1556
Anal. Chem. 1986, 58, 1556-1561
Oil Shale Retort Water Ammonia Determination by Titrimetry, Phenate Colorimetry, Enzymatic Analysis, and Chromatographic Fractionation/Chemiluminescence Christian G. Daughton* Sanitary Engineering and Environmental Health Research Laboratory, University of California (Berkeley), Richmond, California 94804 Richard H. Sakaji and Gregg W. Langlois Applied Science Division, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
A statlstlcal comparlson was made of three modlfled standard methods and a new rapld estlmator for determlnlng ammonlac-N In oil shale retort waters. The modlfled standard methods were (1) dlstlllatlon/ackllmetrlc ttlratlon (automated), (2) phenate colorimetry, and (3) glutamate dehydrogenase enzymatic analysis. The fourth method, reverse-phase fractlonatlon-combustlon/chemllumlnescence (RPF-WCI), used a reversephase chromatographlctechnique to separate polar from nonpolar nltrogenous compounds; combustlon/chemllumlnescence was then used to determlne total-N In the polar tactlon as a rapld estimate of ammonlac-N. Ammonlac-N for 12 retort waters ranged from 1 to 33 g/L. Preclslon was best for the ttlrlmetrlc and colorlmetrlc methods (relatlve standard devlatlons < 1.0%). For all waters, the colorlmetrlc and RPF-C/CL methods ylelded the lowest and hlghest concentratlons, respectlvely. Paired comparlsons and a sequentlally rejectlve multiple test procedure showed that each palr of methods (wlth one exceptlon) gave slgnlflcantly dlfferent results for a majorlty of waters; none of the paired methods, however, gave slgnlflcantly dlfferent results for a composite sample that comprlsed each of the 12 waters. Flsher's test for comblnlng probablllty values from Independent slgnlflcance tests showed no slgnlflcant difference ( P > 0.01) across all waters only when tltrlmetry was compared wlth enrymatlc analysls. The RPF-C/CL method gave the most rapld estlmate of ammonla and would be useful for spot monltorlng or range flndlng for the other methods.
Dissolved ammonia gas and ammonium ion coexist (pK, = 9.3, 25 "C) in wastewaters from oil shale retorting at con-
centrations generally greater than several thousand milligrams per liter (I). These levels of ammonia could be inhibitory to biological treatment, and their emission to the atmosphere would pose worker safety/aesthetic problems. The quantities involved are also sufficiently large to serve as a potential recoverable resource for fertilizer nitrogen. The origin of these high concentrations has not been fully elucidated, but ammonium-silicate mineral assemblages in the raw shale (2),as well as kerogen pyrolytic products, are possible contributors. Methods for the quantitation of ammoniac species in synfuel wastewaters are required for waste treatment research, treatment and effluent monitoring, and establishment of regulatory standards. The method of choice should be sufficiently simple to find applicability in a routine wet chemistry laboratory. In this report, ammonia will be used as a colligative term for both ammoniac species. Several approaches are available for the routine, collective determination of these species: colorimetry, acidimetric titrimetry, ion-selective electrode, combustion/chemiluminescence,UV absorbance (gas phase), 0003-2700/86/03581556$015010
electrical conductivity, enzymatic analysis, and ion, gas, and liquid chromatography. Most of these methods can be applied both directly (to an unaltered wastewater sample) as well as indirectly (to ammoniac solutions derived by distillation or diffusion from a wastewater). Many of these methods have undergone preliminary evaluation for retort waters ( I , & 4, but no statistical comparison of methods has been reported. We have modified/developed and statistically evaluated four methods for an unrelated series of 12 oil shale wastewaters. These methods were (i) distillation of ammonia into boric acid (5) and automated acidimetric titration of the distillate (ii) a direct to a p H end point (using an indicator/dye (6)), colorimetric method (i.e., no predistillation of ammonia from the sample) based on the Berthelot reaction of phenolate, hypochlorite, and ammonia catalyzed by nitroprusside to yield indophenol blue (7), (iii) enzymatic analysis using glutamate dehydrogenase to catalyze the stoichiometric oxidation of reduced nicotinamide adenine dinucleotide and concomitant synthesis of L-glutamate from 2-oxoglutarate and ammonia (8),and (iv) combustion/chemiluminescence(9)to quantify total nitrogen in the polar fraction from a reverse-phase fractionation method (10). The absolute values obtained from these methods were not necessarily representative of waters that would be produced from a shale oil industry; all of the samples had been stored for various years without preservation by acidification, and, to date, no waters have been available from commercial-scale facilities.
