, R. G. Anal. Chim. Acta 1992, 266, 1-12. (39) Lauritsen, F. R.; Kotiaho, T.; Choudhury, T. K.; Cooks, R. G. Anal. Chem. 1992, 64, 1205-1211. (40) Mendes, M. A.; Pimpim, R. S.; Kotiaho, T.; Eberlin, M. N. Anal. Chem. 1996, 68, 3502-3506. (41) Ohorodnik, S. K.; Shaffer, R. E.; Callahan, J. H. Anal. Chem. 1997, 69, 4721-4727.
Received for review March 16, 1998 Revised manuscript received August 10, 1998 Accepted August 17, 1998 IE980164C
