ANI. chem. 1893, 65,3489-3492
3489
Determination of Ammonium Ion in Rainwater and Fogwater by Flow Injection Analysis with Chemiluminescence Detection Xincheng Hu, Norimichi Takenaka, Shiro Takasuna, Masaru Kitano, Hiroshi Bandow, and Yasuaki Maeda. College of Engineering, University of Osaka Prefecture, 1 - 1 Gakuencho, Sakai 593, Japan
Masaharu Hattori Kansai Environmental Engineering Center Company Ltd., Nakazakinishi 2-3-39, Kitaku, Osaka 530, Japan
Reaction between ammonia and hypobromite in alkaline solution was found to give chemiluminescence. The maximum wavelength of the chemiluminescence is -710 nm. This chemiluminescence reaction has been used for the determination of ammonium ion concentration in rainwater and fogwater with a flow injection analysis system. The detection limit of ammonium ion was 6.1 X 104 mol/dm* (3 RSD). The dominant components in rainwater such as NOS-,Sod2-, and C1-, do not interfere with the determination, but humic acid and urea do. The interference can be removed by inserting a glass filter between the chemiluminescence cell and the photomultiplier tube, because the peak wavelengths of the emission are different for both chemiluminescence species. Rainwater and fogwater samples can be rapidly determined by this method without any pretreatment. The results determined by the present method were in good agreement with the ion chromatographic method and the indophenol spectrophotometric method.
INTRODUCTION Ammonia is a significant alkaline pollutant in the atmosphere. Ammonia emitted into the troposphere is readily trapped by acidic cloud droplets and neutralizes the acidity of the droplets to form ammonium salt or reads with acidic gases to form aerosol.' Therefore, the determination of ammonium ion in wet deposition is important in atmospheric chemistry. Furthermore, ammonia was used to widely in an efficient denitrification method in a steam power plant.2There is a need for a simple and rapid method of determination of ammonium ion for controlling the dose of ammonia. Various detection methods and techniques are used for determining ammonia or ammonium ion, such as ion chromatography? selective ion electrode? and spectrophotometry.sv6 Among these, the indophenol spectrophotometric method is the
standard method for examination of water in the U.S.EPA.7 Recently, various new techniques have been investigated to determine ammonia or ammonium ion. Aoki et al.8 have been developed a membrane diffusion technique for continuousflow fluorometric determination of ammonium ion in natural waters. Straws9 reported a method which combined laser photothermal detection with the indophenol spectrophotometric method for the measurement of trace amounts of ammonium ion in water. West10 developed an optical sensor based on incorporation of an ammonium ion-selective ionophore and hydrogen ion-selective chromionphore into plasticized poly(viny1 chloride) membranes for measurement of ammonia in ambient air. The redox reaction between ammonia and hypobromite is well-known. It has been used for application of the determination of ammonia. For example, Jenkins" reported a gas chromatographic method for determination of dissolved ammonia, which was based on measurement of nitrogen liberated by a quantitative oxidation of ammonia in alkaline solution with hypobromite (eq 1). 2NH,
+ 3Br0- = N, + 3Br- + 3H,O
(1)
However, it is not known whether the reaction produces chemiluminescence. We found that the reaction in sodium hydroxide solution produces strong chemiluminescence. The purpose of the present paper is to describe a method for determining ammonium ion in aqueoussolutionthat combines the detection of this chemiluminescenceand a flow injection system. This method was successfully applied in the determination of ammonium ion in rain and fog sampled at Mt. Ikoma, Osaka, Japan.
EXPERIMENTAL SECTION Apparatus. A schematicdiagram of the chemiluminescence flow injection analysis (CL-FIA) system is shown in Figure 1. This system mainly consists of five parts: two reagent feeding streams, a sample injector, a mixing unit of hypobromite and sample, a chemiluminescence reaction cell, and a chemiluminescence detection and recorder unit. A distilled water stream and sodium hypobromite solution are fed into the mixer using a peristaltic pump (Tokyo Rikakikai Model MR-3) with Tygon tubing (i.d. 9/82 in., 0.d. 5/32 in.). A 1.2-mL sample volume is injected into the distilled water stream with a six-way injector. Reagent solutions are mixed in a concentric double tube. The ~~~~
* Author to whom all correspondence should be addreseed.
