Chemiluminescence vs. Kjeldahl determination of nitrogen in oil shale

Oil shale retort water ammonia determination by titrimetry, phenate colorimetry, enzymatic analysis, and chromatographic fractionation/chemiluminescen...
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Anal. Chem. 1985,57,2320-2325

Chemiluminescence vs. Kjeldahl Determination of Nitrogen in Oil Shale Retort Waters and Organonitrogen Compounds Bonnie M. Jones1

Applied Science Division, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720 Christian G. Daughton*

Sanitary Engineering and Environmental Health Research Laboratory, University of California (Berkeley), Richmond, California 94804

The appllcablllty of combustion/chemilumlnescent nitrogen analysls to quantifying nltrogen In oil shale wastewaters and various representatlve chemlcal classes was demonstrated. Only azoxy compounds and those contalnlng the pyrazole nucleus were not amenable to analysis. The majority of 56 compounds tested ylelded from 90 % to 110 % of thelr theoretlcal nltrogen contents; enhanced recovery was found for nitrogen oxide salts. For 12 oll shale wastewaters, combustlon/chemilumlnescence gave total nltrogen values (1100-28800 mg/L) that dld not differ statistically ( P > 0.10) from those obtalned by the tlme-consumlng wet-chemlcal Kjeldahl method. The relative standard devlatlons for ten replicates of each wastewater were less than 3.5%. No matrix or solvent effects were found.

Pyrolysis of oil shale kerogen yields a petroleum-like crude oil and byproducts, including retorted (spent) shale, gases, and wastewaters. Most of the wastewater (retort water) is condensed with the product oil from which it is separated; the remaining water (gas condensate) is condensed from a gaseous stream. Although it is possible that this contamination could be minimized by limiting the oil/water contact time, the retort waters that have been available from pilotscale facilities are highly contaminated with a complex spectrum of inorganic and organic solutes and suspended matter. Hydrophilic contaminants include: ammonia; carbonates; thiocyanate; aliphatic and aromatic carboxylic acids; aliphatic amides, nitriles, amines, alcohols, ketones, and aldehydes; and hydroxylated and oxygenated N-heterocycles. Lipophilic contaminants include phenols, aromatic primary amines, neutral N-heterocycles, and fused-ring N-heterocycles (1-3). The more volatile, neutral species, predominantly inorganic gases and low-molecular-weight organic compounds, are primarily associated with the gas condensate. Ammonia concentrations in these wastewaters range from 1100 to 26000 mg of N / L (4). The organic N, although orders of magnitude lower in concentration than ammoniac N, would be an important determinant in the success of biological treatment schemes because it is associated with a large portion of the organic carbon (5,6), A rapid method for total nitrogen will be essential for the frequent assessment of waste treatment processes designed to remove inorganic and organic nitrogenous compounds from these aqueous waste streams. Since a shale oil industry has not reached commercialization, and since retort wastewaters are not similar to presently known waste streams, many of the air and water regulations Present address: Department of Public Works, City and County of San Francisco, 750 Phelps St., San Francisco, CA 94124-1091.

that may eventually be required do not currently exist. Of particular concern are the numerous organonitrogen compounds (ONCs), which impart much of the characteristic color and noxious odor to retort waters and have mutagenic potential (7). Since the analysis of waters for the individual nitrogenous solutes would require complex chromatographic techniques, routine monitoring by the government and synfuels industry would be aided by a simple and rapid method for total N that could then be applied to individual fractions of solutes. Quantification of total N in solid and aqueous samples has traditionally been accomplished by using the time-consuming wet-chemical Kjeldahl method, which was developed specifically for proteinaceous nitrogen. Its applicability to samples of nonbiological origin has major failings, including the incomplete recovery of nitrogen from many N-heterocycles (8). More rigorous methods exist (e.g., Dumas), but they are even more time-consuming. During the last decade, a new approach has been developed for the quantification of total N based on combustion of the sample followed by reaction with ozone and chemiluminescent detection (9). Samples are first combusted in an oxygen atmosphere a t 1100 "C, and under the proper conditions, nitrogen is released as nitric oxide (NO), which is reacted with ozone to yield either nitrogen dioxide (NO,) or electronically excited nitrogen dioxide (NO2*). The light emitted during relaxation of the metastable NOz* (600-3000 nm, with a maximum near 1200 nm (10))is then amplified by a photomultiplier tube that is sensitive to long wavelengths. A 650to 900-nm band-pass filter eliminates chemiluminescent interference by unsaturated hydrocarbons, chlorine, and sulfur, all of which react with O3but emit light of shorter wavelengths. The principles of operation for commercial analyzers that use this method have been discussed (9, 11). A method for total N that is rapid and reproducible and can be automated has tremendous advantages compared with wet-chemical Kjeldahl analysis. Snodgrass (12) reports that for fertilizer processing wastewater, the sum of total Kjeldahl nitrogen (TKN) and NO3 N equals the total nitrogen (TN) yielded by combustion/chemiluminescent analysis (C/CL). Similarly, Clifford and McGaughey (10) report excellent agreement between C/CL and wet-chemical methods (Le., s u m of TKN, NO3 N, and NO2 N) for a domestic/industrial wastewater sample. For aqueous biological and clinical samples (rat urine and human urine and feces), Ward et al. (13) find no significant difference between C/CL and a Kjeldahl method that uses a mixed CuS04/SeOp catalyst. For the distillate fraction of shale oil, Drushel (9) notes that C/CIJ results are approximately 10% higher than those from Kjeldahl analysis, He attributes this to incomplete recovery by the Kjeldahl method for some of the refractory ONCs in shale oil rather than to a fundamental problem with the C/CL

