Paper Chromatographic Method for the Quantitative Determination of Copper and Zinc 8-QuinoIinoIates M O M A S D. MILES, ARMAND0 C. DELASANTA, and JOSEPH C. BARRY' textile, Clothing and Footwear Division, Quartermaster Research & Engineering Command, Research & Engineering Center, Natick, Mass.
b A quantitative method for determining small amounts of copper 8-quinolinoiate and zinc 8-quinolinolate is described. The metal chelate is quantitatively dissociated into the metal and 8-quinolinol on a paper chromatogram. The metal is titrated with a complexone using a metal indicator. The method can be used to determine the copper 8-quinolinolate content of mildew-resistant treated textiles.
C
OPPER ~ U I N O L I N O L A T E is
widely used as a mildew inhibitor for military textiles (7). Approximately 1% of the compound b e d on the weight of the textile is the usual amount required to protect the cellulosic material from attack by microorganisms. The copper 8-quinolinolate is usually part of a functional finish which may include waxes for repellency, pigments for color, flame retardants (chlorinated paraffins and SbzOa), and also other mildew inhibitors such as copper naphthenate. A specified range of copper 8-quinolinolate is contained in the military specification for the textile material. An example is "copper& quinolinolate, 1.0 to 1.5% of inhibitor based on total weight of finished cloth" (8).
A method for determining small amounts of copper 8quinolinolate without the use of instrumentation is of interest for routine testing of textiles. Both mcthods that are currently available for determining this compound in treated textiles require the use of a spectrophotometer (1, 6). In a method developed by Rose et al. (6) copper 8quinolinolate is separated from copper naphthenate by extracting the textile material with a dilute solution of sulfuric acid and extracting the copper 8-quinolinolate from the acid solution with chloroform. In addition to these methods designed especially for textiles, many other methods have been developed for estimating the compound. Hollingahead'a review (4) of such methods includes a volumetric method by Berg in which Preaent addreas General Transistor Corp., Wooneocket, I.
k.
the chelate is diwlved in hydrochloric acid and the copper determined iodometrically (4). Hill el al. (9) describe a method in which the copper Rquinolinolate is diesolved in glaciul acetic acid, H a bubbled through the solution to precipitate CuS, and the 8quinolinol titrated with perchloric acid, to a potentiometric end point. Of the methods available, none appear to be suitable for estimating the small quantities of the compound used on textiles without instrumentation such as a spectrophotometer. REAGENTS
Whatman 3-mm. chromatographic paper. Disodium EDTA, analvtical grade [disodium(ethylenedinitrilo)tetraaoetate dihydrate] approximately 0.001M ( a p proximntely 0.3721 gram diluted to 1 liter). PAN indicator (0.1% in methanol), J. T. Baker Chemical Co. Murexide indicator (1 mg. of murexide to 1 ml. of ethylene glycol), J. T. Baker Chemical Co. 1-Butanol-HC1 elutent (80 parts butanol, 10 parts concentrated HCI, 10 parts HSO, by volume). PROCEDURE FOR COPPER 8-QUINOLINOLATE ANALYSIS OF TEXTILES
The extraction procedure followed is essentially that of the Rose method (6). Weigh an approximate l-gram a m le, ovendried for 2 hours at 105"C., to tR, nearest milligram. Cut into '/I,,inch squares and immerse in 25 ml. of 10% HBOt in a 125-ml. Erlenmeyer flaak. Heat to 96" C. with agitation. Decant the acid extract into a m m l . beaker. Repeat the extraction procedure twice more with 2 0 4 . porhons of 10% Ha04 and combine extracte. Add to the acid extracts sufficient 25% ",OH to adjust the pH of the solution to the range of 6 to 7 uaing pH indicator paper. Cool to room temperature. Transfer the neutralized solution to a 250-ml. separatory funnel and extract the copper 8-quinolinolate with successive.5-ml. portions of chloroform until the bottom chloroform layer ia colorlese. N t e r the chloroform layer into B 25(Fml. beaker usin ?Vhatman No. 42 filtergsper. Wasf the filter paper and red ue with chloroform. Reduce
this volume to slightly under 50 ml. and adjust the volume to exactly 50 ml. a t room temperature using a volumetric
flask.
