ANALYTICA L EDITION
November 15, 1942
Practical Application The method has'been applied for practical control work with entirely satisfactory results. About 3 minutes is required for each thickness test. It has also been used b y certain potteries for estimating the costs of different type of gold decorations. Some tests have been made on the substitution of Reagent B for hydrofluoric acid in removing undesired gold spots from decorated ware.
width, at a temperature of 25" C., and for gold coatings containing no interfering substances-e, g., platinum and silver. The method would be applicable t o thickness measurements of ceramic coatings of gold alloys, b u t a stripping factor for each particular alloy would have t o be ascertained. The method is rapid and with reasonable care should be accurate to *6 per cent.
Literature Cited
Summary
A jet-test method for measuring the thickness of liquid bright and burnish gold coatings on ceramics and two independent standardization methods for determining the stripping factors Of the ammonium acid-Gardinol reagents have been developed. The stripping factors given apply to tests made on gold bands over 4 mm. in
869
(1)
Blum, W., Strausser, P. W. C., and Brenner, A , , J . Research
Natl. Bur. Standards, 16, 185 (1936). (2) Clarke, S. G., J . Electrodepositors' Tech. soc., 12, 1 (1937). (3) Fink, C. G., and Putnam, G. L., IKD.ENG.CHEM.,ANAL.ED., 14,468 (1942). (4) Hull, R. O . , and Strausser, P. W. C., Monthly Rev. Am. Electroplaters Soc., 22, 9 (1935). (5) Pettenkofer, M.,-\'at. Tech. Comm. .%fdnchen, 1, 159 (1857).
Spectrophotometric Determination of Iron With o-Phenanthroline and with Nitro-o-phenanthroline J. P. MEHLIG AND H. R. HULETT', Oregon State College, Corvallis, Ore.
I
N RECENT years various spectrophotometric metho& of analysis have been developed, making use either of a reference curve correlating transmittancy a t a given wave length with concentration or of the extinction coefficient of the color system at a given wave length. The senior author has determined manganese as permangafiate (4) by the former procedure and copper with ammonia (6) and iron with salicylic acid (6) b y the latter. The orange complex formed by the combination of three molecules of o-phenanthroline with one ion of ferrous iron, first reported by Blau (I), has been used for a number Of years as a n internal indicator in oxidimetric titrations. A more recent development has been the use of the cherry-red nitro-o-phenanthroline ferrous complex for the same purpose. Saywell and Cunningham (7) have applied o-phenanthroline to the visual colorimetric determination of small concentrations of iron in various food products and Hummel and Willard (3) have used it for the colorimetric determination of iron in biological materials. Fortune and Mellon (2) have made a critical spectrophotometric study of the SaywellCunningham method with special attention to the effect of diverse ions and hydrogen-ion concentration and to the stability of the color system. The purpose of the work described in this paper was to apply both o-phenanthroline and nitro-o-phenanthroline to the spectrophotometric determination of iron in ores, making use of the fundamental Lambert-Beer equation Y
z
=
lo
x
10-kZc
in which lo represents the intensity of the light of a given wave length entering the system, Z the intensity of the light transmitted by the system, 1 the length in centimeters of the solution through which the light passes, c the concentration in grams per liter of the substance absorbing the light, and k the specific extinction coefficient, a constant which is a measure of the absorption due to a single molecule.
Apparatus and Solutions -411 spectrophotometric measurements were made with a Cenco-Sheard spectrophotelometer. 0-PHESANTHROLINE. A 0.1 per cent solution of tGe monohydrate prepared by dissolving in water warmed to 80 . NITRO-O-PHEXANTHROLINE. A 0.1 per cent solution in 95 per cent ethanol. 1
Present address, U. S. Army.
