~~
~~~
Table V. Experimental Results a n d Statistical Evaluation of the Precision Associated with the Complexometric Indirect Determination of Mg(I1) in Dolomite (NH3/NH4+Medium; pH 10 f 1) Using Palladiazo as Indicator EDTA 0.9955N9 m l Sample, g
Dilution, m l
Aliquot, m l
Ca(l1) T Mg(I1)
Mg(II)a
n
5.0053 1.0056 1.0057 0.9925
500 100 100 100
5 4 4 4
4.377 4.418 4.41 1 4.362
2.115 2.167 2.148 2.123
10
7 7 7
% MgO, % r S ,
*
21.19 0.20 21.61 j: 0.25 21.43 + 0.32 21.46 k 0.23 Av 21.42 k 0.25
Q T h e volume of t i t r a t o r solution consumed by Mg(I1) was calculated by subtracting t h e pertinent Ca(I1) values report,ed in T a b l e I V f r o m the Ca(I1) Mg(I1) values reported in t h e preceding column of t h i s table. Otherwise, same observations as stated (footnotes) for T a b l e I V .
+
tic pH changes down to 5-6. On the other hand, the lower Ca(I1) limit (about 0.2 mg) could not be reasonably reduced because of unsharp color change. The results of similar investigations carried out with Mg(1I) are reproduced in Table 11, which resemble closely those obtained for the Ca(I1) titrations. Finally, an orientative study was undertaken to establish the applicability of the method for the determination of Ca(I1) in a 0.1M NaOH medium in the presence of different amounts of Mg(I1). The results obtained for titrations involving different absolute amounts of Ca(I1) as well as varying Ca(II):Mg(II) ratios established a t each Ca(I1) level are given in Table 111. The results indicate that optimum conditions are established for the 1-10 mg range of Ca(I1) especially when the Ca:Mg ratio (mg) lies below 4:1, although satisfactory titrations can be carried out even a t 1:1 ratios in the upper Ca(I1) (10 mg) limit and a t 1:10 ratios for the lower Ca(I1) (1 mg) limit, a t the cost in this case of a certain loss of precision. Application of t h e Method to t h e Analysis of a Stand a r d Dolomite Sample. Once the applicability limits of the method were established from the experiments carried out on synthetic solutions, the suitability of the method as applied to real samples was tested on a standard dolomite (Hoepfner Gebr., Hamburg, W. Germany), the nominal composition of which was certified as: moisture (0.49%), Si02(2.78%), Fe203(0.55%), &03(0.76%), Mn0(0.12%), S03(0.16%), Ca0(31.29%), MgO(21.29%), ignition loss less moisture (41.88%). The results obtained are shown in Tables IV and V for the direct Ca(I1) and indirect Mg(I1) titrations, respective-
ly. On the basis of the extensive statistical treatment carried out in connection with these titrations, it can be safely concluded that the new method proposed offers very hopeful possibilities in regard to the accurate and reproducible determination of Ca(I1) and Mg(I1) in dolomite samples. LITERATURE CITED (1) J. A. Perez-Bustamante, Doctoral Thesis, Madrid, 1967. (2) J. A. Perez-Bustamante and F. Burriel Marti, Anal. Chim. Acta, 37, 49 (1967). (3) L. Bocanegra Sierra, J. A. Perez-Bustamante, and F. Burriel Marti, Anal. Chim. Acta, 49, 231 (1972). Anal. Chim. Acta, 43, 51 1 (1968). (4) W. W. Marsh and G. Myers, (5) M. D. Alvarez Jimenez, J. A. Perez-Bustamante, and F. Burriel Marti, Anal. Chim. Acta, 50, 354 (1970). (6) V. Michaylova and N. Kouleva, Talanta, 20, 453 (1973). (7) V. Michaylova and P. Ilkova, Anal. Chim. Acta, 53, 194 (1971). (8) S. B. Savvin, "Organic Reagents of the Arsenazo 111 Group." Atomizdat, Moscow, 1971. (9) G. Schwarzenbach and H. Flashka, "Complexometric Titrations," 2nd ed., Methuen. London, 1969. IO) M. D. Alvarez Jimenez, unpublished results, Doctoral Thesis. 11) W. Poethke and C. Jaekel, fharm. Zentralh,, 107, 417 (j968). 12) J. A. Perez-Bustamante and F. Burriel Marti, Inform. Quim. Anal., 22, 25 (1968). 13) J. A. Perez-Bustamante and F. Burriel Mart(, Inform. Q u h . Ana/., 22, 31 (1968). 14) J. A. Perez-Bustamante and F. Burriel Mart(, Talanta, 18, 183 (1971). 15) J. A. Perez-Bus!amante and R. Parellada Bellod, An. Ouim., 64, 213 (1968). 16) "Metodos Complexometricos de Valoracion con Titriplex," E. Merck A.G., Darmstadt. (17) Anal. Chem. 45, 2450 (1973).
RECEIVEDfor review March 19, 1974. Accepted October 11, 1974.