(1) Seinfeld,J. H.Atmoepheric ChemietryandPhysicsofAirPolLtMn; John Wiley and Sons: New York, 1988. (2) Tanabe, K. Shokubai No Hataraki, (Action of Catalyzer); Kagakudojin: Kyoto, Japan, 1988, Chapter 13, pp 148-50. (3) Small, H.; Stevens, T. 5.;Bauman, W. C. Anal. Chem. 1978,47, 1801-9. (4) Beckett, M. J.; Willson, A. L. Water Res. 1974, 8, 333-40. (5) Harwood, J. E.; Kuhn, A. L. Water Rea. 1970,4,806-11. (6) Tellow, J. A.; Wileon, A. L. Analyst 1964,89,463-65. 0003-2700/93/0385-3489$04.00/0
(7) StandardMethodsfor the Examination of Waterand Wastewater; American Public Health Association: Washington, DC, 1985. (8)Aoki, T.; Uemura, S.; Munemori, M. Anal. Chem. 1983,66,162022.
(9) Straws, E.; Favier, J. P.; Bicanic, D.; Asselt, K. V.; Lubbers, M. Analyst 1991, 116, 77-9. (10)West, S. J.; Ozawa, S.; Seiler, K.; Tan, S. S.; Simon, W. Anal. Chem. 1992,64, 533-40. (11) Jenkins, R. W., Jr.; Cheek, C. H.; Linnenbom, V. J. Anal. Chem. 1966,38, 1257-8. Q 1993 American Chemlcal Soclety
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ANALYTICAL CHEMISTRY, VOL. 65, NO. 23, DECEMBER 1, 1993
u IC I EF
U W
R
I
1
I
1
t--€IlGHHl
I
.1
Flgure 1. Schematlc diagram of chemiluminescence flow InJsctbn system: A, carrier stream of distilled water: B, stream of NaBrO; C, perlstaitlc pump: D, sample Injector; E, scroll CL cell; F, glass filter; G, photomultlpller tube and ampllfler; H, recorder; I, waste.
inner tube is Teflon (i.d. 0.5 mm, 0.d. 1.0 mm) and the outer (i.d. 3/3z in., i.d. 6/32 in.) tube is Tygon. Sodium hypobromite solution flows through the inner tube, and sample solution flows through the outer tube. The samplesolutionand the hypobromitesolution are mixed at the outlet of the concentric double tube, which is connected to the entrance of the chemiluminescence cell. All flow lines are connected with Tygon tube. The chemiluminescence cell is a scroll glass tube (i.d. 2 mm, 0.d. 3 mm, length 15 cm) that is in principle the same as described by Burguera et al.,'2 but they did not use a concentric double tube to mix the reaction solutions. Chemiluminescence is detected by a photomultiplier tube (R-374, Hamamatsu Photonics K.K.).The signal current is amplified and recorded on a recorder. The photomultiplier tube is set directly abovethe chemiluminescence cell. A glass filter for eliminating interference emission produced by other chemiluminescent species is set between the photomultiplier tube and the chemiluminescence cell. The operation voltage of the photomultiplier tube was -800 V. The chemiluminescence cell, the reagent miser, and the photomultiplier tube are packed in a box, which is sealed to prevent penetration of stray light from the outside. To obtain a spectrum,the chemiluminescencewas resolved by a grating spectrometer (Opto-Line 310.01/L) to monochromatic light, and then detected by a photon counter C1230 (Hamamastu Photonics K.K.) using photomultiplier R-649 (Hamamatsu Photonics K.K.). The resolution is 30 nm when a 1000-pm slit is used. In this experiment, the chemiluminescence cell is a straight glass tube (i.d. 2 mm, 0.d. 3 mm) fixed to the front of the silt at the entrance of the spectroscope. The concentricdouble tube mixer as described above is connected with the straight glass tube chemiluminescence cell. A stopped-flow system (Unisoku Scientific Instruments Co., Japan) was modified to use for determination of the time profile of the chemiluminescence. This system permits completemixing of two 0.100-mL reagent solutions with a dead time within 1ms. Sampling. The sampling methods employed for collectionof rainwater and fogwaterwerethe same as described by Takenaka.13 Rain droplets were collected with a funnel (top i.d. 30 cm) into a polypropylenebottle. Fog droplets were collected usinga active strand collectormanufactured