Colorimetric Determination of Copper with Neo-cuproine A. R. GAHLER M e t a l s Research Laboratories, flectro Metallurgical co., Division o f Union Carbide and Carbon Corp., Niagara
and accurate method has been needed for the determination of copper in steels, ferroalloys, and related raw materials and products. illthough many methods have been 1)roposed for the colorimetric determination of copper in such niateriale, most of them require a number of preliminary separations. The method proposed by Hague, Brown, and Bright ( 3 ) for the determination of copper in steels by use of sodium diethyldithiocarbama,te gives good results in most cases, but the use of neo-cuproine would eliminate the addition of complesing agents t o mask interfering ions, and the e x h e t i o n procedure 11-ould be simplified. The possible interference of iron because of faulty estraction technique would be eliminated. Breckenridge, Lewis, and Quick ( 1 ) found, in 1939, that 2,2’-biquinoline was specific for copper. This reagent has been recommended for use in water analysis ( 2 ) , but it has not been commercially available until recently. Early in 1952, Smhh and McCurdy ( 6 ) reported that 2,9-dirnethyl-l,lO-phenanthroline(neo-cuproine) react,s similsrly with copper and that the colored system formed in isoamyl alcohol is slightly more sensitive than the 2,2’-biquinoline system. 10-phenanOther reagents-such as, 2,9-dimethyl-4,7-diphenyl-l, throline-have been suggested, but were not commercially available a t the time of this work. This study was made to acquire specific information regarding the copper( I ) neo-cuproine system with respect to the accuracy and precizion of the system and to determine the effect of certain diverse ions, such as cyanide, fluoride, and sulfide. Early in the work, it was found that copper(1) neo-cuproine can be extracted with a chloroform-ethyl alcohol mixture. Since purified chloroform is readily available, the solvent need not be redistilled as was suggested by Smith and McCurdy, who found that certain lot3 of isoamyl alcohol contained osidizing impurities which cnused erroneous results. Hesanol was tried initially, but it docs not separa1.e from the aqueous solution so quickly as chloroform. In addition! it is more convenient to extract with a solvent which has a density greater than that of the aqueous phase when the organic solvent is to be collected. Consequently, the following preliminary study of the extraction process TTas made before anal>-si3of Sational Bureau of Standards samples. \RAPID
-
Falls, N. Y.
Effect of Copper Concentration. The yellow-colored system measured a t 457 mp follows Beer’s law from 0.01 to 0.20 mg. of copper(1) in 25 ml. of organic solvent using 1-cm. cells. The system follows Beer’s law by dilution with ethyl alcohol to a 50-ml. volume. The sensitivity of the complex in the chloroform-ethyl alcohol mixture is identical with that of the compleu in heuanol. Effect of pH. Full color developnient was obtained with the p H of the aqueous phase between 2.3 and 9.0 (see Table I).
Table I. Effect of pH upon Extraction of Copper(1) Seociiproine with a Chloroform-Ethyl Alcohol Mixture (0.1 mg. of copper) Recovery, %E
PH
Stability of the Hue. The system is stable for a t least 4 days, even when esposed to diffused sunlight. EXTRACTION PROCESS
Order of Addition of Reagents. The order of addition of reagents is not important, escept that it is convenient to add sodium citrate to prevent precipitation of the metals present before adjusting the p H of the solution.