EXPERIMENTAL SECTION Reagents. Unless otherwise noted, all reagents were analytical reagent grade. When used as a reagent, water refers to ASTM Type I quality produced by a Millipore RO/Milli-Q system. For all of the methods, it is extremely important that ambient levels of ammonia in the laboratory atmosphere be minimized. All ammoniac-N standards were made from ammonium sulfate (dried at 104 "C). Hellige standards (Hellige, Inc., Garden City, NY) were used to verify the accuracy of these standards. Wastewater Samples. The origins and storage conditions for the 12 retort wastewaters have been described (9, 11). To remove particulate and suspended materials, each water was centrifuged (12000g,20 min), and the supernatant fluid was pressure-filtered (0.4-pm-pore-diameter polycarbonate membrane) and stored at 4 "C in glass containers with minimal headspace; the composite water comprised equal volumes of each of the 12 filtered waters. The exact sarhe water samples were used for all four methods. All analyses for a given method were run within 3 consecutive days (replicates on the same day) and by the same operator. Distillation/Titrirnetry. Quantitation by titrimetry requires quantitative distillation of ammonia from an aqueous sample to minimize interference by other titratabla species (e.g., carbonate alkalinity) and by color. The method reported here incorporates numerous modifications to the APHA method (5) as reported previously ( I ) . Samples are diluted t o give subsample ammoniac-N masses in the range of 0.1-5 mg. The appropriate sub@ 1986 Amerlcen Chemical Society
ANALYTICAL CHEMISTRY, VOL. 58, NO. 7, JUNE 1986
sample volume (generally 5-300 mL) is added to an 800-mL Kjeldahl distillation flask and adjusted to a final volume of 300 mL with water. Two drops of phenolphthalein indicator (0.5 g of phenolphthalein in 50 mL of 95% ethanol and 50 mL of water) and 10 mL of alkaline borate buffer are added. The buffer is prepared by adding 88 mL of 0.1 N NaOH to approximately 500 mL of 0.025 M sodium tetraborate solution (5.0 g of Na2B40,or 9.5 g of Na2B,O7.1OH2O/L) in a 1-L volumetric flask and adjusting to volume with water; store in polyethylene or polypropylene containers. The amounts of ammonia in each flask should be as equal as possible because this affected the reproducibility of the indicator end point, A distilled blank (300 mL of HzO) is treated in parallel. Immediately after the addition of sufficient 50% NaOH to bring the pH of the solution to about 9.5, the flask is connected to the distillation/condensation apparatus. This is important to avoid the escape of ammonia; losses can be further minimized by carefully adding the dense caustic down the inside of the flask so that it underlays the sample solution. The flask contents (about 300 mL) are thoroughly mixed after connection to a spray trap/condenser on a 12-unit Labconco combination digestion/distillation apparatus, The block tin condenser tubes were replaced with Pyrex condensers, stainless-steel elbows and unions, and Teflon ferrules; incomplete recoveries were found when the stock tin condensers were used. The contents are heated to a boil (the distilland must remain pink to ensure alkaline conditions), and the first 100 mL of distillate is collected by bubbling it through 50.0 mL of boric acid receiving solution (40 g of H,B03/L), which ensures quantitative capture of the ammonia gas as ammonium ion with a concomitant stoichiometric rise in pH. For titration to the indicator end point, 10 mL of a mixed indicator/dye solution (300 mg of acid methyl red indicator and 200 mg of methylene blue dye in 250 mL of 95% ethanol) is added to the boric acid receiving solution prior to distillation. The volume of the receiving solution is important for good precision. Although most of the ammonia is distilled in the first few minutes, the distillation is continued until over 100 mL of distillate is collected. Each of three nondistilled blanks comprise 50 mL of receiving solution/indicator that is exposed to the ambient laboratory atmosphere together with the sample-receivingflasks. The distillates and blanks are diluted with water to give equal final volumes (masses) and titrated with standardized 0.02 N H2SO4 (Hellige, Inc.). Determination of the distilled ammonia by acidimetric titration requires detection of the equivalency point in the receiving solution (ca. pH 4.8). We have found that direct measurement by electrode gives inaccurate results; a pH indicator is required. Although there are no pH indicators that give sharp end points at the equivalency point, methyl red is the most widely used indicator, and it exhibits little salt error (12). Protonation of the benzoic azo nitrogen of methyl red yields the red form in the acid region of the pH range 4.2-6.2; at the basic end of this range, the nonprotonated form is yellow. Titration of distillates that contain ammonia therefore proceeds from the higher end of the range (yellow) to the lower end (red). The intermediate colors of the two forms are gradations of pink, and the end