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Anal. Chem. 1985, 57,2326-2333
Organic Nitrogen Determination in Oil Shale Retort Waters Christian G. Daughton* Sanitary Engineering and Environmental Health Research Laboratory, University of California (Berkeley), Richmond, California 94804 Bonnie M. Jones’ and Richard H. Sakaji Applied Science Division, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
Two new approaches were used to separate ammonia from varlous fractions of organonitrogen compounds In oil shale wastewaters, thereby permlttlng the application of a rapid, but unseiective, method for total N determlnatlon (combustion/ chemiluminescence) to the dlrect estimation of organic N. The first method uses reverse-phase chromatography to separate polar from nonpolar nitrogenous compounds. The second uses nonosmotlc dlssolved-gas dialysis to separate volatile from nonvoiatlle nltrogenous solutes. For 12 oli shale retort waters, correlation of the resulting measures of organic N agalnst organlc Kjeldahl nltrogen values gave correlation coefficients for the nonpolar and nonvoiatlle nltrogen values of 0.920 and 0.996, respectively. Relative standard deviations averaged 3.9 %. Combining the two methods ylelded higher estimates of organlc N; correlation against organlc KJeldahl nltrogen yielded a correlatlon coefflclent of 0.989. Organic N concentrations for the waters measured by all four methods ranged from 15 to 5000 mg/L. These data showed, that on the average, at least one-half to three-fourths of the organlc carbon was associated with nltrogen.
Organonitrogen compounds (ONCs) are a predominant class of organic solutes in oil shale process wastewaters (1-7). These waters also usually contain high concentrations of ammonia, often an order of magnitude greater than the organic N concentration (8). A rapid method for quantifying organic N within this ammonia matrix would be useful to regulatory agencies for setting monitoring standards, to the synfuels industry for routine monitoring, and to researchers studying waste treatment processes. Quantitation of total N in aqueous solutions is usually done by the time-consuming, wet-chemical Kjeldahl method (9). For organic N, however, a predistillation step is required to remove endogenous, free ammonia from the sample. The problems with determining organic N by the Kjeldahl method include (1) hydrolysis of primary amines in the distilland (caused by use of high pH and temperature), (2) unavoidable codistillation of volatile ONCs, (3) incomplete recovery of nitrogen from certain classes of ONCs, and (4) lengthy analysis time. A new method for determining total N, one that uses combustion/chemiluminescence (C/CL), has been validated for oil shale wastewaters (10). This method is extremely rapid, with analysis times of about 90 s. It has no current use in directly determining organic N, however, because a rapid method for selectively removing endogenous ammonia is not available. The disparity in concentrations of ammoniac N and organic N precludes the indirect determination of organic N by means of subtracting ammoniac N values (which can be obtained by a rapid method such as phenate colorimetry) from total N values. We present here two methods for separating ‘Present address: Department of Public Works, City and County of San Francisco, 750 Phelps St., San Francisco, CA 94124-1091.
ammonia from various fractions of ONCs in oil shale wastewaters. The ammonia-free sample can then be directly analyzed by C/CL to yield a rapid estimate of organic N. The first method uses chromatographic “reverse-phase fractionation” (RPF). The sample is applied to a cartridge containing (&-bonded silica prewetted by methanol. Polar solutes (including all inorganic forms of nitrogen) are not retained; certain ONCs that contain polar functionalities also pass through and are collected with the aqueous effluent. Most N-heterocycles and aromatic amines (the major ONCs that have been identified in retort waters (1-7)) are retained by the stationary phase. Methanolic eluates can then be analyzed for total N. The resulting value is a direct measure of “nonpolar” organic N (NPON). The second method uses what we term “nonosmotic dissolved-gas dialysis” (NOGD). Samples are placed in tubular, microporous poly(tetrafluor0ethene) membranes that are sealed and submerged in an acid solution. Ammonia and other volatile nitrogenous compounds rapidly diffuse through the membrane, but water and its less volatile solutes are retained. The dialyzed sample can then be analyzed for total N. The resulting value is a direct measure of “nonvolatile” organic N (NVON). Both separation methods are more rapid and selective than distillation and do not subject the sample to high temperature. Values for NPON and NVON were obtained by C/CL for 12 oil shale retort waters and compared with the respective organic N values obtained by Kjeldahl analysis (OKN). As with OKN, neither NPON nor NVON is a complete measure of organic N in a wastewater. The ONCs contained in the nonpolar and nonvolatile fractions comprise interesecting subsets. These two methods can be combined in an alternative approach by determining nonvolatile N in the polar fraction and adding this value to that for nonpolar N to yield a higher estimate of organic N. The only ONCs not recovered by this combined method are those that are both polar and volatile, such as aliphatic amines. The 12 oil shale wastewaters were also analyzed by this combined method, and the results were compared with NPON, NVON, and OKN. The various acronyms are listed in the Glossary at the end of this paper.
