ACKNOWLEDGMENT
Table IV.
2: 1 HAC-CHC18 present, ml. 25 20 15 25
Effect of Acid Concentration on Peroxide Recovery
Solvent Benzene
Present, ml.
Chloroform
20
0 5 10 0 7
10
15
2-Propanol
25
20 15 10 5
0 5 10 15 20
Active Present
02,
420 420
rg.
Found 431 43 1
K o t miscible 329 329
323 326
43 1 431 43 1 43 1 43 1
438 445 438 448 43 1
S o t miscible
The authors thank the Lucidol Division, Wallace & Tiernan, Inc., and Hercules Powder Co. for supplying the samples of commercial peroxides used in this study. The assistance of A. E. Mertes with some of the analyses reported here is also appreciated. LITERATURE CITED
(1) Altshuller, A. P., Schwab, C. >I., Bare, M., ANAL.CHEM.31, 1987 (1959). (2) Dugan, P. It., Ibid., 33, 696 (1961). (3) Ibid.. D. 1630. (4) Ibid.; i5, 414 (1963).
(5) Eiss, M. E., Geisecke, P., Ibzd., 31,
determine the active oxygen levels at a n y particular time. Effect of Acidity. T o determine whether variations in t h e acid concentration of t h e reaction mixture had a n y effect on peroxide recovery in t h e presence of solvents, t h e rccovery of active oxygen from solutions containing known amounts of hydroxyheptyl peroxide and varying amounts of 2 t o 1 acetic acid-chloroform was checked (Table IV). All the solutions were made u p t o volume with the solvent under test. The ratio of acetic acid-chloroform and solvent can be varied between fairly wide limits without affecting the quantitative recovery of active oxygen. The main limitation on the volume of sample that can be used is its miscibility with the
acetic acid-chloroform mixture. I n almost all cases, 5 ml. of the solvents tested were miscible with 20 ml. of acetic acid-chloroform. Recovery of peroxide was quantitative when as little as 20% by volume of acetic acidchloroform was present in the solvent mixture. It should therefore be possible to determine peroxide groups on polymers and other organic solids if the solution of the material is compatible with the minimum amount of acetic acid-chloroform required for the reaction of the peroxide with iodide. Attempts to determine di-tert-butyl peroxide by using HCl to increase the acidity were unsuccessful. Ten milligrams of this peroxide gave a pale yellow 2 hours after solution in 1 to 1 HCl and the addition of KI.
1558 (1959). (6) Heaton, F. W., Uri, K.,J . Sci. Food Agr. 9, 781 (1968). (7) Kolthoff, I. L l . , Xedalia, A. I., AN.41,. CHEM. 23, 595 (1961). (8) I,ea, C. H., Proc. Rou. SOC.108B, 17n (1931).
(9) Martin. A. J., “Organic Analysis,” Yol. 4, p. 3, Interscience, New York, 1960. (10) Pobiner, H., ANAL. CHEM.33, 1423 (1961). ( I 1) Ryland, A. L. , Division of Analytical Chemistry, 142nd Meeting ACS, .4tlantic City, zi. J., September 1962. (12) Silbert, L. S., J . .Ana. 022 Chemists’ SOC.39,480 (1962). (13) Silbert, L. S., Witnauer, L. T., Swern, D., Iticciuti, C., J . =Im.Chem. SOC.81, 3244 (1959). (14) Sorge, G., Ueberreiter, K., Angew. Chem. 68, 352 (1956). (15) Wolfe, W. C., ANAL. CHEM. 34, 1328 (1962). RECEIVED for review Xovember 21, 1963. Accepted December 30, 1963.
