Anal. Chem. 1986, 58,1537-1541
Registry No. HNOz, 7782-77-6; HN03, 7697-37-2; NOz, 10102-44-0; HCN, 74-90-8; HSCN, 463-56-9; NO, 10102.43-9; NaCN, 143-33-9; KSCN, 333-20-0; H2Cz04,144-62-7; NaN03, 7632-00-0; KNOB,7757-79-1. LITERATURE CITED (1) Johnston, H. .; Greham, R. Can. J . Chem. 1974, 52, 1415-1423. (2) Cox, R. A.; Derment, R. G. J . Photochem. 1076/1077, 6 , 23-24. (3) Braman, R. S.; Shelley, T. J.; McCienny, W. A. Anal. Chem. 1982, 38 358-364. (4) Braman, I?.S.; de la Cantera, M. T.; Han, Q. X. Anal. Chem. 1006,
58, 1637-1541.
1537
(5) King, G. W.; Moule, D. Can. J . Chem. 1062. 4 0 , 2057-2065. (6) Braman, R. S.; Trlndaie, M. Han, Q. X. "A Sequential and Specific Hollow Tube System for Tracing Nitrogen Compounds in Air". Presented at the Third National Symposium on Recent Advances in Pollutant Monitoring of Amblent Air and Stationary Sources, May 3-6, 1983.
RECEIVED for review November 19, 1985. Accepted January in part by the Air Re277 1986* This work was sources Board, State of California.
Sequential, Selective Hollow Tube Preconcentration and Chemiluminescence Analysis System for Nitrogen Oxide Compounds in Air Robert S. Braman* and Maria A. de la Cantera Department of Chemistry, University of South Florida, Tampa, Florida 33620 Qing Ximg Han
Fushun Petroleum College, Peoples' Republic of China
A serles of hollow tubes havlng, In sequence, tungstlc acld, potasslum-iron oxide, copper( I)Iodide, and cobah( I II) oxide interior coatings preconcentrate, in order, "OB, HNO,, NO2, and NO from amblent air. Thermal desorption and detection of the NO released by a chemiluminescence detector provided an analysts of air for these NO, compounds ai subparts-per-billion concentrations. Ammonla assoclated with these analytes may also be determlned. Initial use of the method lndlcates that "0, Is a major NO, component and that the Saltzman method for NO, measures the sum of NO2 and "0,.
The importance of nitrogen oxide compounds as a component of air pollution is evidenced by extensive monitoring and research on the subject. The main NO2 and NO, monitoring approaches have employed the use of colored dye formation by nitrites, Le., the Saltzman method or its modifications (1-3) and the chemiluminescence monitor (4, 5). Automated chemical analysis methods have also been reported (6). Although some attempt at detection selectivity has been made, the term NO, has appeared, recognizing the difficulty of selectively detecting "OB, HNOZ,NOz, and NO in air by these methods. The colorimetric method (I), which is considered to be selective for NO2, actually analyzes the sum of HNOz and NOB. The chemiluminescence monitors employ catalytic reactors and attempt to be selective for NO2 and NO by selection of the gas route through a molybdenum catalyst bed in the analyzer. The fate of peroxyacetyl nitrate (PAN) and HNOz in such a system is not clear and likely is split between detection as NO and NOz and nondetection if the molybdenum causes reduction to N2, More recently considerable effort has gone into the devblopment of specific methods for nitric acid and particle nitrate in air. The so-called denuder difference methods (7) measure the difference between total nitric acid plus nitrates collected on a nylon filter and the nitrates only collected on a nylon filter after removal of nitric acid on a MgO interior 0003-2700/86/0358-1537$01.50/0
coated hollow tube. Hollow tube methods have also been developed using nylon coatings (8),tungstic acid (9), and sodium carbonate (10, 11). The use of sodium carbonate (11,12)interior coated hollow tubes provides also a possible method for nitrous acid as the tube coating can be analyzed by ion chromatography. The integrity of the collected nitrates and nitrites on long exposure to photochemical oxidants during sampling is unknown and bears examination. Long-path optical absorption methods have been developed and studied (13, 14). While this may be the best approach when the concentrations are above 1 ppb from the point of view of selectivity, the method is complex experimentally and requires substantial