Take a 4-ml. aliquot of this solution using a 4ml. pipet with s ueeze bulb attached. The pipet wi?h bulb is placed in the buret holder. Cut a circle of paper 1 inch lar er in diameter than the Petri dish. from the edge to the center of the paper circle, cut a l/=inch wide strip. This serves as a wick to carry the solvent. To confine the spot by evaporating the chloroform rapidly, a hot plate is used. The paper to be spotted is placed over a Petri dish on top of the hot plate. The pipet (with holder) is placed over this assembly with the tip of the pipet in contact with the center of the paper firm enough to hold the paper steady. The solution is spotted by B controlled-flow squeeze bulb. The 801vent is evaporated during ap lication with the hot plate set a t low Reat. A 1-inch diameter spot is suitable. When the entire 4 ml. is spotted, place the paper over a Petri dish containing the HC1-butanol solvent. The wick is immersed in the solvent which should half fill the Petri dish. Cover the dish with another of the same size. As the solvent wicks along the paper, the spot breaks up into two rings. When the rings are slightly separated, remove the and allow to airdry thorougf?? or 2 hours. EYose the paper to fumes from a reagent ottle of concentrated HC1. Cut 03 and discard the nick. The compounds present on the paper are copper ancl 8quinolinol in two rings slightly green in color. The paper containing these compounds is removed by cutting just inside (at a distance of approximately inch) the solvent edge. Cut the paper into small pieces (of a size to fit through the neck of a 250ml. Erlenmeyer flask). Place in a 25C~ml.Erlenmeyer flsak. Add 20 ml. of water free of trace metals (this can be checked with the indicator), 1 ml. of glacial acetic acid, and 10 drops of PAN indicator solution. The color of the solution with the indicator and co per present is purplish red. Swirl the k k and allow to stand for a few minutes. Titrate with the EDTA solution. The color of the solution changes during titration from purplish red to a reddish orange. The end point is a yellowish green. Experience with the end point should be obtained by titrating copper solutions of known
g
VOL 33,
NO. 6, MAY 1961
685
Table 1. Analysis of Chloroform Sobtionr of Copper and Zinc 8-Quinolinolate by Chromatotitrimetric Method (Murexide Indicator) Copper &quinolinolate,gram Preaent Found O.OO066 0.00087
O.OOO64
0.00085 0.00067
O.ooo88
0. ooo64
Av. O.OOO66 fO.00001
O.OOO33
0.00032
O.OOO33 0.00035 0.00031 Av. 0.00032
*O.ooOOl
Zina &quholinolate, gram 0.00078 O.OOO78
0.00080
0.00079
O.ooo83 0.ooOsl Av. 0.00080 f0.00002
Table II. Copper 8-Quindinolate Content of a 3-Gram Sample of Mildew Resistant Cotton Webbing Using Two Method$ Chromatotitrimetric Spectrophotometrio (Murexide (8) mdicator) 0.019 Gram 0.019Gram 0.018 0.018 0.017 Av. 0.018
concentration (such as 0.040 mg. of copper per ml.). Copper 8quindnolata (grerm) = 4.40 X molarity EDTA X ml. EDTA PROCEDURE FOR ZINC 8-QUINOLINOU?E
Freshly prepared chloroform solutiom of ainc 8quinolinolate were used. (A precipitate formed on several hours’ atanding. A thorou hly dried redistilled chloroform extende8 the solution stability.) The spotting medure ia the same as that deacribdt for co per 8quinolinolate. m e =me Hcl-tutanol solvent is used. When the solvent haa covered two thirds of the area within the Petri dish, the paper is removed and airdried for 24 to 48 hours. The area between the uinolinol ring and the solvent edge ia t en cut out and placed (after cutting into small pieces a p proximately */&oh square) in a 250. ml. Erlenmeyer flask and 10 ml. of dietilled water is added. After 5 to 10 minutea, 10 ml. of ethyl alcohol ia added and sufficient murexide indicator solution to Droduce a vellow-oranne color (a pro&tely 15 drops). TitraG with E8TA.