Simultaneous Spectrophotometric Determination of Calcium and Magnesium with Chlorophosphonazo 111 JERRY W. FERGUSON, JOHN J. RICHARD, JEROME W. O’LAUGHLIN, and CHARLES V. BANKS lnstitute for Atomic Research and Department of Chemistry, lowa State University, Ames, lowa
b A rapid and sensitive spectrophotometric procedure for determining calcium and magnesium with Chlorophosphonazo 111 is described. Either calcium or magnesium may b e determined a t p H 7.0 in the range of 0.1 pg. per 25 ml. (0.004p.p.m.) to 10 pg. per 25 ml. (0.4 p.p.m.). In mixtures of calcium and magnesium, calcium is determined a t pH 2.2 a t a wavelength of 667.5 mp. The magnesium is then determined by difference a t p H 7.0 and 669 mp, where the absorbances due to the two metal complexes are additive. Milligram amounts of the alkali metals can b e tolerated but most other metals interfere.
A
spectrophotometric procedure for the determination of trace amounts of calcium and magnesium was needed for a study of the SENSITIVE
796
ANALYTICAL CHEMISTRY
extraction of the alkaline earths with organophosphorus compounds. Reagents used for the spectrophotometric determination of calcium include murexide (22, 23, 24, 26, 27, Sf),ocresolphthalein complesone (23), chloranilic acid (6,29),and Eriochrome Black T (32). Most of these reagents have fairly low sensitivities and are not stable. Their use requires very close control of experimental conditions for reliable results 4 recently suggested reagent for calcium is glyoxalbis-(2hydroxyanil) ( 8 , 12). It is sensitive and small amounts of magnesium are reported not to interfere. The spectrophotometric determination of magnesium with lake-forming reagents such as Titan Yellow (7, 10, I S , 14, SO), Thiazole Yellow (11, 18, f9), and Brilliant Yellow (28) has been reported. These reagents are fairly sensitive but, like most such lake dyes,
require estremely close attention to experimental details for reliable results. Eriochrome Black T has been used for the determination of magnesium (4, 9, 26, 23, 32) and for the simultaneous determination of calcium and magnesium (32). A recently reported reagent for magnesium, Magon (1, 16, l y ) , is sensitive and forms a fairly stable complex with magnesium. The use of 2,7-bis-(4-chloro-2-phosphonobenzeneazo) - 1,8-dihydrosynaphthalene-3,6-disulfonic acid (Chlorophosphonazo 111) as a sensitive reagent for both calcium and magnesium is reported here. The synthesis and use of this reagent for the spectrophotometric determination of uranium were reported by Nemodruk et al. (20). Chlorophosphonazo I11 has also been used for the spectrophotometric determination of titanium, zirconium, thorium, and scandium ( 5 ) , quin-
0.6
-
0.5 0 W
z a
m
0.1 -
450
550
5 00
600
650
700
750
WAVELENGTH IN mp
Figure 1 .
Effect of pH on Chlorophosphonazo 111
1.6 X lO-5M Chlorophorphonozo 111 in water
quevalent actinide elements ( 2 ) , and protactinium (3). Chlorophosphonazo I11 was found to be a very sensitive reagent for both calcium and magnefium at p H 7.0. Only calcium was appreciably complexed a t a p H of 2.L!, however. I t is therefore possible to determine calcium alone a t p H 2.2 and calcium and magnesium a t p H 7.0.