equipment. Continuation of research on selective hollow tubes for NO, compounds (15) has led to the development of a series of tube coatings that when used in proper sequence, can separately preconcentrate "OB, HN02, NO2, and NO. This work started with the development of the tungstic acid tube system for nitric acid and ammonia in air (9) and continued with work on NiO tubes and Co203tubes for NOz and NO in air (15). The development of a high-purity source of HNOz in air and NO2in air (16) was key to the study of candidate selective hollow tube coatings. During the development of the hollow tube system reported here a number of different tube coatings were prepared and tested for NO, absorption selectivity. These included carboh, MgO, A1203,Ni, NiO, Cu, CuO, MnO, Fez03,Na2C03,NaOH, W03.Hz0, CozO3, and mixed oxides such as K20.Fe203and Na20Coz03,the latter being prepared from metal complex salts. Most of the above except the tungstic acid, mixed oxide, and molybdic acid tubes were found to absorb to some extent both HNOz and NOz. Nitric acid is absorbed at least to some extent by all of the tube coatings. Nitric oxide was found to be absorbed only by a specially prepared cobalt(II1) oxide. The mixed oxide tubes were specific and selective for HNOz but only after removal of nitric acid by a tungstic acid tube. After establishing the sequential tube order of W03, POtassium-iron oxide (KFe), NiO, and CoZO3(C0)tubes for isolating the NO, analytes, tube capacity and other tests were 0 1986 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 58, NO. 7, JUNE 1986
run. Tests of NiO tubes indicated breakthrough capacities well below 1pg for NOz. Consequently, a higher capacity tube was sought for NOz. Eventually, copper(1) iodide was discovered as a substitute for NiO and was used in all subsequent work. The efficiency of hollow tubes in chemisorptive preconcentration can be estimated from the first term of the Gormley-Kennedy equation ( 1 7 ) eff = 1 - 0.819 exp(-3.6568rDaL/F) which assumes a practical 100% reaction efficiency on wall collision of analytes. If a 30-cm active coating tube length is used with a flow rate of 1.0 L/min, the NO, components should be collected with the following approximate efficiencies: HNO,, 96%; NOz, 98%; and NO, 99%. Efficiency of the tubes in actual operation can be determined by using sequential pairs of hollow tubes. This was done in testing experiments and in some air analyses to verify separation of the analytes. In application to air analysis it is also possible to analyze for particle nitrates (plus nitrites), particle ammonium ion, and gaseous ammonia. Ammonia associated with HNOz and on the NO2 and NO preconcentration tubes can also be determined. EXPERIMENTAL SECTION NO, Analysis System. The apparatus for hollow and packed tube analysis, calibration, and applications to air analyses have been described in prior work (9,16). A Bendix commercial model chemiluminescence-typedetector is used with a WO, transfer tube to remove ammonia from analytes desorbed from the hollow tubes. A gold interior coated catalyst bed tube is used to convert ammonia to NO. All NO, components on the hollow tubes are thermally desorbed and detected as NO. The detection limit of this system is near 0.03 nmol of nitrogen compound. Calibration of detector response is performed by analysis of W03 packed tubes to which 5-100-pL amounts to potassium nitrate standard solutions have been added. Repeatability of analyses is on the order of rt3-5% relative. Hollow and Packed Tube Preparation. Tungstic acid tubes were prepared by vacuum deposition as described previously (9). After slow (2 h) deposition onto cleaned Vycor brand 6-mm-0.d. tube walls, the blue reduced tungsten oxide was carefully oxidized to WOa by heating while passing oxygen through the tube. The ends of the glass tubes were cleaned of tungsten oxide using reagent grade hydrofluoric acid and a pipe cleaner. The excess acid was removed by using distilled water. After the tubes are heated to give a blank analysis, they are ready for sampling and analysis. Tungstic acid tubes should be reoxidized occasionally to remove any deposited organic matter. This is done by heating the tubes well above analysis temperature while passing oxygen through them. Potassium oxide-iron oxide (KFe) interior coated tubes were prepared from a 50% (w/v) solution of potassium ferrocyanide, K3Fe(CN)6or potassium ferricyanide K2Fe(CN)@The solution is drawn up a 6-mm-0.d. X 18-in.