HYDROXYLAMISE HYDROCHLORIDE. An aqueous solution con-
T1.0.25
t a ! $ ~ ~ ~ $ a ~ L ~ ~ solution ~ ~ o prepared by dissolving 56.49 grams of the dihydrate in 350 ml. of 6 M hydrochloric acid and diluting. to 1000 ml. with water. STAXDARD IROSSOLU&ON.A standard solution was prepared by dissol.i.ingo.7029 gram of 99.9 per cent pure ferrous ammonium sulfate hexahydrate in water and diluting to 100 ml. Ten milliliters of this solution were made up to 1000 ml. with distilled viater slightly acid with hydrochloric acid. Each milliliter Of this final solution contained 0.01 mg. Of iron. DIVERSE10s SOLUTIOYS.Standard solutions, each milliliter containillg mg, of the ion in question, were prepared from the chloride or nitrate salt of the cations and from the sodium, potassium, or ammonium salts of the anions.
The Color Reaction To produce the color system the amount of the standard solution of iron required t o give the desired concentration of iron was measured into a 100-ml. volumetric flask and 1 ml. of hydroxylamine hydrochloride solution was added to reduce any iron which might have been oxidized by dissolved oxygen. The solution was diluted to approximately 75 ml., 10 ml. of o-phenanthroline or nitro-o-phenanthroline solution were added, and the volume was accurately made up to 100 ml. The solution containing nitro-o-phenanthroline was allowed to stand 2 hours for the full development of the color. All transmission measurements were made with a Cenco-Sheard spectrophotelometer by setting the wave-length scale, adjusting the incident light by means of a diaphragm to provide the desired displacement of the pointer on the photometer scale, and reading the transmission of the standard solution and of the blank solvent. The transmittancy was calculated by dividing the former by the latter. A 1-cm. cell was used throughout. The spectral transmission curves for the two systems are very similar with the peak of the absorption band in each case at about 508 mp. Since they closely resemble the curves obtained for the o-phenanthroline-iron system by Fortune and Mellon ( 2 ) using the self-recording PurdueGeneral Electric spectrophotometer, they are not shown.
T h a t Beer's law is followed b y both color systems is proved by the straight line which resulted when the logarithms of the observed transmittancies at 505 m p for five solutions containing from 0.5 to 4 p. p. m. of iron were plotted against the respective concentrations. This is in accord with the observations of Fortune and Mellon (2) for o-phenanthroline.
Determination of Specific Extinction Coefficients Specific extinction coefficients were determined for both color systems a t 490 and 505 m p by obtaining the respective transmittancies a t those wave lengths of a series of known iron
Vol. 14, No. 11
INDUSTRIAL AND ENGINEERING CHEMISTRY
870
TABLE I. RESULTSOBTAIh'ED WITH Iron by Sample Dichromate No. Method
Iron Obtained from Tranamittancy at 490 mp 505 mp
0-PHENANTHROLINE
Average
Iron Found
Deviation
%
%
%
%
%
37.62 36.84 36.12 35.11 54.04 50.68 49.59 52.83
37.66 36.90 36.20 35.10 54.00 50.55 49.63 52.79
37.71 36.86 36.19 35.08 53.90 50.51 49.70 52.93
37.69 36.88 36.20 35.09 53.95 50.53 49.67 52.86
$0.07 +0.04 +0.08 -0.02 -0.09 -0.15 +0.08 f0.03
solutions as above. The average values calculated for the o-phenanthroline-iron system are: 490 mp, 10,590; 505 mp, 11,080; and for the nitro-o-phenanthroline-iron system: 490 mp, 11,130; 505 mp, 11,410.
certain ions commonly encountered, the authors measured the transmissions a t 490 and 505 mp of solutions of the system containing 2 p. p. m. of iron reduced by hydroxylamine hydrochloride and as much as 500 p. p. m. of the ion in question. When the difference between the transmission of the solution and that of the standard iron solution was less than 0.1 scale division, i t was assumed that the added ion caused no interference. The following ions gave no interference : acetate, bromide, chloride, nitrate, sulfate, aluminum, ammonium, calcium, lead, magnesium, potassium, and sodium. Chromic and cupric ions produced a change in hue, but their interference is negligible below 10 p. p. m. TABLE11. RESULTS OBTAINED WITH KITRO-O-PHEXAXTHROLINE Sample No.