EXPERIMENTAL SECTION Samples. The 12 oil shale wastewaters were obtained from modified in situ, true in situ, and surface retorting processes (experimental and pilot scale) (see ref 10 and 11). All samples were pressure-filteredthrough 0.4-wm pore-diameterpolycarbonate membranes and stored at 4 “C in glass containers with Teflon closures. Composite water for the NOGD study comprised equal volumes of each of nine waters (excluding Oxy-6 rw [nc], Oxy-7&8, and LANL); that for the RPF study also excluded the Paraho water. The sources of many of the compounds used in the selectivity studies are listed in ref 10. Those not listed were obtained from Chem Service, Inc. (West Chester, PA; Nitrogen Chem Supply Unit, Model 0n-275), with the exception of pyrrole (98%), 2methylimidazole (98%),and 1-ethylimidazole (99%) (Crescent Chemical, Hauppauge, NY) and pyrrolidine (99%),2-pyrrolidone (99%),5-methyl-2-pyrrolidone (98.5%),and 1-methyl-4-piperidone
0003-2700/85/0357-2326$01.50/00 1985 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 57, NO. 12, OCTOBER 1985
(98%) (Aldrich Chemical Co., Milwaukee, WI). RPF Apparatus. Miniature reverse-phase cartridges are available from several manufacturers (e.g., CISSep-PAKs from Waters Associates, Inc., Milford, MA; disposable extraction columns from J. T. Baker Chemical Co., Phillipsburg, NJ; Bond Elut extraction columns from Analytichem International, Harbor City, CA; SPICE Cartridges from Analtech, Newark, DE). The RPF method uses CISSep-PAK (sample enrichment purification) cartridges, which are made from virgin polyethylene tubes that contain, under compression, about 350-400 mg of Cls-bonded Porasil A silica (80-pm diameter particle size); the bonded silica is held in place by fritted polypropylene disks. The cartridges have interchangeable influent and effluent female Luer-slip ends to which a 10-mL male-Luer syringe is attached for introduction of solvents and sample. RPF Procedure. For reverse-phase fractionation, the cartridges must first be activated (wetted), achieved by applying 5 mL of methanol to the cartridge followed by rinsing with 20 mL of ASTM type I water. Excess, unretained water was expelled from the cartridge with about 20 mL of air. The syringe must be disconnected from the cartridge before the plunger is pulled back or removed for filling the barrel; this prevents pulling liquid back through the cartridge. The sample was then passed through the cartridge at a sufficiently slow rate (e.g., 5 to 10 mL/min for retort waters; 100 mL/min can be used successfully on cleaner waters). The maximum volume of sample applied must be predetermined from breakthrough experiments; these volumes are commonly 2.5 to 10 mL for retort waters and up to several liters for cleaner waters. The cartridge should be held vertically to prevent channeling during sample application and elution. The aqueous, polar effluent (hydrophilic fraction; HpF) was discarded. The retained, nonpolar organic compounds (lipophilic fraction; LpF) were eluted after the 400-pL hold-up volume of aqueous sample was rinsed from the cartridge with 1mL of water. Since the LpF concentrates at the inlet to the cartridge, it is best to elute from the effluent end. Enrichment of solute in the eluent is effected by using a minimum of solvent. Nearly all retort-water ONCs that have not been irreversibly bound to the stationary phase can be eluted with methanol (4 mL) followed by tetrahydrofuran (1mL). The eluents are pooled in a volumetric flask and diluted to volume with methanol. NOGD Apparatus. Microporous poly(tetrafluor0ethene) (PTFE) tubing (1mm i.d., 0.4 mm wall thickness) was obtained from W. L. Gore and Associates, Inc. (Biomedical Division, Flagstaff, AZ). Each PTFE dialysis assembly was made from a 28.5-cm length of PTFE tubing; this length could hold 200 pL of sample with minimal headspace. Two 1.1-cm pieces of 19-gauge stainless steel tubing with chamfered ends were carefully inserted into both ends of the PTFE tubing so that 0.5 cm of the stainless steel tubing protruded from either end. These connections were secured by stretching a 1-cm length of silicone tubing (1mm id.) around both the PTFE tubing and the 19-gauge stainless steel tubing. This was done by first stretching the silicone tubing around a piece of thin-wall, 2.6-mm i.d. 10-gauge metal tubing; the stainless steel protruding from the PTFE tubing was then placed within this assembly, and the silicone tubing was gradually pushed off onto the PTFE tubing and then onto the stainless steel tubing. The remaining exposed portion of the 19-gauge stainless steel tubing from each end of the PTFE tubing was then inserted into another 1-cm piece of 1mm i.d. silicone tubing. Each dialysis unit was sealed after sample introduction by connecting the two silicone tubing ends to an 8-cm length of 1.5 mm 0.d. stainless steel rod that was bent at right angles into a “U” shape. NOGD Procedure. Depending on the ammonia concentration and buffering capacity of the retort water, each sample was first diluted with water so that a subsequent equal-volume dilution with aqueous 2 M Na2C0, solution yielded ammoniac N concentrations of no more than 1500 mg/L. Samples (200 pL) were placed in each dialysis apparatus with an air-displacement pipet; the plastic tip fit snugly into the silicone tubing end-connector. The assembly was immediately sealed with the U-shaped rod, and the membrane was immediately submerged in a 1-L beaker containing deionized water (room temperature); this prevented evaporative water loss and solute enrichment during preparation of the remaining samples. The membranes were suspended in the water from the stainless steel U-shaped rods that rested on
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two glass rods placed in parallel across the top of the beaker; the rods were held apart so that the stainless-steel U’s hung down. When all of the samples were prepared, the membranes were removed from the water bath by lifting the glass rods. They were then lowered into a 1-L beaker containing 1 N sulfuric acid (technical grade) sufficient only to cover the membranes; this beaker was submerged in a water bath maintained at 30 “C and stirred with a magnetic stir bar. A timer was started, and after 15.0 min the membranes were removed from the acid bath and resubmerged in the room-temperature water bath. For each dialysis assembly, the stainless-steel U was disconnected, and the dialyzed sample was expelled from the tubing with air from a disposable Pasteur pipet into a suitable vial. The tubing must be cleaned between uses with an appropriate organic solvent (e.g., methanol). Since many organic solvents will “wet” PTFE, making it permeable to water, it is important that the solvent be completely removed from the tubing before reuse. This is best done by heating the dialysis assemblies in an oven (95 “C) after preliminary air-drying. A complete protocol for the NOGD process is available (12). Combined RPF/NOGD Procedure. For the combined measurement of nitrogen associated with either NPON or NVON, the RPF procedure was followed as outlined except that the HpF was collected in a 10-mL volumetric flask, pooled with a 1-mL water rinse (which removed the 400 pL of residual sample), and diluted to volume with water. The NOGD procedure was then applied to the HpF. Both the LpF and the dialyzed HpF were analyzed for total N by C/CL, to yield NPON and polar/nonvolatile organic nitrogen, P(NVON), respectively. These values were added together to yield (NP&NV)ON values. Analysis. Dialyzed samples were analyzed for totalN by C/CL using an Antek Model 703C nitrogen analyzer (IO);LpF samples were analyzed by C/CL after dilution to 5 mL. Dialyzed wastewater samples were analyzed for residual ammonia by an adaptation of the phenate colorimetric method using a wavelength of 635 nm (13). OKN was determined by following the ASTM recommended procedure (14) with automated titration (9). Selectivity of RPF. To determine the types of ONCs that would partition into the LpF, 10 mL of various mixtures of 28 nitrogenous compounds were fractionated by RPF. The HpF and LpF were analyzed by isocratic, reverse-phase high-performance liquid chromatography (Supelco LC-8DB column, 50/50 methanol/phosphate buffer [pH 7 and 0.1 mL/L triethylamine], and refractive index detection) and by headspace analysis using capillary gas chromatography (J&W Scientific, Inc., Carbowax amine-deactivated column with nitrogen/phosphorus flame thermionic detection). Selectivity of NOGD. To determine the types of ONCs that would permeate the PTFE membrane during dialysis, individual aqueous solutions of 66 N-containing compounds from representative chemical classes were dialyzed. Each compound was dissolved in ASTM type I water so that the total N concentration was approximately 160 mg/L. Each solution was diluted with an equal volume of 2 M Na2C03. A portion of each diluted sample was stored as the time-zero sample, and a 200-pL portion of the remainder was dialyzed for 20 min at 30 “C. pH Effects. The effect of pH on removal of ammonia by dialysis was demonstrated in a time-course study using an ammonium hydroxide solution (1213 mg of NIL). Two sets of ammonium hydroxide solutions were made using buffers of pH 7 and 10. Each sample set was dialyzed for times up to 5 min at 25 “C.