-longVycor glass tube and then allowed to run out leaving a wet layer of solution on the tube walls. If an even coat is not obtained, the glass tube is chemically cleaned with hydrofluoric acid or by heating with a glass blowing torch while passing oxygen through the tube prior to recoating. The solution on the tube walls is then dried by passing an air stream through the tube while warming. A reasonably even coating of crystalline compound on the walls is produced. The coating is oxidized by passing oxygen through the tube while heating with a torch. This converts the coating to a mixed iron-potassium oxide layer also likely with some reaction with silica from the tube walls. After the ends of the tube are cleaned, the tube is then heated to blank. Potassium ferrocyanide appears to give the best coating. Copper(1) iodide coated tubes are prepared from a watercopper(1) iodide slurry. The slurry is drawn up the 6-mm-0.d. X 18-in.-long tubes, allowed to run out leaving a slurry coating, and is then dried by passing air through the tube. The tube is prepared for use by heating to 300-400 "C while passing an inert gas through it. This causes some sublimation of the copper(1) iodide, and the tube ends must be cleaned. Oxygen or air is to
' H H H
I
Figure 1. Folded hollow tube sampling arrangement.
be avoided, since this oxidizes the copper and the efficiency of NO2 absorption is lost. Copper(1) iodide tubes are blanked or analyzed at 250-350 "C with the carrier gas and cooled to near room temperature before exposure to air. Cobalt(II1) oxide coated tubes are prepared from a saturated solution of cobalt(I1)nitrate. After the tubes are coated and dried in a manner similar to the KFe tubes, the nitrate layer is converted to the oxide form by rapidly heating the tube while an air stream is passed through. This results in a rapid decomposition reaction on the tube walls and evolution of NO2leaving a black cobalt oxide layer. Heating is discontinued quickly after the interior tube layer reaction is completed. After the tube ends are cleaned, the tube is heated to blank. This can require some time to remove the last traces of nitrates on the tube walls. Preparation of cobalt oxide tubes from cobalt hydroxide resulted in a tube having a poor capacity for NO absorption. Packed tubes were prepared by coating cleaned silica sand (40-60 mesh) with tungstic acid as described in prior work (9). The packed tube was used to collect particulate analytes present. Ambient Air and Standard Source Sampling and Analysis Procedures. Air sources of HNO,, HN02,NO2,and NO described previously (16) were used to provide these components in air at a flow rate near 1.0 L/min. Single tubes or a sequence of hollow tubes under test were simply attached to the outlet of the source for sampling. Outside air was sampled with a small air pump and rotameter calibrated with a mass flowmeter, also properly calibrated. Ordinarily, a sequence of five tubes, WO3-KFe-CuI-CwPT (packed tube), is used to analyze for NO, components. In order to determine the efficiency of tube types, a set of tube pairs was used. In this latter case a folded tube set configuration was used to accommodate the 12-ft total hollow tube length. Figure 1 shows this configuration,which was mounted on a board fitted with small plastic clamps. When only four hollow tubes were used, folding was not needed. After sampling for the selected periods of time, the tube sets were disassembled and analyzed one at a time in the analysis system. Heating rapidly removes NO, compounds, usually within 3 min for any of the hollow tubes. After the NO, compound was detected, the ammonia signal associated with it can also be determined by