1 .o
I
0.20
1
4 APPARATUS AIYD REAGENTS
All absorbance measurements were made in 1.000-cm. cells with a Beckman Model DU spectrophotometer. The p H measurements were made with a Beckman Model H line-operated p H meter. (neo-cuproine) was obThe 2,9-dimethyl-l,lO-phenanthroline tnined from the G. F. Smith Chemical Co., Columbus. Ohio. Chloroform. Baker analyzed reagent grade. C O W R RE4CTIO3
Effect of Solvent. The absorption curves from 320 to 800 niw of copper(1) neo-cuproine in a chloroform-ethyl alcohol system exhibit maximum absorbance a t 487 mp. The range of ninuimum absorption is shown in Figure 1. This is in contrast u i t h the complex in hesanol and isoamyl alcohol, in which the maximum occurs a t 454 mw. A small amount of alcohol must be present a t the time of extraction with chloroform for masimuni development of the yellow color. The volume of chloroforni pieqent does not affect the colored system, provided that a minimum of 2 m]. of ethyl alcohol is present in 25 ml. of chloroform. .I solution containing lees than 2 ml. of ethyl alcohol usually is turbid. If no ethyl alcohol is present, very little color forms in the chloroform layer. In the recommended procedure, the reagent is added as an ethyl alcohol solution to satisfy this requirement
0.5
I 0 400
500
600
700
C U C O N C E N T R A T I O N , MG./P5 ML.
Figure 1. Range of Maximum Absorption Number of Extractions. The copper complex is completely extracted, within about 30 seconds, into 10 ml. of chloroforn~. The aqueous phase, however, is usually washed with an additional 8 ml. of chloroform. Volume of Aqueous Phase. The volume of the aqueous phase may he a t least 128 ml. without the loss of copper in the extraction process. Reagent Concentration. A volume of not less than 2 ml. of a 0.1 yoethyl alcohol solution of neo-cuproine is required to extract 0.1 mg. of copper. Since a solution of neo-cuproine in a chloroform-ethyl alcohol mixture absorbs very little a t 457 mp, the volume of reagent added to the blank and sample does not need to be accurately measured.
A N A L Y T I C A L C HE hl I S T R Y
578 _____
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~~
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FERROTLTGSTES. To the sample in :t
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Table 11. Colorimetric Determination of Copper in NBS Standards with
~ ~ ~ ~ ~ ~ c ~ s mise. After the reaction has subsided, Certificate S o . of 1) and add 5 ml. of sulfuric acid (1 Value, Deter.4veragea Range, Standard b Fo cu minations x-alue, % cu % c,l De,.iation evaporate to fumes. Cool. Add a little Type of Steel or 4110y water, 5 ml. of hydroxylamine hydroSBS3j Cast iron 1 .oo 1 1.009 0.020 0.010 chloride (100 grams per liter), and 10 NBS6d Cast iron 0.131 2 O.l496 0.0019 0.0013 ml. of sodium citrate (300 grams per NBS7 IronE ... 4 0.0168 0.0007 0.0003 liter). Add ammonium hydroxide until NBS22C Bessemer steel 0.011 4 0.0107 0.001:! 0.0003 slightly basic (pH 8) or until the prcXBS36a Cr-Mo steel (2.4 - 0.9) 0.114 7 o.llol 0.002i 0.0013 cipitate dissolves. Karni, if the preSBS75 Ferrotungsten (73% W) 0.030 8 0,0389 0.003% 0.0013 cipitate does not go into solution iniSBSlOlc Cr-Ki steel (18 - 9) 0 124 4 0.1198 0.0033 0.ooi.j Cool. Extract as described XBS130 Pb-bearing steel (0.2) 0 018 6 0.01'6 0.0009 0.0003 Run a blank simultancS B S l 3 3 hIo-W-Cr-V-Co steel (8.4 ously for the possihle presence of copper 1.6 - 4 - 2 - 8.5) 0.099 8 0,0946 0.010 0.003 in the reagents. KBS159 Cr-Mo-Ag steel (1 - 0.4 TUNGSTEN ORE (SCHEELITE).To the 0.1) 0 181 4 0.1771 0 ,OOOi 0.0003 sample in a 250-ml.. beaker, add 100 ml. of hydrochloric acid. Stir n-ell while -4verages are reported t o additional deciinal place i o show range. warming the solution to prevent, caking. /E, r\fter the sample is in solution, evaporate b d = T n - l t o about 5 to 10 ml. Add 10 nil. of . . . . ~ ~ sodium citrate solution (300 grams per liter) and then ammonium hydroxide until t,he pH is about 8. Warm until the precipitate dissolves. Cool, and proceed with the ext'raction after adding hydroxylamine hydrochloride to Effect of Diverse