0003-2700/85/0357-2320$01.50/00 1985 American Chemical Society

ANALYTICAL CHEMISTRY, VOL. 57, NO. 12, OCTOBER 1985 Combustion Tube (1100°C)

GL,-/-3 /

, ,

A-N

+ 0,

7

\

NO

+ CO, + H,O

Ozone Generatoi

0,)

--(NO,, --(NO2,

J U I L ' U ' J0. O 0, + +NNO ,

O N

,

:

>

0,

1NO.i

L

650.900 nm

I

+

-

HP 975

t

jandpass hv

:;::!:

6CD

PMT

+ NO: Chemiluminescent Detector

Figure 1. Reaction schematic of a chemiluminescence total-nitrogen analyzer (Antek Model 703C).

method of analysis. In this report, we compare TKN and C/CL for the recovery of nitrogen from oil shale process waters and from individual compounds of representative chemical classes.

EXPERIMENTAL SECTION C/CL. The C/CL nitrogen analyzer was obtained from Antek Instruments (Model 703C; Houston, TX). A 5-pL liquid sample was injected (10-pL septum-piercing syringe) through a Teflonlined silicone rubber septum at a constant rate of 1.2 pL/s using a syringe pump (Model 735, Antek Instruments, Inc., Houston, TX). The sample was swept through an orifice and delivered as an aerosol into a quartz combustion tube that was packed with quartz Raschig rings and maintained at 1100 "C. Oxygen was delivered to the combustion tube at two points: as carrier gas (100 cm3/min) for sweeping the sample through the injection port and orifice, and as combustion gas within the combustion zone (275 cm3/min) (Figure 1). The integrated amplified binary output of the voltage signal from the detector was coded into decimal (BCD) and was received by a Hewlett-Packard (HP-97s) programmable printing desk-top calculator, which was programmed to perform the initial data manipulation. The detector-calculator interface was designed and made in-house (11). Except for replacing inert carrier gas (Ar) with oxygen to enhance combustion, the manufacturer's recommended procedures were followed for determining total N. Although replacing Ar with O2is safe for aqueous samples, care should be exercised when using these conditions for organic solvents. The reactions and gas flow rates are summarized in Figure 1. A detailed operator's protocol is available (11). Standard curves, used to correlate integrator counts with nitrogen concentration, were derived from ammonium sulfate standards. A stock solution (100 mg of N/L) was made from analytical reagent grade ammonium sulfate (dried at 105 "C). Dilutions were made by transferring the appropriate quantity of stock solution, using positive-displacement pipets, to a 10-mL class A volumetric flask and bringing to volume with ASTM type I water to yield standards of 20, 40, 60, 80, and 100 mg of N/L. Kjeldahl Analysis. The ASTM recommended procedure (14), using either the digestion solution (an acidic solution of potassium sulfate and mercuric sulfate) or the alternative premeasured reagent packet (Kel-Pak 5 ; now available as Kelmate N 500; EM Science, Gibbstown, NJ), was followed for all Kjeldahl analyses. Twenty-five milliliters of retort water or solutions of individual pure compounds and 100 mL of digestion solution (or 20 mL of concentrated H2S04and one Kelmate packet) were introduced into 800-mL Kjeldahl flasks. A 12-unit Labconco (Laboratory Construction Co., Kansas City, MO) combination distillation/ digestion rack was used to first digest the samples, and then the flasks were transferred to the upper portion of the rack for distillation. Ammonia captured in boric acid receiving solution during distillation was quantified by automatic titration (15) using a Sybron/Brinkmann autotitrator (Metrohm Model 655 Dosimat, E 526 titrator, 643 control unit/624 autosampler; Westbury, NY)