analyzing the transfer tube in the analysis system. In ambient air ammonia was usually found associated only with the WO,, KFe, and packed WOBtubes but almost never to any appreciable extent with the Cu(1) and Co tubes. Colorimetric Method. The modified Saltzman method (6) for NO2in air was used to compare hollow tube analysis results for NO2. During testing of this method, it was found that both HN02 and NO2 are quantitatively determined. Solutions prepared were as follows: 4 g of NaOH and 1 g of sodium arsenite in 1L of water (gas-scrubbing solution), 20 g/L sulfanilic acid reagent, and 0.002% N-(l-naphthy1)ethylenediamine dihydrochloride in water. A microimpinger gas scrubber, 25 mL volume, filled with 15 mL of gas-scrubbing solution was used to collect analytes from air at a flow rate of 0.40 L/min. After
ANALYTICAL CHEMISTRY, VOL. 58, NO. 7, JUNE 1986
1539
Table I. NO, Source Analyses" hollow tube order
source
W03
HNOB
98.8
HNOz NO2
0
NO
2.1
0
KFe
CUI
co
0
0
90.9 3.4
0.9 87.7
1.2 8.2 6.7 100
0
trace
Values in mol % . air scrubbing, 10 mL of the sulfanilic acid and 2.0 mL of developing reagent were mixed. After color development for 10 min the optical absorption was read vs. distilled water at 545 nm. A reagent blank was also analyzed. The response was calibrated by using standard sodium nitrite solution.
RESULTS AND DISCUSSION Tungstic Acid Tubes. Tungstic acid tubes have been characterized in prior work (9). Tube efficiencies are in the 90-95% range for 35-cm active-length tubes at air flow rates of 1.0 L/min for nitric acid and ammonia, which are reasonably nonhydrated with diffusion coefficients larger than 0.080 cmz/s. Tube capacities are approximately 15 nmol for tungstic acid tubes. The specificity of W 0 3 tubes is indicated by the source analyses given in Table I. Nitrous acid, NOZ, and NO are not chemisorbed. KFe Tubes. KFe tubes were found to chemisorb both nitric acid and nitrous acid while not reacting with the other NO, components. The specificity of this tube is indicated by source analysis data given in Table I. Chemisorption efficiencies for HNOz were close to those expected for tubes a t the flow rates and active tube lengths as calculated from the Gormley-Kennedy equation. The diffusion coefficient of nitrous acid was determined by using pairs of KFe tubes and the HNOz source. The diffusion coefficient was found to be D, = 0.169 f 0.013, N = 7. This is in reasonable agreement with 0.171 cm2/s, the diffusion coefficient calculated by using D, = 0.148 cm2/s for HN03 and Graham's law. It is apparent that nitrous acid is not hydrated or dimerized at the 44% relative humidity (RH)of the source. Tube capacities were estimated by measuring the breakthrough of HNOz with hollow tube pairs at a flow rate of approximately 1.0 L/min. The KFe tubes started to deviate from calculated efficiency near 2 pgltube. This is likely variable with the amount of KFe active compound present and with tube length. Paired tubes used in out-of-door analyses in long-term sampling indicate that HNOz is strongly held. Upon thermal desorption NO is formed and detected. Desorption is slower than that of the other NO, components as is shown in Figure 2.
The identification of HNOz as the NO, component was studied by use of the Saltzman method. The permeation oven source of HNOz was analyzed by using a W03-KFe tube pair followed by a microimpinger bubbler to collect any HNOz passing the tube set. This same source was also analyzed by using the W03 tube alone. Comparison data are given in Table 11. Good agreement was obtained between the colorimetric and hollow tube methods. Note that the HNOz source signal is removed by the KFe tube. It is obvious that the colorimetric method is 100% responsive to HNOz and that the Saltzman method responds to the sum of HNOz and NOz. Copper(1) Iodide Tubes. Copper(1) iodide tubes were found to chemisorb "OB, HN02, and NOz but not NO in preliminary experiments with the NO, sources (16). Several other types of metal tubes, NiO in particular, also appeared
Figure 2. Thermal desorption patterns for NO, compounds.