gP,
686
0
AMrncAL CHEMSI TRY
Grams Zn = 0.06638 X molarity EDTA X ml. EDTA solution Gram Zn 8quhoholab grama Zn X 6.68 DISCUSSION OF RESULTS
Copper 8quinolinolate can be dismciated quantitatively into copper and 8quinolinol on a paper chromatogram with a butanol-hydrochloric acid elutent. Methods are available for titrating m a l l amounts of copper using complexones with metal indicators (8). (Ethy1enedinitrilo)tetraacetic acid was chosen aa the complexone and murexide and PAN [l-(Zpyridylaso)-2-naphthol] as the metal indicators. Whm copper 8quinolinolate is spotted on a paper chromatogram with butanol-HCl 88 the solvent, two rings (in a horisontal chromatogram) appew, one a t R j 0.4 and the other at Rj 0.7. When mall amounts of copper 8quinolinolate are used (in the range of 2.1 pg. of copper as chelate), the ring at Rf 0.4 is not visible even when developed with ammonia fumes. However, the ring at Rf 0.7 which fluorescee (ultraviolet light) is evident even in amounts of copper 8-quinolinolate smaller than 2.1 pg. of copper as chelate (6). The ring at Rf 0.4 is copper. The fluorescence (ultraviolet) of the ring a t Rf 0.7 is due to 8-quinolinol. In quantitatively measuring the copper on the chromatogram, not all of the copper from copper 8-quinolinolate waa contained in the riog at &f 0.4 and some was ala0 contained in the 8quinolinol ring at Rj 0.7. Since this does not occur with very small amounts, it may be a function of sample sizee. Testa included descending chromatograma in which there was considerable distance between the rings. Analysis of these papem showed no copper between the Rf 0.4 and &f 0.7 rings, but the copper in each ring added up to the quantitative amount of copper from the copper 8quinolinolate. It was concluded from them testa that the copper 8-quinolinolate diasociates quantitatively into copper and 8quinolinol but that some of the copper is carried into the 8quinolinol ring. Table 1 shows that the copper was quantitatively analyaed from known amounts of copper 8quinolinolat.e. There is no evidence that the copper in the Rj 0.4 and Rj 0.7 r i n g are in different forms. (It ia possible that the acidity of the HC1-butanol elutent prevents. chelation of the copper and oxine in the same ring.) Both are titrated with EDTA. Copper in the copper 8quinolinolat.e form is not titrated with EDTA. A meaaurement of the 8quinolinol from the chromatogram waa attempted
by reacting it with a standard copper solution and titrating the excess copper with EDTA. Trials rising reagent grade Squinolinol eluted on paper were promising; however, an ammoniacal d u t i o n wm required for the 8-quinolinol to react quantitatively with the copper in thc small amounts used. Many metals interfered in this pH range. Another d d v a n t a g e is that some of the dissociated copper is in the quinolinol ring on the paper and has to be separated. The direct titration of the dissociated copper appeared to be the most promising approach. A method waa then developed in which a chloroform solution of the compound is spotted on a horizontal paper chromatogram using butanolhydrochloric acid as the solvent. After drying, the paper is titrated with EDTA and the amount of copper 8quinolinolate is calculated from the copper present. The method has several advantages. Whether or not metal interferences (which would make the indicator the same color as its copper complex) are present can be determined by the EDTA titration of the spotted paper prior to using the butanol-IIC1 solvent. If interferences are present on the paper or in the copper &quinolinolate solution, they will show up at this point. The copper Squinolinolatc does not change the color of the metal indicators. Another advantage ia that the copper 8quinolinolate can be identified qualitatively, if necessary. The ring at Rf 0.4 can be identified as copper by placing the paper in ammonia fumes and the ring at Rf 0.7 as &quinolinol by its ultraviolet fluorescence. The method can be used to determine the copper 8-quinolinolate content of textiles without using instrumentation such as a spectrophotometer. The textile can be extracted according to the method of Rose et ul. (6),and the chloroform extract titrated instead of measured with a Spectrophotometer. This extraction procedure will separate copper 8quinolinolate from copper naphthenate (6). Table I liats the results of analysis of chloroform solutions of reagent grade copper 8quinolinolate. Table 11 lists the results of the analysis of treated webbing by the chromatotitrimetric method and by the spectrophotometric method (6). Murexide was used aa the metal indicator. PAN indicator had several advantages over murexide. With PAN the color in the flaak during titration doea not fade on standing. The color at the end point is also easier to distinguish. Table 111 lists the results of analysie of webbing, thread, and fabric using PAN indicator. Spectrophotometer measurements of the copper 8quinolinolate were also made (6).
Of the mildew-resistant textiles analyzed, the fabric containing the smallest amount had a copper %quine linolate content of 0.041 f 0.005% (the average and average deviation for five determinations). To find out whether the method was applicable to other metal quinolinolates, zinc 8-quinolinolate was analyzed. The conditions for titrating zinc with EDTA and murexide differed slightly from those used for copper. Ethyl alcohol was added to the solution being titrated and a pH range of 6 to 7 was found desirable. The chromatograms were airdried from 24 to 48 hours prior to titration. Paper dried for short periods of time reduced this
PH.