Determination of an Ozone interference in the Continuous Saltzman Nitrogen Dioxide Procedure Ralph E. Baumgardner, Thomas A. Clark, J. A. Hodgeson, and Robert K. Stevens Environmental Protection Agency, National Environmental Research Center, Chemistry and Physics Laboratory, Research Triangle Park, N.C. 2771 1
A detailed study was undertaken to determine whether an ozone interference exists in the continuous Saitrman NOP procedures and to quantify the effect if present. Generation of dynamic mixtures of nitrogen dioxide and ozone required in the interference tests necessitated the examination of the ozone-nitrogen dioxide gas phase reaction. Newly deveioped chemiluminescent analyzers for ozone and nitrogen
dioxide were used to monitor the ozone-nitrogen dioxide stream. A negative interference was found in both the continuous Saltzman and modified Saltzman procedures. The interference is dependent on the ratio of ozone to nitrogen dioxide. Ozone and nitrogen dioxide data from four cities are compared to determine ozone to nitrogen dioxide ratios that exist in the atmosphere.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 3, M A R C H 1975
515
Since 1972, methodology for the measurement of nitrogen dioxide in ambient air has been under review by the Environmental Protection Agency. During this review, serious deficiencies were discovered in the promulgated reference method for the monitoring of N02. A reevaluation of potential sampling techniques for NO2 has been necessary. One of the techniques being studied for possible acceptance as a reference method is the continuous Saltzman procedure (I). This procedure was first described in 1954 by Saltzman ( 2 ) for the manual determination of sub-ppm concentrations of NO2 in the atmosphere. The analysis consisted of absorption of NO2 and subsequent color formation in a solution of sulfanilic acid, ethylenediamine dihydrochloride, and acetic acid. Colorimetric measurement was made at 550 nm. The procedure was automated in 1956 by Thomas et al. ( 3 ) for continuous analysis. In 1960, Saltzman ( 4 ) altered reagent concentrations to better fit continuous sampling. Lyshkow ( 5 ) modified the Saltzman reagent and sample flow to further facilitate measurement in a continuous manner. The Lyshkow or modified Saltzman Procedure has been used in continuous air analyzers while the original Saltzman procedure has been used for both manual and automated measurement. Both procedures have been used widely for determination of NO2 concentration not only in the United States but also in many other countries (6-8). A number of comparison and evaluation studies have been reported recently dealing with the continuous Saltzman and the modified Saltzman procedure (9-11). Operating parameters, response characteristics, and maintenance requirements have been examined. Evaluation of potential interferent gases, however, has not been undertaken. Discussion of interferents in the two procedures has been limited to the original work by Saltzman on the manual determination of NO*. The possible interference of ozone is of particular interest because of the coexistence of NO2 and ozone in the atmosphere (12). Saltzman in his original work stated that the determination of an ozone interference was difficult because of the reactivity of ozone and because of the possible reaction between ozone and NO2 in the sample stream. The reaction rate between NO2 and ozone gas been determined by a number of researchers. Hampson et al. (13) have reviewed the available data and recommended a rate conppm-' sec-l. Saltzman determined in stant of 1.51 X the manual procedure a t a five to one ozone to NO2 ratio that a change in reagent color was detectable and, at a ten to one ratio, the reagent was destroyed. Later reports on automating the procedure by Thomas, Saltzman, and Lyshkow did not refer to possible interference of ozone. In a paper on interferences in continuous air monitors by Mueller et al. j14), reference was made to the original work by Saltzman as well as a 1959 report by ASTM that a 1pprn concentration of ozone would decrease the NO2 response by 10%. Much of the difficulty in determining the interference of ozone in the Saltzman procedures or other atmospheric monitoring techniques was that a sensitive specific ozone analyzer and a sensitive, specific independent method for NO2 measurement were not available. These instruments would enable measurement of the ozone-N02 stream to monitor the reaction taking place. Between 1970 and 1973, new instrumentation was developed for the measurement of ozone and NOz. In 1971, EPA established the chemiluminescent ozone-ethylene technique as a reference method for the measurement of ambient concentrations of ozone (15). This technique is sensitive and virtually interferencefree. During this same time, a monitor was developed based 516
ANALYTICAL CHEMISTRY, VOL. 47,
NO. 3,
on the chemiluminescent reaction of ozone with NO for NO measurement and by conversion of NO2 to NO for measurement of NO2 with the same monitor. With these new techniques available, it was possible to reexamine the interference of ozone in the continuous Saltzman and modified Saltzman procedures. This report describes an in-depth study to determine whether an ozone interference exists in the Saltzman or the modified Saltzman procedure and to quantify the effect if present. Since dynamic mixtures of NO2 and ozone are required in the interference tests, it was necessary to determine the extent of the 03-NO2 reaction occurring in the gas phase prior to absorption by the Saltzman reagent.