Table 11. Comparison of Colorimetric and Hollow Tube
Methods hollow tube method, colorimetric method, nmol/min
nmol/min
HNOz Source Rate 1.44 f 0.08 (N = 2) 0.065 (under KFe tube)a
1.34 f 0.08
( N = 2)
NO2 Source Rate 11.17 f 0.35 ( N = 3) 0.17 (under CUI tube)" aHNOz
12.74 f 0.12
( N = 2)
or NOz that passes through KFe or CUItubes.
to function well in absorption of NOz. The CUI tubes were selected for use because of good mechanical integrity and superior capacity and ease of thermal desorption of NOz. The capacity of the CUItube was found to be over 10 pg in studies using a NOz source and a continuous feed to the detection system at 1.0 L/min. Nitrogen dioxide is strongly held by the copper(1) iodide tubes and is absorbed with Gromley-Kennedy efficiency. Thermal desorption during analysis produces nitric oxide with a rapid removal of analytes as is shown in Figure 2. Nitric oxide produces two or three peaks on thermal desorption. As is the case for KFe tubes, outdoor air analyses indicate that the tube is highly efficient in analyte preconcentration. The diffusion coefficient of NOz in dry air (24% RH) from a plastic system was determined by using pairs of CUItubes after removal of HN03 and HNOz by hollow tubes. The D, value found was 0.1685 f 0.0021 cmz/s (N = 5). This is near the predicted 0.173 cmz/s for NOz calculated using 0.148 cmz/s for nitric acid and Graham's law. Consequently, NO2 is likely not hydrated, dimerized, or aggregated to an appreciable extent. The high efficiency of NOz absorption also found in outdoor air analyses also suggests no hydration or aggregation in the environment except perhaps a t relative humidities above approximately 80% RH. The identification of NOz as the NO, component absorbed by CUItubes was studied by use of the Saltzman colorimetric method. A plastic system NOz source was analyzed by using a W03-KFe-CUI hollow tube set. The same source was also analyzed by using a W03-KFe tube set in front of a microimpinger bubbler used to collect NOz. Comparison data given in Table I1 indciate that the two different analyses agree reasonably well and that the CUI tube removes NOz. Cobalt Oxide Tubes. Cobalt(II1) oxide tubes were found to absorb all of the NO, components. Tests with N20 indicate no detectable absorption of NzO or conversion to detectable NO, compounds. This tube was the most difficult to develop and characterize. No other metal or metal oxide tube prepared
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ANALYTICAL CHEMISTRY, VOL. 58, NO. 7, JUNE 1986
Table 111. Humidity Studies With Nitrogen Dioxide" tube W
KFe CUI W
KFe CUI W
KFe CUI W
KFe CUI
relative humidity, % 88 88 88 77 77 77 72 72 72 22 22 22
Table IV. Environmental Analyses with Tube Pair Sets
mol % on tube
units
HNO, HNOZ NOz
0
9.3 90.7
not used 3.2 96.8 1.2 0 98.8
"Flow rate 1.0 L/min, 23 "C.