in our laboratory. Droplets of fog are collected hy impact on the vertical of a two-row (200 lines, 25-cm width) net of 0.435-mm Teflon strands using a fan. Air sample rates of 0, 6.0, and 17.3 mg/min were used. Droplets of fog coalesce on the strands and are pulled down into a polypropylene bottle by gravity. The samples were filtered with 0.2-rm membrane filters just after collection, placed in polypropylene bottles, and stored at 4 OC in a refrigerator. Reagents. Saturated bromine water (Wako Pure Chemical Industries, Co.) was used without further purification. A sodium hypobromite solution (contains 0.3% of bromine) was prepared just before use, containing 1.0 molldm3 sodium hydroxide and 1.0molldm3sodiumbromide. This solution contains -0.02 moll dm3 hypobromite. For measurement of the time profiie of this chemiluminescence and the spectra of the chemiluminescence, 0.2 mol/drns hypobromite was used, which also contains 1.0 mol/ dm3 sodium hydroxide and 1.0 molldm3 sodium bromide. The concentration of hypobromite was titrated by the thiosulfateiodide method. Ammonium ion standard solution was prepared by dissolving ammonium chloride (Wako, Special Grade, at least 99.0%, dried at 65 "C) in distilled water. The other chemicals (12)J. L.Burguera, J. L.; Townshend, A.; Greenfield,S. Anal. Chirn. Acta 1980,114,209-14. (13)Takenaka, N.;Maeda, Y. Bunseki 1992,885-93.
-80
0
80
120
200
280
3 0
reaction time (ms) Figure 2. Time proflle of the chemllumlnescence: ammonlumchkrlde, 0.2 mol/dmg;sodium hypbromite, 0.2 mol/dmg:sodlum hydroxide, 1.0 rnollde potassium bromide, 1.0 mol/dm3;sodlum hydroxide, 1.O mol/
dm3; potasslum bromide, 1.0 mol/dma.
Flgwe 3. Comparison of the chemllumlnescence Intensity at various mixlng points of reagents: (a, left) withln the chemllumlnescencecell: (b, middle) at 2.5 cm before the chemlluminescencecell; (c, right) at 5.0 cm before the chemiluminescence cell.
were of reagent grade and obtained from Wako Pure Chemical Industries, Co.
RESULTS AND DISCUSSION Time Profile of the Chemiluminescence. In order to measure the chemiluminescence at maximum sensitivity, the time profile of the chemiluminescence was examined by the stopped-flowsystem. A plot of chemiluminescence intensity vs reaction time after mixing 0.2 mol/dm3 ammonium chloride solution and 0.2 mol/dm3 sodium hypobromite solution is shown in Figure 2. Within 20 m after mixing, maximum chemiluminescence intensity was obtained and then died within 120 ma. Since the lifetime of the chemiluminescence is very short, the point of mixing was designed to be inside of the chemiluminescence cell. As shown in Figure 3, if ammonium chloride and sodium hypobromite were mixed at 5.0 and 2.5 cm before the entrance of the chemiluminescence cell,the intensities declined rapidly. Therefore, the concentric double tube mixer was used, and the mixing point was set in the inside of the chemiluminescence reaction cell. Enhancing Effect for Chemiluminescence by Bromide Ion. As Figure 4 shows, when potassium bromide was added to the sodium hypobromite solution, the chemiluminescence intensity was increased. This is probably because addition of bromine of water to sodium hydroxide solution resulted in hypobromite and bromide formation (eq 2). Br,
+ 20H- = BrO- + Br- + H,O
(2)
Hypobromite is less stable and disproportionates to bromate
ANALYTICAL CHEMISTRY, VOL. 85, NO. 23,DECEMBER 1, lQQ3 9481 25
Table I. Relative CL Intensity for Other Substances concn, concn, substances mol/dmg ratifl substances m0udm3 ratio0
M t
a
-1
15
V
L
.-
h
.-
10
2
5
0 0.0
0,s
1.0
concentration of KBr ( moUdm
1.5
')
Flgure 4. Enhancing effect of bromide on the chemiluminescence lntenslty: ammnlumchlorlde, 2.0 X lo4 mol/dm? sodium hypbromlte, 2.0 X moi/dm3; sodium hydroxide, 1.0 mol/dms.