compound was prepared using the procedure Savvin (26) used for the preparation of Arsenazo 111 but substituting 2-amino-5-chlorobenzenephosphonic acid for the o-aminophenylarsonic acid used in this procedure. The 2 - amino - 5 - chlorobenzenephosphonic acid was prepared by the method of Lukin (15). The chief disadvantage of the latter method for the preparation of Chlorophosphonazo
I11 is the introduction of calcium, which is strongly complexed by the reagent. The calcium was removed by passing the reagent through a cation exchange resin (Dowex 50R-X8 in the acid form). A 2 X 10-4N solution of the reagent was prepared by dissolving 165.8 mg. of the reagent in 1 liter of water. Procedure at pH 7.0. Pipet a n aliquot containing 1 to 10 pg. of calcium and/or magnesium into a 25-ml. volumetric flask. In case of a sample, adjust to approximately p H 7 with dilute acid or tetrabutylammonium hydroxide. Add 5 ml. of 2 X 10-4Jf Chlorophosphonazo I11 and 5 ml. of the p H 7.0 buffer. Dilute to volume with distilled water and read the absorbance a t 669 mp in 1-cm. silica cells. Read all solutions against a reagent blank prepared by the same procedure. For 0.1 to 1 pg. of calcium or magnesium, use 5 ml. of 2 x 10-5Jf Chlorophosphonazo I11 and read the solutions in 5-cm. silica cells. Procedure at pH 2.2. Pipet an aliquot containing 5 to 30 pg. of calcium or calcium and magnesium into a 50-ml. beaker. Add 5 ml. of 2 X 10-4M Chlorophosphonazo I11 and adjust the p H to 2.2 with dilute hydrochloric acid. Transfer to a 25-ml. volumetric flask, using a pH 2.2 hydrochloric acid solution to rinse the beaker and to dilute to volume. Read a t 667.5 mp in l-cm. silica cells against a reagent blank prepared by the same procedure. RESULTS AND DISCUSSION
Figure 1 shows the spectra of solutions of Chlorophosphonazo I11 as a function of pH. Spectra of the calcium
EXPERIMENTAL
Apparatus. All spectra were obtained on a Cary Mcidel 14 recording spectrophotometer. Absorbance measurements were made on a Beckman Model DU spectrophotometer. All spectrophotometric m ?asurements were made in matched silicna cells 1.000 and 5.000 cm. in length All p H measurements were made with a Beckman Model G p H meter Reagents. Analytical grade reag e n t s were used unlws otherwise indicated. The p H 7.0 buffer solution was prepared froni tetra-n-butyla m m o n i u m hydroxid: and boric acid. T h e tetra-n-butylammonium hydroxi d e was prepared by adding 10 grams of tetra-n-butylammonium iodide and 6 . 3 grams of powdered silver oxide t o about 400 ml. of water. After stirring for 1 hour, the silver iodide was filtered off and thl: solution diluted to 500 ml. One hundred milliliters of this solution and 20 grams of boric acid were used to make 1 liter of the buffer solution. Additional boric acid was then added to the buffer until a 5-ml. aliquot diluted to 25 .nl. gave a p H of 7.0. The authors were unable to prepare Chlorophosphonazo 111 by the method proposed by Nemodruk et al. (20). The
0.5
-
0.4
-
0.2
-
-
C
u
2m 9
-0.2-
450
500
550
600
650
700
740
WAVELENGTH IN mp
Figure 2. Spectra of Chlorophosphonazo Ill and its complexes with calcium and magnesium a. 1.2 X 1 O-6M Chlorophosphonazo 111 in water b. pH 7.0 procedure: 5 pg. calcium read against reagent blank c.
pH 7.0 procedure:
5 fig. magnesium read against reagent blank VOL. 36, NO. 4, APRIL 1964
797
and magnesium complexes and of the reagent itself at pH 7 are shown in Figure 2. The variation in the apparent molar absorptivity, calculated from the difference in absorbance of the sample and a reagent blank at 669 nip, of the calcium and magnesium complexes is shown as a function of p H in Figure 3. One-centimeter silica cells were used to obtain all data for the three figures. The apparent molar absorptivity of both the calcium and magnesium complexes is greatest near p H 7. The absorptivity of the magnesium complex decreased much more rapidly with p H and is almost negligible at pH 2.2. At this pH calcium can be determined with only a very small interference from magnesium. The total magnesium and calcium can then be determined a t pH 7 and in the case of larger amounts of magnesium the absorbance a t p H 2.2 can be corrected for the minor contribution due to magnesium. The apparent molar absorptivities at p H 7.0 at 669 mp were 64,000 and 48,000 liters per mole-em. for calcium and magnesium, respectively. The apparent molar absorptivities at p H 2.2 and 667.5 mp were 14,600 and 66 liters per mole-cm. for calcium and magnesium, respectively. Range. The absorbance of both t h e calcium and magnesium complexes at pH 7.0 was found t o follow Beer’s law up to 10 pg. per 25 nil. The absorbance of the calcium complex a t p H 2.2 follows Beer’s law up to 30 pg. per 25 ml. When both calcium and magnesium were present at pH 7.0, the absorbances of their complexes w-ere additive. By using 5-cm. cells, amounts
Table 1.