RESULTS AND DISCUSSION The major advantage of C/CL in analyzing waters for total N is speed. A method for removing endogenous ammonia from an aqueous sample so that CICL can be used to quantify the remaining total N as an estimate of organic N should likewise be rapid. For the Kjeldahl method, removal of endogenous ammonia from aqueous samples is accomplished by distillation. This is not a selective process, nor is it rapid. The high temperature and pH that are required to distill the ammonia also serve to remove volatile organic compounds. The distilland, which contains a portion of the ONCs, is not amenable to C/CL analysis because of its extremely high salt and alkali
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 12, OCTOBER 1985
Table I, Organic Kjeldahl Nitrogen (OKN), Nonpolar Organic Nitrogen (NPON), Nonvolatile Organic Nitrogen (NVON), and Nonpolar/Nonvolatile Organic Nitrogen [ (NP&NV)ON] Valuesn for 12 Oil Shale Process Waters
process water Paraho LANL 150-Ton s-55 TOSCO HSP
Geokinetics Oxy6 rw
Omega-9 Oxy-6 rw (nc) Oxy-78~8gc OXY-6gc Rio Blanco sour
average
OKN
RSD, %
NPON
RSD, %
NVON
RSD, %
4299 2070 541 372 305 194 183 112 41 38 21 14 683
1.8 0.7 3.4 0.9 1.2 3.4 3.0 0.9 9.8 3.0 1.4 4.8
645 586 295 172 236 133 159 81 100 130 79 21 220
5.7 3.7 2.7 0.5 1.9 3.2 1.7 2.0 0.8 2.7 1.2 2.9
4839 2769 587 414 470 242 218 100 67 131 30 17 824
1.1 8.4 3.7 1.5 1.9 4.1 0.5 2.9 6.3 24.7 17.9 2.3
(NP&NV)ON* 5072 3319 671 569 484 245 208 203 133 243 133 66 946
"All values are means of three replicates (mg of N/L). bSee Figure 2; RSD's not applicable, since these values derive from the sum of NPON and P(NV0N).
content. The nitrogen remaining in the distilland also is not necessarily exclusively associated with organic compounds (e.g., nitrogen oxide salts and cyanates); these nonvolatile inorganic compounds occur in low concentrations, however, in retort waters (15). In a preliminary study, gas stripping at elevated temperature and pH was evaluated as an alternative to distillation. Stripping was extremely inefficient, and as with distillation, volatile ONCs would also be lost. The ammonia-removal methods reported here are more rapid than distillation, their selectivities are partly complementary, and the treated samples are amenable to C/CL analysis. RPF. Reverse-phase separation cartridges have been used in numerous methods, primarily for what is referred to as "solid-phase extraction". Use of this method for fractionation of organic carbon in retort waters has been discussed (16) and the process is termed reverse-phase fractionation (RPF). Factors important to the R P F process include: (1) stationary-phase alkyl-chain length and percentage of surface coverage, ( 2 ) organic solvent used in the activation step, and (3) sample pH, osmolality, volume, and flow rate. Distribution of nitrogenous compounds between the HpF and LpF is determined by the relative polarities of the solutes. Inorganic nitrogenous compounds would be expected to remain exclusively in the HpF. Of the ONCs reported to be present in retort waters, those that should remain in the HpF include only lower aliphatic amines and nitriles and certain oxygenated and hydroxylated N-heterocycles. Of the compounds that were evaluated, those that remained totally in the HpF were alkylamines and nitriles (dimethyl-, triethyl-, and butylamine, and propionitrile) and saturated or oxygenated heterocycles or those containing two ring-nitrogens (nicotinic acid, pyridazine, imidazole, piperazine, pyrrolidine, pyrazine, piperidine, pyrazole, and 3-hydroxypyridine). With increasing alkylation/arylation, the arylamines and pyridine congeners (pyridine, l-methyl-4-piperidone, 2-hydroxy-6-methylpyridine, aniline, 2- and 3-methylpyridine, 4-methylaniline, 2,6-dimethylpyridine, 2-ethylpyridine, 2,4-dimethylpyridine, 2,4,6-trimethylpyridine, 2-n-propylpyridine, and 3-ethyl-4methylpyridine) partitioned exclusively into the LpF; 5methyl-2-pyrrolidone and pyrrole partitioned to both fractions. Nonpolar ONCs, if not irreversibly retained by the CIScartridge, will be present in the organic eluate (LpF). Generally, with the conditions used for the liquid and gas chromatographic analyses, compounds with retention times longer than pyridine partitioned to the LpF, while those with shorter retention times partitioned at least partly to the HpF. Analysis of the LpF for total N by C/CL yields a direct measure of nonpolar organic N (NPON). These data, along with respective OKN values, are listed for each of the 12 retort
waters (Table I). The NPON values ranged from 15 to 376% of the respective OKN values, with RSD values less than 4% (excluding Paraho). The NPON value for the composite water was 311 mg/L, compared with an average NPON value of 147 mg/L for the eight constituent waters, whose average OKN value was 218 mg/L. The discrepancy between these NPON values probably resulted from the different pH values and solute concentrations of the individual waters vs. the composite sample. Correlation analysis of the NPON and OKN values gave a correlation coefficient of 0.920. The same R P F procedure has been used for determining the polarity distribution of organic carbon in these waters (16, 17). On the basis of these reported values for organic carbon in the LpF and the assumption that each nitrogen is associated with at most five carbons (e.g., pyridine), then on the average, at least half of the organic carbon in the LpF comprises ONCs (Table 11). Of the organonitrogen compounds reported in retort waters, pyridine has one of the lowest carbon-nitrogen ratios. These calculated percentages of organic carbon associated with nitrogen are therefore underestimates. Smaller fractions would result only by the presence of lower alkylamines and nitriles. NOGD. Microporous fluorinated polymeric membranes, developed by W. L. Gore and Associates, Inc. (Elkton, MD), are manufactured by a proprietary process from poly(tetrafluoroethene) film