Zinc 8-quinolinolate dissociated quantitatively using the HC1-butanol solvent. The zinc appeared a t Rf 0.8 and the 8-quinolinol a t Rf 0.7. All of the zinc was contained in the Rf 0.8 ring. It is also possible to determine whethcr any interferences-i.e., zinc or other metals-are present in the solution by titrating prior to dissociating the chelate. Zinc 8-quinolinolate can be identified by color reactions of the Rf 0.8 ring
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Table 111. Copper 8 Quinolinolate Content of a 1-Gram Sample of Treated Textiles Using Two Methods
Chromatotitrimetric Spectrophotometric (PAN indicator) Cloth, webbing (water repellent and mildew reaietant) 0.006 Gram 0 005 0.008
0.006 0.006 Av. 0.006
Cotton duck fire, water, weather, and m’ dew resietant) 0.002 0.002
d
0.003
0.002 0.002 0.002 Av. 0.002
Cotton thread (mildew resietant) 0.008 0.007 0.007 0.008
0.007 0.007 Av. 0.007
for zinc, such aa the pink color with dithiaone and the ultraviolet fluoresence of the 8quinolinol ring at Rf 0.7. Table I lists the results of analysia of chloroform solution of zinc and copper 8quinolinolatea. LITERATURE CITED
(I) Darbey, A., Am. Dywtufl Reptr. 42,
453 1953). (2),,F era1 S Scation . CCCD-950, Dyeing anrMtertreatmg Proceeeea for Cotton Fabrics,” September 30, 1959. (3) Hill, C. H., ct al., ANAL. CHEM.28, 1688 (1956). (4) Hollingahead, ,F. 0.W. “Oxine and Ita Derivatives Vol. I, butterworth’s Scientsc Pubdcation, London, 1954. ( 5 ) Miles, T. D., Delasanta, A. C., Am. Dyestuf Reptt. 48, 31-2 (1969). (6) Rose, A., Hutchinson, A., Witt, H., Sharkey, 1. R., Zbid., 45,3624 1956). (7) Siu, R. G. H. “Microbial ecomgroeition of Cefiuloee with S ecial eferences to Cotton Textiles,” %einhold, New York, 1951. ( 8 ) Welcher, F. J., “The Analytical Us? of Eth lenediaminetetraacetic Acld Van doatrand. Princeton. N. j,. 1958. RECEIVEDfor review October 5 . Accepted February 20, 1961. divlaon of Anal ice1 C h e e t r y , 137th Meeting, ACS, Cceland, Ohio, April 1960.
e6
b
Effect of Take-Off Angle on Electron Probe Calibration L. S. BlRKS
and R. E. SEEBOLD U. S. Naval Research laboratory, Washington 25, D. C.
b The effect of take-off angle on calibration curves for quantitative electron probe analysis is illustrated using the Ni-Fe and Ni-Cr systems and takeoff angles from 6 to 90 degrees. In both the Ni-Fe and Ni-Cr systems, there is strong matrix absorption of NiKa radiation ond the Ni calibration curve is sensitive to take-off angle. Low take-off angles lead to the greatest deviation from linearity in the x-ray intensity vs. composition curve. For FeKa or CrKa’radiation, the matrix absorption by Ni is about the same as the self-absorption of the element for its own radiation. There is little effect of take-off angle on Fe and Cr calibration. With careful specimen preparation, precision of a few per cent of the amount present was obtained in the Ni-Cr system for take-off angles from 6 to 45 degrees and for electron energies of 20 to 45 k.e.v. Poor specimen preparation with local inclinations of 5 degrees to the average surface leads to errors as large as 10 to 15% of the amount present in the Ni calibration.
Q
ANALYSIS with the electron probe requires calibration curves relating measured x-ray intensity to per cent composition. These curve8 are similar in appearance to those used in fluorescent x-ray spectroscopy and may be obtained from a series of known composition standards provided the standards are solids, homogeneous on a 1-micron size scale, and with a smooth surface. For electron excitation they may also be obtained by calculation techniques (1) that make use of the mass absorption coefficients, excitation efficiencies (g), and a single standard such as 100% of the element to be calibrated. One of the important parameters that affect the calibration curves is the take-off angle for x-rays-i.e., the angle between the emerging x-rays and the specimen surface. For small take-off angles, the path length for emerging radiation is increased and the x-ray intensity is reduced according to the usual x-ray absorption law. Calibration curves a t various take-off angles are most easily compared if one plots UANTITATIVE
relative rather than absolute x-ray intensity. By relative intensity we mean: the characteristic intensity from an element a t an intermediate composition divided by the characteristic intensity from a 100% standard of the same element at the same take& angle. Thus all calibration curves pass through the same zero and 100% end points. In the present paper, the Ni-Fe and Ni-Cr systems were chosen for study because the strong absorption of NiKa radiation by Fe or Cr leads to very nonlinear calibration curves and illustrates the effect of take-off angle dramatically. EXPERIMENTAL RESULTS
Calibration curves were prepared for the Ni-Fe and Ni-Cr systems a t takeoff angles of 6, 20, and 90 degrees using the calculation technique (1) and 100% standards. All of the curves are plotted in terms of relative x-ray intensity as explained in the introduction. Nickel-Iron. Figure 1 shows the results for the Ni-Fe system. The different character of the Ni and Fe VOL 33, NO. 6, M A Y 1961
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