EXPERIMENTAL Instrumentation used in the study included the Bendix Model 8100, NOn, NO, NO, Monitor (chemiluminescent), the Technicon Model IVA NO2 Monitor (modified Saltzman procedure), and a Bendix Model 8000 Ozone Monitor (chemiluminescent). An ozone generator and standard cylinder of NO were also used to provide gas concentrations needed in the study. A NO2 permeation bottle (NBS) (16, 17) was also used as an independent method of generating NOz. The Bendix NO, NOn, NO, Monitor and Bendix Model 8000 Ozone Monitor were set up according to procedures specified in the instruction manuals. Since the Technicon Model IVA NO2 Monitor uses the modified Saltzman procedure, it was necessary to change reagent and reagent flow rate when tests were performed using the Saltzman procedure. Reagent flow rate was increased from 0.30 cm3/min to 0.40 cm3/min and sample air flow was increased from 315 cm3/min to 420 cm3/min. Reagent formulation for the Saltzman procedure was 5 grams of sulfanilic acid, 50 ml of glacial acetic acid, and 0.10 gram of N-(1-napthy1)ethylenediamine dihydrochloride (NED) dissolved in 1 liter of distilled water. This formulation was recommended by Saltzman for use in continuous analyzers (18).Reagent for the modified Saltzman (Lyshkow) consisted of the following: 0.050 gram (NED), 0.050 grams 2-naphthol3,6 disulfonic acid disodium salt, 1.50 grams sulfanilamide, 15.0 grams of tartaric acid dissolved in 1000 ml of distilled water ( 5 ) . The Technicon IVA NO2 Monitor was selected as an example of an automated colorimetric analyzer which was designed to use the Saltzman and modified Saltzman procedure (19).Other colorimetric analyzers are available which may differ in design and performance. Saltzman (18)and Lyshkow ( 5 ) found that performance in an automated system was related to reagent formulation, absorbing column, sample and reagent flow rate. Results obtained using the Technicon monitor and the conditions as stated may differ in degree from other available colorimetric NO2 analyzers. Instrument Calibration. The ozone generator was calibrated using the KI method as described in the Federal Register (15). Using the ozone generator to produce known concentrations of ozone, a standard cylinder of NO (nitric oxide) was calibrated by 03-NO gas phase titration (GPT technique) (20).A plot was made of decrease in NO detector response us. increments of ozone added. From the equivalence point in the titration, the cylinder concentration was determined. The NO1 concentration in the standard NO cylinder was determined to 22629 gg/m3 (12 ppm) by the manual Saltzman procedure. This NO2 concentration, 10% of the NO value, is an abnormally high value. Thus, the concentration produced by flow dilution of residual NO2 in the cylinder is added in subsequent calculations to the NO2 concentration produced by GPT. The Bendix NO, NO*, NO, Monitor as well as the modified Technicon IVA NO2 Monitor were calibrated using the gas phase titration as described. Known concentrations of NO2 in the range of 0-0.50 ppm were generated using an excess of NO and adding known amounts of ozone. A linear response was obtained for each instrument from 0-0.50 ppm. Both instruments were spanned on the 0-0.50 pprn full scale range using a 858 gg/m3 (0.45 ppm) concentration of NO*. The Bendix ozone monitor was calibrated directly from the ozone generator. After calibration of both the Bendix and Technicon instruments was completed by GPT, the calibration was checked using a NO2 permeation tube whose rate had been determined using a Cahn Electrobalance. The two calibration methods agreed within f6%. The span was not changed from the initial adjustment, and all subsequent measurements are related to the calibration by GPT.
MARCH 1975
A sampling and gas generating system was constructed as shown in Figure 1. It was possible using this system to generate concentrations of NO2 by mixing NO from a cylinder with ozone from a generator or NO2 from a permeation system. Ozone for the interference test was generated using the ozone generator and could he added to either source of NOz. Diluent air used in each generating technique was provided from the same clean air supply. Interference Tests. Once the modified Technicon and Bendix were calibrated and zeroed on a sample of ozone free air, an ozone concentration of 98.3 pg/mS (0.05 ppm) was added to each instrument. The ozone concentration was then changed to 295 pg/m3 (0.15 ppm). No change from the zero reading was noted on either instrument. Ozone in varying amounts was then added to the instruments which were sampling a constant concentration of NOz. Both the gas phase titration and the NO2 permeation tube were used to generate the NOz. The gas phase system was used first. A NO concentration of 123 pg/m3 (0.10 ppm) was generated using the gas phase system. An ozone concentration of 393 pg/m3 (0.20 ppm) was added to produce 188 pg/m3 (0.10 ppm NOz) and a residual of 196 yg/m3 (0.10 ppm) ozone. The NO2 response was noted on both the Bendix and the Technicon. The residual ozone was measured on the Bendiz ozone monitor. The NO concentration was held constant at 0.10 ppm and the ozone concentration was varied to give residual ozone concentrations of 196 pg/m3 (0.10 ppm) to 786 pg/mS (0.40 ppm). The NO2 concentration during each step was constant; therefore, the NO2 response of the two monitors should remain constant. Table I shows the calculated and observed concentrations in pprn by volume, residuals, and response values for each instrument. Also included in the table are the OZ/NO2 ratios created by the residual ozone, and the 96 decrease in response with increasing ozone/NOz ratios and the calculated NO:
