CS
=
Cm
=
Cs
- Cm
=
POAA equivalent in original sample, y/mL = Ca x lO/Vs P O L 4 equivalent in medium, y/ml. = Cb X 1O/ V m real concentration of POAA, 7,’ml.
Extraction and Estimation of Penicillin V. PROCEDURE. One milliliter of t h e treated sample, TI hich was used in t h e estimation described above, is pipetted into a suitable centrifuge tube and further treated with 1 ml. of I S sulfuric acid and 2 grams of dry, powdered ammonium sulfate to furnish a saturated solution of the salt at about p H 2 . Five milliliters of redistilled methyl isobutyl ketone are added, and the tube is shaken vigorously for 45 seconds and then centrifuged for 5 minutes. ilfter separation in this manner a suitable aliquot is removed for drying and subsequent color development. The value taken from the standard curve represents the sum of the values for free POAA and P O A h
derived from penicillin T’ and after making due allowance for the values obtained in the blank for a similarly treated aliquot of methyl isobutyl ketone alone, is calculated in micrograms per milliliter (or parts per million) in the manner described above.
If B y per ml. represent the value so obtained and A micrograms per ml. the value obtained for free phenoxyacetic acid the amount of penicillin V in micrograms per nil. may be calculated from the formula 2.3 ( B - A ) or read directly from the standard curve for penicillin V. I n the presence of phenoxymethylpenicilloic acid-formed under certain conditions from penicillin V in fermentation broth-the acid will be extracted by methyl isobutyl ketone and hence estimated as penicillin. ACKNOWLEDGMENT
The author gratefully acknowledges
the advice and encouragement received from E. C. Mason throughout the course of this work and wishes to thank J. R. Garnet for help in the preparation of this paper. LITERATURE CITED
(1) dnderson, G., Davis, L. J., Davey, V, F., Australian Patent 215,879. ( 2 ) Beilstein, E. K., “Handbuch der organischen Chemie,” Yol. 6, 4th ed., p. 161, Springer, Berlin, 1923.
(3) Levey, K., Leurs, H. B., J . Bid. C h n . 168, 213-21 (1947). (4) Lykken, L., Treseder, R. S.,Zohn, \-., ISD. ESG. CHEM,~ A L ED. . 18, 103 (1946).
( 5 ) Pan, S. c., .kS.\L. CHEX. 26, 1438 (19,541 \ - - -
- 3 .
(6) Pan, S. C., Perlman, D., Zbid., 26,
1432 (1954). (7) Stoughton, R., J . Biol. C h e m 115, 293 (1936). RECEIVED for review June 5, 1958. h c cepted September 8, 1958. Kork performed a t the Commonwealth Serum Laboratories, Melbourne, Australia. Published with the approval of the director.
Chelometric Analysis of Manganese-Magnesium and Manga nese-Magnesium-Zinc Mixtures Fluoride Ion as a Demasking Agent WILLIAM G. SCRIBNER Research and Engineering Division, Monsanfo Chemical Co., Dayton, Ohio
b The use of fluoride ion to demask magnesium selectively from a mixture of manganese and magnesium (ethylenedinitri1o)tetraacetate (EDTA) chelonates permits rapid analysis of manganese-magnesium mixtures b y consecutive titration of a single sample solution. Total manganese and magnesium (and zinc) are first determined by direct EDTA titration a t a pH of 10 employing Eriochrome Black T as indicator. Addition of a soluble fluoride causes formation of magnesium fluoride with the liberation of EDTA equivalent to magnesium, which is titrated with standard manganese. Zinc, if also present, can b e determined by demasking the zinc-EDTA with cyanide and titrating the liberated EDTA with standard manganese. Initial manganese in either case is calculated by difference. The method has been successfully applied to ferrites -e.g., manganous oxide-magnesium oxide-ferric oxide and manganous oxide-magnesium oxide-zinc oxide-
ferric oxide. Extension to other metal combinations is suggested.