to yield a microporous (heterogeneous) hydrophobic membrane. Although these membranes have an effective pore size of about 2.0 Mm, their extreme hydrophobicity prevents the passage of liquid water (i.e,, osmosis cannot occur). Therefore, the passage of nonvolatile aqueous solutes is also prevented. Gases, however, can rapidly permeate because the process involves diffusion through large, gas-filled pores, as opposed to solvation in the membrane matrix itself. Permeation through nonporous (homogeneous) membranes such as silicone elastomer (18), and as with the process of pervaporation (19, 20), requires that diffusion occur after solvation of the solute in the polymer matrix. Nonporous membranes have been extensively used for separating gaseous mixtures and for degassing solutions, but the use of tubular microporous PTFE membranes for analytical applications has only recently been described. The only applications reported have been for the analysis of dissolved gases, such as for determining molecular chlorine in aqueous medium (21). Use of microporous PTFE tubing for separating ammonia from aqueous samples has been evaluated (22). In these instances, the analytes (Le., dissolved gases) are removed from the sample and then quantified. For the method reported here, the analytes (i.e., ONCs) remain in the dialyzed sample. As a tool for quantitatively separating ammonia from organic N, NOGD relies on the
ANALYTICAL CHEMISTRY, VOL. 57, NO. 12, OCTOBER 1985
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Table 11. Minimum Percentages of Dissolved Organic Carbon in Oil Shale Process Waters Associated with Nitrogen as Calculated from Organic N Values" process water Paraho LANL 150-Ton Oxy-6 rw TOSCO HSP s-55 Geokinetics Oxy-78~8gc Oxy-6 rw (nc) Omega-9 OXY-6gc Rio Blanco sour
DOC:L~F-DOC,~ mM 3502:558 1253:307 271:175 245:133 227:135 190:113 138:94 104:93 85:68 60:35 53:44 17:12
% of DOC accounted for by:
OKN'
NPONd
NVONe
(NP&NV)ONc
44 59 71 27 48 70 50 13 17 67 14 29
41 68 60 43 62 54 51 50 53 83 64 63
49 79 77 32 74 78 63 45 28 60 20 36
52 95 88 30 76 107 63 83 56 121 90 139
"Calculations assume a minimum C:N molar ratio of 5:l (e.g., pyridine). bFor nine waters, dissolved organic carbon (DOC) and LpF-DOC values reported in ref 11 and 16; the values for Oxy-6 (nc), Oxy-7&8, and LANL were determined using the methods reported in refs 11 and 16. CCalculatedas 100 X [(mol of N) X 51/(mol of DOC). dCalculated as 100 X [(mol of N) X 51/(mol of LpF-DOC).
greater volatility of ammonia compared with the ONCs. Volatility is commonly expressed as a dimensionless grouping that describes the equilibrium partitioning between a gas and a liquid. Volatility of a solute in water is not easily quantified, however, since it is a function of solubility, molecular weight, vapor pressure, and the nature of the gas-liquid interface (23). Increased solubility and molecular weight impede volatilization; increased vapor pressure enhances volatilization. Ammonia volatility increases as the temperature is increased because its vapor pressure increases and its solubility is reduced. For compounds with ionizable functional groups (such as many ONCs), the relationship of sample pH to solute pKa is also important. For compounds with pKa values greater than ammonia, volatilization will be impeded. Data required for quantifying volatility are not available for most compounds, but values for solubility in water, boiling point, and vapor pressure are presented for nitrogenous compounds of representative classes (Table 111). Certain compounds, such as alkylamines, that have high vapor pressures will not volatilize as fast as ammonia because their pKa values are higher. Those that have lower pKa values, such as pyridines, will not volatilize as fast because their vapor pressures are lower (higher boiling points) and their solubilities in water are higher. Variables that affect the permeation rate of ammonia through the membrane include temperature and pH, membrane wall thickness and internal diameter, and pressure across the membrane. Increased temperature lowers the water solubility of ammonia, decreases the pK, of ammonia ionization (favoring the formation of dissolved ammonia gas), and increases its vapor pressure and diffusivity. The permeation rate can therefore be maximized by increasing the temperature and pH. The process can be made more selective for the separation of ammonia from ONCs, however, if the temperature and pH of the sample are kept as low as possible. Several time-course experiments with the composite retort water showed that total N in the dialyzed sample never stabilized when the temperature was high (85 "C) or when the pH was high (>12); ONCs were being removed together with ammonia. Results for 25 "C and pH 10.5 showed that the total N concentration stabilized between 15 and 20 min, at which time the phenate-colorimetric method could not detect ammonia in the dialyzed sample. For the NOGD protocol, the dialysis conditions were standardized at 30 "C and pH 10.5 for 15 min. The concentration gradient of ammonia across the membrane was maintained by using an acidic dialysate solution to absorb and protonate the ammonia gas. Sulfuric acid was chosen because it is not volatile. Samples cannot be dialyzed against air because of water vaporization, causing additional