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to the methyl red/methylene blue colorimetric end point using a colorimeter with submersible fiberoptic probe (1cm path length) and 545-nm filter (Brinkmann PC 800). Organic Carbon. Carbon content of 3,5-dimethylpyrazolewas determined with a UV-peroxydisulfate low-temperature oxidative unit coupled with an automatic coulometric titrator (16). Chemicals. The nitrogen compounds used in the pure compound studies were the highest grades available commercially and were used without further purification; the sources and purities are listed in Table I. Solvents were either ASTM type I water, HPLC grade methanol, or nanograde toluene. Wastewater Samples. The origins of 9 of the 12 waters and some of the retorting process information have been reported (16); collection and initial storage conditions, however, were often unknown. After receipt, the samples were kept at 4 "C in polyethylene-lined 30- or 50-gallon drums or polyethylene reagent bottles. TOSCO HSP retort water was provided directly by The Oil Shale Co. (TOSCO, Golden, CO). LANL retort water was supplied in June 1983by Los Alamos National Laboratory; it was an equal volume composite from their bench-scale retort (runs 33, 35, 36, 41, 46, 51, 64, 74, 79, and 88). The other ten waters were obtained from the Department of Energy's cold-storage facility in Laramie, WY. The Oxy-6 retort water noncomposite (nc) sample was taken from the same sampling point during burn 6 as the composite sample, but at a different time. Oxy-7&8gas condensate was collected simultaneously during modified in situ burns 7 and 8 at Occidental Oil Shale Company's Logan Wash site in 1982. The 12 waters ranged from a relatively dilute sour water (dissolvedorganic carbon concentration of about 200 mg/L) to an extremely concentrated direct-mode retort water (dissolved organic carbon concentration of over 42 000 mg/L). Sample Preparation. To investigate the effect of solvent on recovery of nitrogen by C/CL, standard curves between 20 and 100 mg of N/L were produced for 2,4,6-trimethylpyridine(in either toluene or water), ammonium sulfate (in ASTM type I water), and 9-methylcarbazole(in toluene). These solutions were prepared from 1000 mg of N/L stock solutions by dilution of portions that were measured with positive-displacement pipets into class A 10-mL volumetric flasks. For the pure-compound C/CL study, each of 56 compounds was placed in a class A volumetric flask (25 to 100 mL) and weighed with a semimicro analytical balance (Mettler HL52); the amount of each compound was chosen to yield standard solutions of approximately 80 mg of N/L. The solutions were made to volume with ASTM type I water, except for 4,4'-azoxyanisole, 1,5-dimethyltetrazole,2,5-dimethyl-1,3,4-thiadiazole, indazole, 0-, rn-,and p-nitrophenol, 6-nitroquinoline, and quinoline (each in methanol) and carbazole, 9-methylcarbazole, indole, and isoquinoline (each in toluene). For the pure-compound TKN study, 25-mL portions of 1 2 of these solutions were added directly to Kjeldahl flasks; for five other compounds (4-amino-2,3-dimethyl-l-phenyl-3-pyrazolin-5-one, 3,5-dimethylpyrazole,pyrazole, cyanuric acid, and nicotinic acid), 1.5-mL samples were drawn from 1000 mg of N/L stock solutions in ASTM type I water and were added directly to Kjeldahl flasks. Stock solutions were stored at 4 "C in 25-mL glass scintillation vials with Teflon-lined screw caps; working samples were stored at 4 "C in either 25-mL glass scintillation vials or 100-mL glass reagent bottles, both with Teflon-lined screw caps. Sample Analysis. For the C/CL pure-compound study, three single-operatorreplicates of each of the 56 solutions were analyzed. For the Kjeldahl study, two to four replicates of each of the 17 solutions were analyzed, and their TKN values were compared with the total nitrogen (TN) values from C/CL. To determine if the oil shale process waters exerted a matrix effect, a standard-additions study was designed to compare TKN and T N values. A composite sample of unfiltered oil shale process waters (equal volumes of nine of the process waters) was diluted 1part in 200 so that the nitrogen concentration was approximately 35 mg/L. Nicotinic acid was added to samples of the diluted composite water so that the spike levels of nitrogen were 15, 35, and 55 mg of N/L. The final total N concentrations of these spiked samples were 50, 70, and 90 mg of N/L. To compare T N and TKN values for different retort waters and to determine method imprecision, samples of each of 12 oil shale process wastewaters and the composite sample were pressure