Determination of Iron in Ores Approximately 0.5 gram of iron ore was accurately weighed and transferred to a 250-ml. beaker. Twenty-five milliliters of concentrated hydrochloric acid were added, the beaker was covered with a watch glass, and the mixture was warmed on a hot plate until solution had been effected or only a white, siliceous residue remained. The solution was transferred to a 1000-ml. volumetric flask, filtering if necessary and thoroughly washing any residue, diluted to the mark, and thoroughly shaken. An aliquot of 10 ml. was measured into a 100-ml. volumetric flask, diluted to the mark, and well mixed. A 10-ml. aliquot of this solution was placed in a second 100-ml. volumetric flask and 1 ml. of hydroxylamine hydrochloride solution was added together with enough water to make the volume about 75 ml. Ten milliliters of the o-phenanthroline or nitro-o phenanthroline solution were then added and the solution was diluted to the mark. Transmission measurements of this solution in a 1-cm. cell were made a t 490 and 505 mp. The wave length of maximum absorption, 508 mp, was not used because the scale setting can be more accurately made at wave lengths ending in 0 or 5. Repeated readings on a single setting instead of readings at different settings are recommended for routine work. The transmittancy was obtained by multiplying the transmission by 100 and dividine by the transmission a t the same wave length of a blank solution. The percentage of iron was calculated by use of the appropriate value fork, the specific extinction coefficient, as found above for the wave length in question. The results obtained with o-phenanthroline for eight ores and with nitro-o-phenanthroline for thirteen ores are shown in Tables I and 11, respectively, which also include for comparison the values given by the dichromate method.
Reducing Agent In a search for a less expensive reductant than hydroxylamine hydrochloride Fortune and Mellon ( 2 ) found that sodium sulfite, sodium formate, and formaldehyde are unsatisfactory because they form complexes with ferric iron. Khile they did not try stannous chloride, they did determine that as much as 20 p. p. m. of stannous ion and 50 p. p. m. of stannic ion do not interfere with the color. The authors made a series of determinations on ten iron ores with nitro-o-phenanthroline as above, substituting for the hydroxylamine hydrochloride 1 ml. more than enough 0.25 M stannous chloride solution to reduce all the iron. The deviation from the dichromate results was less than 10.10 per cent in five cases, but ranged as much as *0.40 per cent in the others. The average difference was *0.13 per cent compared to * 0.07 per cent for the hydroxylamine procedure. Stannous chloride is not recommended as the reductant for the spectrophotometric method, but i t could be used in the less precise visual colorimetric method.
Effect of Diverse Ions I n a comprehensive study of the effect of 55 diverse ions on the o-phenanthroline-iron color system Fortune and Mellon (2) found that very few interfere. T o determine the effect on the nitro-o-phenanthroline-iron color system of
1 2 3 4 5 6 7 8 9 10 11 12 13
Iron by Dichromate Method
Iron Obtained from Transmittanoy a t 505 mu
490 m r
%
%
37.62 36.84 36.12 35.11 54.04 50.68 49.59 52.83 51.52 52.20 56.00 34.45 57.62
37.84 36.68 36.07 35.05 54.07 50.71 49.53 52.83 51.50 52.18 55.91 34.56 57.55
% 37.60 36.87 36.10 35.03 54.24 50.95 49.66 52.90 51.58 52.13 56.00 34.57 57.51
Average Iron Found
70 37.72 36.78 36.09 35.04 E4.16 50.83 49.60 52.87 51.54 52.16 55.96 34.57 57.53
Deviation
% +0.10 -0.06 -0.03 -0.07 +0.12 +0.15
+o.oi 4-0.04 $0.02 -0.04 -0.04 +0.12 -0.09
Discussion The spectrophotometric method for the deterrmnation of iron in ores by use of either o-phenanthroline or nitro-ophenanthroline gives results which are n7ell within *0.20 per cent of those given by the dichromate titrimetric method and most of them are within *0.10 per cent. Results may be duplicated on the same sample with a precision of *0.10 to *0.20 per cent. The method is most sensitive for concentrations of about 0.5 t o 4 p. p. m. of iron when nitro-ophenanthroline is used and of about 1 to 3 p. p. m. when ophenanthroline is used. The nitro reagent has the disadvantage of requiring about 2 hours for full development of the color. It is also more expensive than o-phenanthroline. This method has the advantage over the dichromate and similar titrimetric methods of not requiring a standard solution. Since the method can be used to determine iron in concentrations as low as 0.5 p. p. m. and since very few diverse ions interfere with the color, it can advantageously be adapted to the determination of iron in food and biological materials and in analytical reagents. Two important advantages of this method over many colorimetric methods for iron are that the p H value need not be regulated closely (2) and the color formation occurs in acid solution, eliminating the difficulties usually caused by precipitation of metal hydroxides and hydrated oxides in alkaline solution. The advantages of this method over the salicylic acid spectrophotometric method for iron (6) are its much wider p H range and greater freedom from interference b y diverse ions. Both methods give equally satisfactory results.