point can be visually detected only with difficulty by carefully comparing the distillate color with that of a nondistilled blank (13). Visual detection of the end point can be ameliorated, however, by addition of a blue "enhancer" dye such as methylene blue (6) whose color does not change with pH. For samples containing sufficient ammonia, the initial color is bright green. During titration, the color progresses through darker shades of blue-green until the grayish transition point is reached; the samples will then develop more intense hues of violet. This is an inferior end point detection method except when the detection is performed by determining the absorbance of the solution and matching it to that of the blank. This was achieved by automated colorimetry. Uniformity of volumes, ionic strength, and pH of the distillates is important because of their effects on salt error and color intensity of the indicator (12). A Sybron/Brinkmann (Westbury, NY) autotitrator (Metrohm Model 655 Dosimat, E 526 titrator, 643 control unitJ624 autosampler) was used with appropriate buret module (e.g., 10 or 20 A), submersible colorimeter probe with 1-cm path length, 545-nm filter, and colorimeter (Brinkmann PC 800). The samples were titrated to the average transmittance (545 nm) of the three nondistilled blanks. A detailed protocol is available (1). For the
1557
results reported here, five replicates of each sample (5 mL) were analyzed after dilution to give ammoniac-N concentrations of about 300-400 mg/L. Ammonia concentrations were calculated as NH3-N (mg/L) = (sample titrant vol (mL) blank titrant vol (mL) X normality of acid (mequiv/mL) X 1000 mL/L X 14 mg/mequiv)/sample volume (mL)
Colorimetry. Quantitation by direct colorimetry (i.e., without distillation) relies on the formation of an ammoniac reaction product with a molar absorptivity sufficiently high to accommodate for dilution of endogenous interferences to below background levels. The method reported here is an adaptation of the phenate method reported by Weatherburn (7). Samples are diluted to give ammoniac-N concentrations in the ranges of 10-100 mg/L or 1WlOOOmg/L. Five millilitersof phenol/nitroprusside reagent (5 g of phenol and 25 mg of nitroferricyanide dihydrate, diluted to 500 mL with water) is added per tube to 20- X 150-mm Pyrex culture tubes with Teflon-lined screw caps. Samples or standards (prepared from ammonium sulfate) are withdrawn with 20-wL glass capillaries that are calibrated "to-contain" (end-to-end) (e.g., Drummond Microcaps). The entire capillary is carefully added to the reagent mixture, and the tube is sealed and shaken vigorously; vortex mixing is inadequate to flush the capillary. Immediately after adding 5 mL of alkaline hypochlorite solution (2.5 g of sodium hydroxide and 4.2 mL of 5% sodium hypochlorite, diluted to 500 mL), the tubes are resealed, shaken vigorously, and immersed in a 37 OC bath for 20 min. The tubes are cooled to room temperture, and the absorbance values are read vs. water (this allows detection of high absorbance in the reagent blank) at 636 nm or 520 nm for low or high concentration ranges, respectively, using a spectrophotometer equipped with a 1-cmpath-length, micro flow-through cell (e.g., Bausch & Lomb Spectronic 100). Ammonia concentrations were interpolated from five-point (triplicate) standard curves. For the data reported here, the samples/standards were not measured by using glass capillaries. Rather, this sampling step was combined with the alkaline/hypochlorite addition step with the aid of an automatic dilutor-pipettor (Brinkmann Instruments, Inc., Digital Dilutor 9200). The sample was drawn into the Teflon dispensing tip (pipetting mode) and then expelled (dilutionmode) together with the alkaline/hypochlorite reagent into the phenol/nitroprusside reagent, which had been measured with the dispense mode into each tube. It is extremely important that the reaction mixtures be vigorously mixed and heated within 30 rnin of sample addition. Five replicates of each sample were analyzed after dilution to the 10-100 mg/L range. Enzymatic Analysis. Enzymatic analysis uses glutamate dehydrogenase (GlDH) to catalyze the synthesis of L-glutamate from 2-oxoglutarate and ammonia, while the coenzyme, reduced nicotinamide adenine dinucleotide (NADH), undergoes concomitant stoichiometric oxidation 2-oxoglutarate
+ NH4++ NADH
GlDH
L-glutamate
+ NAD+ + HzO
Ammonia is quantified by calculating the decrease in solution absorbance (365 nm) related to the oxidation of NADH. A modified version of the protocol reported by Kun and Kearney (8)was used; the sample tissue preparation portion of the protocol was omitted. The 90-min reaction time was reduced to 45 rnin because successive readings taken from 10 to 90 min (21 "C) indicated reaction completion after 20 min. The standard curve for ammoniac-N of 0.14-1.12 mg/L was extended to 2.5 mg/L. The biochemical reagents, 2-oxoglutarate (98%, CalBiochem, La Jolla, CA), GlDH (bovine liver, specific activity 1678 IU/mL at 30 "C, CalBiochem), and /3-nicotinamide adenine dinucleotide (reduced form) (Sigma Chemical Co., St. Louis, MO) were prepared at the following respective concentrations: 14.6 g/L, undiluted, and 1.04 g/L. Reagent storage (4 O C , not frozen) and frequency of preparation have been discussed (14). The volumes were increased threefold, and the order of addition to the reaction mixture was changed to 500 mM Tris buffer (0.6 mL), 2-oxoglutarate (0.3 mL), sample/standards (1.5 mL), and NADH (0.54 mL). All wastewater samples were diluted to give ammoniac-N concentrations in the range 0.5-2.5 mg/L, and each was analyzed