losses of ONCs and necessitating dilution of the dialyzed samples to a known volume before quantitation. At 20 "C, the rate of water loss from the membranes in quiescent air ranged from 1.55 to 2.22 mg/min, corresponding to an average mass flux of 0.18 to 0.22 mg/(cm2.s). The duration of dialysis required for complete ammonia removal is also dictated by the ammonia concentration. As ammonia is removed, the release of protons makes the dialyzed solution more acidic and inhibits further formation of dissolved ammonia gas. The need for buffering was evident from initial results with two retort waters. When a neat sample of Oxy-6 retort water was dialyzed, the total N concentration of the dialyzed solution (representing NVON) was very close to the OKN value. In contrast, the NVON values for neat samples of Paraho retort water were up to 3000 mg/L higher than the OKN value, a result of incomplete degassing of ammonia. Although the initial pH of either water exceeded 8.0, the pH values of dialyzed Paraho samples were between 4.7 and 6.7. In contrast, the dialyzed samples of Oxy4 retort water had pH values of 8.5. The Paraho water had insufficient carbonate alkalinity to maintain degassing. To standardize the NOGD procedure, 2 M Na2C03was selected as a buffer. A major problem with using the sodium carbonate buffer was the continual plugging of the injection port of the combustion tube used for C/CL analysis. This resulted from deposition of sodium carbonate when the aqueous sample was vaporized and from devitrification of the combustion tube by diffusion of sodium into the quartz. Devitrification lowers the melting temperature and increases the coefficient of thermal expansion. This problem was not solved, but the lifetime of the tube is improved when a ceramic insert is used and the tube is packed with quartz chips; a platinum boat could also be used with ladle introduction. The only other alternative would be to use a buffer that does not contain nitrogen or alkaline metals. In addition to volatilization, ONCs can be removed during dialysis by sorption/solvation in the membrane. The ability of a membrane to reject or allow permeation of organic solutes has been found to correlate with the solubility parameter, a measure of the energy per unit volume that holds a liquid together (also known as the cohesive energy or energy of evaporation) (19,29). Compounds that have similar solubility parameters will exhibit mutual affinities. Compounds with solubility parameters close to that of PTFE will have a greater tendency to sorb to the membrane. The solubility parameter used by Hansen (30)relates a liquid's cohesive energy, E , to a linear combination of dispersive interactions, Ed (London forces), polar interactions, E, (permanent dipole-dipole), and hydrogen-bonding forces, Eh, by the equation: E = Ed E,
+
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 12, OCTOBER 1985
Table 111. Correlation of pK,, Boiling Point, Vapor Pressure, and Solubility with PTFE Membrane Permeability for Nitrogenous Compounds of Representative Classesa
no.
compound
PK,'
bpPb("C)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67
ammonia dimethylamine trimethylamine ethylamine diethylamine triethylamine allylamine butylamine n-dibutylamine cyclohexylamine acetamide propionamide ethyl carbamate N,N-dimethylformamide urea ethanolamine 2-aminobutanoic acid ethylenediamine EDTA aniline N-methylaniline acetanilide o-toluidine p-toluidine o-aminophenol p-aminophenol p-aminobenzoic acid 1,l-dimethylhydrazine acetonitrile propionitrile pyrrole 1-methylpyrrole pyrrolidine 2-pyrrolidone 1-methyl-2-pyrrolidone 5-methyl-2-pyrrolidone indole imidazole 2-methylimidazole 1-ethylimidazole benzimidazole pyridine 2-methylpyridine 2,6-dimethylpyridine 2,4,6-trimethylpyridine 2-n-propylpyridine 3-ethyl-4-methylpyridine nicotinic acid 2-aminopyridine 2-hydroxypyridine 3-hydroxypyridine 2-hydroxy-6-methylpyridine quinoline piperidine 2-methylpiperidine 1-methyl-2-piperidone 1-methyl-4-piperidone pyridazine pyrazine 2-methylpyrazine piperazine cyanuric acid melamine nitrobenzene p-nitrophenol p-nitrobenzoic acid potassium nitrate
9.3e 10.73 9.75 10.87 10.98 10.75 9.49 10.77 11.25 10.68 0.37, -1.40 na na na 0.12 9.50 na 9.93, 6.85 na 4.6 4.84 0.5 4.45 5.10 na na 4.65, 4.86 7.2 (30°C) 4.3 na -3.8 -2.90 11.27 na na na -2.4 6.95 7.20 7.30 5.5 5.21 5.94 6.60 7.43 na na 2.0, 4.85 6.71 1.25, 11.99 5.10, 8.60 na 4.8 11.12 10.95 na na 2.2 1.1 na 5.55, 9.8 na 5.00 -11.26 (18) 7.2e na na
-33.4 7.4 3.5 16.61 -57 90 53 78 166 134 222 213 183 152 dec 172 subl 118 dec 18d 195.7 305 200.0 200.3 subl subl na 64f 82 97.2 130 na 89' 24d 202 na 253f 257f na na >366 115 129 144f 1711 na 196 na 204 na na na 238f
1od na 202 na 20@ 1171 na 146 dec subl 211 279 subl na
vapor pressure,b mmHg ("C)
solubilityb in H20, mg/L ("(2)
7600 (26) 1292 (20) 1444 (20) 912 (20) 200 (20) 50 (20) nah 72 (20) na na na na na 2.7 na 0.4 (20) na 9 (20) na 1 (63) 0.3 (20) na 0.1 (20) na na na na 157 74 (20) na na na na na na na na na na na na 14 (20) 8 (20) na na na na na na na na na 1 , (60) 3Y na na na na na na na na 50 (315) 0.2 (20) 2.2 (146) na na
531000 (20) very solf s01f miscf 815000 (14) 15000 (20) na misc 3100 (unk)l miscf 975000 (20) na 2000000 (unk)f miscf 1193000 (25) misd 210500 (25)' na 500 (25)f 34000 (unk) sparingly solf 5410 (unk)f 15000 (25) 7400 (21) 17000 (0) 11000 (0) 3400 (9.6) miscf miscf 119000 (40)f sparingly solf na miscf miscf na na solf s01f na na sparingly solf miscf solf 272000 (45)' 35000 (20)' na sparingly solf 16666 (unk)f solf na na na 6110 (unk) miscf na na na miscf solf na solf 2500 (17) sparingly sol' 1900 (20) 16000 (25) 240 (25) 35714 (unk)f
PTFE permeabilityd >0.99
>0.879 >0.87 >0.87 >0.87 >0b7 >0.87 >0.87 >0.87 >0.87 0.06 0.00 0.40 0.36 0.08 0.04 0.16 0.04 0.00 >0.87 >0.87 0.00 >0.87 >0.87 0.18 0.37 0.00 0.72 >0.87 >0.87 >0.87 >0.87 >0.87 0.02 0.00 0.05 >0.87 0.08 0.00 0.18 0.11 >0.87 >0.87 >0.87 >0.87 0.82 >0.87 >0.87 0.33 0.00 0.00 0.00 >0.87 >0.87 0.83 0.07 0.25 0.05 >0.87 0.83 0.00 0.00 0.00 >0.87 0.01 0.01 0.00
"Undefined abbreviations from Windholz (24). bAll values for boiling point (760 mmHg), vapor pressure (25 "C), and solubility from Verschueren (25), unless noted otherwise. All values for 25 "C (26), unless noted otherwise. dFraction of initial concentration (approximately 80 mg of N/L) lost after NOGD (20 min, 30 "C). "Dean (27). fWindholz (24). 8Limit of detection is 10 mg of N/L; the value of [l - (10 mg of N/L)/(80 mg of N/L) = 0.871. hNot available. 'Unknown. jWeast (28) (linear interpolation of tabularized data).
