Reversed-Phase Partition Chromatographic Separation of Several Alkaline Earths from Each Other and from Yttrium JEROME W. O'LAUGHLIN, GEORGE J. KAMIN, DAVID L. BERNER, and CHARLES V. BANKS Institute for Atomic Research and Department o f Chemistry, lowa State University, Ames, lowa
b The separation o f trace amounts o f calcium a n d magnesium from yttrium and the separation of calcium, magnesium, and strontium from each other is described. The former separation i s achieved on a column packed with Kel- F impregnated with bis(di-n-hexylphosphiny1)methane and the latter on p a p e r impregnated with the same reagent. Microgram amounts of t a l cium and magnesium were separated from up t o 10,000 times as much yttrium and determined spectrophotometrically using the very sensitive chromogenic reagent, Chlorophosphonazo Ill. Calcium, magnesium, and strontium, following their separation using radial p a p e r chromatography, were titrated coulometrically with a relative standard deviation of approximately 0.5% for mixtures containing about the same amount o f each element.
T
HE SEPARATIOX of various cations by means of reversed-phase partition chromatography using bis(di-nhesylphosphiny1)methane ( H D P M ) as the stationary phase has been reported by O'Laughlin and Ranks ( 7 ) . An application of this separation technique to the determination of small amounts of calcium and magnesium in yttrium and to the separation of calcium, magnesium, and strontium is described. LIicrogram amounts of calcium and magnesiuni are separated from up to 100 nig. of yttrium on a column packed with Kel-F impregnated with H D P M . Calcium, magnesium, and strontium are separated on paper impregnated with HDPXI. Calcium and magnesium have been se1)arated using ion exchange methods (1, 3. 5 ) and trace amounts determined by various spectrophotometric procedures reviewed briefly in a previous 1)ut)lication ( 2 ) . In the present work trace amounts of calcium and magneh i l i were determined using Chlorophosphonazo 111 ( 2 , 7 ) . Larger amounts of the above elements as \+-ellas strontium \yere drterniined after separation on palier with increased precision using a .qlight niodification of a previously pro])(JSed cwdometric procedure (4. 8).
21 10
ANALYTICAL CHEMISTRY
Ynder certain conditions the precision of the latter method, including the preliminary chromatographic separation procedure, is shown to rival conventional gravketric or volumetric techniques. EXPERIMENTAL
Apparatus. h Beckman D U spectrophotometer was used to make all the absorbance measurements and a Model 11 pH meter for pH and potential measurements. -ISargent Coulometric Current Source, Model IV, was used for the coulometric determinations. The titration cell for the coulometric work, roughly patterned after that of Monk and Steed ( d ) , was conqtructed from a m a l l weighing bottle with a glass taper top. h 12-cm. glass tube fused into the cell wall and bent upnards about 2 to 4 cm. from the cell wall served as the anode compartment. I t was isolated from the cell proper by a fine-pore fritted-glass disk in the short horizontal region. &Iplatinum spiral electrode served as the anode. The mercury pool cathode was formed by segmenting off a portion of the cell bottom with a low glass nall to give an electrode surface of about 2 sq. cm. Two platinum-n ire indicator electrodes about 1 cm. apart and a lead to the mercury pool were led through the cell wall. Gas inlet and outlet tubes were fused into a tightly fitting cover to permit removal of oxygen by flushing the cell with nitrogen. Stirring was accomplished with a I-cm. Tefloneo\ ered magnetic stirring bar. Reagents. T h e reagents used xere analytical grade unless otherwise specified. Chlorophosphonazo 111 and HDPAI were both synthesized in this laboratory ( 2 , 9 ) . The Kel-F (polychlorotrifluoroethane, Molding Powder Grade 300) mas obtained from the Minnesota Mining and Manufacturing Co. The yttrium was hmes Laboratory stock material. A stock electrolyte solution was prepared by dissolving 8.75 grams of mercuric oxide in 50 ml. of 1.5.U nitric acid. Thir solution a a s added to an aqueous solution containing 15.8 grams of the disodium salt of E1Yr.I (as the dihydrate) and the pH was adjusted to 10.5 with ammonium hydroxide. The solution was then diluted to 1 liter. The working electrolyte was prepared by diluting 365 nil. of the stock elec-
