Accordingly, the structure of 2,3quinoxalinedithiol could be written
thus,
The cobalt concentration was 1 p.p.m.; the nickel was 2 p.p.m. With these concentrations, in t h e absence of interfering ions, the absorbances were 0.617 and 0.596, respectively, for the cobalt and nickel complexes. The results are summarized in Table 111. LITERATURE CITED
and its cobalt and nickel salts
Effect of Diverse Ions. Two limiting values for concentration of t h e diverse ion were used : t h a t concentration which causes a n error in absorbance of Zk270; and t h a t concentration which causes a n error of &5%.
(1) Ayres, G. H., Janota, H. F., ANAL.
CHEM.31,1985 (1959). (2) Clark, R. E. D., Analyst 83, 431 (1958). (3) Clark, R. E.D., Cambridge, England, 1962: Drivate communication. (4) Feigc F., “Spot Test in Inorganic Analysis,” 5th ed., p. 4, Elsevier, New York, 1958. (5) Harvey, A. E.,Manning, D. L., J . Am. Chem. SOC.72,4488 (1950). (6) Jacobs, W. D., Yoe, J. H., Anal. Chim. Acta 20,332 (1959). (7) Job, P., Ann. 109, 113 (1928). (8) Krebs, von H., Weber, E. F., Fass-
bender, H., 2. Anorg. Allgem. Chem. 276, 128 (1954). (9) McKaveney, J. P., Freiser, H., ANAL. CHEM.29,290 (1957). (10) Morrison. D. C.. Furst, -4.. J . Ora. . Chem. 21, 470 (1956). (11) Morrison, G. H., Freiser, H., “Solvent Extraction in Analytical Chemistry,’’ pp. 157-9, Wiley, New York, 1957. (12) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 3rd ed., p. 97, Interscience, New York, 1959. (13) Skoog, D. A., Lai, M., Furst, A., ANAL.C H E M30, . 365 (I!>58). (14) Steinbach, J. F., Freiser, H., I b i d . , 25, 881 (1953). (15) ‘Vosbure. ‘W. C.. CooDer. G. R.. ’ J. Am. Chem. SOC. 63; 437 (1941). (16) Wolbling, H., Steiger, B., Mikrochemie 15, 295 (1934). (17) Yoe, J. H., Jones, A. L., IND.ENG. CHEM.,A N ~ LED. . 16, 11 l(1944). RECEIVEDfor review June 12, 1962. Accepted August 10, 1962. I
,
Dinitrosoresorcinol as a Microanalytical Reagent for the Estimation of Iron(l1) HASSAN EL KHADEM and SAAD ELDlN ZAYAN Faculty o f Science, University o f Alexandria, Alexandria, U.A.R.
b The e5ectiveness of 2,4-dinitrosoresorcinol as a microanalytical spectrophotometric reagent is described. Within the proper p H range (3.5 to 12) iron(l1) reacts with dinitrosoresorcinate ion to give a bluish green complex with a maximum absorption band between 690 and 640 mp, depending upon the DNR concentration. In nearly neutral solution, Beer’s law is obeyed within the concentration range of 0.1 to 10 p.p.m., and 0.1 p.p.m. of iron(1l) may b e determined accurately b y a spectrophotometric procedure. The effect of acids, acid salts, and interfering ions is discussed.