ANALYTICAL CHEMISTRY, VOL. 57, NO. 12, OCTOBER 1985 1 .oo
q 47
0.80 -
0.80
0.70
2331
1
f$$:
I I
@
1 -
I I
20
A
PTFE
I
n 0.30
0.20
0.10
0
L
0
10
20
30
40
60
Solubility Parameter Flgure 1. Correlation of PTFE permeability with polar solubility parameter. Solubility parameters calculated directly from tabularized data (32)
are plotted as triangles; those calculated from functional-group contributions (32)are plotted as circles.
+
Eh. When both sides of the equation are divided by V, the molar volume of the solvent, the following equations result: E h / V where E / V = 6') Ed/V = 8d2, E / V = E d / V E,/V EP/V = 6,2, and Eh/V = 6h2. Solubility parameters can be used to explain the removal of solutes that are not volatile; those removed by this mechanism tend to be nonpolar. To determine the types of ONCs that would permeate the membrane during NOGD, individual samples of 66 nitrogenous compounds of a broad range of chemical classes were evaluated. The fraction of nitrogen removed by dialysis was determined by C/CL (Table 111). This fraction is an indicator of the permeability of the membrane to each compound. Although it was not possible to directly determine whether the primary mechanism of removal was volatilization or sorption, calculation of solubility parameters was useful in showing when sorption was possibly a factor. Sorption to Teflon of aromatic cationic compounds has been reported (31). Sorption was probably the major removal mechanism for compounds such as quinoline and indole, since they have relatively high boiling points. Under the pH conditions of the NOGD procedure, those compounds whose volatilization would have been prevented because they were ionized included p-nitrophenol, potassium nitrate, nicotinic acid, 3-hydroxypyridine, and pyrrolidine. The PTFE permeabilities listed in Table I11 would therefore not necessarily be applicable to the ionic forms of these compounds. With the exception of potassium nitrate, each of these compounds was also dialyzed under conditions in which it would not be ionized. Pyrrolidine, piperidine, and nicotinic acid were removed under these conditions, but p-nitrophenol and 3-hydroxypyridinewere not (Table 111). To visualize the role that sorption played in removal of the nitrogenous compounds, PTFE permeability was correlated with the polar solubility parameter, g2h-,, a linear combination of the polar interaction, 6,, and hydrogen-bonding force, bh, terms (b2h-, = b2, + 6'h) (Figure 1). Three regions of the plot are evident: (1)the region closest to the PTFE line, in which
+
+
all the compounds are removed by dialysis, (2) a middle transition zone, where only some compounds are removed, and (3) the region closest to the water line, where most of the compounds are removed. The region closest to the PTFE line contains those compounds whose polar solubility parameters are closest to that of PTFE (i.e., 0). The PTFE and solute have mutual affinity for each other, up to a solubility parameter of 8.8. The region in which the solubility parameter exceeds 12.4 contains those compounds that do not exhibit an affinity for PTFE and are therefore removed only by volatilization during dialysis (e.g., acetonitrile and 1,l-dimethylhydrazine). The region between 8.8 and 12.4 contains about equal numbers of compounds that do and do not exhibit an affinity for PTFE. Of the compounds in this region, those removed by dialysis have at most a single nitrogen in the ring structure; of those compounds that are not removed, each contains two ring nitrogens or another electron-rich functional group. In summary, the primary shortcoming of NVON as an estimate of organic N is that it comprises only those compounds that are nonvolatile or do not sorb to PTFE. The reproducibility of NOGD for retort waters was assessed with triplicate determinations for each of 10 dialyzed samples of composite water. The mean NVON concentration was 763 mg/L, and the RSD was 1.95%. This value agrees remarkably well with the average NVON value of 769 mg/L obtained for the nine constituent oil shale wastewaters. The NVON data for each of the 12 retort waters are listed along with the respective OKN values in Table I. The NVON values ranged from 89 to 345% of the respective OKN values, with RSD values less than 8.5% (excluding Oxy-6 and Oxy7&8 gas condensates, both of which contained very volatile solutes). Correlation analysis of the NVON and OKN values gave a correlation coefficient of 0.996. The high correlation of NVON and OKN suggests that the classes of ONCs removed by dialysis comprise a small portion of the spectrum of ONCs in the retort waters or that the same compounds are also lost during the distillation step of Kjeldahl analysis.
2332
ANALYTICAL CHEMISTRY, VOL. 57, NO. 12. OCTOBER 1985
I
'.............................................................
...........'
A
Flpm 2. Concs~hlaWfkw chart of organic N & ~ n in dl shab retat water by sequential application of two methods for removing ammonia: (1) reveme-phase fractbnaUm (RFf) separates polar N (PN) from nonpolar organic N (NPON region bounded by diamond) and (2) nonosmotic dissoivedgas dialysis (NOGD) separates volatile N from nonvolatile organic N (NVON region bounded by circle). Application of NOGD to me PN fracfion yields pdar-nonvolatileorganic N, P(NV0N). Adding the values obtained for NPON and P(NV0N) gives a measure of (NP8NVWN (i.e.. organic N that comprises eM7erNPON or NVON); interseCtion of the circle and diamond represents organic N which is both nonpolar and nonvoiatiie.