Summary
h spectrophotometric method has been developed for the determination of iron in ores which depends upon reducing the iron with hydroxylamine and measuring the light transmittancy at 490 and 505 mp of the colored solution produced by either o-phenanthroline or nitro-o-phenanthroline. The results agree closely with those obtained by the dichromate titrimetric method.
ANALYTICAL EDITION
November 15, 1942
87 1
(3) Hummel, F. C., and Willard, H. H., Ibi,d., 10, 13 (1938).
The method is easily carried out and requires no longer, possibly little less, time than usual titrimetric methods. Very few diverse ions interfere with the color and a \\ride range in p H values is possible. An alternate procedure for reducing the iron ivith stannous chloride is not recommended.
{:;,:!$E $$'**(:izj. 79
27 (1935)*
Ibid., 9, 162 (1937); 136 (1938). (7) Saywell, L. G., and Cunningham, B. B., Ibid., 9,67 (1937).
ABSTRACTED from a thesis submitted bg- H . R . Hulett t o t h e Graduate School of Oregon State College in partial fulfillment of the requirements for the degree of master of science. Published with the approval of the Monographs Publication Committee, Oregon State College. Research paper No. 65, School of Science, D e p a r t m m t of Chemistry
Literature Cited (1) Blau, F., Monatsh., 19, 647 (1898). (2) Fortune, W. B., and bfellon, M G., 1x0. ESG.C H G U . . - 1 s ~ E D~. .. 10, 60 (1938).
Detection and Semiquantitative Estimation of Group I Cations S. S. LEIKIYD, ROBERT JIAURAIEYER, AND hIILTON CUTLER, Rrookl!n College, Brooklyn, N. Y.
IK
THE classical procedure for the qualitative analysis of Group I (silver, lead, mercury), the chlorides are precipitated and the lead chloride is extracted with hot ~ ~ a t e r . The residue is then treated with aqueous ammonia to separate the silver from the mercury. Two valid objections to this procedure are: The extraction of lead chloride is complete only after many washings and hence is necessarily time-consuming. Silver ion in the presence of comparatively large amounts of mercury sometimes escapes detection (in the hands of a beginner) when ammonia IS added to separate the silver from the mercury. This is due to the reduction of silver ion to metallic silver by the mercury formed as a result of the reaction between mercurous chloride and ammonia. Small amounts of silver may thus escape detection due t o their absence in the ammonia extract. Of course, the silver may be recovered later when the mercury residue is treated with aqua regia and then diluted. (The silver chloride separates out.) I n the authors' procedure these objections are overcome by extracting the lead chloride with an ammonium acetate solution containing acetic acid. Acetic acid is added to the ammonium acetate t o reduce to a minimum the hydrolysis of the latter. This must be done t o avoid loss of mercury, for the ammonia formed by hydrolysis interacts with the mercurous chloride and the resulting HgNHzCl enters into the lead chloride extract. The residue is then treated with aqua regia and after subsequent dilution with water and centrifuging, thelsilver is separated as chloride from the mercury.