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ANALYTICAL CHEMISTRY, VOL. 57, NO. 12, OCTOBER 1985

Table I. Sources and Purities" of Nitrogen Compounds Aldrich, Milwaukee, WI 4,4'-azoxyanisole (NAb) 2,3-dimethyl-l-(4-methylphenyl)-3-pyrazolin-5-one (99+ % ) 3,5-dimethylpyrazole-l-carboxamide(NA)

1,5-dimethyltetrazole (97+%) 2,5-dimethyl-1,3,4-thiadiazole (99%) 2-hydroxy-6-methylpyridine(9770) 2-hydroxypyridine (97%) 3-hydroxypyridine (97%) imidazole (99%) indazole (98%) 1-methyl-2-piperidone (99%) 1-methyl-2-pyrrolidone (99+ % ) 6-nitroquinoline (98%) piperazine (99%) pyrazine (99+%) pyrazole (98%) pyridazine (97%) Alfa Products, Danvers, MA piperidine (98%) J. T. Baker, Phillipsburg, NJ

acetonitrile (HPLC grade) diethanolamine (99.9%) potassium nitrate (AR grade) Burdick & Jackson, Muskegon, MI N,N-dimethylformamide (HPLC grade) Calbiochem-Behring, La Jolla, CA nicotinic acid (NA) Carnegie-Mellon University, Pittsburgh, PA

Crescent Chemical, Hauppauge, NY 1-methylpyrrole (99%) Eastman Organic Chemicals, Rochester, NY o-nitrophenol (NA) m-nitrophenol (NA) p-nitrophenol (98%) Fisher, Fair Lawn, NJ glycine (NA) Fluka AG, Buchs, Switzerland 5-ethyl-2-methylpyridine(NA)

Hellige, Garden City, NJ nitrite salt solution (50 mg of N/L) urea (NA) MalIinckrodt, St. Louis, MO 4-amino-2,3-dimethyl-l-phenyl-3-pyrazolin-5-one (NA)

Matheson Coleman & Bell, East Rutherford, NJ ethylenedinitrilotetraacetic acid (NA)

NOAH Chemical, Farmingdale, NY 3-ethyl-4methylpyridine (NA) 4-ethyl-3-methylpyridine (NA) 2-ethylpyridine (NA) 3-ethylpyridine (NA) 4-ethylpyridine (NA) 2-n-propylpyridine (NA) 2,3,6-trimethylpyridine (NA)

9-methylcarbazole (NA) Chem Service, West Chester, PA benzimidazole (NA) carbazole (99+%) cyanuric acid (NA) 3,5-dimethylpyrazole (99%) 2,4-dimethylpyridine (NA) 8,6-dimethylpyridine (NA) indole (99+% ) isoquinoline (NA) 2-methylpiperidine (95%) 2-methylpyrazine (99%) 8-methylpyridine (NA) 3-methylpyridine (NA) 4-methylpyridine (99%) pyridine (99%) quinoline (NA) 2,4,6-trimethylpyridine (99%) a

Purities given in parentheses. bNot available.

filtered (0.4-kmpore-diameter polycarbonate membranes; Bio-Rad Laboratories, Richmond, CA) and diluted to yield nitrogen concentrations between 30 and 75 mg/L to OW for statistical testing by analysis of variance. These samples were stored in a manner identical with the standards. Ten single-operator replicates of each process water sample were analyzed by CJCL, and three single-operator replicates were analyzed by the Kjeldahl method. Statistical Analyses. All statistical analyses were based on the appropriate sections in Rohlf and Sokal(17) and Sokal and Rohlf (18).