Using the dissolved organic carbon values for these waters (11)and their NVON values, and assuming that each nitrogen is associated with a t most five carbons, then on the average, at least half of the organic carbon comprises ONCs (Table II). This agrees with the analogous calculations using the OKN and NPON values. Combined RPF/NOGD. The organonitrogen compounds contained in NPON and NVON probably comprise subsets of the totalorganic N. These subsets could overlap to vaious degrees; they could be identical, intersecting, or nonintersecting. For this reason, a more accurate estimate of organic N cannot be obtained by adding respective values for NPON and NVON. The compounds contained in the intersecting subset must first be eliminated from one of the measurements The two methods can be combined sequentially by first separating the sample into polar and nonpolar fractions using the RPF procedure. The NPON was determined directly on the LpF; the HpF was analyzed for NVON (using NOGD) to yield a measure of polar/nonvolatile organic N, P(NV0N). This procedure is conceptually diagrammed in Figure 2. The sum of these two measurements, (NP&NV)ON, is a more comprehensive measure of organic N, assuming that NPON and NVON are not identical subsets (Figure 2). The values obtained by this combined method for the 12 oil shale wastewaters are listed in Table I. As indicated by Figure 2, the values from the combined method could not be less than either NPON or NVON (if the two measures comprised identical sets), and they had to be less than the sum of NPON and NVON (if the two measures comprised nonintersecting seta). The regulta were either equal to or greater than the values obtained by any of the other three methods (NPON, W O N , or OKN). Values ranged from 114 to 633% of the respective OKN values. Correlation analysis of the
(NP&NV)ON and OKN values gave a correlation coefficient of 0.989. From the DOC values for these waters (11)and the assumption that each nitrogen is associated with a t most five carbon atoms, then, on the average, more than three-fourths of the organic carbon was associated with ONCs (Table 11). This is a significantly larger percentage than similar calculations using the W O N , NVON, or OKN values and reflects the improved recovery of organic N by the combined method. The major disadvantage of the combined method is the compounding of error. For two of the wastewaters (Oxy-6gas condensate and retort water), quantitative identifications have been made for constituents sufficiently volatile for gas chromatography (2). Calculation of the total N values contributed by these compounds (48 and 57 mg of N / L for the gas condensate and retort water, respectively) and comparison with the organic N values in Table I show that leas than half of the organic N has been characterized. With either the RPF or NOGD procedure, approximately 40 samples can be fractionated (or dialyzed) and analyzed in triplicate within 8 h; each fractionation requires 5 min, each batch of dialyses requires 20 min, and each replicate C/CL determination requires 90 s. In contrast, 5 h is required for analysis of three samples (in triplicate) using the Kjeldahl method with a 12-place digestion/distillation unit and automated titration. Either method represents an &fold time savings. GLOSSARY
C/CL HPF LPF
combustion/chemiluminescence hydrophilic fraction from RPF lipophilic fraction from RPF
NOGD nonosmotic dissolved-gas dialysis (NP&NV)ON organic nitrogen comprising either W O N or NVON WON nonpolar organic nitrogen (LpF-TN) NVON nonvolatile organic nitrogen (NOGD-TN) OKN organic Kjeldahl nitrogen ONCs organonitrogen compounds PN polar nitrogen (HpF-TN) P(NV0N) polar/nonvolatile organic nitrogen PTFE poly(tetrafluor0ethene) RPF reverse-phase fractionation TKN total Kjeldahl nitrogen TN total nitrogen (by C/CL) ACKNOWLEDGMENT We thank Michael R. Davis (Gore and Associates) for the generous gift of tuhular microporous PTFE membrane. The authors express their gratitude to Gloria J. Harris for her invaluable input and attention to detail in executing many of the experiments and performing many of the nitrogen anal-. We thank Gregg W. Langlois for the HPLC analand Frank Mandola for his laboratory assistance.
Registry No. PTFE, 9002-84-0: EDTA, 6000-4: H,O, 7732185; N, 7727-37-9;ammonia, 7664-41-7;dimethylamine, 124403; trimethylamine, 75-50-3; ethylamine, 75-04-7; diethylamine, 109-89-7; triethylamine, 121-44-8;allylamine, 107-11-9;bu@lamine, 109-73-9; n-dibutylamine, 111-92-2;cyclohexylamine, 108-91-8; acetamide, 60-35-5; propionamide, 79-05-0;ethyl carbamate, 5179-6; Np-dimethylformamide, 68-12-2; urea, 57-13-6; ethanolamine, 141-43-5;2-aminohutanoic acid, 80-60-4; ethylenediamine, 107-15-3;aniline, 62-53-3;N-methylaniline, 100-61-8;acetanilide, 103-84-4:0-toluidine,95-53-4; p-toluidine, 106-490; 0-aminophenol, 95-556;p-aminophenol, 123-308;p-aminohnzoic acid, 150-13-0; 1,l-dimethylhydrazine,57-14-7; acetonitrile, 75-05-8;propionitrile, 107-12-0;pyrrole, 109-91-7; 1-methylpyrrole. 96-54-8;pyrrolidine, 123-751; 2-pyrmlidone, 616455; 1-methyl-2-pymolidone,872-604
ANALYTICAL CHEMISTRY, VOL. 57, NO. 12, OCTOBER 1985
5-methyl-2-pyrrolidone, 108-27-0; indole, 120-72-9; imidazole, 288-32-4;2-methylimidazole,693-98-1; 1-ethylimidazole,7098-07-9; benzimidazole, 51-17-2; pyridine, 110-86-1; 2-methylpyridine, 109-06-8;2,6-dimethylpyridine, 108-48-5;2,4,6-trimethylpyridine, 108-75-8;2-n-propylpyridine, 622-39-9; 3-ethyl-4-methylpyridine, 529-21-5; nicotinic acid, 59-67-6; %aminopyridine, 504-29-0; 2hydroxypyridine, 142-08-5; 3-hydroxypyridine, 109-00-2; 2hydroxy-6-methylpyridine,3279-76-3; quinoline, 91-22-5;piperidine, 110-89-4; 2-methylpiperidine, 109-05-7; l-methyl-2piperidone, 931-20-4;l-methyl-4-piperidone,1445-73-4;pyridazine, 289-80-5;pyrazine, 290-37-9; 2-methylpyrazine, 109-08-0;piperazine, 110-85-0; cyanuric acid, 108-80-5; melamine, 108-78-1; nitrobenzene, 98-95-3;p-nitrophenol, 100-02-7;p-nitrobenzoic acid, 62-23-7; potassium nitrate, 7757-79-1.