Experimental
aid of a 1-ml. pipet add 1 ml. of concentrated hydrochloric acid. Stir for 2 minutes (to allow lead chloride to crystallize) and centrifuge for 3 minutes. The supernatant liquid now contains Groups I1 to V. Pour off and set aside. To the residue in the tube add 5 ml. of L reagent (a solution 2.6 M in ammonium acetate and 0.8 iM in acetic acid). Stir thoroughly for 0.5 minute and centrifuge until clear (not more than 3 minutes). Pour extract into another tube. Rrpeat with 5 ml. more of L reagent. Test for and estimate lead in the combined extracts by adding 2 ml. of potassium chromate. [A known number of milligrams of lead (say 20) are pipetted into a calibrated centrifuge tube (the blank or control) and the volume is made the same as in the unknown by using water and identical volumes (or weights) of reagents. When the potassium chromate is finally added simultaneously to both, the lead chromate which forms is allowed to settle under the influence of gravity (5 minutes). The number of milligrams of lead in the unknown is proportional to the volume of lead chromate in the blank. The procedure is similar for the silver (estimate as silver chloride) and the mercury (estimate as mercuric sulfide)]. Add 2 ml. of aqua regia to the residue in the centrifuge tube and boil down by inserting the tube in an upright position in a sand bath (to prevent bumping and subsequent loss of solution) until the aqua regia is destroyed (to about 1 ml.). Dilute the mixture to 10 ml. and centrifuge until the supernatant liquid is clear (an exceedingly faint cloudiness may be ignored). The residue is silver chloride. Pour off supernatant liquid equally into two tubes. To the first add stannous chloride reagent. A gray to black precipitate indicates the presence of mercury. Estimate it as mercuric sulfide (by passing in hydrogen sulfide) in the second tube only if a test has been received with the stannous chloride reagent. Add concentrated ammonia with stirring to the final residue (in the second paragraph preceding) until it dissolves. Add dilute nitric acid until the solution is just acid. Dilute to 10 ml. and estimate silver as chloride.
A new method proposed for the detection and semiquantitative estimation of Group I cations is much less timeconsuming than the classical one. It allows for the detecAND SEMIQUANTITATIVE ESTIMATION OF GROUP I CATIOKS tion Of about loo mg* Of TABLEI. RESULTSOF DETECTION metal as maximum with the (As performed by beginners in analysis a t Brooklyn College) lower limit of 0.2 mg. for silver Unknowna Ions Present Repprted b y Student Reported by Student Reported b y Studen? and mercury, and 15 mg. of A g + P b + + Hg+ Ag P b + + Hg A g + P b + + Hg A g + P b + + Hg Mg. Mg. M g . Mg. Mg. Mg. Mg. Mg. Ng. M g . Mu. Mg. lead, each metal alone or in 1 20 60 None 30 70 None 20 45 None 5 30 None the presence of each other. 2 5 95 None 25 40 None 3 5 70 None 10 45 None This method may be used in a 5 4 0 3 5 5 5 8 5 5 5 5 3 5 3 5 4 0 4 None 90 20 None 50 80 None 45 20 None 6 5 10 semimicro system of analysis. 40 10 25 75 10 25 25 50 25 15 5 30 30 6 None 30 40 None 15 40 None 45 50 None 20 80 Time of analysis is less than 40 None 10 50 None 30 30 None 55 7 50 None 10 30 minutes. 20 10 None 40 20 None None 50 20 None 40 30 8
In a 15-ml. centrifuge tube take the solution of the unknown (not more than 100 ma. of metal) and dilute to 10 ml. With the
a
20 None 9 20 10 10 None 40 None 10 20 11 100 20 5 12 13 25 None 25 14 None 20 None Three different students for each
15 None 20 20 None 25 220 10 50 None 50 None 50 None unknown: 42 etudents 25 None 20 5
10
20 40
10 20
None 15 None 15
None 26 None
None 10 80 75 70 None
60 None 25 30 10 None
30
30 None 25 None 25
None a
30
30 25
None
PRESENTEDbefore the Division oi Physical and Inorganic Chemistry at t h e 99th hleeting of t h e AXORICAN CHEMICAL SOCIETY, Cincinnati, Ohio.
