~
Table VII. Mass Spectral Fragmentation D a t a of the Hydrogenation Product of NDEA-HFBA Derivative (M) Mass of fragment, measured
Assigned formula
C12H,N,0,Fl, Cj?H,N,OF,, C,H,N?OF,
478.0358 441.0240 291.0377
Error of mass measurement
0.0012 0.0029 0.0009
Table VIII. Hydrogenated Products of Nitrosamine-HFBA Derivatives NDEA and NPYR
E-\~L.(
NPIP
M + 2H M-F-0 M-CsF7-0
sponding to the addition of more than two hydrogen atoms, indicating that the divinyl moiety did not give rise to a diethyl product. On this evidence and by comparison with the data presented in Table IV, it is concluded that a saturated cyclic structure had been formed (see Table VIII). Mass measurements on the hydrogenation products of the MDPA and NDBA derivatives gave similar results. The possibility of ion molecule reactions in the mass spectrometer was ruled out, since the proportion of M 2H produced from any of the above derivatives could be varied merely by changing the temperature of the hydrogenation chamber. At temperatures below about 150 “C, no hydrogenated material was detected. The temperature a t which the maximum proportion of hydrogenation occurred, increased as the series was ascended, but over 230 O C , pyrolysis occurred. Hydrogenation products of the heterocyclic nitrosamine derivatives were also studied under high resolution and both the NPIP and NPYR derivatives gave rise to some M 2H and M 4H, the structures being given in Table VIII. The result of saturating the ring in the case of the NPYR derivative is to produce a compound having the same structure as the hydrogenated NDEA derivative. The effect of using hydrogen as carrier gas was particularly interesting in the case of the dimethyl derivative, since one product was eluted a t the retention time of the NDEA de-
+
+
F
Source of fragment c-\(C‘OC
F
I
rivative and behaved in the same manner in the hydrogenation chamber. Somc unchanged NDMA derivative, together with a mixture of pyrolysis products, was eluted at the expected retention time. The exceptional behavior of the reaction between nitrosodimethylamine and HFBA is worthy of further study. The hydrogenation of the long retention dimethyl, and the diethyl and pyrrolidyl nitrosamine derivatives to give a common product is of potential analytical value. LITERATURE CITED (1) A. E. Wasserrnan, “N-Nitroso Compounds, Analysis and Formation,” International Agency for Research on Cancer, Publication No. 3, Lyon, 1972, p 10. (2) T. A. Gough and K. S. Webb, J. Chromatogr., 79, 57, (1973). (3) T. G. Alliston, G. B. Cox, and R. S. Kirk, Analyst (London). 97, 915 (1972). (4) D. D. Clarke, S. Wilk, and E. S. Gitiow, J. Gas Chromatogr., 4, 310 (1966). (5)J. B. Brooks, W. B. Cherry, L. Thacker, and C. C. Alley, J. hfec. Dis., 126, 143 1972). (6) J. N. Seiber, J. Agr. FoodChem., 20, 443 (1972). (7) J. July/August W. Blake, 1973. R . Huffman, J. Noonan. and R. Ray, Int. Lab., pp 57-61,
+
(8) J. B. Brooks, C. C. Alley, and R. Jones, Anal. Chem., 44, 1881 (1972) (9) T. A. Gough and K. S.Webb, J. Chromatogr., 64, 201 (1972). (10) M. Beroza and R. Sarmiento, Anal. Chem., 35, 1353 (1963).
RECEIVEDfor review May 20, 1974. Accepted November 1, 1974. Published by permission of The Government Chemist.
Selective and Sensitive Complexometric Determination of Calcium and Magnesium in Dolomites Using “Palladiazo” as a Metallochromic and an Adsorption Indicator Simultaneously M. D. Alvarez Jimenez, J. A.