NH4+ NHzCONHz humic acid NHzOH NH2NH2 NHzCSNHz Pyrogallol histidine glutamine a-alanine @-alanine oxamide HCONHz ascorbic acid a
0.001 o.oO01
1 1.1 10 PPm 10 0.025 0.03 0.0028 0.06 0.01 0.03 0.001 0.5 0.01 1.2 0.01 0.015 0.01 0.015 0.01 0 0.001 1 0.01 0 0.01 0
HCOOH CHaCOOH NaNO2
0.01 0.01 0.01 0.01 0.1
NaN03 KCl
Na2SO4 NaZSOs
0.001 0.001 0
0 0 0
0.1
0 0 0 0
0.1 0.1 0.1 0.1 0.02 0.02 0.02 0.02
Na2C03 NQO4 KBr
CHsNH2 NHzCHzCHaNH2 (CHdsN (CH&Hz)zNH
0 0
0 0
Ratio of the CL intensities to that for 1.0 X 1W mol/dms NH4+.
and bromide according to following equilibrium. 3Br0- =B i r09
+ 2Br-
(3) If bromide ion is added to the sodium hydroxide solution beforehand, the disproportionation reaction should be suppressed and a higher concentration of hypobromite can be obtained; therefore, the chemiluminescence intensity was increased. For the purpose of enhancing the chemiluminescence intensity, 1.0 mol/dm3 sodium bromide was added to the hypobromite solution. Optimum Conditions. The effects of varying concentrations of bromine water, sodium hydroxide, and sodium bromide and varying the flow rate were tested in this flow system. The effect of sodium hydroxide on the chemiluminescence intensity was most important. This chemiluminescence reaction occurred only in strong alkaline solution. When the sodium hydroxide concentration was smaller than 0.08moVdm3,no chemiluminescencesignal was detected. Over 0.08moVdm3, the chemiluminescenceintensity increased with an increase in the sodium hydroxide concentration and reached a maximum at 1.0 mol/dmS. An increase in the flow rates of the carrier stream of distilled water and sodium hypobromite made the chemiluminescenceintensity increase. When the flow rates of both streams were over 10 mL/min, the intensity became constant. The chemiluminescence intensity increased with a increase in bromine concentration, and the maximum intensity was obtained at 0.3% bromine. Over a 0.3 7% bromine concentration, the chemiluminescence intensity decreased slowly. The optimal conditions for the chemiluminescence reaction were summarized as follows: sodium hydroxide, l.OmoVdm3; bromine water, 0.3% ;sodium bromide, 1.0 mol/dm3, flow rate of hypobromite, 10 mL/min; flow rate of carrier, 10 mL/min. Effect of Sample pH. Because the pHs of the natural water samples varied in a wide range, it was necessary to examine whether the pH of the sample affects the chemiluminescence intensity. Results shown that sample solution pHs from 3 to 11 had no effect on the chemiluminescence intensity. This implies that for almost all natural water samples, especiallyrainwater and fogwater,determination of ammonium ion can be made without adjustment of the pH of the sample before determination. Interference of Other Compounds. In order to assess interference from other compounds to the determination of ammonium ion, various compounds were investigated as whether they gave chemiluminescence with hypobromite under the optimal conditions. As shown in Table I, alkylamines do not chemilumineace, carboxylic and amino acids yield weak chemiluminescence, and urea, pyrogallol, and
30
50
1s
0
300
400
500
600
700
800
900
1000
Wavelength (nm)
Flgure5. Spectra of the chemiluminescence of ammonium ion, urea, pyrogallol, and humic acM reacting with hypobromite: H, 1 mol/dms ammonlum chloride; A, 0.1 mol/dm3 urea; A,0.1 % humic acld; 0 , 1 % pyrogallol; 0.2 moi/dd sodlum hypobromlte contalnlng 1 mol/ dm3 sodium hydroxide was used; 1.0 mol/dms potasslum bromide; broken Ilne, senslthrlty of the R-649 photomultlpiier.
humic acid yield strong chemiluminescence. The interference from inorganic compounds was also examined. Sulfate, nitrate, phosphate, chloride, and metal cations such as Fe3+, AP+,Ca2+,Mgz+, Co3+, and CrS+ did not interfere with the chemiluminescence reaction. However, at higher concentrations (for example, 0.01 mol/dma), sulfite and nitrite consumed hypobromite and diminished the chemiluminescence. In general, however, the natural water samples do not contain high concentrations of sulfite and nitrite; therefore, their interference can be negligible. Spectrum of the Chemiluminescence. The chemiluminescence spectra produced by reactions between hypobromite and ammonium ion, urea, pyrogallol, and humic acid are illustrated in Figure 5. The intensities of chemiluminescence should be corrected because the sensitivity of the photomultiplier is varies with wavelength, but in Figure 5, the values of the intensities were raw data. Therefore, the wavelength sensitivitycharacteristicsof photomultiplier R649 was also illustrated in Figure 5. The spectrum of the chemiluminescenceproduced by ammonium ion had a broad emission range from 600 to 800 nm with a peak at -710 nm. The spectra of chemiluminescence produced by urea, pyrogallol, and humic acid show emission from 450 to 650 nm, from 460 to 710 nm, and from 400 to 600 nm, respectively. It is clear that the emission species of ammonium ion is different from the emission species of urea, pyrogallol, and humic acid. Removal of Interferences. From the spectra illustrated above, interference from urea, pyrogallol, and humic acid can be removed by using a 50 5% transmission wavelength of glass
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ANALYTICAL CHEMISTRY, VOL. 65, NO. 23,DECEMBER 1, 1993
Table 11. Removal Effect of Interference from Urea, Pyrogallol, and Humic Acid with and without the Glass Filter R690 chemiluminescence intensities without with R690 samples filter filter NH4Cl2.0 X lo-' mol/dm3 NH4Cl2.0 X lo-' mol/dm3 + urea 5.0 X 1O-emol/L NHdCl2.0 X lo-' mol/dm3 + ' urea 1.0 x 1o-b mol/L NH4Cl2.0 X lo-' mol/dm3 + humic acid 2 ppm NHbCl2.0 X lo-' mol/dm3 + humic acid 1ppm NH4Cl2.0 X lo-' mol/dm3 + pyrogallol 1.0 x 10s mol/dm3
25 47
6.0 6.3
69
9.5
47
8.0
36
6.0
95
6.0
Table 111. Determination of Ammonium Ion in Rainwater and Fogwater [",+I, X 10.'mol/dm3 no. sampling timea b C d 1 2 3
4 5 6 7 8 9 10 11 12
June 18-19, rain June 20, rain 000-3:OO June 24, rain under trees 12:00-15:00 June 27, rain 600-10:30 July 5, rain 6:00-10:30 July 5, rain under trees June 27-28, fog1 21:00-23:00 July 5, f o g 21:00-23:00 July 5, f o g 21:00-23:00 July 5, fogf 23:00-1:00 July 6, fogf 3:00-1:00 July 6, f o g
1.3 0.33 0.11
0.83 0.38 0.12
1.77 0.39 0.033
0.0 0.33 0.67
0.078 0.39 0.11
0.11 0.50 0.256
5.67 1.3 1.3 2.3 2.3 2.7
5.44
5.07 1.22 1.22 2.42 2.26 3.24
1.1 1.1
1.8 1.9 2.9
~
filter 690 nm. Various concentrations of urea, humic acid, and pyrogallol were added to 2.0 X 10-4 mol/dm3 ammonium chloride solution, and the chemiluminescent intensities of those solutions were measured. As shown in Table 11, the interferences of 5.0 X 10-6mol/dm3 urea, 1.0 ppm humic acid, and 1.0 X 1o-L mol/dm3 pyrogallol can be almost eliminated. However, above these concentrations of urea and humic acid, the interferences could not be removed sufficiently. Calibration and Reproducibility. Under optimum conditions, the calibration graph gives a straight