RESULTS A N D D I S C U S S I O N Solvent Effects. Water has been reported to depress detection of nitrogen with C/CL by lowering the combustion-tube orifice temperature (9), quenching the chemiluminescence, and contributing to two- and three-body reactions (10, 19, 20). An 1100 "C furnace mitigates t h e effect of burner-tip temperature depression by aqueous samples;

elimination of the inert-carrier-gas component (e.g., Ar) and increase in the total oxygen flow rate promote recovery of nitrogen from biological and aqueous samples (13). The h t e k 7 0 3 nitrogen ~ analyzer a membrane dryer to eliminate water from the combusted gas stream and thereby minimizes quenching' The slopes of standard curves between 20 and 100 mg of N/L (attenuation = 20) for 2,4,6-trimethylpyridine in either toluene or water were nearly identical: 6.07 X lo6 and 6.14 X lo6 counts/mg of N, respectively. These slopes were nearly the same as those for ammonium sulfate in water and 9methylcarbazole in toluene: 6.08 X lo6 and 6.07 X lo6 counts/mg of N, respectively. Compounds dissolved in methanol (quinoline and 6-nitroquinoline) did not exhibit a different response when compared with an ammonium sulfate standard in water. These results indicated that water does not significantly interfere with sample combustion or with

ANALYTICAL CHEMISTRY, VOL. 57, NO. 12, OCTOBER 1985

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Table 11. Percent Recovery of Nitrogen from Solutions of Pure Compounds by Combustion/Chemiluminescence (C/CL)and Total Kjeidahl Nitrogen ( T K N )Analysis

0 I1 H2N--C--NH2

“-4’ -C=N

Q

Oo Qi=NQ

Canpound

mean

potasslu nltrate nitrlte salt standard pnltrophenol r n IttophenoI pnltrophenol g Iyclne

waa

TKNP range

range

mean

114 122 95 102 106 110

(112-116) (120-122) (91- 98) (101-106) (103-107) (106-113)

n 6 57 51 nt

urea d I ethano I rn I ne ethylenedlnltrllotetraacetlc acld bl.N-d Imthy I forvr I de acetonitrile 1-methyipyrrole

104 102 90 104 101 100

(100-108) (99-103) (87- 93) (104-105) (101-101) (95-103)

nt nt nt nt nt nt

l-methyl-2-pyrrolldone tndole carbazole 9-methylcarbazole 4.4r-azoxyani sole pyrazole

112 99 100 98 41 15

(110-114) (92-104) (99-101) (95-100) (39- 41) (13- 16)

nt nt nt nt 71 16

12 54

( 1 1 - 12) (53- 56)

17 nt

(17- 18)

&

(53- 63) (49- 53)

(70- 72) (15- 16)

3.5-dlmethylpyrazole 3.5-dlnethylpyrazol~l-carboxaide 4-an1n0-2~3-dImethyl-l-phenyI3-pyrazollw-5-one 2.3-dlmethy I-l-(4-methyI pheny 1 ) 3-pyrazollw5-one I ndazol e 2r5-dImethyl-l.3.4-thiadlazoIe

99

(98-102)

48

(47- 50)

78 34 109

(77- 79) (32- 37) (108-110)

81 47 8

(80- 81) (46- 47) (7- 8 )

I m I dazol e benzImIdazole 1.5-dlmethyltetrazole py r I d I ne P-methyI pyr I d I ne 3-methy I pyr Id I ne

100 105 47 94 98 103

( 98-101) ( 103-1 09)

25 nt

(24- 25)

(46- 49)

46

(91- 96) (96- 99) ( 101-1 04)

84 nt nt

(45- 46) (83- 8 4 )

4-methyI pyr 1 d 1 ne 2.4-dlmethylpyrldlne 2.6-dlmethylpyrldlne 2r316-trImethyIpyridlne 2r416-trlmethyIpyrIdlne 2-ethylpyridlne

98 106 101 106 101 98

(95- 99) (105-108) (101-101) (105-107) ( 98-104) (94- 99)

nt nt nt nt nt nt

3-ethylpyrldlne 4-ethylpyrldlne 2-n-propy I pyr I d I ne 5-ethyl-2-methylpyrldlne

99 100 100 104 109 102

(98-102) (98-102) (98-101) ( 1 00-108) (108-110) (95-108)

nt nt nt nt nt nt

2-hydroxypyridlne 3-hydroxypyrldlne 2-hydroxy-6-methylpyrldlne nlcotlnlc acld pl per 1 dl ne 2-mthylplperldlne

99 101 109 104 nt 106

( 95-1 01 1 (99-104) ( 108-1 10) ( 103-105) ( 105-107)

nt nt nt 99 87 nt

l-methyl-2-plperldone qulnol Ine lsoqulnol Ine 6-nltroqulnoline pyr ldaz lne pyraz I ne