Perez-Bustamante, and F. Burriel Marti
Departamento de Q u h i c a Analhica, Faculad de Ciencias y C.S.I.C., Universidad Complufense, Ciudad Universitaria, Madrid-3, Spain
The suitability of the palladiazo reagent for the complexometric (EDTA) titration of Ca( II) and Mg(ll) in dolomite has been demonstrated on the basis of the statistical evaluation of the experimental results obtained for the analysis of a certified standard dolomite sample. A curious and original feature of the method derives from the fact that the palladiazo reagent can act both as a metallochromic reagent (titration of Ca(ll) alone) or as an adsorption indicator (Ca Mg sum), thereby bullding a Ca-Mg-palladiazo blue ternary lake on the MZI(OH)~precipitate which turns purple upon the equivalent titration of Ca(ll) which is liberated from the lake while a binary purple Mg(OH)2-palladiazo lake remains undissolved. One to ten mg Ca(ll) can be determined directly in the presence of up to 10 mg Mg(ll) in 0.1 M NaOH
+
512
+
medium while the Ca( II) Mg( II) sum can be determined in a separate aliquot in a NH3-NH4+ medium (pH 10 f 1). The method shows an average standard deviation of f0.4% for Ca(ll) while for the indirect subtractive Mg( II) determinatlon, a maximum f0.6% value has been established.
1,8-Dihydroxy-3,6-disulfonic-2,7-bis(azophenyl-p -arsonic)acid, trivially known as “palladiazo” ( I ) , has proved to be a useful reagent for the spectrophotometric determination of Pd(I1) (2, 3 ) , although no suitable application has been shown so far in connection with the complexometric determination of metal cations. Its structural isomer arsenazo I11 is far more useful in this respect, acting as a valuable metallochromic indicator in the complexometric de-
ANALYTICAL CHEMISTRY, VOL. 47, NO. 3, MARCH 1975
termination of the lanthanons ( 4 ) , bismuth ( 5 ) , calcium and magnesium (6, 7) and a few other elements (8). Despite the unfavorable prospects of palladiazo for indicator applications, we succeeded recently in obtaining very promising results in connection with the already classical but always interesting and actual task of determining Ca(I1) in the presence of Mg(II), which invariably poses serious problems of interference as discussed elsewhere (6, 7, 9).
The present method is based on the fact that Mg(I1) and Ca(1I) (as well as Sr, Ba, and the lanthanons, although to a much lesser extent) give rise to the formation of colored complex species with palladiazo in alkaline media ( 1 0 ) which can be easily demasked by EDTA. On the other hand, the considerable solubility differences exhibited by the corresponding hydroxides, together with the strong tendency of Mg(OH)2 to build stable lakes with palladiazo in alkaline media (in contrast to Ca(OH)2 which does not) provide the basis to carry out the complexometric titration of Ca(I1) in the presence of Mg(I1) under suitable experimental conditions, as well as the possibility of the simultaneous determination of both elements if two different aliquots are titrated in different media. EXPERIMENTAL Reagents. The 0.1N EDTA solutions were prepared by dissolving “Merck” p.a. products as supplied, followed by standardization us CaC03, Hg, and P b as described elsewhere (11 ). A 0.1% palladiazo solution was used by dissolving solid samples prepared, purified, and analyzed by the authors (1, 12-15). These solutions remain stable over the years. Ca and Mg stock solutions were prepared and standardized by common methods ( 1 6 ) . Apparatus. A heating plate; a magnetic stirrer “Metrohm,” Model E 394A; a “Metrohm” pH-meter Model E516 in connection with a combined SCE-glass electrode system Type EA 120 U, and precision self-filling 5- and 10-ml “Afora” burets were used. Procedure. The 0.5- to 5-g dolomite samples are transferred into tall 250-ml beakers placed on a heating plate and small portions of diluted (1:3) HC1 are carefully added until no more effervescence is produced. Five to six ml of HC1 are then poured and the mixture is let boil under reflux for 1 hour in the beakers covered with watch-glasses. Upon cooling, the solutions are filtered and carefully washed into 50-500 ml measuring flasks. Then 1-10 mg Ca(I1) and/or Mg(I1) aliquots (1-10 ml) are pipetted into 50-ml beakers followed by the addition of water to make a volume of about 20 ml (if samples containing only one of the two elements are to be analyzed, the other component being only present as microimpurity, the aliquot size can be enlarged to correspond to 20 mg of the pertinent element). Then 1 ml 10% (v/v) triethanolamine solutions is added to the slightly acid solution for masking purposes(A1) as well as to establish a pH slightly alkaline. If the solution after this addition is still acid, it should be neutralized (pH meter) to pH 7-8 by addition of 0.1-1M NaOH. At this step, depending on whether Ca(I1) alone or the Ca(I1) + Mg(I1) sum is to be titrated, the following procedure has to be carried out taking two different aliquots: Aliquot 1 (Titration of the Ca(I1) Mg(I1) Sum). Add 5 ml of a 0.1M ammonia solution brought previously to pH 11.0 by addition of 0.1M HC104 (pH meter); followed by the addition of 2 drops of palladiazo solution (the volume of the titrand should amount a t this step to about 25-30 ml) and immediately start the EDTA titration until the initially bluish color changes neatly to rosy or pink a t the end point. Aliquot 2 (Titration of Ca(I1) Alone). Add 3 ml 1M NaOH followed by enough water to make a volume of about 30 ml and 2 drops of palladiazo solution, immediately starting the EDTA titration until the color changes in the same fashion as indicated above. The indirect determination of Mg(I1) is carried out by subtracting the reagent volume needed for the titration of aliquot 2 from that of aliquot 1.