Ion added Li + Na +
K’
KH1+ Sr +2 Ba +z
Interferences
Amount of ion giving A
=
0.010
pH 7 . 0
pH 2 . 2
13 rg. 182 pg. 770 pg. 250 pg. 0 . 3 2 pg. 0 . 6 0 pg.
800 pg. 9 mg. 22 mg. 5 . 5 mg. 0 . 9 pg. 1 . 5 pg.
Table II. Simultaneous Determination of Calcium and Magnesium
Calcium Magnesium Present, RePresent, Repg./ml. covered, 70 ug./ml. covered, % 0.50 1.00
1.50 2.00 2.50
798
100.0 102.0 97.0 97.0 100.0 100.7 100.0 101.0 100.0 101.2
2.50 2.00 1.50
1.00 0.50
ANALYTICAL CHEMISTRY
104.8 99.6 101.0 101.5 100.7 99.3 97.0 100.0 98.0 100.0
PH Figure 3. Effect of p H on calcium and magnesium complexes with Chlorophosphonazo 111 Absorbance measurements made againrl reagenl blanks at same pH
down to 0.1 fig. per 25 ml. of calcium or magnesium can be measured fairly accurately at p H 7.0. Effect of Time. A time study was r u n at both p H 7.0 and p H 2.2 for samples containing various amounts of calcium, and at p H 7.0 for samples containing various amounts of magnesium. Readings were taken a t time intervals ranging from 10 minutes to 1 week. The absorbance was found t o be stable for the entire time period in all cases. Complex Ratios. Job’s plots indicated t h a t both calcium and magnesium form 1 t o 1 complexes with Chlorophosphonazo I11 at pH 7.0. Interferences. Barium and strontium interfere at both pH 7.0 and p H 2.2; large amounts of lithium, sodium, potassium, and ammonium ions interfere at pH 7.0. Table I shows the tolerance limits for each of these ions. It is expected t h a t most of t h e other metal ions would also interfere. Milligram amounts of chloride, nitrate, sulfate, perchlorate, phosphate, carbonate, acetate, and fluoride salts (sodium or ammonium) showed no interference from these anions. Precision. The relative standard deviation was *3.47YC for 32 determinations using t h e p H 7.0 procedure. The calcium content varied from 1 to 10 pg. per 25 ml. I n the range from 0.1 to 1.0 pg. per 25 ml., 20 determinations were run, giving a relative standard deviation of *17.601,. The relative standard deviation was &2,34% for 22 determinations covering the range of 5 t o 30 pg. per 25 ml. using the pH 2.2 procedure. It was *2.54’% for 32 determinations over the range of
1 to 10 fig. of magnesium per 25 ml. I n the range of 0.1 to 1.0 pg. of magnesium per 25 ml., 20 determinations were run with a relative standard deviation of 516.4%. Simultaneous Determination of Calcium a n d Magnesium. I n mixed solutions of calcium and magnesium, calcium was determined by the p H 2.2 procedure. Magnesium was determined by the p H 7.0 procedure by subtracting t h e absorbance due t o calcium from the total absorbance at pH 7.0. The relative standard deviation for the 10 determinations was &1.82% for calcium and 12.04% for magnesium. Table I1 shows the results of these determinations. LITERATURE CITED
(1) Apple, R . F., White, J. C., Talanta 8 , 419 (1961). (2) Chudinov, E. G., Yakovlev, G. N., Radzokhimiya 4, 601 (1962). (3) Zbid., p. 605. (4) Dirscherl, W., Brener, H., Mikrochemie ver. Mikrochim. Acta 40, 322 (1953).