106 106 108 102 93 102

(106-106) (106-106) (105-109) (99-104) ( 93-94) (100-102)

nt nt ‘nt nt 94 nt

2-methylpyrazlne p I peraz 1 ne cyanuric acld

105 97 103

( 105-105) ( 95-100) ( 103-105)

nt nt 102

3-ethyl-4-methylpyrldlne

4-ethyI-3-methylpyrldine

(97-101 1 (86- 88)

(92- 95)

( 101-102)

Values from three replicate injections. *Valuesfrom two to four replicate determinations. Not tested. Not detected.

nitrogen detection by chemiluminescence and that either toluene or methanol can be used interchangeably with water, as may be required by the solubility of the analyte. Pure Compounds: Recovery Study. To ensure that the C/CL method would be applicable to oil shale process waters, the recovery of nitrogen was evaluated for compounds reported to be both resistant to Kjeldahl digestion and prevalent in

oil shale process waters (pyridines and quinolines), as well as for compounds from other major classes of N-heterocycles. The majority of the 56 compounds tested yielded 90% to 110% of their theoretical nitrogen contents (Table 11). Preliminary studies indicated that 3,5-dimethylpyrazole either was refractory to high-temperature oxidation or did not yield nitric oxide; perhaps molecular nitrogen was the combustion

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ANALYTICAL CHEMISTRY, VOL. 57, NO. 12, OCTOBER 1985

product. Carbon analysis indicated 103% of theoretical carbon content. Recovery of nitrogen from three other related compounds (Table 11) confirmed the observation that the pyrazole nucleus gave low recovery. The important aspect of this chemical structure appears to be an N-N bond coupled with only one N=C double bond in a five-membered ring that is able to tautomerize. Less than 15% of the nitrogen was recovered from pyrazole, whereas 35% of the nitrogen was recovered from indazole (benzopyrazole). The four-membered unsaturated structure coupled with the five-membered pyrazole nucleus either slightly destabilized the compound or prevented tautomerization. Half of the nitrogen in tetrazole, a five-membered ring consisting of four nitrogen atoms and one carbon, was recovered by C/CL; the resistance to oxidation may be restricted only to the N=N double-bonded portion of the structure. In contrast to the resistance of pyrazole, complete recovery of nitrogen was obtained from pyridazine (six-membered ring with a resonant N-N bond), imidazole (five-membered ring with two nitrogen atoms, but without an N-N bond), 2,5dimethyl-1,3,4-thiadiazole(five-membered ring with an N-N bond, two N=C double bonds, and a sulfur substituted for a carbon atom in the 4-position of pyrazole; this substitution appears to prevent tautomerization), and 4-amino-2,3-dimethyl-l-phenyl-3-pyrazolin-5-one (4-aminoantipyrine;fivemembered ring with an N-N bond but without an N=C double bond). Curiously, only 78% recovery was observed from 2,3-dimethyl-l-(4-methylphenyl)-3-pyrazolin-5-one, which has a structure similar to 4-aminoantipyrine. Another compound from which recovery of nitrogen was incomplete was 4,4'-azoxyanisole. Azo compounds have been reported to be somewhat resistant to C/CL nitrogen analysis (9,2I), presumably because of liberation of the N=N moiety as molecular nitrogen. Complete recovery of nitrogen was observed, however, from organic nitro compounds. These results disagree with previous work, which reported from 73 to 92% recovery from nitrobenzene and nitrotoluene and 72 to 74% recovery from nitroso compounds (9). The response from inorganic nitrate and nitrite salts in this study was enhanced; apparent responses of 114% and 122% of actual nitrogen contents, respectively, were obtained. This is attributed to relatively higher efficiencies of conversion to NO because of the higher oxidation state of nitrogen oxide salts (IO). This may be a serious drawback for the application of C/CL methods to agricultural wastewaters or biological samples. Since inorganic nitrogen oxides, pyrazoles, and azoxy compounds are present a t insignificant concentrations in oil shale process wastewaters (3,22), the application of C/CL to the determination of nitrogen in oil shale wastewaters seemed justified. For the Kjeldahl method, only 3 of 17 compounds tested yielded greater than 90% recovery of their theoretical nitrogen contents (Table 11). Despite the reported resistance of nicotinic acid to Kjeldahl digestion (23), however, 99% of the theoretical nitrogen was recovered from this compound. Pyridazine and cyanuric acid also yielded more than 90% of their theoretical nitrogen values. Compounds containing the pyrazole nucleus and tetrazole, however, yielded only 15% to 79% of their theoretical nitrogen values. Imidazole and 2,5dimethyl-1,3,4-thiadiazoleyielded only 5% to 25% of their theoretical nitrogen. These results are not surprising, because the N-N linkage in pyrazolones and similar compounds has been reported as extraordinarily resistant to Kjeldahl digestion (24-27). None of the three nitrophenols yielded its theoretical nitrogen content. Approximately half of the nitrogen was recovered from m-nitrophenol and p-nitrophenol; o-nitrophenol was completely resistant to Kjeldahl analysis. Although the