I
interest in ferrites [mixed oxides with magnetic iron(II1) oxide] has necessitated the development of analytical methods for their estimation. Determination of iron in ferrites by cerate or permanganate oxidimetry presents no difficulty. However, analysis of certain mixed oxides by the classical methods may involve tedious, time-consuming separations, and precipitations. I n the author’s laboratory, titration with (ethylenedinitri1o)tetraacetate (EDTA) was investigated for the routine analysis of divalent metal ions in manganese-magnesium ferrite and manganese-magnesium-zinc ferrite, Because iron in high concentration is difficult to mask, and it interferes with E D T A titrations in alkaline solution, a prior separation is necessitated. The cupferron extraction method of Fritz. KCREASIKG
Richard, and Bystroff (4) effects rapid, efficient separations of iron from divalent metal ions. K N O W N EDTA M E T H O D S F O R M A N G A N E S E M A G N E S I U M MIXTURES
For the E D T A analysis of a manganese-magnesium mixture, the pH effect alone cannot be utilized to achieve selectivity when the end point is determined with the aid of a metallochromic indicator (3). Analysis by potentiometric E D T A titration of manganese a t a pH of 5 followed by titration of magnesium at a pH of 9 is possible (8). However, if zinc is also present, it cotitrates with the manganese. Although for the E D T A titration of magnesium or calcium, triethanolamine can be employed as a masking agent for small amounts of manganese (e), in ferrites the ratio of manganese to niagnesium prohibits its use. Separation of manganese as the dioxide or sulfide is possible. Flasclika VOL. 31,
NO. 2,
FEBRUARY 1959
273
ride, 1 to 200.
Grind together 0.15 gram of Eriochrome Black T and 30 grams of reagent grade sodium chloride until homogeneous. Demasking Agents. Reagent grade sodium fluoride, potassium cyanide. and hydroxylamine hydrochloride were employed.
Table 1. Analysis of Manganese-MagnesiumMixtures Manganese, hlg. Magnesium, Rlg. Error Taken Found Error Taken Found 20 00 30 00 35 00
40 00
20 20 30 34 35 40
10 03 13 92 08 05
+o
$0 +0 -0 $0 $0
10 03 13 08 08 05
11 87 5 93
7 69 11 87
11 5 5 7 7 11
83 95
92 66 62 90
-0 $0 -0 -0 -0
04
02
01 03 07 +O 03
PROCEDURE
Table 11. Analysis of Manganese-Magnesium-Zinc Mixtures Manganese, l f g . Magnesium, Mg. Zinc, Mg. Taken Found Error Taken Found Error Taken Found Error 15.0 20 00
15.0 15.0 l5,O 20 11 20 03 20 00 19 97
11.87
+O 11 +O 03
5 93 9 550
-0 03
and Abdinc (Z), for example, used thioacetamide to separate manganese from magnesium and calcium. Pribil (‘7) studied use of the fluoride ion to mask magnesium, calcium, and aluminum in the E D T A titration of zinc. He suggmted that manganese also could be selectirely titrated with EDT,4 if magnesium were masked a ith fluoride. Kehber demonstrated that fluoride ion does not interfere in the EDTA titration of manganese (9). FLUORIDE ION AS A DEMASKING AGENT
Analysis of Manganese-Magnesium Mixtures. The use of fluoride ion t o demask magnesium selectively from its E D T A chelonate presents a new approach to t h e analysis of manganese-magnesium mixtures. This modification permits rapid analysis of both components of the mixture by consecutive titration of a single sample solution. For ferrite analysis, this has the added advantage that only one sample need be processed by the cupferron extraction technique. I n practice, the sum of manganese and magnesium is determined by direct E D T A titration. After the end point, solid sodium fluoride is added. If an excess of a standard solution of manganese is also added, the following reaction occurs at room temperature: Mg[EDTA]-2 $ 2 FMnt2 4 MgF2 Mn[EDT.4]-Z __
+ +
Fluoride ion in effect demaslis magnesium-EDTA with respect to the formation of manganese-EDTA. The excess standard manganese is determined by back-titration with EDTA. The amount of standard manganese consumed is e luivalent to the E D T A “liberated” by the fluoride, which i b in turn equivalent to the magnesiuni in the sample. The displacement of EDTA from magnesium-EDTA by t1.e fluoride ion
274
ANALYTICAL CHEMISTRY
11.86 11.90 11.82 5 90 9 478 9 567 9 595
-0.01 $0.03 -0.05 -0 03 -0 022 +0 017 +O 045
15 1 13.6 17.0 13 6 17 0
15.2 13.5 17.0 13 5 17 1 17 0 16 9
+0.1 -0.1 -0 1 +0 1 -0
1
is accelerated if free manganese ions are present, or if a large ewess of fluoride ion is available. The use of manganese to promote the reaction has another advantage. The back-titration of excess manganese with EDTA using Eriochrome Black T as indicator proceeds to a very sharp end point. Analysis of Manganese-Magnesium-Zinc Mixtures. Mixtures of manganese, magnesium, and zinc can be similarly analyzed. T h e first end point (EDTA) gives the sum of the three ions. Fluoride is added and the EDTA liberated from the magnesiumE D T A is titrated with manganese. Following this second end point, cyanide is added to displace zinc from its EDTA chelonate and to form the stable zinc cyano-complex. The liberated EDTA (equivalent to the zinc) is titrated n ith standard manganese. REAGENTS