+
RESULTS AND DISCUSSION Influence of Experimental Conditions. A number of interesting observations have been made in connection
with the influence of the medium ionic strength (p),aging of the eventual properties prior to the titrations, order of addition of the indicator, etc. Since the sample is submitted to acid attack and must be neutralized to establish the proper medium, special care must be taken not to use a too great excess of HC1 which may result in a too high final ionic strength. Blank experiments carried out with pure acid-free Ca(I1) solutions t o which varying amounts of NaCl were added (the 0.1-2 ionic strength interval was investigated) indicate that even for values as high as = 2 the titration is feasible. However, the lower the total salinity of the titrand, the sharper the end-point color change becomes. For practical purposes, it has been concluded that the amount of HCl to be added for the dissolution of the sample should be calculated in such a way as to establish (upon neutralization) a final p = 0.1-0.5 value in the final volume of titrand (about 30 ml). Other points of special interest are related to the type of titration, aging of precipitates, and way and moment of addition of the indicator: Ammonia-Ammonium Medium (Starting p H 11 ). Both ionic Ca(I1) and Mg(I1) build a blue complex (the former being more intensively colored and brilliant) with palladiazo which sharply turns to pink a t the end point upon the equivalent addition of EDTA. If Mg(OH)2 is built before the addition of palladiazo, it causes the reagent to become immediately adsorbed on its surface, building a characteristic lake. In the absence of Ca(II), this lake exhibits a purple color; while if Ca(I1) is present, the formation of a bluish ternary Mg-Ca-palladiazo lake takes place. Special care must be taken not to allow this lake to age unduly (10 minutes is even too long a time) for titration purposes since the end-point color change deteriorates markedly as a function of the aging process. To restrict or to avoid insofar as possible both the initial formation of Mg(0H)z as well as the origination of an irreversible aged lake if too much time (5-10 min) is let elapse upon the addition of palladiazo before starting the titration, it is strongly recommended to proceed as quickly as possible with the addition of palladiazo just upon establishing the suitable alkaline medium carrying out the titration immediately. No problem of this kind arises when Ca(I1) ions alone are to be titrated. Sodium Hydroxide Medium (O.1M). In this case, Mg(OH)2 precipitates instantaneously giving rise to the formation of the purple lake with palladiazo just upon the addition of the indicator. In the presence of Ca(II), the lake is blue as derived presumably from the formation of a ternary-complex adsorbate. A very interesting set of phenomena occurs, however, when the titration is carried out immediately after the addition of NaOH and palladiazo (in this order) to the sample: the blue lake turns pink just a t the equivalence point for Ca(I1) and the color remains stable; on the other hand, the sharp color change associated with the Ca(I1) titration has been shown to take place on the surface of Mg(OH)2 suspended precipitate. If a great EDTA excess is added after the equivalence point, the Mg(OH)2 precipitate redissolves progressively, whereby both the supernatant liquid and the remaining precipitate exhibit the characteristic rosy palladiazo color (alkaline medium). Titration Features Using Synthetic Solutions. The titration features of Ca(I1) with EDTA have been investigated within a wide concentration interval (0.2-25 mg Ca2+)as shown in Table I. The final pH value a t the upper limit investigated was shown to lie between 9-9.5. When the titration of a greater amount of Ca(I1) was attempted &e., 36.8 mg), it proved to be unfeasible as shown by dras-
ANALYTICAL CHEMISTRY, VOL. 47, NO. 3, MARCH 1975
513
Table I. Study of the Complexometric Titration Characteristics of Ca(I1) Using Palladiazo as Indicatola EDTA consumption, m l
W W , mg n 24.55 15 14.73 15 9.82 15 4.91 15 2.45 10 2.45 15 0.982 15 0.491 15 0.2555 15 a Ammonium-ammonia medium; starting pH 11.