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ANALYTICAL CHEMISTRY, VOL. 58, NO. 7, JUNE 1986
in triplicate. The reaction mixtures were contained in 10-mm Pyrex test tube cuvettes. After vortex mixing, the initial absorbance (365 nm) was determined for each sample with a Bausch & Lomb Spectronic 100; this wavelength does not provide the sensitivity of others, but the stability is greater. After the GlDH was added and mixed thoroughly, the final absorbance was measured at 45 min. Ammoniac-N concentrations were interpolated from a five-point (triplicate)standard curve and corrected for the blank. Fractionation Coupled with Combustion/Chemiluminescence. The use of combustion/chemiluminescence(C/CL) for determining total- and organic-N in retort waters has been reported (9,10). Since the method only determines total-N, its applicability for organic-N necessitates prior separation of ammonia from the organonitrogen compounds. In the published method (IO),this was accomplished with two alternative techniques, one of which was "reverse-phase fractionation" (RPF). An aqueous sample is passed through a methanol-activated, reverse-phase (C18)chromatographic cartridge. Nonpolar solutes are retained (lipophilic fraction), while polar solutes reside in the unretained aqueous, hydrophilic fraction (HpF); for retort waters, the polar nitrogen comprises mainly ammonia. Since ammonia partitions exclusively to the HpF, direct determination of total-N in the HpF yields an estimate of ammoniac-N. For the protocol reported here, the published method for organic-N (10) was modified only by collecting the HpF in a 5-mL volumetric flask. The initial aqueous effluent from a 3-mL sample followed by a 1-mL water rinse were pooled, and the volume was adjusted with water. Samples were fractionated in triplicate (three separate cartridges); the HpFs were diluted to yield ammoniac-N concentrations of 20-60 mg/mL, and each HpF was analyzed in triplicate using an Antek 703C combustion/chemiluminescence nitrogen analyzer with a five point (triplicate) ammonium sulfate standard curve (10-100 mg of N/L) (9). This method will be referred to as C/CL. Statistical Analyses. Based on the variance of preliminary data sets, the number of replicates (i.e., sample size = n) required for each analytical method was estimated by use of the procedure of Sokal and Rohlf (15). All arithmetic means were rounded to the nearest significant figure based on the magnitude of their respective standard deviations (5). For paired comparisons of methods, an approximate t test was used that calculates the statistic t' for two samples with unequal variances (15). The sequentially rejective Bonferroni (SRB) multiple test procedure (16) was used for significance testing of the null hypotheses associated with all the paired comparisons for each water. This procedure is structured such that the overall significance level is a;a! = 0.05 was used in this study. Fisher's test for combining independent p values ( 1 7 ) was used to determine, for each pair of methods, if the combination of the comparison probabilities for all waters was significant. R E S U L T S A N D DISCUSSION Interferences. Of the advantages and disadvantages of the four methods (Table I), interferences are of primary concern. The major positive interferences include simple alkyl amines (colorimetry, distillation/titrimetry, RPF-C/CL), distillable bases (distillation/titrimetry), hydrolyzable organic amines and cyanates (distillation/titrimetry), and oxygenated or hydroxylated (polar) nitrogenous compounds including cyanates (RPF-C/CL). Retort waters also generally contain particulate and colloidal materials, including oils, tars, and shale particles; these materials could exert numerous effects on any of the methods, but primarily on the enzymatic and colorimetric methods because of light scattering and side reactions. Enzymatic analysis is the most specific of the four methods, but since various biochemicals can interfere (14), mainly by NADH oxidation or enzyme inhibition, this method would require a separate evaluation before use for retort water effluents from biological waste treatment processes. Effect of Filtration. The effect of particulates was evaluated by using the colorimetric method. A comparison was made for all 12 waters. Five replicates of each water were analyzed with and without pressure filtration. Two-way
Table I. Four Methods for Determining Ammoniac-N in Oil Shale Wastewaters method no.