EDTA, 0.0500.11. Dissolve 18.61 grams of reagent grade disodium(ethy1enedinitr0)tetraacetate dihydrate in 1 liter of distilled water. Standardize by titration with a standard zinc solution in an ammonia buffer, using Eriochrome Black T as indicator. Metal Ions. T o demonstrate the method. approximately 0.05M solutions of manganese sulfate and magnesium chloride were prepared by dissolving 0.05 mole of the salts in 1 liter of water. Aliquots of the solutions were buffered to p H 10 and standardized by direct EDTA titration using Eriochrome Black T indicator (1, 5 ) . The standard zinc solution was prepared by dissolving a weighed portion of reagent grade zinc shot in a minimum amount of 1 to 1 nitric acid, boiling to expel the oxides of nitrogen, and diluting to an appropriate volume. Ammonia Buffer, p H 10. Dissolve 80 grams of ammonium nitrate in 650 ml. of distilled water and add 350 ml. of concentrated ammonium hydroxide. Eriochrome Black T-Sodium Chlo-
Analysis of Manganese-Magnesium or Manganese-Magnesium-Zinc Mixtures. Dilute t h e sample solution containing no more than 1 mmole of divalent metal ions to approximately 100 ml. Stir the solution magnetically. Add 0.2 gram of hydroxylamine hydrochloride and buffer it to a p H of 10 n-ith 10 nil. of ammonia buffer and a 1 to 1 arnnionia Folution as required. Add sufficient Eriochrome Black T-sodium chloride to produce a definite rPd color. K a r m to 40” C. and titrate with standard EDTA until the color of the indicator changes from red to pure lilue. After the end point, add 2 to 3 grams of solid sodium fluoride and continue stirring for about 1 minute. From a buret, add standard manganese, 1 ml. a t a time, until a permanent red color is obtained. Stir for 1 minteu. Titrate the excess manganese with EDTA until the color changes to pure blue. After the second end point, if zinc is also present, add 2 nil. of 10% potassium cyanide for every 0.25 nimole of zinc ion. From a buret, add standard manganese until the color changes from blue to red. Then back-titrate the excess manganese with EDTA (red to blue). The back-titration can be performed immediately. ANALYSIS OF FERRITES
Select a sample size such that approsimately 20 ml. of standard EDTA will be required to titrate the total divalent metal content. The equations below are convenient to estimate the sample size, when approximate percentages of the divalent metal osides in the ferrites are known. Grams =
{%higo
x
4.0 X 7 . 1 7.1) (47,LInO X 4.0)
+
and Grams
=
4 0 x 7 1 x 8 1
(YJlgO X 7.1 X 8.1) $ (WJlnO X 4 0 X 8.1) (%ZnO X 4 1 X 7.1)
+
Dissolve the sample In 1 t o 2 nil. of hot concentrated hydrochloric acid. Cool and dilute to 20 ml. with distilled water. Proceed exactly as described by Fritz, Richard, and Bystroff (4) for the removal of iron by extraction of iron cupferrate with a 1 to 1 benzene-isoamyl alcohol solution. The aqueous phase, containing the divalent metal ions, I S then treated by the procedure described above, except that after addition of hydroxylamine, the pH is adjusted to 10 with a 1 to 1 ammonia solution. In this laboratory, result? for the
analysis of several fcrrites I\ (’re precise and compared fal-orably with results reported b\- an independent laborator\-. RESULTS
Typical results for tllc analysis of slathetic inanganese-Inagnesiuin and manganese-magnesium-zinc mixtures are presented in Tables I and 11. The data indicate quantitative recoveries of the mctals, the crror heing generally 0.1 nig. or less. The analyscs may bc performed rapidly. Complete analysis of a svnthetic ternary mixture, including calculations, \vas usually conipletd in less than 40 niiiiuteq.
The fluoride demasking technique can be extended to the determination of other divalent metal ion-magnesium combinations. Also, by utilizing the technique of selectively demasking zinc (\vith formaldehyde) from its cyanide complex, as many as four metal ions can be analyzed by consecutive titration of a single sample solution-e.g., manganese - magnesium - zinc - nickel. Finally, combination of the cupferron extraction method with the fluoride dellinsking procedure makes possible the determination of magnesium in conibination n-ith other metals after reinoval of the interfering species suck a$ titaniuni, zirconium, thorium, bismutli, sild tin, in addition to iron.