M
and Moss (1) observed t h a t dinitrosoresorcinol (DNR) forms a lake with iron(I1) ammonium sulfate in the presence of ammonia. On boiling with concentrated hydrochloric acid, this lake showed only the reactions of iron(III), denoting that its formation was accompanied by oxidation. They also prepared the normal iron(II1) ammonium lake, (C6Hz04NzIYHz)3Fe, by adding a n aqueous solution of D N R and ammonia t o iron(II1) alum. Later Nichols and Cooper (2) found that when an aqueous solution of D N R is added to a solution of iron(III), a green precipitate or coloration is produced, depending upon the amount of salt present. I n neutral solution,
1382
ORGAN
e
ANALYTICAL CHEMISTRY
this reagent was able to detect 0.0035 mg. of iron(II1) ion per ml. of solution. I n the present work, the iron(I1)dinitrosoresorcinate complex was obtained by reducing iron(II1) chloride with hydroxylamine hydrochloride (3) or with hydroquinone and then adding D K R . This complex shows a maximum absorption between 640 and 690 mp, depending upon the ratio of the molecular concentration of dinitrosoresorcinate to that of iron. Up to a 2 to 1 ratio of dinitrosoresorcinate to iron, the maximum absorption occurred a t 690 mp; further increase of the D N R concentration caused a shift toward shorter wavelengths down to 640 mp. I n nearly neutral solution, the intensity of the color produced increased with the amount of iron(I1) present and Beer’s la\T was obeyed in the concentration range 0.1 to 10 p.p.m. The molar absorptivity a t 630 m p was 12,600. Acids-e.g., HC1, H2SOl, and H3B03-caused the color of the complex to fade and suppressed it completely below p H 2. Appreciable interference was caused by Pd, Co, Cu, Ni, W, and Cr(II1) because of the formation of their complexes; Ag and Bi interfered because of formation of precipitates. X procedure for the microdetermination of iron(I1) using dinitrosoresorcinol is described.
EXPERIMENTAL
Apparatus. Absorbance measurements were made with a Unicam S.P. 500 spectrophotometer ( 5 ) . The p H values were measured by a Cambridge p H meter with an accuracy to 10.02 p H unit. Reagents. STANDARDIRONS o ~ n TION. The standard stock solution of iron was prepared by dissolving analytical reagent ferric chloride (1.3656 grams) in 1 liter of doubly distilled water containing sufficient hydrochloric acid (about 15 ml. of analytical reagent grade, cpncentrated HC1) to suppress hydrolgsis. The iron content was determined by precipitation of iron as ferric hydrodde, which was then ignited t o ferric oxide. Appropriately dilute solutions of iron (111) were reduced by adding an excess (1 ml.) of hydroxylamine hydrochloride reagent, followed by the required amount of D X R reagent. The absorbance of the bluish green complex solutions was measured using 1-em. cells and a blank solution containing the same amount of hydroxylamine hydrochloride and disodium dinitrosoresorcinate The absorbances were measured over a wavelength range of 500 to 800 mp. DINITROSORESORCINATE REAGENT. As D S R is slightly soluble in water, solutions of its disodium salt were prepared by dissolving 1.86 grams of 2,4-dinitrosoresorcinol, C6H404N2.H20 (British Drug Houses), in a solution of 1.06 grams of sodium carbonate and then diluting to 1 liter.
HYDROXYLAMINEHYDROCHLORIDE REAGENT. 10% aqueous analytical reagent hydroxylamine hydrochloride ( B D H ) in doubly distilled water. BUFFERS. Walpole buffer (6) was used to regulate the p H value of the solution within 0.65 to 5.20, while Clark and Lubs buffers (7) were used over the p H ranges 5.8 to 8.0 and 7.8 to 10, respectively. Ethyl alcohol, ethylene glycol, isopropyl alcohol, and acetone were purified as described by Vogel (4). Microdetermination of Iron(I1). To the 25-ml. solution containing 0.2 to 20 p.p.m. of iron(II1) is added 1.0 ml. of hydroxylamine hydrochloride followed by 3.75 ml. of 0.1% disodium dinitrosoresorcinate and 0.5 ml. of 0.lX Na2C03and the solution is finally diluted to 50 ml. The absorbance a t wavelength 630 mp is then measured against a blank solution containing 1.0 ml. of hydroxylamine hydrochloride and 1.0 ml. of disodium dinitrosoresorcinate. The iron content is determined by comparison with standard iron solutions or from the molar absorptivity, e, which amounts to 12,600 a t wavelength 630 mp. DISCUSSION