advantages
1: distillation/ standard method
acidimetric titrimetryO
high precision organic N can be determined with extra step
disadvantages interferences: distillable bases, cyanates time-consuming autotitrator and distillation units required
2: phenate
rapid interferences: colorimetryb high precision alkyl amines, high sample throughput particulates only requires spectrophotometer easily automated
3: enzymatic
methodC
highly specific low detection limit high sample throughput necessitates high only requires dilutions spectrophotometer interferences: certain biochemicals expensive reagents
4: RPF-C/CLd very rapid
organic N can be determined with extra step
interferences: all inorganic N, polar organic N only gives estimate N analyzer required
"Published method (5) with modifications noted in text. bPublished method (7) with modifications noted in text. Published method (8) with modifications noted in text. dAdaptation of published method (9, 10) as discussed in text. analysis of variance (ANOVA) showed a significant difference (P< 0.01) between the two sets of data. Because filtration had a significant effect on ammonia concentrations (with only three exceptions, values from the filtrates were lower), all subsequent analyses using the four methods were done by using filtered waters. This eliminated any possible confounding effects of particulates or colloids. Whether the filterable fraction in retort waters contributes negative or positive interferences or acts as a reservoir for ammoniac-N requires additional investigation. S t a n d a r d Additions. Standard additions studies were used to determine if the complex matrix of solutes in oil shale wastewaters had an effect (synergistic or antagonistic) on any of the four methods. For each method, a series of ammonium sulfate spikes were added to replicate samples of the composite retort water. The amount of ammonia recovered was correlated against the amount of ammonia added (Table 11). Recovery percentages were calculated by dividing the ammoniac-N concentrations (X100) of the unspiked, diluted waters by the respective negative x intercepts extrapolated from the regression equations (Table 11). For each method, the ammonia spike recoveries were linear, but the recoveries were closest to stoichiometric for the colorimetric and enzymatic methods (98.5% and 99.1%, respectively). This indicated that these two methods were unaffected by positive or negative interferences. In contrast, the recovery for the distillation method was high, probably because of positive interference by other distillable bases such as aromatic amines and N-heterocycles. The recovery for the RPF-C/CL method was even higher, almost certainly because of positive interference by polar nitrogenous solutes (e.g., hydroxylated Nheterocycles, low-molecular-weight nitriles, and cyanates). Accuracy a n d Precision, The mean ammoniac-N concentrations and relative standard deviations (RSDs) obtained for each of the 12 waters and composite sample using each of the four methods are presented in Table 111;the waters are listed in descending order of concentration. Because of the
ANALYTICAL CHEMISTRY, VOL. 58, NO. 7, JUNE 1986
Table 11. Standard Additions: Recovery of Ammonia from Composite Oil Shale Process Water Spiked with Ammonium Sulfate" method noab
m
b
r2
zero % spikec recoveryd
1: distillation/
1.037 341.1 0.998 348.7 titrimetry 0.987 33.05 0.999 32.99 2: colorimetry 1.32 0.990 1.34 3: enzymatic analysis 0.977 1.122 36.52 0.986 37.02 4: RPF-C/CL
106.0 98.5 99.1 113.7
" Regression equations (excluding zero spike) for amount of ammoniac-N recovered vs. amount added; n = regression coefficient (slope), b = y-intercept, r2 = coefficient of determination. bAmmoniac-N spike levels for each method were 1 (100, 200, 300, 400, and 500 mg/L), 2 and 4 (10, 20, 25, 40, and 50 mg/L), and 3 (0.25, 0.50, 0.80, 1.00, and 1.25 mg/L); n = 3 for each spike level. Ammoniac-N concentration of unspiked, diluted composite sample (see Table I11 for undiluted concentrations); n = 3. (Value of zero spike divided by extrapolated x intercept) X 100 (Le., ( b / m )X 100).
large range in concentrations among waters (1-33 g/L), the RSDs were preferred over the standard deviations as estimates of precision. The RSDs ranged from 0.2 to 5.3%. Precision was best for the titrimetric and colorimetric methods (RSDs < 1%); RPF-C/CL had the greatest imprecision, responsible for three of the four samples with RSDs > 3%. All methods, except for the enzymatic method, were most imprecise for the composite sample. Of the first six waters listed in Table 111, all were from above-ground, surface retort processes or from gas condensates of in situ processes. Both of these types of waste streams would indeed be expected to have greater solute concentrations than would the water streams from in situ processes (the last six waters with the exception of Tosco HSP), which can become diluted by input stream or mine drainage water. The composite sample was used to check the internal consistency of each method by comparing its value with the respective grand mean from the 12 waters. The composite values were 102%, 99%, 95%, and 92% of the respective grand means for methods 1-4, respectively (see Table I1 for method numbers). For method 4 (RPF-C/CL), the composite value was lower than the grand mean probably because of a lower overall concentration of polar nitrogenous compounds than present in the more concentrated Paraho and LANL samples; this is a function of the fractionation process (10). The enzymatic method yielded a lower composite value than the grand mean possibly because of the presence of negative interferences in
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at least one of the constituent waters. The absolute concentrations (Le., accuracy) determined for these water samples are of unknown significance because of the aged nature of the samples and their varied storage conditions. This is particularly important because of the high pH and alkalinity, characteristic of retort waters (3,18). Ahern (19) noted that for a tar-sand water, acidified samples when stored yielded higher ammonia values, probably because of lessened volatilization. We have noted together with others, however, that acidification of these alkaline retort waters requires the addition of large amounts of acid and produces much precipitate, including elemental sulfur and organic acids (19,20). No judgment can be made with respect to the true values of ammonia that occurred in these waters when they were produced. Although these samples had been stored in closed containers at 4 "C, the elevated pH undoubtedly led to the gradual loss of ammonia to available headspace from repeated opening and closing of containers over a period of years. This cannot explain, however, the discrepancy between some of the ammoniac-N values in Table I11 and the corresponding total-N values previously reported (9);some of the ammoniac-N values were larger than the reported total-N values. Mean concentrations determined on different days for a water sample were found to vary because subsamples were obtained from different storage lots and because of degassing during subsample storage. Degassing is probably a major cause of discrepancies in interlaboratory comparisons. A multimethod interlaboratory comparison reported for Omega-9 retort water gave a best value for NH,-N of 3125 mg/L (20). Wallace and co-workers ( 3 , 4 )reported values from different methods of 3110-3600 mg/L for Omega-9. The values reported here for Omega-9 ranged from 3570 to 3790 mg/L. It is not known, however, whether each of these samples of Omega-9 came from the same grab sample. Interlaboratory comparison values far other waters are not available, although one multimethod study has been reported for a tar-sand wastewater (19). Other NH3-N values (mg/L) that have been reported (3,4)for the waters of this study generally fall within the ranges in Table I11 Paraho (26400),Oxy-6 gas condensate (6870-8600), and Oxy-6 retort water (1060-1130). Statistical Comparison. For a given water, the colorimetric and RPF-C/CL methods yielded the lowest and highest concentrations, respectively (Table 111). With only one exception, colorimetry yielded lower values than distillation/titrimetry; this is the opposite of the finding of Ahern (19) for a tar-sand water. In general, the enzymatic and
Table 111. Comparison of Four Methods for Determining Ammoniac-N" in Filtered Oil Shale Wastewaters process water
acidimetric titrimetryb
phenate colorimetryb
enzymatic analysisc
RPF-C/CL'
Paraho LANL 150-Ton Oxy-78~8 OXY-6gc s-55 Omega-9 Tosco HSP Oxy-6 rw (nc) Geokinetlcs-9 Oxy-6 rw Rio Blanco
25 500 (0.60) 14490 (0.46) 10240 (0.66) 9 110 (0.34) 7 060 (0.64) 4160 (0.42) 3 650 (0.56) 2 330 (0.98) 2 000 (0.68) 1578 (0.43) 1108 (0.69) 1056 (0.66)
25400 (0.55) 13540 (0.52) 10 500 (0.42) 8800 (0.49) 6730 (0.63) 4080 (0.56) 3570 (0.49) 2 220 (0.99) 1920 (0.70) 1426 (0.49) 1094 (0.31) 1012 (0.69)
25000 (2.80) 14800 (0.95) 12000 (1.16) 9400 (1.20) 6960 (1.05) 4 250 (1.65) 3630 (0.50) 2290 (0.23) 2200 (1.44) 1550 (1.31) 1190 (2.23) 1040 (4.33)
32 700 (1.58) 17200 (0.43) 11700 (1.96) 9600 (1.54) 7 330 (1.29) 5050 (3.38) 3 790 (1.98) 2670 (0.93) 2 140 (1.50) 1790 (1.32) 1260 (3.12) 1240 (1.43)
grand meand 6 856 6 692 7030 78 400 032 (5.26) 6600 (1.20) 6700 (0.41) compositee 7 000 (1.79) a All values are arithmetic mean concentrations (mg of N/L) and percentage relative standard deviations (in parentheses) for sample filtrates from 0.4-pm-pore-diameter polycarbonate membranes. n = 5. n = 3. dArithmetic mean of all replicate values for all 12 waters. e Equal-volume composite sample of all 12 waters; n = 3.
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ANALYTICAL CHEMISTRY, VOL. 58, NO. 7, JUNE 1986 0.12
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Flgure 1. Ammoniac-N (mg/L) concentrations (log transformed means) and 95% Confidence intervals (log transformed data) for 12 oil shale wastewaters and composite water: Distillation/titrimetry (U), phenate colorimetry (O),enzymatic analysis (A),and RPF-C/CL (0). The means from each data set were normalized to their respective colorlmetric means by subtraction.