NH, NH4+ NOy
Claremont, CA"
4.6 95.4 0
NO
(9/15/85 5:lO p.m., 33 O C , 17% RH)
nmol/L ppbv ng/L
0.147 3.3 9.3
0.080 1.8 3.8
0.016 0.086 0.074 0.196 0.070 0.35 1.92 1.7 4.4 1.6 0.72 2.6 1.3 3.3 4.4
Claremont, CAb (9/15/85 855 p.m., 21 O C , 46% RH)
nmol/L ppbv ng/L
0.22 5.0 14.0
0.34 7.6 15.9
0.87 19.7 40.4
0.20 4.6 6.1
0.083 0.45 1.9 9.6 1.4 7.7
0.41 9.1 25.7
Claremont, CAC and tested exhibited any appreciable absorption of NO. Only cobalt oxide prepared from the nitrate exhibited NO absorption. Tube capacities were near 1pg for 25-cm tubes at 1.0 L/min. Table I shows that the cobalt tubes are used after removal of all the other NO, compounds. Nitric oxide is absorbed with less than expected efficiency as calculated from the Gormley-Kennedy equations and the estimated diffusion coefficient, 0.214 cmz/s. Diffusion coefficient measurements at 1 L/min gave D, = 0.0925 f 0.012 cmz/s ( N = 8). This suggests a very high degree of aggregation or hydration. A more likely explanation is a slow absorption rate. Nevertheless, NO is strongly held by the cobalt tubes, since desorption of NO requires a higher temperature (380 "C) than does removal of analytes from the other tubes. Desorption during analysis is shown in Figure 2. Humidity Effects a n d Interferences. Because of its reactivity on surfaces (16),nitrogen dioxide was studied for reaction on prior hollow tubes in the sequence and as a function of humidity. This was done by preparing NO2 in air at several humidities and analyzing sequences of W03, KFe, KFe, and CUItubes after removal of HN03 and HNOz in the humid source with a NaZCO3tube. Table I11 summarizes the results of these experiments. Very little indication of NO2 reaction with W03 is noted. The KFe tubes appear to react to a small extend with NO2. This is evidenced by the signal found on the second KFe tube in a paired sequence. This may constitute a small interference in the HNOz analysis and is on the order of 3-10% of the NO2 signal, or it may be a small amount of HN02 impurity still. in the NO2 source. Ammonium nitrate or ammonium nitrite, if present in the molecular size range, may absorb on several of the hollow tubes but should produce an ammonia response when analyzed by use of a transfer tube. Some ammonia has been observed in ambient outside air analyses associated both with nitric acid (W03 tubes) and with H N 0 2 (KFe tubes). Some interference is expected from nitrated organic compounds and possibly peroxyacetyl nitrate (PAN) type compounds depending upon their site of absorption. PAN absorbed on the KFe tube would be an interferent in the HNOz analysis. Interference by particle deposition on the hollow tubes depends upon particle size and flow rate. Penetration of 0.1-rm-diameter particles through the four hollow tubes is 99.9% at a flow rate of 1.0 L/min as calculated by the Gormley-Kennedy particle equation (17). Application to Air Analyses. Sequential pairs of hollow tubes have been used in outdoor air analyses both in the Tampa, FL, and Claremont, CA, locations. Pairs of hollow tubes were used to test for removal efficiency of each analyte. A folded configuration of sampling tubes was used as shown
(9/16/85 11:05 a.m., 34
nmol/L ppbv
ng/L
0.47 10.4 29.3
0.59 13.1 27.5
0.24 5.33 11.0
OC,
0.38 8.5 11.4
26% RH) 0.98 21.9 16.6
0.49 11.1 8.4
0.42 9.3 26.1
Tampa, FLd (10/14/85 5:OO p.m., 21 OC, 56% RH)
nmol/L ppbv ng/L
0.073 3.6 4.6
0.053 1.2 2.5
0.285 0.085 0.005 0.014 0.14 6.4 1.9 0.11 0.32 3.2 13.1 2.6 0.08 0.25 8.9
Tampa, FLe (10/14/85 7:30 p.m., 15 "C, 72% RH)
nmol/L 0.033 0.487 1.04 0.16 0.006 0.36 0.80 10.9 23.3 3.6 0.13 8.2 17.9 ppbv 0.73 23 48 4.8 0.10 6.2 50 ng/L 2.1 "Efficiencies: HNO, 76%, HNOz loo%, NOz 72%, NO 95%. bEfficiencies: HNO, 79%, HNOz 85%, NOz 88%, NO 94%. 'Efficiencies: HNOB 75%, HNOz 87%, NOz 88%, NO 85%. dEfficiencies: HN09 81%, HNOz 99%, NOz 82%, NO (not paired). "Efficiencies: HNO, 80%, HNOz 64%, NOz 77%, NO (not paired). in Figure 1. Table IV gives results of some of these air analyses. Results were calculated in terms of nanomoles per liter so that a comparison of the relative amounts of each analyte could be made. A major finding is that nitrous acid is a ubiquitous and large component of ambient air. It is, on occasion, larger than "Os, NOz, and NO and appears to increase at night. A five-tube (W03, KFe, CUI, CO, and packed tube) sequence has been assembled, automated, and used in semicontinuous air analyses. Registry No. WO,, 11105-11-6; KzO, 12136-45-7; FezO3, 1309-37-1; CUI,7681-65-4; CoZO3,1308-04-9; "OB, 7697-37-2; "02, 7782-77-6; NOz, 10102-44-0; NO, 10102-43-9; "3, 766441-7.
