and transmitted illumination. W t l i the proper combination of lighting, the reaction spots for sulfuric acid appear as milky yellow, perfectly circular areas on a blue background. Most other acids will give yellow spots, but these d l not contain the milky precipitate of barium sulfate. Phosphoric acid will also cause a milky precipitate within the reaction area; however, the barium phosphate formed is birefringent, in contrast to barium sulfate. The two can therefore be distinguished by means of crossed polnrs. Other sulfates and phosphates \Till give circular milky areas, but for the most part were not found to be sufficiently acidic to change the color of bromophenol blue. It vias difficult to reproduce precisely the relationship between sulfuric acid droplet diameter and react>ionspot tii-
anieter, presumably because of tlic sensitivity of the sulfuric acid droplet diameter to relative humidity. HOB-ever, as a result of a large number of euperiments. i t is believed that thy equation Dh = 2.5 Da nhere Dhis the diameter of the reaction spot or "halo" and Dd is the equivalent diameter of a droplet of pure sulfuric acid, represents the droplet size within =k30%. The equation is not valid above approximately 90% relative humidity. At extremely high humidities. the test fails because of the extreme dilution of the sulfuric acid drops. LITERATURE CITED
(1) Gerhard, E. R., Johnstone, H. F.. . \ S A L . CHElf. 27, 703 (1955).
( 2 ) Lodge, J. P., Jr., J . Jfeteorol. 13,
310 (1956).
P.,Jr., Subila 2 [ I ] , 58 (1959). ((4) Lodge, J. P., Fanzoi, H., ASAL. CHEY.26,1820 (1954). ( 5 ) Woodcock. A. H.. Gifford. hI. 11% J . Marine Research 8; 177 (1949). ( 3 ) Lodge, J.
JAMES P. LODGE, JR. JAMES FERGWXW~ BERNICE It. HAVLIK*
Chemical Research & Development Air Pollution Engineering Research Robert A4. Taft Sanitary Engineering Center U.S. Public Health Service Cincinnati 26, Ohio 1 Present address, hlcXicholas High School, Chemistry Department, Cincinnati 30, Ohio. 9 Present address, U. S. Xaval Propellant Plant. Indian Head, hId.
Spectrophotometric Determination of Copper Following Extraction with 1,5-Diphenylca rbohydrazide in Benzene SIE: -4 procedure for the determination of copper in aqueous solution is based 011 earlier studies (I) of the cheluting properties of diphenylcarbazone and 1,5_diphenylcarbohydrazide (synidiphenylcarbazidc) . Although stable c o p p u coinplexes were formed with both reagents in a number of organic solvcmts, 1,5-cliphenylcttrbohydrazidc \viis studied because a colorless blank was obtained with this reagent,. \vhercus diphcnylcarbazone produced :I colorec~ blank. In thv procedure finally adoptctl. the aqueous solution to be analyzed vias extractid with a b e n z e n e solution of 1,5-diphcnylcarbohydrazide and the colored mtract read in a spectropliotomctw. Carbon tetrachloride, chloroform, or isoamyl alcohol could be sui)st,itutcd equally well for bimziwe as :I solvent for the reagent. Although the method of Turkingtoii and Tracy for the determination of copper with 1,5-diphenylcarbohydraeide in aqueous solution ( 3 ) is niorc sensitive (molar absorptivities 158,000 arid 55,000, respectivcly), ours has a number of advantages. The blank is colorlcsu. in:tximum color dewlopment in tlw test solution is almost instantanrous. :iiid the color intensity does not chaiigc, ovcr n 24-hour period. Furtherniorc~. the. benzene solution of lj5-diphenj.lcnrbnliytlmzide is stable for at' lcast 2 weeke when stored in borosilicatc, containtw. EXPERIMENTAL
Apparatus.