RPF-C/CL methods yielded respectively figher Values. With only two exceptions (both from the enzymatic method), each of the values from methods 1-3 was lower than the respective RPF-C/CL values. This would be expected because the RPF-C/CL method is an estimate of polar nitrogenous species, which include oxygenated organonitrogen compounds (10). Although each of the four methods used totally different principles of detection, statements regarding the accuracy of the ammoniac-N concentrations cannot be made because the "true" concentrations are unknown. The results of the four methods were compared with one another, however, to determine if significant differences existed between the methods. For the following discussion, a "data set" is defined as the results obtained from one method applied to one water. For all data sets, the variances correlated positively with the , tests showed several instances of means. Furthermore, F significant differences (P C 0.05) between pairs of data set variances. Transformation of the data (common logarithms) did not eliminate the dependence of the variance on the mean. Since this violates an assumption of some parametric statistics (e.g., ANOVA and Student's t test), the approximate t test (i.e., t 3 was used; the SRB multiple test procedure was then used for significance testing of the null hypothesis associated with the paired comparisons for each water. Results of the SRB paired method comparisons are in Table IV. For 8 of the 13 waters, the majority of the paired comparisons yielded significant differences (P < 0.05). For each paired comparison of methods (except for the titrimetric-enzymatic comparison), a majority of waters yielded significant differences (P 0.05). Only one-third of the individual comparisons showed no significant difference (P> 0.05). For two waters (LANL and Tosco HSP), all of the paired comparisons showed a significant difference (P < 0.05). Furthermore, significant differences (P < 0.05) existed for five of the six paired comparisons for four other waters (150-Ton, Oxy-6 gas condensate, Oxy-6 retort water (noncomposite), and Geokinetics-9); the only paired comparisons that were not significantly different (P> 0.05) for these waters were titrimetry X enzymatic analysis and enzymatic analysis X RPF-C/CL. Only for Oxy-6 retort water and the composite sample were no significant differences (P
Table Iv. &suits of Sequentially Rejective Bonferroni Multiple Test Procedure on Paired Comparison Analysis of Intermethod Ammonia Data process water
paired methoda comparisons* 1x2 1x3 1x4 2x3 2x4 3x4
-
Omega-9 Tosco HSP Oxy6 rw (nc) Geokinetics-9 Oxy-6 rw Rio Blanco
+ ++ + + t + + + +
+ -+ + + -
+ + ++ + + + + +
+ ++ + + + + -
+ ++ + + + + + +
+ -+ ++ + +
composite
-
-
-
-
-
-
Paraho LANL 150-Ton Oxy7&8 OXY-6gc s-55
-
+
t
Method identification numbers correspond to those in Table I. *No significant difference (P > 0.05) denoted by minus (-); significant difference ( P C 0.05) denoted by plus (+).
> 0.05) found for any paired comparison. The comparisons that yielded the highest number of significant differences were titrimetry X colorimetry and colorimetry X RPF-C/CL. The results from Fisher's test showed that paired comparisons of methods across all waters differed significantly (P C 0.05). The titmetry X enzymatic analysis comparison, however, did not differ significantly at a! = 0.01; this comparison differed significantly only for 4 of the 13 waters. Comparison of the data is most easily visualized in Figure 1, where the means and 95% confidence intervals (calculated on log transformed data) are presented for each water; each data set is normalized to the respective colorimetric mean. Here it can be seen that the best agreement between methods Qccursfor the titrimetric and enzymatic methods, corroborating the statistical findings. The titrimetric and colorimetric means also show close agreement, but since their confidence intervals overlap in only one instance (a result of their low variances, or RSDs), significant differences were shown for
Anal. Chem. 1988, 58,1561-1563
means that looked similar (e.g., Omega-9 and Oxy-6 retort water). Conversely, other means that did not appear to be in agreement, such as some of those from the RPF-C/CL method, could not be shown to differ significantly because of one or two large variances. From the data reported here, no recommendation can be made on a statistical basis for not using any of the three modified “standard” methods for accurately measuring ammonia in retort waters. From a practical point of view, however, we feel that any of these three methods would be satisfactory for use a t retort facilities or treatment plants for routine monitoring. For these methods, the largest discrepancy in the grand means (Table 111) existed for colorimetry and the highly specific enzymatic method; they differed, however, by only 5%. This contradicts the recommendation of Wallace and Alden (3) that phenate colorimetry not be used for synfuel wastes because the values were 31% higher thari those from ion chromatography. The only problem that we sporadically encountered with the colorimetric method was one of high background absorbances; this problem could not be traced to glassware or reagents. Although the RPF-C/CL rapid estimate was significantly different from the other methods for most of the waters and it was more imprecise, its speed would be useful in range finding for other methods or for spot monitoring. It should be noted that another ammonia removal technique, nonosmotic dissolved gas dialysis (10) also could be coupled with the C/CL rapid detection method (after modification) for rapid determination of ammonia.
ACKNOWLEDGMENT We thank Adele Cutler and Richard Cutler (University of California, Berkeley, Statistics Department Consulting Service) for help with application of the statistical analysis procedures. Registry No. NH3, 7664-41-7;NH4+,14798-03-9;HzO, 773218-5.