LITERATURE CITED (1) Sakzman, B. E. Anal. Chem. 1954, 26, 1949-1955. (2) Lahmann, E.; Seifert, 8.; van de Wlel, H.; Huygen, C.; Lanting, R. W.; Hartkamp, H.; Gies, H. Afmos. Environ. 1976, 10, 835. (3) Beard, J. H.; Michael, E.; Suggs, J. C. J. Air. folluf. Control Assoc. 1977, 27, 553-556. (4) Stevens, R. K.; Hodgeson. J. A. Anal. Chem. 1973, 45, 443-449. (5) Helas, G.; Fianz, M.; Warnek, P. Int. J. Environ. Anal. Chem. 1981, 10, 155-166. (6) EPA Fed. Reglsf. 1973, 38,(June 8), 15174. (7) Shaw, R. W.; Stevens, R. K.; Bowermaster, J.; Tesch, J.; Tew, E. Afmos. Environ, 1982, 16, 845-853. (8) Durham, J. L.; Spiller, L. L,"Measurernent of Gaseous, Volatile and Nonvolatlle Inorganic Nitrate in Riverside, California". Presented at the 184th National Meeting of the American Chemical Society, Kansas City, Mo, 1982. (9) Bram'an, R. S.; Shelley, T. J.; McCienny, W. A. Anal. Chem. 1982, 54, 358-364.
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Anal. Chem. 1986, 58, 1541-1547 Possanzini, M.; Febo, A.; Liberti, A. Atmos. Environ. 1983, 77, 2605-26 IO. Ferm, M.; SJodin, A. Atmos. Environ. 1985, 79, 979-983. Sjodin, A.; Ferm, M. Atmos. Mvlron. 1985, 79, 985-992. Platt, U.;Perner, D.; Harris, G. W.;Winer. A. M.; Pitts, J. N., Jr. Nature (London) 1980, 2 8 5 , 312. Harris, 0. W.; Carter, W.P. L.; Winer, A. M.;Pitts, J. N., Jr.; Platt, U.; Perner, D. Environ. Scl. Techno/. 1982, 16, 414-419. Braman. R. S.;Trindade, M.; Han, Q. X. "A Sequential and Specific Hollow Tube System for Trace Nitrogen Compounds In Alr". Presented at the Thlrd Natlonai Symposlum on Recent advances in Pollutant Monitoring of Ambient Alr and Stationary Sources, May 3-6, 1983.
(16) Braman, R. S.; de la Cantera. M. A. And. Chem. 1988, 5 8 , 1533-1537. (17) Gormley, P.; Kennedy, M. R o c . Roy. I r . Acad., Sect. A 1949, 52A, 163-169.
RECEIVED for review November 19,1985.Accepted January 27,1986. The development of this specific hollow tube system was in part by NASA 'Ontract 16844 and by the Air Resource Board of the State of California.
Masking, Chelation, and Solvent Extraction for the Determination of Sub-Parts-per-Million Levels of Trace Elements in High Iron and Salt Matrices Mary Carol Williams* and Edward J. Cokal Los Alamos National Laboratory, Los Alamos, New Mexico 87545
Thomas M. Niemczyk Department of Chemistry, University of New Mexico, Albuquerque, New Mexico 87131
The ammonium pyrroiidlnsN-carbodthloate(APCD or APDC) and 4methyl-2-pentanone (methyl Isobutyl ketone or MIBK) system for the chelation and extraction of transition metals was investigated over the pH range of O< pH