Absorbancxe
III(~B~UI~-
3t
( 5
-4
-
520
60 3
681:
h 4 V E L E N G T H UILLIMICROhSI
Figure 1 . Absorption spectrum for 1,5diphenylcarbohydrazide-copper cornplex in benzene
\$-(is cooled and diluted t o 100 nil. \vit h benzeii e. Most lots of benzene were used as received. However, two lots were encountered which, when used as solvents for the reagent, caused a reduction of Libout .50yoin sensitivity in the copper cietermination. Distillation did not r ~ iiiove the interference. R t d t s wcrc atisfactory, however, after they iverc passed through a column of activated dumina (Alorco, Grade F-20, freshly yeactivated by heating 4 hours a t 400" C.). S o such difficulty was encouiitered when isoamyl alcohol, chloroiomi, or carbon tetrachloride was u s i d :IS solvent for the reagent.
SODIEM PHOSPHATE SOLUTIOX.A 3aturated solution n-as prepared by adding 30 grams of reagent grade tri>odium phosphate dodecahydrate to 100 nil. of freshly boiled redistilled \ v a t u . The mixture was allowed to qt:ind overnight and the supernataiit \vas separated from the crystals 1))tiwantation or centrifugation. 'I'hiq .;ohtion had a p H of about 12. A4s shown hclow. tlic pH is not criticd \ritliin certain limits. STASDARD COPPERSoLu,rIom. 'l'lic qtock standard solution was prepared by dissolving 39.3 ing. of reagent grade copper sulfate pciitahydrate in redistiilcd water and diluting t o 100 ml. A c'oppc~rn-orking solution was prepared by diluting 1.0 nil. of the stock standard t o 100 nil. with redistilled water (1 pg. of copper per nil,). dliquots vwre ~lilutrdas requircd.
meiits were made with a Coleuian Universal Model 14 spectrophotonicter using 19 x 105 m m . euvet,tei having a light p a t h of 1.5 cm. A Beckman Model G pH meter \vas used t o determine p H values. Redistilled Water. Lahoratorydistilled water n-as redistilled through a borosilicate glass still unt'il i t was free from metal ion contaminants a s determined by extracting aliquotwith a 0.001% solution of dithizonc in chloroform (2). The still consistd of :L Keninierer-Hallet micro-Kjcldahl steam generator (Fisher Scientific Co.), whiclr prevents mechanical carry-over, and was connected to the condenser b y :I glass to glass joint'. Reagents. ~,~-DIPHENTLCARBOPROCEDURE HYDRAZIDE (Fisher Reagent'). Ten milligrams were added t o 50 nil. of To an aliquot of solution containing benzene (Fisher, certified) and heated 0.5 t o 3.0 p g . of copper in a glasst o boiling. T h e resulting solution h p p e r e d centrifuge tube were added 2 VOL. 32, NO. 9, AUGUST 1960
1207
ml. of the saturated sodium phosphate solution. After the volume had been adjusted to 5.0 ml., 7 . 0 ml. of the 1,5diphenylcarbohydrazide reagent were added. A blank was similarly prepared, except that redistilled water was substituted for copper solution. The tubes were stoppered and shaken vigorously for 1 minute. The stoppers were removed and the tubes were centrifuged for 2 minutes to hasten the separation of the immiscible solvents. The benzene Iayers were transferred to the cuvettes and the copper solution was read against the blank a t 540 mp, DISCUSSION
Absorption Spectrum. Figure 1 shows t h e absorption spectrum of the benzene solution obtained after extracting a mixture containing 2.0 ml. of sodiuni phosphate solution and 3 ml. of standard (3 pg. of Cu) with the diphenylcarbohydrazide reagent. The absorption niaxinium lies between 530 and 550 mp. The molar absorptivity of copper 1,5-diphenylcarbohydrazide complex in benzene is 55,000 a t 540 mp. The absorbance of the copper comp1e.r conforms to Beer's law over the range of 0.5 to 3.0 pg. The color is stable for 24 hours when precautions are taken to prevent evaporation of benzene. Copper determinations carried out on the aqueous phase following extraction with the reagent indicate that 95% of the copper is extracted in this procedure. Maximum color intensity was obtained in the benzene layer after 30 seconds of shaking and longer periods did not increase the extraction of the copper. Pro-
Table I.
Ion Ca + 2 Mgti" Ba K+ Cr04-2
+
Amount Added, pg.