Table 111. Determination of Total Nitrogen in Oil Shale Process Waters: Combustion/Chemiluminescence (TN) vs. Kjeldahl (TKN) RSD,

RSD,

process water

TN"

%

TKNb

%

70 diffr

Paraho LANL 150-Ton Oxy-7&8 OXY-6gc s-55 Omega-9 TOSCO HSP Oxy6 rw (nc) Geokinetics Oxy-6 rw Rio Blanco sour

28805 16157 10084 9676 6886 4196 3574 2826 2 145 1844 1313 1133

3.5 1.5

29661 15988 10453 9587 6985 4379 3698 2809 2016 1826 1349 1074

1.9 3.9

-1.1

1.3

1.7 3.5 2.1 1.9 2.6 1.5 2.1

1.8 3.4

1.2

1.4 1.9 2.3 1.3 1.7 7.2 0.5

0.9 1.5

Mean of 10 replicates. *Mean of three replicates. TN)/(TKN)] X 100.

2.9 3.5 -0.9 1.4 4.2 3.4 -0.6 -6.4 -1.0 2.7 -5.5 [(TKN -

purity of o-nitrophenol was not known, full recovery of nitrogen was obtained by C/CL, indicating that the compound was in fact resistant to Kjeldahl digestion. These results do not agree with earlier work on nitroaromatic compounds; Margosches and co-workers, in 1919 to 1923 (cited in ref 8), tried to develop a correlation between the recovery of nitrogen and the position of substituent groups in mononitro compounds. They found that only ortho substituents could be determined without modification of the standard Kjeldahl digestion procedure. By the addition of 1 g of salicylic acid, as a reducing agent, meta nitro groups could be recovered, but para nitro groups remained resistant. The reasons for the discrepancy between these results and ours are unknown. In general, the Kjeldahl method gave incomplete recovery of nitrogen for more compounds than did C/CL. Matrix Effects: Standard Additions. The addition of nicotinic acid to retort water to give various known concentrations was used to detect matrix effects. The recovery of nicotinic acid spikes from diluted composite samples ranged from 98% to 103% for C/CL and from 102% to 104% for the Kjeldahl method. The extrapolated x intercept values for amount recovered vs. amount added were within 5% of the respective zero-spike values indicating that matrix effects were minimal. For the diluted samples, the extrapolated x intercept for the C/CL method was 36.5 mg of N/L, and the zero-spike value was 38.6 mg of N/L. The extrapolated x intercept for the Kjeldahl method was 35.5 mg of N/L, and the zero-spike value was 34.3 mg of N/L. Total Nitrogen: Comparison of C/CL and Kjeldahl Analysis for Retort Waters. The values for T N were compared with those for T K N for 12 oil shale process waters. The values obtained by the two methods agreed remarkably well (Table 111). The difference in recovery of nitrogen by the two methods ranged from -6.4% to +4.2%. The relative standard deviation (RSD) values for T N were less than 3.5%, and those for T K N were generally less than 2.5%. The average T N and TKN values for the nine waters that comprised the composite water agreed with the actual T N and T K N values for that composite water (6740 and 6915 mg/L vs. 6712 and 7108 mg/L, respectively); this verified the internal consistency of the values. T o determine if a significant difference existed between the two methods, a two-way analysis of variance (ANOVA) was conducted using the first three of each of the 10 replicate T N determinations and the respective triplicate T K N results. There was no significant difference (P > 0.10) between the two methods, F , < F,,,, (0.03 < 2.82), although there was a significant interaction effect between methods and wastewaters, F, > F,,,, (2.70 > 2.66). The results of Tukey's test

ANALYTICAL CHEMISTRY, VOL. 57, NO. 12, OCTOBER 1985

for nonadditivity indicated that an insignificant portion (P > 0.10) of the interaction was nonadditive; therefore the assumptions of the ANOVA were not violated. This interaction effect was most likely a result of the wide range of nitrogen concentrations among the waters and not a fundamental variation between the two methods. A cost comparison of the macro-Kjeldahl apparatus and the Antek 703C nitrogen analyzer showed that the capital expense of the Kjeldahl apparatus and flasks was approximately half that of the Antek nitrogen analyzer and syringe drive ($7800 vs. $14 800). The yearly costs of expendable parts were approximately equal for the two approaches. Assuming two full-rack Kjeldahl digestions per day, 100 days per year, the acid, base, and digestion reagents would cost approximately $1600. For the nitrogen analyzer, replacement combustion tubes, syringes, scrubbers, septa, and high-purity oxygen for 100 days of operation would be approximately $1950 per year. None of these estimates, however, includes electrical demand or operator time. Approximately 90 samples can be analyzed in triplicate in 8 h (5.3 min/sample) by the C/CL method using manual injection. In contrast, in the same amount of time, only six samples can be analyzed for T K N in triplicate (80 min/sample), and the method requires almost constant operator attention during digestion, distillation, and titration. Additionally, the C/CL system is amenable to automation and requires less professional supervision for routine application. T o date, there have been no alternative methods proposed for the rapid determination of organic N. We are currently developing techniques for the rapid separation of ammonia from various classes of organic nitrogen (28). This will allow the use of C/CL for the direct estimate of organic nitrogen.

ACKNOWLEDGMENT The authors express their gratitude to Gloria J. Harris for her valuable input and attention to detail in performing many of the nitrogen analyses. Registry No. Nitrogen, 7727-37-9;potassium nitrate, 775779-1; potassium nitrite, 7758-09-0; o-nitrophenol, 88-75-5; mnitrophenol, 554-84-7; p-nitrophenol, 100-02-7;glycine, 56-40-6; urea, 57-13-6;diethanolamine, 111-42-2;ethylenedinitrolktraacetic acid, 60-00-4; N,N-dimethylformamide, 68-12-2; acetonitrile, 75-05-8; l-methylpyrrole, 96-54-8; l-methyl-2-pyrrolidone, 87250-4; indole, 120-72-9; carbazole, 86-74-8; 9-methylcarbazole, 1484-12-4;4,4'-azoxyanisole, 1562-94-3;pyrazole, 288-13-1; 3,5dimethylpyrazole, 67-51-6; 3,5-dimethylpyrazole-l-carboxamide, 934-48-5;4-amino-2,3-dimethyl-l-phenyl-3-pyrazolin-5-one, 8307-8; 2,3-dimethyl-l-(4-methylphenyl)-3-pyrazolin-5-one, 5643008-1; indazole,271-44-3;2,5-dimethyl-1,3,4-thiadiazole, 27464-82-0; imidazole, 288-32-4;benzimidazole, 51-17-2;1,5-dimethyltetrazole, 5144-11-6; pyridine, 110-86-1; 2-methylpyridine, 109-06-8; 3methylpyridine, 108-99-6; 4-methylpyridine, 108-89-4; 2,4-dimethylpyridine, 108-47-4;2,6-dimethylpyridine, 108-48-5;2,3,6trimethylpyridine, 1462-84-6; 2,4,6-trimethylpyridine, 108-75-8; 2-ethylpyridine, 100-71-0; 3-ethylpyridine, 536-78-7; 4-ethylpyridine, 536-75-4; 2-n-propylpyridine, 622-39-9; 3-ethyl-4methylpyridine, 529-21-5; 4-ethyl-3-methylpyridine, 20815-29-6; 5-ethyl-2-methylpyridine, 104-90-5;2-hydroxypyridine,142-08-5; 3-hydroxypyridine, 109-00-2; 2-hydroxy-6-methylpyridine, 3279-

2325

76-3; nicotinic acid, 59-67-6; piperidine, 110-89-4; 2-methylpiperidine, 109-05-7; l-methyl-2-piperidone, 931-20-4; quinoline, 91-22-5;isoquinoline, 119-65-3; 6-nitroquinoline, 613-50-3;pyridazine, 289-80-5; pyrazine, 290-37-9; 2-methylpyrazine,109-08-0; piperazine, 110-85-0;cyanuric acid, 108-80-5;water, 7732-18-5.

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RECEIVED for 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-ACOS76SF00098.