LITERATURE CITED (1) 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., Ed.;
1581
Lawrence Berkeley Laboratdry: Berkeley, CA, 1984; Chapter IV, LBL-17421 (NTIS DE84015967/NAB). Cooper, J. E.; Evans, W. S. Science (Washington,D . C . ) 1983, 219, 492-493. Wallace, J. R.; Alden, t.Methods of Chemical Analysis for Ionic Constltuents In Synfuel Wastewaters, final report for DOE Contract DEAS20-82LC10934; Denver Research Institute, University of Denver: Denver, C O 1984; pp 28-37, 47. Wallace, J. R.; Alden, L.; Bonomo, F. S.; Nlchols, 3.; Sexton, E. Methods of Chemical Analysis for 011 Shale Wastes, NTIS Order PB 84-21 1 226; Denver Research Institute, University of Denver: Denver, CO; 1982; Chapter 5. APHA Standard Methods for the Examlnation of Water and Wastewater, 15th ed.; American Public Health Association, American Water Works Association, Water Pollution Control Federation: Washington, DC, 1981; pp 16-17, 355-362. Johnson, A. H.; Green J. R. Ind. Eng. Chem., Anal. Ed. 1930, 2 , 2-4. Weatherburn, M. W. Anal. Chem. 1967, 39, 971-974. Kun, E.; Kearney, E. B. I n Methods of Enzymatic Analysis; 2nd English ed.; Bergmeyer, H. U., Ed.; Verlag Chemie Weinheim, Academic Press: New York, 1974; Vol4. pp 1802-1806. Jones, B. Id.; Daughton, C. G. Anal. Chem. 1985, 5 7 , 2320-2325. Daughton, C. G.; Jones, B. M.; Sakaji, R. H. Anal. Chem. 1985, 57, 2326-2333. Langlois, G. W.; Jones, 8. M.; SakaJI, R. H.; Daughton, C. G. J. Test. €vel. 1984, 12, 227-237. Stover, N. M.; Sandin, R. B. Ind. Eng. Chem., Anal. Ed. 1931, 3 , 240-242. Wagner, E. C. Ind. Eng. Chem., Anal. Ed. 1940, 12, 771-772. Schmidt, E.; Schmidt, F. W. I n Methods of Enzymatic Analysis, 3rd ed.; Bergmeyer, H. U., Ed.; Verlag Chemie: Deerfield Beach, FL, 1983; VOI. 111, pp 218-227. Sokal, R. R.; Rohlf, F. J. Siometty; W. H. Freeman and Co.: San Franclsco, CA, 1969; pp 246-249, 374-376. Holm, S. Scand. J. Statlstlcs 1979. 6 , 65-70. Fisher, Sir. R. A. Statlstlcal Methods for Research Workers, 14th ed.; Hafner: New York, 1973; pp 99-101. Healy, J. B., Jr.; Langlols. 0. W.; Daughton, C. G. Water Res. 1985, 19, 1429-1435. Ahern, J. J. MUM-Method, Multi-lab Study of a Tar-Sand Water Sample ; Wyoming Water Research Center, University of Wyoming: Laramie, WY, 1984; NTIS DE85003373. Farrier, D. S.; Poulson, R. E.; Fox, J. P. I n Oil Shale Symposlum: Sampling, Analysis and Ouallty Assurance; Gale, C., Ed.; IERL, US. EPA Clnclnnatl, OH, 1979; pp 182-210 (EPA-600/9-80-022).
RECEIVED for review December 2,1985. Accepted February 10,1986. This work was supported by the Assistant Secretary for Fossil Energy, Office of Oil Shale, Division of Oil, Gas, and Shale TechnoIogy, of the U S . Department of Energy under Contact DE-AC03-76SF00098.
Measurement and Control of Water Content of Organic Solvents H. L. Goderis,* B. L. Fouwe, S. M. Van Cauwenbergh, and P. P. Tobback Laboratory of Food Technology, Catholic University of Leuven, Kardinaal Mercierlaan 92, 3030 Heverlee, Belgium
An isotopk dilution procedure is described for the quantitative determination of the solubility of water in organic solvents as a function of the relative humidity at which the sample is equilibrated. ‘H,O Is used as a tracer, and the relative humidity conditions are realized by Incubation of the organic solvent above a saturated salt solution having a known water activlty. The technique is applicable independent of the concentration range of water present, the minimum amount of moisture being only limited by the concentration of the trltium label used. Solubility isotherms of water in hydrocarbon solvents such as n-hexane are sigmoldal in shape, reflecting cooperative effects in the soiubiliraition of water molecules at the higher relative humidity portion of the curve. Solubility increases with Increasing temperature. 0003-2700/86/0358-1561$01.50/0
For a number of technological applications, knowledge as well as precise control of the amount of water present in an organic solvent is very important. A large number of methods for the measurement of water content of solvents have been put forward, especially for those applications where water is present at about the 1 % level (1-4). Determination of very low amounts of water, however, such as those present in liquid hydrocarbons, suffers from the drawback of tedious methods, which are most often complex in nature and most of the time approximative (5). Moreover, a technique for the equilibration of an organic solvent at a given relative humidity and for measurement of the water present under these circumstances has never been described. This paper describes a simple method for the determination 0 1986 American Chemical Society