LITERATURE CITED
Riedermann, Schwttlzenbach, G,, Chimia 2 , 56 (1948). ( 2 ) Flsschka, H., Abdine, H., ChemzstA n a l y ~ 44, t 8 (1955). ( 3 ) Flaschka, H., Barnard, J., Broad, W.C., Ibad., 46, 106 (1957). (,
(4) Fritz, J. s., M, J , ~ ~ ~ t ~ ~ f .4 s., h A L . CNEM. 29, 577 (1957). ( 5 ) Kinnunen, J., Xferikanto, B., C h e m s f S n n l y s t 4 3 , 9 3 (1954). ( 6 ) Pribil, R., Collectzon Czechoslov Chem.
c
~
,19, 58~ (1954). ~ ~
( 7 ) Zbtd., p. 64. 18) Reillev, C.
~
9
~
~
K,,Schmid, R IT’., -45.4L. ~ Chenb. 154, ~ 122
(1956).
R~~~~~~~ f o r ~ ~ 1 ) .i j 1958, ilccepted September 25, 1958
Se pa ratio n of Pa raf f in- Cyc Io p a raff in Portio n of Naphtha into Normal, Branched, and Cycloparaffins MATTHEW S. NORRIS and J O H N G. O’CONNOR Gulf Research and Development Co., Pittsburgh, Pa.
b Separation of the saturate fraction of
naphthas into straight-chain, branched, and cyclic classes has been investigated using Molecular Sieves and silica gel adsorption with a d d e d components. The saturate fraction o f a naphtha was chargcd to a column of 5-AMolecular Sieves. The branched and cyclic componsnts were eluted with isopentane, then the straight-chain paraffins were removed with n-pentone. After the pentanes had been distilled off, a sample of n-paraffins and a sample containing both the branched and cyclic classes were obtained. The branched and cyclic material was subjected t o a separation using silica gel adsorption with a d d e d components. A high pore volume silica gel saturated with diethylene glycol monomethyl ether (methyl Carbitol) was used. The branched and cyclic mixture was then charged to the column and eluted with a perfluorocyclic ether. Examination o f the chromatogram o f the eluate revealed that the branched material issues from the column first in high purity, followed b y eluent fractions which show a progressive g r a d a tion in terms of decreasing branched material content and o f increasing naphthenic content. The tail end o f the elution yields cyclic materials in high purity.
T
usefulness of liquid adsorption chromatography for the separation of hydrocarbons into aromatic, olefin, HE
and saturated classes has been knon n for some time (7, IO). Additional separation of these classes, especially the saturate fraction, into subclasses becomes more difficult. Mair and others (4) recently separated a CI8to Czsoil fraction of a MidContinent petroleum into an aromatic portion and a paraffin-cycloparaffin portion by adsorption on silica gel. The aromatic portion was further separated into mononuclear, dinuclear, and trinuclear aromatics using alumina gel. The paraffin-cycloparaffin portion was separated with urea into a n-paraffin and a branched plus cycloparaffin portion. The further separation of paraffincycloparaffin hydrocarbons has been described by Sauer and others ( I I ) , who used liquid displacement chromatography with aniline as the stationary phase supported on silica gel. The samples were displaced from the columns with isopropyl alcohol and benzene, making recovery of the fractions relatirely easy. Although separations were not complete, fractions of high purity in paraffins and cycloparaffins were obtained for the separation of binary mixtures of paraffin and cycloparaffins and separation of a naphtha. Mair, Montjar, and Rossini (5) separated branched paraffins from cycloparaffins using either ethylene glycol inonomethyl ether or diethylene glycol monomethyl ether supported on a high pore volume silica gel. They showed that the niethod was good for the sep-
aration of two-component hydrocarbon SJ steins using either heptacosafluorotributylaniine 01’ a perfluorocyclic ether as eluent. The method is hascd on li iuid part it ion ch rotnat og ra ph y . The branched components tend t o concentrate in the inobile fluorochemical phase, d d e the cycloparaffins concentrate in tlie adsorbed phase. Thus, the branc~liedinaterial comes off tlie coliinin first, followed bj- the cycloparaffins. .I nunibcr of methods h a w Iwen used
A L L OlYENSlONS IN CENTIMETERS
A 35/25 SPnERlCAL JOINT B RESERVOIR,IOOOYL. CAPACITY C STAINLESS STEEL BALL B E A R I W S , 3/B* 0 SLASS WOOL PLUG E PRETREATED ADSORBENT F WATER JACKET G 24/40 $ JOINT H FRITTED 6LA¶9 OISK (MI I PRESSURE STOPCOCK, 2 YY BORE J 10136 $ JOINT
Figure
1.
~
Glass adsorption
column
V O L . 31, NO. 2, FEBRUARY 1959
275
~
~