Ions. Smith and hIcCurdy ( 5 ) report that 110 cation other than copper( I ) forms a colored complex that is 'e'~L;"s~h~~~~"~,.R~i~sRlt"e"",gS ~~$tstsr;itl,ic extractable. It vias desirable to study the effect of certain anion. Ltcid (1 + 3 ) and 10 of hydrogen peroxide (30%). After in greater detail. At least 10 ml. of perchloric acid (70%) did the sample is in solution, boil ddrvn to a low volume ( 5 to 10 ml.), Add hydroxylamine hytlrochloride (100 grams per liter) and not interfere, Complete recovery resulted lvith 5 ml. of pliopsodium citrate (300 grams per lit,er), adjust the pH, and extr:ict'. ,vith (85%l! but only 9s% recovery n-as phoric A h s u r e the absorbance o l the resulting colored solution against nil. of phosphoric acid. Fluoride (0.9 gram) added as sodium :i blank fluoride and ammonium ion (6.7 grams) added as ammonium COR.~LT-I\IOLYBDENUU-TUNGSTE.\~ STEEL. Add t,o the sample :&bout5 ml. of hydrochloric acid and warm until the reaction is chloride caused no interference, Only a trace of cyanide (>0.1 complete. Add several drops of hydrofluoric acid and 2 ml. of mg. and -of the copper. Columof perchloric acid (;'o%). ~~l~~ to fumes and fume until the bate, molybdate, tantalate, tungstate, and vanadate do not insample is completely dissolved. Cool, take up wit,h water, add sodium citrate (300 grams per liter) and hydroxylamine hydroterfere, Luke and Campbell (4)have tested the effect of 56 chloride (loograms per liter), adjust the pH, and extract. different metals on the extraction of the copper complex ant] Neo-cuproine
~~
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+
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:{('::: 2 tki
+
found no interfwenee
RESULTS PROCEDURE
The follon-ing general method was used in the analysis: Dissolve the sample by any appropriate means, preferably with hydrochloric acid and then sufficient nitric acid to oxidize the iron. Evaporate to a small volume to remove excess acid. Transfer to a volumetric flask and dilute to the mark with distilled water if an aliquot is t o be taken. Transfer the sample or the aliquot, containing up to 0.2 mg. of copper, to a separatory funnel, add 5 ml. of hydroxylamine hydrochloride (100 grams per liter) t o reduce the copper and 10 ml. of sodium citrate solution (300 grams per liter) to complex the metals present. Add ammonium hydroxide until the pH is 4 to 6 (pH paper). Add 10 ml. of the reagent (2,9-dirnethyl-l,lO-phenanthroline, 1 gram per liter of absolute ethyl alcohol) and 10 ml. of chloroform. Shake about 30 seconds, allow the two layers to separate, and draw off the chloroform layer into a 25-m1. volumetric flask containing about 3 t o 4 ml. of absolute ethyl alcohol. Repeat the extraction of the aqueous phase in the separatory funnel with 5 ml. of chloroform. Allow the layers to separate and draw off the chloroform solution into the 25-ml. flask. Dilute t o volume with ethyl alcohol and mix. Measure the solution a t 457 m r using, in the reference cell, a blank on the reagents which has been carried through the same treatment as the sample. Determine the copper concentration by referring t o a n absorbance-concentration curve prepared by taking different volumes of a standard copper solution through the procedure. Dissolution of Alloys and Ores for Copper Determination. Most alloy steels will dissolve in hydrochloric and a little nitric acid. Those that did not respond to this treatment were dissolved by other methods. Examples of other methods found acceptable for dissolution of ferrotungsten, manganese ore, and Scheelite, are as follows:
The results for various 8teels and ferro:tlloys are shown i n Table 11. The determinations m r e carried out under ordinary !aboratory conditions. Determinations on Kational Bureau of Standards standards were run in duplicate on different days, except for NBS 7 and 159, in which case all four samples mere run simultaneously. S o attempt was made to measure the solutions :tt constant temperature. The standard deviation ( u ) is shown in Table 11. -4good indication of the reliability of the method was obtained by comparing the values obtained on KBS 36a by four of the laboratory chemists using the method for the first time. The avcrage value f,)r the four analysts was 0.109% copper (0.108, 0.109, 0.109, and 0.111%) as compared t o 0.110% copper obtained by the writer as an average for seven samples. I t was of interest to check the reliability of the method for copper in manganese ores. Standard sample KBS 25b was selected as representative of a manganese ore. The Sational Bureau of Standards has not issued a value for copper on this ore, so recovery of copper was tested by the following procedure. Two $amples were run similarly except that to one sample was added 0.10 mg. of copper. The recovery of copper was 102%. Two samples of t,ungsten ore, run by conventional methods by the Electro Metallurgical Works Laboratory, were reported to rontain "0" and 0.15% copper. By the colorimetric method described, the values were 0.002 and 0.15% copper. DISCUSSION
The advantages of this method are its sensitivity, specificity, rapidity, and simplicity. At least four samples and a blank may be run in less than 45 minutes after dissolution of the samples. The accuracy and precision compare favorably with other colori-
~
~
V O L U M E 26, NO. 3, M A R C H 1 9 5 4 metric methods for copper and with the older methods used for the determination of copper which involve hydrogen sulfide and sodium hydroxide separations or a thiocyanate precipitation before final estimation of the metal either by titration or by deposition. Often, more separations are required On material$. ACKNOWLEDGMENT
The author is grateful to Robert
and Other members of the laboratory for helpful suggestions and assistanre.
579 LITERATURE CITED
Breckenridge, J. G., Lewis, R. W., and Quick, L. A , , Can. J . Research, B17,258 (1939). ( 2 ) Butts, p- G., Gahler, A. R.3 and M e l h AI. G., Ekwwe a n d I n d . Wastes, 22,1543 (1950). (3) Hague, J. L., Brown, E. D., and Bright, H. A., J. Research .VatZ. Bur.Standards, 47,380 (1951). (4) Luke, C . L., and Campbell, 11.E., ANAL.CHERI., 25, 1588 (1953). (5) Smith, G.F.,and McCurdy, W. H., Ibid., 24,371 (1952). (1)
RECEIVED for review August 18, 1953 Accepted October 2 6 , 1953. Presented before the Pittsburgh Conference o n Analytical Chemistry and 4 p plied Spectroscopy. hlarch 3, 1953
Partition Chromatography of a Homologous Series of Volatile Primary Amines R. A. CLAYTON' and F. M. STRONG Department o f Biochemistry, University o f Wisconsin, Madison 6,
IT
APPEARS that no satisfactory procedure is available for the chromatographic separation of milligram quantities of volatile amines. James et al. ( 4 ) have described the separation and microestimation of ammonia and mono-, di-, and trimethylamines, using gas-liquid partition chromatography. The method employs a Celite column containing a mixture of 5-ethylnonan2-01 and liquid paraffin as the liquid phase. The column was operated a t 7'3" C., and the amines emerged in the order of their boiling points. James ( 3 ) extended this study to include higher aliphatic amines and pyridine homologs. I n addition to liquid paraffin, the author employed Lubrol 110 and DC 550 as stationary liquid phases. KOfractions w r c collected, but the amines jvere estimated by continuous titration of the column effluent. Fuke and Rappoport ( 1 ) used a 1-butanol-water system on a column of starch mixed with calcium hydroxide to separate aninionia and the methylamines. The amines were run as the free bases and were estimated by continuous titration of the effluent. Lagervist ( 6 ) separated ammonia ant1 methylamine on a starch column n-it,h 1-propanol-aqueous hydrochloric acid as the solvent system. Resolution was followed by the quantitative ninhydrin method. Other systems have been described for the separation of prirnarJ-, secondary, and tcrtiary aromatic amines (91, and the sepnration of S-alkylated aromatic amines (6). The partition system des(-ribed in the present papcr allovied good resolution of a homologous series of primary amines from ('-3 to C-8. The use of phenolphthalein as a column indicator afforded a convenient means of following the separation.