( 5 ) Fadeeva, V. I., Alimarin, T. P., Zh. Analit. Khim. 17, 1020 (1962). (6) Frost-Jones, R. E. U., Yardley, J. F., Analyst 77, 468 (1952). (7) Glemser, O., Dantzenberg, W., 2. Anal. Chem. 136, 253 (1952). (8) Goldstein, D., Stark-Mayer, C., Anal. Chim. Acta 19, 437 (1958). (9) Harvey, A. E., Jr., Komarmy, J. &I., Wyatt, G. RI., ASAL. CHEM.2 5 , 498 (1953). (10) Hunter, J. G., Analyst 7 5 , 91 (1950). (11) Kenyon, 0. A., Oplinger, G., ANAL. CHEM.27, 1125 (1955). (12) Kerr, J. R. W., Analyst 8 5 , 867 (1960). (13) Kolthoff, I. M., Chem. Weekblad 24, 254 (1927). (14) Ludwig, E. E., Johnson, C. R., IND.
ENG.CHEM.,ANAL.ED. 13, 499 (1941). (15) Lukin, A. M., Kalinina, I. D., Zavarikhina, G. B., Zhr. Obshch. Khim. 30, 4072 (1960). (16) Mann, C. K., Yoe, J. H., ANAL. CHEM.28. 202 (1956). (17) hIann,'C. K., Yoe, J. H., Anal. Chim. Acta 16, 155 (1957). (18) Mikkelsen, D. S., Toth, S. J., J . -4m. Sac. Agron. 39, 165 (1947). (19) Mikkelsen, D. S.,Toth, S. J., Prince, A. L., Sod Sci. 66, 385 (1948). (20) Nemodruk, A. A. Novikov, Yu. P., Lukin, A. SI., Kalinina, I. D., Zh. Analit. Khim. 16, 180 (1961).
(21) Ostertag, H., Rinck, E., Compt. Rend, 231, 1304 (1950). (22) Pohl, H., Mptall 10, 709 (1956). (23) Pollard, F. H., Martin, J. V., Analyst 81, 348 (1956). (24) Roaflaub. J.. Helzi. Phusiol. Pharmacol. iZcta 9, C33 (1951). (25) Savvin, S B., Talanta 8 , 673 (1961). (26) Schwarzenbach, G., Gysling, H., Helv.Ckim. Acta 32, 1314 (1949)(27) Tammelin, L. E., Mogensen, S., Acta ChPm. Scand. 6, 988 (1952). ( 2 8 ) Taras, M., ANAL. CHEM.20, 1157 (1948). (29) Tyner, E. H., Ibid., p. 76.
(30) Urback, C., Baril, R., Mikrochemie 14, 343 (1934). (31) Williams, SI. B.. Moser. J. H.. ANAL.C H E 25. ~ 1414 (1953). (32) Young, A . , Sweet,'T. R . , Baker, B.B.,Ibid., 27,356 (1955).
~
RECEIVE^
for
review
July
1, 1963.
Accepted October 25, 1963. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1964. Contribution 1344. Work performed in the Ames Laboratory, U. S. Atomic Energy Commission.
Spectrophotometric Determination of To ta I Nitrogen Dioxide and Nitrogen Tetroxide in Air STANLEY
W. COMER and ANDREAS V. JENSEN
Chemical and Matericlls Branch, Rocket Propulsion laboratories, Edwards, Calif.
b A spectrophotometric method for determination of totcil NO2 and Nz04 in air is described. Nitrogen dioxide is detected a t 400 m p and a correction for undissociated N 2 0 4 is applied. Accuracy of 3,5y0 iii shown for concentrations up to 4.0%. Calibration data and curves determined a t 685 torr and 25" f 2 " C. are given.