trolyte to 1 liter with water, followed by a readjustment of the pH to 10.5. Separation of Calcium and Magnesium from Yttrium. Dissolve t,he yttrium metal or oxide in 1 : 1 nitric acid. Transfer an aliquot Containing not more than 105 mg. of yttrium and between 5 and 40 pg. of calcium and maqnesiuni to a 30-nil. beaker. Evaporate to dryness and dissolve the residue in 2.5 nil. of 3.11 nitric acid and place nn a previously prepared column packed with Kel-F impregnated \\-it11 H D P N and equilibrated with 3.11 nitric acid. The preparation of the Kel-F and the column packing procedure hare been previously described (6). -1bed height of 15 em. in a 1-em. column is sufficient to hold up to 105 mg. of yttrium. Rinse the beaker which contained the sampk with 2.5 ml. of 3Mfnitric acid and add to the colmun. Then elute the column with 332 nitric acid, keeping the flow rate less than 1.0 ml. per minute. Collect 25 ml. of the effluent and reserve for the determination of calcium and magnesium. The yttrium can be removed from the column by eluting with 450 ml. of l J 2 hydrochloric acid at a flow rate of 4 to 5 nil. per minute. Radial Paper Chromatographic Separation of Magnesium, Calcium, and Strontium. .In aqueous soliit'ion which may contain magnesium, calcium, and strontium, but no nonvolatile acids or anions of nonvolatile acids, is treated with 1 or 2 ml. of perchloric acid and evaporated to dryness. The residue iq taken u p in water and evaporated to dryness several times to remove any traces of perchloric acid. Finally the residue is dissolved in a small amount of water and transferred quantitatively to the center of an 11em. paper disk impregnated with HDPM. The preparation of the paper disks has been previously described (6). The quantitative transfer of the neutral aqueous perchlorate salts can be accomplished in several ways. With small amounts of the salts the solution can be evaporated to about 0.1 ml. and then transferred by means of a small syringe to the paper. I t is necessary to keep the area of the spot in which the salts are applied small and this can be done by adding the sample from the syringe slowly vihile drying the paper with a gentle stream of hot air. The syringe and beaker are rinsed and the rinsings added to the paper in a similar manner.
Airlother technique for quantitatively transferring the sample to the paper is more con\-enient for larger amounts of the d t s . The sarnple i3 initially Iilaced in a small spotting pipet fabricated from a small (approximately 5nil.) heaker by liartially closing the top and drawing it out into a capillary qiout. The sample is evaporated to clryneFs in this vessel and then dissolved in a 1 : 1 water-acetone mixture. By in\.eiting the vessel on one side with the cai)illary qiout down, the contents are cniliticd through the rapillary dirtctly to the center of the treated paper disk. The size of the slmt is kept small by witable choice of the capillary diameter and b y gently heating the paper at the point of application with a stream of hot air. 'The paper i.; then developed with 0.1.11 or 0.2.11 perchloric acid until the solvent front is nearly at the edge of the paper. T h p developed papers are dried and then -prayed with an slcoholic solution of 8-quinolinol (0.5%, 8-quinolinol in 60% cthanol) and exposed to fumes of ammonia. lecture.-$ized bottle of ammonia is convenient for this purpose. 1 he zones due to calcium. niagneqiuni. and strontium are readily visible under ultraviolet light and appear in that order from the center of the paper. 'The, >trontirim is displaced by the per( ~ l ~ l o i ~ iwid c . and appmrs a t the acid front as does barium if the latter is present. ,.1 he zones containing the various elements are cut out snd reserved for the determination of the individual elements:. r 7
Spectrophotometric
Determination
of M a g n e s i u m and Calcium. T h e determination of the sniall amounts of calcium and magnesium can be acc o ni plkl led without se p ar a t ion. u