Wis.
N. J., was used in this stud).
The column w-as packed as a slurry under 20 cm. of mercury air pressure. A cork tamp was used for the final packing, and the column height was 100 mm. The petroleum ether, which had been equilibrated with the stationary phase in the preparation of the column, was used as the mobile phase for development of the chromatogram. Operation of Column. Five milliliters of the diluted samples (ca. 0.05 meq. of each amine) were introduced onto the column and the column was operated a t a flow rate of 0.5 to 1 ml. per minute. The appearance of five pink bands after 2 hours of development enabled one to follow the resolution. N o color was given by the C-8 amine, probably owing to its low solubility in the inside phase. Approximately 80 ml. of forerun were collected before the C-8 amine came off the column. Two-milliliter fractions were then collected and shaken into 5 ml. of water which contained 2 drops of methyl orange (prepared by dissolving 0.5 gram of the free acid in 1 liter of water). The fractions mere titrated with 0.0165S hydrochloric acid to the first noticeable change in color. Figure 1 depicts the resolution of these amines, while pertinent data are compiled in Table I.
5
n
EXPERITIENTA L
Preparation of Samples. Samples of n-propyl, n-butyl, n-amyl, n-hexyl, n-heptyl, and 1-methylheptylamines were obtained from the Eastman Kodak Co. hpprovimately 1 meq. of each amine was weighed into a weighing bottle. I n order to prevent loss by evnporntion, in so far as possible, the order of weighing the individual amines T T ~ Sthat of decreasing molecular weights. The conibined samples were diluted to 100 ml. with the mobile phase. Preparation of the Column. Celite 545 (23 grams), a diatomaceous earth filter aid obtained from Johns-Manville Co., Chicago, Ill., was shaken Lvith 750 ml. of petroleum ether (boiling point, 60" to 71" C.) in a 1-liter separatory funnel until the powder was evenly wetted. The stationary phase, which consisted of IS nil. of methanol, 3 ml. of water, and 2 ml. of an ethyl alcohol solution of phenolphthalein (prepared by dissolving 5 grams of phenolphthalein in 500 ml. of 95% ethyl alcohol and diluting to 1 liter with water) was added to the funnel. Twenty minutes of shaking was required to produce a uniform slurry. h ground-glass, graduated chromatographic column (38 mm. in internal diameter), supplied by Scientific Glass Co., Bloomfield, 1 Present address, Department of Biochemistry. The George Washington University School of Medicine, 1335 H S t , N W , Washington 3, D C
I
2'0
40
6
b710
IbO
FRAC TlON
I50
145
Figure 1. Chromatographic Separation of Homologous Series of Volatile, Primary Amines [Solution containing ca. 0 05 meq. of each amine ('2-3 to C-8) was introduced onto Celite 545 column 38 X 100 mm. Column was operated at flow rate of 0.5 to 1.0 fnl. per minute. Two-milliliter fractions were extracted into 5 ml. of water and titrated with dilute hydrochloric acid Stationary phase consisted of methanol, ethyl alcohol, a n d water; petroleum ether, equilibrated with stationary phase, was used as mobile phase.]
Identification of Amines. The identity of theamines was established by paper chromatographic comparison with known samples. Whatman No. 1 paper was used throughout. The standard samples were prepared by dissolving ca. 50 mg. of each amine in 1 ml. of I . O N hydrochloric acid and diluting to 10 ml. with water. One- to 2-microliter spots were applied to the paper.