R
WORK in this laboratory made it necessary to monitor the concentration of NOz-Nz04 in air. The analytical procedure had to provide a n immediate and continuous indication of the down-wind conceitration of KOzN204 coming from a supply of liquid N204. It was derided that a spectrophotometric procedure would be best for the analysis under investigation. h n apparatus for visual comparison of the intensity of the reddish brown color of KO2 was used by White and Tolman ( 8 )and Coon ( 2 ) . -4simple, inexpensive photometer was used by Harris and Siege1 (3) for their investigation of the reaction of NO2 with other gases. =1 spectrophotometric apparatus was designed by Mills and Johnston (6) for their investigation of che effect of NO,
ECEKT
loo w
i E
k
on the decomposition of Kz05. Colorimetric procedures were used by H u n t and Daniels ( d ) , Saltaman (6), and Altshuller and Wartburg (1). These published methods of analysis were either time-consuming, not accurate enough, or not adaptable to the requirements of the analysis. This paper describes the method used by the authors to monitor the concentration of N02-N20ain air and the procedure used to obtain a calibration curve. EXPERIMENTAL
Apparatus. -4 Beckman DK-2 spectrophotometer was used with a 10-cm. Vycor cylindrical gas cell. T h e cell was modified so t h a t a continuous supply of air-NOn-SnO4 could be pumped through it by a 1I.S.A. diaphragm pump ( P a r t No. 78810, Mine Safety Appliances Co., Pittsburgh, Pa.). An air-filled 10-cm. Vycor cell was used in the reference beam. The spectrophotometer was equipped with a time-drive mechanism t o obtain yoT us. time at constant wave length. A cell compartment cover was built to allow the passage of inlet and outlet sample lines. This cover must be light-tight. Black Tygon tubing was used to prevent light from entering the cell compartment through the tubing. Materials. Anhydrous nitrogen tetroxide as received from Allied Chemical Corp. was used.
Figure 1 . Dissociation of N,O, in air at 2 5 O - C : and 0.9 atmospheric pressure.
m m ea
:I- - -I
$0
1.0
15
N204
25
20
VOLUYE C
x
L N O L IN AIR
LO
15
ao
Wavelength. A wavelength scan through the visible region of t h e spectrum indicated that 400 mp was the best wave length to detect NOn in air. Procedure. Small, thin-walled ampoules were macle from 9-mm. glass tubing. They were shaped like elongated teardrops drawn to a capillary opening. T h e ampoule bulb was warmed gently (heat of the hand) and then cooled by a pellet of d r y ice while the capillary end was immersed in liquid NzO4 (0" C.). The sample in the ampoule was allowed to evaporate (capillary end immersed in Nz04) to expel the air in the bulb. The ampoule was then filled by again chilling it with d r y ice. When the desired amount of Nz04had been drawn into the ampoule, it was sealed off by flame. The sample weight was determined by difference. The ampoules broke on impact when dropped into a 56.5-liter bottle. The bottle was stoppered immediately so no S02-N204 escaped, and the entire system was at atmospheric pressure. The gases were pumped through the spectrophotometer cell. A constant absorbance value was obtained almost instantly, indicating that the sample and air had reached equilibrium. Erroneous results were obtained if the ampoule did not break completely when it was dropped into the bottle. There should be no liquid S204in the stem of the ampoule when it is dropped into the bottle, for this entrapped liquid will evaporate very slowly, making it difficult to obtain equilibrium conditions. Between each calibration point, the apparatus was purged with nitrogen until zero absorbance was obtained. DISCUSSION
The purpose of the analytical procedure was to determine the concentration of combined NO, and Nz04 from the measured concentration of NOz. Since KO2 but not Nz04 is "seen" by the spectrophotometer, the degree of disVOL. 36, NO. 4, APRIL 1964
799