E 03Y)
4
02 -
Figure 2. Effect of pH on color development
longed shaking did, in fact, cause a fading of the color in some instances. Effect of pH. Solutions varying in p H were prepared b y adding 1 S hydrochloric acid t o portions of the sodium phosphate solution. Two milliliters of these solutions were added t o aliquots of standard containing 3 pg. of copper and the pH's of the resulting mixtures were determined. The niiitures w r e extracted with the color reagrnt and absorbances of the extracts plottcd against the p H of the sample (Figure 2). The saturated sodium phosphate solution is added to the test sample prior to extraction to adjust and buffer the p H a t 11 to 12. Under ordinary conditions the p H does not require readjustment. Reagent Concentration and Stability. The diphenylcarbohydrazide
Form Added
on
1 ml. 5% KI
10 100 10 10 100
ANALYTICAL CHEMISTRY
Copper Recovered, % 98.3 97.0 101,6 97.0 103.0 98.3 106.0 98.8 105.0 103.0 (Off scale) 102 4
100
Present as Cr04-' a t pH's involved.
1208
04-
z 0
-1- _
10 10
+ citrate
I -1
100 100 100
10 10
+ citrate
a
I
05'
Effect of Impurities on Recovery of 1 pg. of Copper
soh.
Ni +$ Cd +2 c o +2 Fe +S
Mn +2 lMn+2
06-
100
Zn + 2 Pb+2 UO, + 2 Citrate Hg +2 H g f 2 I-
Fe+3
I
Ni(CH,C0,)2 4H20 CdCL 21/2H20 Co(CH3COq)*4Hzq Standard iron wire dissolved in HC1 Standard iron wire Na3C6Hb0,2 H 2 0 MnS04 4H20 hInS04 4H20 Na3CsHsOi 2H20
101,7 100.0 103.0 77.3 103,2 74.0 97.0
reagent is present in excess in t h e procedure described. KO differences in absorbance values were obtained by varying the reagent concentration from 5 to 10 mg. per 100 ml. of benzene. Seven milliliters of benzene allowed sufficient volume t o be used in the cuvettes employed. Effect of Diverse Ions. An aqueous solution, containing the ion t o be studied, n a s added to a solution containing 1 pg. of copper and the resulting mixture was treated according t o the procedure described. The results of these analyses, expressed as the per cent of copper which was recovered, are given in Table I. Hg+2 was the only ion tested which gave a positive interference-Le., apparent Cu+? concentration was increased. This interference could be overcome by the addition of KI. Nickel, cadmium, and cobalt interfered with the determination of 1 pg. of copper when added in 100-pg. amounts, but not when present in 10pg. quantities. Iron and manganese interfered at both the 100- and 10-pg. levels. The interference of both of these metals could be eliminated a t the IO-pg. level by the addition of citrate to the test solution. h-o other ions tested interfered a t the 100-pg. level (Table I). The noninterference of chromate permits the use of chromic acid solutions for cleaning the glass\?-are used in this determination. Phosphate, which interferes to some extent in the method of Turkington and Tracy ($), does not interfere in this method, as over 100 mg. of are added to each sample in the form of trisodium phosphate prior t o extraction as an integral step in the procedure. Purines and pyrimidines inhibit the reaction as they do in the method of Turkington and Tracy. Precision. Analyses of 25 eonsecutive samples containing 3.0 pg. of copper yielded a mean of 3.008 pg. with an average deviation of 0.059 pg. (2%) and a standard deviation of 0.080 pg. (2.7%). LITERATURE CITED
(1) Dasler, W., Stoner, R. E., Erperientia 15. 112 (1959). (2) Stout,' P. R., Arnon, D. J.: Am. J. Botany 26, 144 (1939). (3) Turkington, R. W.,Tracy, F. M., .4N.4L. CHEN. 30, 1699 (1958). RAMON E. STONER DASLER
1VALDEMAR
Chicago hledical School Chicago 12, Ill. WORK supported by research grant A1427 from the Kational Institute of Arthritis and RZetabolic Diseases, TJ. S. Public Health Service.