(14) (15) (16)
(17) (18) (19)
LITERATURE CITED
(20)
(1) Hawthorne, S. B.; Sievers, R . E. Environ. Sci. Technol. 1984, 18, 483-490. (2) Leenheer, J. A.; Noyes, T. I.; Stuber, H. A. Environ. Sci. Technol. 1982, 16, 714-723. ( 3 ) Pellizzarl, E. D.; Castlllo, N. P.; Willis, S.; Smith D.; Bursey, J. T. I n “Measurement of Organlc Pollutants in Water and Wastewater”; Van Hall, C. E., Ed.; Amerlcan Soclety for Testlng and Materials: Denver, CO, 1979; ASTM STP 686, pp 256-274. (4) Raphaelian, L. A.; Harrison, W. “Organic Constituents in Process Water from the In-Situ Retorting of Oil from Oil-Shale Kerogen”; Argonne Natlonal Laboratory report ANL/PAG5, 1981, (5) Rlchard, J. J.; Junk, G. A. Anal. Chem. 1984, 56, 1625-1628. (6) Sievers, R. E.; Conditt, M. K.; Stanley, J. S. I n “Environmental Speciation and Monkorlng Needs for Trace MetalGontalning Substances from Energy-Related Processes”; NBS Special Publicatlons, Gaithersburg, MD, 1981; NO. 618, pp 93-103. (7) Stuber, H. A.; Leenheer, J. A. Anal. Chem. 1983, 55, 111-115. (8) Daughton, C. G., Ed. “A Manual of Analytical Methods for Wastewaters”, 2nd ed.; Lawrence Berkeley Laboratory: Berkeley, CA, 1984; Appendlx A; LBL-17421 (NTIS DE84015967). (9) Jones, B. M.; Harris, 0. J.; Daughton, C. G. I n “A Manual of Analytical Methods for wastewaters”, 2nd ed.; Daughton, C. G., Ed.; Lawrence Berkeley Laboratory: Berkeley, CA, 1984; Chapter V; LBL-17421 (NTIS DE84015967). (10) Jones, B. M.; Daughton, C. G. Anal. Chem., precedlng paper in this issue. (11) Langlois, G. W.; Jones, B. M.; Sakaji, R. H.; Daughton, C. G. J. Test. Eva/. 1984, 12, 227-237. (12) Daughton, C. G.; Sakaji, R. H. I n “A Manual of Analytlcal Methods for Wastewaters”, 2nd ed.;Daughton, C. G.. Ed.; Lawrence Berkeley Laboratory: Berkeley, CA, 1984; Chapter 11; LBL-17421 (NTIS DE84015967). (13) Daughton, C. G.; Cantor, J.; Jones, B. M.; SakaJI, R. H. I n “A Manual of Analytical Methods for Wastewaters”, 2nd ed.; Daughton, C. G.,
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Ed.; Lawrence Berkeley Laboratory: Berkeley, CA, 1984; Chapter IV; LBL-17421 (NTIS DE84015967). ASTM “Annual Book of ASTM Standards, Part 31, Water”; American Soclety for Testing and Materials: Philadelphia, PA, 1980; pp 743-747. Wallace, J. R.; Alden, L. “Methods of Chemical Analysis for Ionic Constituents in Synfuel Wastewaters”; Denver Research Institute, University of Denver: Denver, CO; 24 September 1984, pp 6-22. Daughton, C. G.; Jones, B. M.; Sakaji, R. H. I n “A Manual of Analytical Methods for wastewaters”, 2nd ed.; Daughton, C. G., Ed.; Lawrence Berkeley Laboratory: Berkeley, CA, 1984; Chapter I;LBL-17421 (NTIS DE84015967). Healy, J. B., Jr.; Jones, B. M.; Langiois, G. W.; Daughton, C. G. I n Sixteenth Oil Shale Symposium Proceedings“; Gary, J. H., Ed.; Colorado School of Mines Press: Golden, CO, 1983; pp 498-511. Yasuda, H.; Peterlln, A. J. Appl. Polym. Sci. 1973, 17, 433-442. Hwang, S.-T.; Kammermeyer, K. I n “Techniques of Chemistry”; Weissberger, A., Ed.; Wlley-Intersclence: New York, 1975; Vol. V I I . Zhu, C. L.; Yuang, C.-W.; Fried, J. R.; Greenberg, D. B. Environ. Prog. 1983, 2, 132-143. Aokl, T.; Munemori, M. Anal. Chem. 1983, 55, 209-212. Aoki, T.; Uemura, S.; Munemori, M. Anal. Chem. 1983, 5 5 , 1620-1622. Thomas, R. G. I n “Handbook of Chemical Property Estlmation Methods”; Lyman, W. J., Reehi, W. F., Rosenblatt, D. H., Eds., McGraw-HID: New York, 1982; Chapter 15. Windholz, M., Ed. “The Merck Index”, 10th ed.; Merck & Co.: Rahway, NJ, 1983. Verschueren, K. “Handbook of Environmental Data on Organic Chemicals”; Van Nostrand Reinhold: New York, 1977. Perrin, D. D. “Dlssociation Constants of Organic Bases In Aqueous Solution”; published as a supplement to Pure Appl. Chem., Butterworths: London, 1965. Dean, J. A., Ed. “Lange’s Handbook of Chemistry”, 12th ed.; McGrawHill: New York, 1979. Weast, R. C., Ed. “CRC Handbook of Chemistry and Physics”, 59th ed.; CRC Press: West Palm Beach, FL, 1978. Klein, E.; Eichelberger, J.; Eyer, C.; Smith, J. Water Res. 1975, 9 , 607-811. Hansen, C. M. Ind. Eng. Chem. Prod. Res. Dev. 1989, 8, 2-11. Josefson, C. M.; Johnston, J. B.; Trubey, R. Anal. Chem. 1984, 56, 764-76a. Barton, A. F. M. “Handbook of Solubility Parameters and Other Cohesion Parameters”; CRC Press: Boca Raton, FL, 1983; 594 pp,
RECEIVEDfor review January 16,1985. Resubmitted February 21,1985. Accepted June 4,1985. This work was supported by the Assistant Secretary for Fossil Energy, Office of Oil Shale, Division of Oil, Gas, and Shale Technology of the U S . Department of Energy under Contract No. DE-AC0376SF00098.