EDTA x 0.9839 (N)
Theoretical
0.1 0.1 0.1 0.05 0.05 0.01 0.01 0.01 0.001
6.225 3.737 2.490 2.490 1.245 6.225 2.490 1.245 6.225
Experimental (Z + s)
6.283 3.749 2.506 2.505 1.250 6.270 2.492 1.258 6.290
i 0.036 f 0.008 i 0.012
* 0.009
i 0.006 i 0.010
i 0.013 i f
0.007 0.030
Table 11. Study of the Complexometric Titration Characteristics of Mg(I1) Using Palladiazo as IndicatoF EDTA consumption, m l Mg
”
(W,mg
EDTA x 0.9839 ( N )
Theoretical
0.1 0.1 0.1 0.01 0.01 0.01
4.650 2.325 1.162 4.650 2.325 1.162
11.12 15 5.560 15 15 2.780 1.112 15 0.5560 15 0.278 15 a Ammonium-ammonia medium; starting pH 11.
Experimental (Si
S)
4.651 i 0.012 2.335 i 0.008 1.170 i 0.007 4.642 i 0.001 2.334 0.025 1 . 1 8 1 i 0.01
*
Table 111. Complexometric Titration of Ca(I1) in the Presence of Mg(I1) Using Palladiazo as Indicator (0.1MNaOH medium) EDTA consumed by Ca(II), m l
CaW), mg
9.82 9.82 9.82 9.82 9.82 0.982 0.982 0.982 0.982 0.982 0.982 0.0982 0.0982
h%(%
mg
11.12 5.56 2.78 1.11 0.111 10.01 5.00 0.945 0.477 0.239 0.111 0.556 1.11
”
EDTAx 0.09758 ( N )
Theoretical
6 6 6 6 6 6 6 6 6 6 6 6 6
0.1 0.1 0.1 0.1 0.1 0.01 0.01 0.01 0.01 0.01 0.01 0.001 0.001
2.511 2.511 2.511 2.511 2.511 2.511 2.511 2.511 2.511 2.511 2.511 2.511 2.511
Experimental (% i S)
2.46 2.48 2.48 2.48 2.46 2.50 2.49 2.48 2.47 2.48 2.50 2.49 2.48
i
0.02
i 0.03 i 0.03 i 0.03 i 0.04
* 0.00 i 0.02 i 0.03 i 0.02
0.03 0.00 0.02 i 0.02 i i i
Table IV. Experimental Results and Statistical Evaluationa of the Precision Associated with the Complexometric Determination of Ca(I1) in Dolomite ( 0 . M NaOH medium) Using Palladiazo as Indicator % CaO, .?a s 31.25 0.10 31.31 f 0.12 31.54 i 0.09 31.24 i 0.10 31.52 f 0.20 31.50 i 0.12 Av. 31.39 5 0.12 a Carried out according to the recommendations stated in ( 1 7 ) . Ordinary “AFORAI’ calibrated glassware was used throughout this research.
514
Sample, g
Dilution, m1*
Aliquot, mlb
EDTA 0 . 9 9 5 5 ~ , m l b
n
0.5111 0.4976 5.0053 1.0056 1.0057 0.9925
50 50 500 100 100 100
5 5 5 4 4 4
2.861 2.791 2.828 2.251 2.262 22 4 0
8 8 20 7 7 6
ANALYTICAL CHEMISTRY, VOL. 47, NO. 3, MARCH 1975
*
~~
~~~
Table V. Experimental Results and 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 at 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 at 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, at 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). (4) W. W. Marsh and G. Myers, Anal. Chim. Acta, 43, 51 1 (1968). (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-Bustamanteand 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
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