line from 1.0 X 106to 1.0 X l W m o l / d d f o r ammonium ion. The calibration graph was made using 1.0 X lod, 5.0 X 106, 1.0 X 10-4, and 1.0 X 10-3 mol/dm3 ammonium chloride, and the correlation coefficient was 0.9999. Under the optimum conditions of the chemiluminescence reaction, for 24 replicate measurements of 5 X 106 mol/dmg standard ammonium chloride solution, the relative standard deviation was 3.9 96. The limit of detection for ammonium ion is 6.1 X 10-6 mol/dmg (3 SRD). Application. This method was applied for the determination of ammonium ion in rainwater and fogwater sampled at Mt. Ikoma, Osaka, Japan, during June 20,1992-July 10, 1992. The mountain is located 15 km east from the center of Osaka. Rain samples were taken in an open space and under trees. Fog samples were taken in an open space with three different rates of sample air. The concentrations of ammonium ion determined by the present method were compared with indophenol spectrophotometry and ion chromatography. The results are shown in Table 111. The results showed that the concentrations in rainwater (experiments 1-5) and fogwater (experiments 7-8) samples are in good agreement for those three methods, but, in experiment 6, the concentration of ammonium ion determined by the present method is higher than the others. This is probably because the samples contain too many humic substances that the interference from these could not be completely removed. The results also showed that the concentration of ammonium ion in fog was significantly higher than that in rain from both open space and under trees. The concentrations of ammonium ion in both types of rain sample are not significantly different.
OSampling duration from June 20, 1992 to July 10, 1992. Determined by indophenol spectrophotometry. Determined by cation chromatography. Fog samples were collected with an active strand fog sampler. e Rate of sample air at 6.0 m3/min. f Rate of sample air at 17.3 m3/min. 8 Sampled without fan, at the same place.
* Determined by the present method.
CONCLUSION Although indophenol spectrophotometry is widely used to determine ammonium ion, the procedure is complicated and takes a long time. Ion chromatography is a simple method for determination of ammonium ion, but if the sample contains arelatively highconcentration of sodium ion, this will interfere with the resolution of ammonium in the chromatographic output. Also,ion chromatography usually take more than 10 min to determine one sample, and the ion chromatographic instrument is expensive. The present method can determine ammonium ion speedily within at least 1 min, and the instrument is inexpensive and simple. Samples need not have any pretreatment for the present method.
-
ACKNOWLEDGMENT The authors thank Dr. Hideo Horii of the Research Institute for Advanced Science and Technology for his helping in determining the time profile of the chemiluminescence reaction. Acknowledgment is also given to Dr. Keisuke Taguchi of the Environmental Pollution Control Center of Osaka Prefecture for offering the results of ammonium ion in rain and fog analyzed by chromatographic method. This study was partially supported by a Grant-in-Aid for Scientific Research (02650547) from the Ministry of Education, Science and Culture, Japan. RECEIVED for review June 4, 1993. Accepted September 21, 1993." e Abstract
published in Advance ACS Abstracts, November 1,1993.