Absorption Spectrum of Iron(I1)Dinitrosoresorcinate Complex. I n one set of experiments, the iron(I1) concentration was kept constant a t 5 X 10 and the dinitrosoresorcinate concentration was varied from 5 x 10-5 to 60 x 10-5~-1ri~., 1 : I to 1:12. 111 solutions with a molar ratio of iron(I1) to dinitrosoresorcinate from 1: 1 to 1:2, the absorbance maxima n we the same-viz., 690 mp-showing t h t a t such conditions only one colored complex is formed. However, maxima shifted toward shorter wavelengths when higher concentrations of dinitrosoresorcinate ion were added (Figure 1). This indicates the possible stepwise formation of other complexes richer in dinitrosoresorcinate. In another set of experiments, the concentration of disodium dinitrosoresorcinate was kept constant a t 0.001M and the iron(I1) concentration was varied from 5.0 x lop6to 10.0 X l O - 5 M (2O:l to 1O:l). The absorbances of these solutions n ere similarly measured over the same wavelength range. KO shifts in the maximum absorptions were olmrved, denoting that the formation of complexes rich in dinitrosoresorcinate drpends on the dinitrosoresorcinate concentration and not on the iron(I1) concentration as long as dinitrosoresorcinate is present in excess. Similar results were obtained for solutions buffered a t p H 4 (curves 1, 2, and 3) and a t p H 10 (curves 7, 2, and 8, Figure 2). Absorption Spectrum of Iron(II1)Dinitrosoresorcinate Complex. Results for 5.0 x 10-6M iron(II1) solu-
500
550
600
650
750
700
WAVELENGTH
!N
800
850
mp
Figure 1 . Variation in absorbance of Fe(ll) dinitrosoresorcinate with increasing dinitrosoresorcinate concentration Fe(1l).
5 X
DNR,M X lo-’ I.
J
2. 10 3. 15
tions [free of iron(II)] a t pH 4.4and 10 are illustrated by curves 4 and 2 in Figure 2. Although the curves for the iron(I1) and iron(II1) solutions of the same concentration and under the same experimental conditions show maximum absorption a t the same wavelength, the absorbances differ widely. These results show that both iron(I1) and iron(II1) react with dinitrosoresorcinate to give iron(I1) and iron(II1)-dinitrosoresorcinate complexes. Conformity to Beer’s Law. With a moderate amount of dinitrosoresorcinate [ I 3 6 ml. of a 0.1% dinitrosoresorcinate for every part per million of iron(I1) neutralized with 0.1N NazCOS and diluted t o 100 ml.], maximum absorption was found a t 660 mp (Figure 3) and Beer’s law was applicable within the concentration range 0.1 to 10 p.p.m. of iron(I1). Beer’s law mas also applicable within the same concentrations a t 630 mp, which is the wavelength we propose for the microestimation of iron(I1) by DNR, because a t this wavelength conformity to Beer’s law is not affected by excess-DNR used.
4. 25 5. 50 6. 60
Factors Affecting Stability of Color. REDUCINGAGENTS. Sodium sulfite, sodium formate, and formaldehyde inhibited the color of the complex. Hydroquinone and hydroxylamine on the other hand were satisfactory for the reduction of iron(III), b u t because of the brown color of hydroquinone solutions, hydroxylamine hydrochloride was preferred. P H OF SOLUTIONS.If the pH is less than 2.0, the color is not developed; from pH 2.3 to 3.5, the color is incompletely developed, and from 3.5 to 7, development of color is normal. On further increase of the pH, the color density increases and the position of maximum absorption is shifted to longer wavelength (Figure 2). TIMEOF DEVELOPMENT.On using 0.1% aqueous or alcoholic solutions of D N R , the color density of the iron(I1) complex increases with time and reaches a limiting value after 60 to 90 minutes. However, Fvhen the disodium salt of D N R is used, the color is completely developed in a few minutes; this is attributed to the small concentration of dinitrosoresorcinate ion in the first VOL. 34, NO. 1 1 , OCTOBER 1962
1383
godl
8-
0.7r
l.5
Z
1.4
pj 1.3
n 4oppn
Z
2 1.2 [x
0 I./ cn m Q
1.0 0.9
500
0.8
600
700
WAVELENGTH 0.7
800
IN n/p
Figure 3. Variation in absorbance of iron dinitrosoresorcinate solution with iron concentration (p.p.m.) in presence of moderate amount of dinitrosoresorcinate in neutral solution
0.6
acetate, bromide, chloride, citrate, tartrate, perchlorate, iodide, nitrate, sulfite, thiosulfate, and thiocyanate.
0,5 0.4
LITERATURE CITED
0.3
(1) Morgan, G. T., Moss, J. E., J . Chem. SOC.121, 2857 (1922). (2) Nichols, M. L., Cooper, S. R., J . Ani. Chem. SOC.47, 1268 (1925). (3) Saywell, L. G., Cunningham, B. B.,
0.2 0.1
600
500
700
WAVELENGTH
800
IN
my
Figure 2. Variation in absorbance of iron dinitrosoresorcinate with increasing iron concentration DNR. 10-W Fe(ll), M X 1 0 - 5 I , 5; 2, 7.5; 10. pH 4.4 1 . 5 ; 2, 7.5; 3, io. p~ i o
3,
Fe(lll), M
X lo-’
Correction
4, 5. pH 4.4 5. pH 10
4,
case. I n both cases the colored complex was stable under atmospheric conditions for 12 hours. EFFECTOF TEMPERATURE. On heating solutions of iron(I1)-dinitrosoresorcinate complex, the color faded gradually, turning yellow at about 65’ C., and was slowly restored on cooling. EFFECT OF ORGANIC SOLVENTS. Ethyl alcohol and ethylene glycol when present in high concentration caused a negligibly small increase in the color intensity of the complex, whereas isopropyl alcohol and acetone caused fading of the color, and in the latter solvent the solution became dirty green after a few hours. EFFECTSOF IONS. The possible interference of ions was studied on solutions ‘containing 2.0 p.p.m. of 1384
IND.ENG. CHEM., ANAL. ED. 9, 57 (1937). (4) Vogel, A. I., “Textbook of Practical Organic Chemistry,” pp. 166, 169, 170, 171, Longmans, Green, London, 1959. (5),Vogel, A. I., “Textbook of Quantitative Inorganic Analysis,” pp. 628-9, Longmans, Green, London, 1959. (6) Zbid., p. 869. (7) Ibid., p. 870. RECEIVEDfor review January 15, 1962. Accepted July 5, 1962.
ANALYTICAL CHEMISTRY
iron(I1). The absorbance curves were determined and then compared with the standard for the same amount of iron(I1) without the added ions. No interference was caused by 1000 p.p.m. of lithium, sodium, and potassium; 500 p.p.m. of ammonium, calcium, strontium, barium, aluminum, magnesium, and manganese(I1) ; 100 p.p.m. of U02+2 and molybdenum; and 50 p.p.m. of zinc. On the other hand, 20 p.p.m. of chromium(III), 10 p.p.m. of tungsten, 2 p.p.m. of. copper(I1) and nickel, and 1 p.p.m. of palladium and cobalt caused appreciable interference. Bismuth and silver must be completely absent from the solution because of the formation of precipitates. No interference was shown in concentration as high as 500 p.p.m. for
Use of an Ionization Chamber for Measuring Radioactivity in Gas Chromatography Effluents I n this article by James Winkelman and Arthur Karmen [ANAL. CHEM.34, 1067 (1962) 1, two references were omitted inadvertently. On page 1067, column 2, second full paragraph, follow ing “Proportional counters have been constructed suitable for operation a t high temperatures” there should be a reference to Wolfgang, R., Rowland, F. s., ANAL.CHEM.30,903 (1958), and following “ionization chambers have been used at room temperature following combustion of the sample,” there should be a reference to a paper by Cacace, F., Guarino, A,, Inam-ul-Haq, Ann. Chim. (Rome) 50, 919 (1960).
