curve. The calibration curve should be checked frequently, and a new one is required whenever fresh batches of reagents are used. If desired, standard saniples may be carried with the others and the calculations carried out by the method of Calkins and Stenger (I).
LITERATURE CITED
(1) Calkins, R. C., Stenger, T’. .I.,AXIL. CHEM.28, 399 (1956). (2)A Evans, ~ 0$Lc. C.~ Z., ~TvIcHargur, Chemists ~ , J.30,S., 308 J. (1947).
(3) Hat,cher, J. T., Wilcox, L. I-.,.ASAL. CHEL 22, 567 (1950).
(1)Kawaguchi, H., Japan Analyst 4, 307 (1955). (5) Po~yell,W. *., private communication, ( 6 ) Smith, W. C., Goudie, A. J., SievertSOI’, J. N.,ANAL.CHEM. 27, 295 (1955).
RECEIVED for review September 10, 1958. Accepted April 24, 1959.
Separation of Microgram Quantities of Boron by Mixed Resin Bed ion Exchange DURWARD L. CALLICOAT’ and JOHN D. WOLSZON* Marshall College, Huntington, W. Vu. JOHN R. HAYES Pennsylvania State University, University Park, Pa.
b A mixed resin bed ion exchange technique previously reported for separation of milligram quantities of boron has been evaluated for the separation of microgram quantities. The precision obtained on simple or complex samples falls within the probable error to =k 0.3 y of boron inherent in the carminic acid colorimetric procedure employed. The accuracy obtainable is dependent on the ability to make corrections for resin blanks which are anomalous in behavior, and dependent also on the total salt content of the sample. Such a procedure is limited to those cases where the total salt content of the sample can b e controlled during preparation, and a comparable sample of known boron content is available for comparison.
gram quantities of boron prior to colorimetric determination because of errors of the magnitude of + 3 to 5 y of boron on samples containing about 20 y of boron. The purpose of this work was to investigate the source of these high results and, if possible, provide a method to eliminate or compensate for them. Silverman, Jones. and Trego (3) have since reported the successful use of the same anion exchange resin, Aniberlite IR-45, in the fully regenerated chloride form and a separate cation exchange column for the determination of microgram amounts of boron in graphite. Their results are not necessarily coniparable to the results of this report, because of differences in procedure and treatment of resin. EXPERIMENTAL PROCEDURES
A
procedure for the separation of milligram quantities of boron from known titrimetric interferences, n ith the exception of fluoride ion ( 4 ) , utilized a mixed resin bed of a strong acid cation exchange resin, Salcite HCR (Donex 50), in the acid form, and a neak base anion exchange resin, Amberlite IR45. in the hydroxide form. Passage of a sample through the resin bed resulted in a near-drionized effluent containing boric acid and other very [Teak acids such as silicic and carbonic acids. The resins were used in the fully regenerated form as obtained from the manufacturer and i t mas recommended that they not be regenerated and re-used without rigidly checking the resin blanks after regeneration. The procedure was not recommended for separation of microPRETIOUS
Present address, International Xickel Co., Huntington, W. Va. * Present address, University of Missouri, Columbia, Mo.
Ion Exchange Procedures. T h e experimental equipment and procedures used for t h e treatment of resins, preparation of columns, passage, and collection of samples were identical x i t h those employed for separation of milligram quantities of boron (4). Colorimetric Determination of Boron. Boron mas determined b y a carminic acid colorimetric procedure exactly as recommended by Callicoat and Wolszon ( 2 ) . Precision to +0.3 y of boron is claimed. RESIN BLANK CHARACTERISTICS
The high results obtained with the initial attempts to apply the ion exchange procedure to microgram separations of boron indicated the probable presence of boron in the anion exchange resins asobtained from the manufacturer. This was found to be true. The resins could be completely regenerated with sodium hydroxide and all residual boron
removed from the resin so that none could be found by distilled water-rinsing of a mixed resin bed. However, when samples containing small amounts of boron Tvere passed through a mixed resin bed containing the fully regenerated anion exchange resin, no boron was found in the effluent. Four successive water samples, each containing 20 y of boron, were passed through one 50-ml. resin bed without the appearance of boron in the effluent. This is consistent with earlier findings that regenerated resins were not recommended for separations of milligram quantities of boron. Further investigation of the resins as obtained from the manufacturer yielded the data of Table I. Resin columns containing approximately 50 ml. of mixed resins were rinsed at a flow rate of 2.5 to 2.8 nil. per minute n ith distilled water. Successive 250-ml. portions of the effluent were tested for boron. Other typical data indicated that the boron found in such continuous rinsing started out a t relatively high values and rapidly dropped to lorn constant values. On all columns tested, the blank had reached a constant value with the fourth 250 Inl. of rinse. The normal amounts of rinsing employed in filling a column and back-washing to settle the resin appear sufficient to reduce any boron blank in the resin to negligible values with milligram quantities of boron, but this is not true in the microgram range. When columns of resin that had been rinsed to a low constant value were allowed to stand for several days, the values for the boron in rinse water rose again, although not so high as the initial rinse. This is indicated by the data in the second column (Table I). That this behavior is due to boron in the resin and not to possible extraction from the glass columns used is indicated by the VOL. 31,
NO. 8, AUGUST 1959
1437
*3 z
P L $ 4 -
0
s
10
10
30
MILLIEOUIVALENTS OF SODIUM CHLORIDE
Figure 1 . Boron elution vs. salt content of sample
I.
Successive Resin Column Blanks (250 ml. of H,O) _ Boron, _ ~-/ _ _ Blank (1 week Column Blank later) -4 6 0 64
Table
1.2 0.5 0.4 3.1 2.1
B
2.8 1.4 0 8 2.7 1.8 1.1 0.7 4.3 2.0 1.0 0.6
1.2
0.8 5.1 2.4 1.1 0.6
C, (plastic)
Table 11.
Sample
Analysis of Synthetic Blood Ash Solution Boron Found, _ __!_ Column il Column B Boron blank
Rinse
6.3 1.3 1.1
9.8 2.1
2.0
1.0
20 ml. B.A.S.
Rinse
20ml.B.A.S. Rinse Corrected parentheses. 0
2.0 ( 1 . 0 )O.ga (2.0) l . l a 1.0 2.0 0.9 2.0 (0.9)0.9a (2.0)0.9" 0.9a 1.04 1.0" 0.8" 1.0 2.2 0.9 2.0 Av. 0 . 9 0.9 for preceding resin in
Table 111.
Determination of Boron in Synthetic B.A.S. All samples contained 21.00 -J B (1.05 p.P.m. 1 -~ Boron Founda Column A Column B-i P.p.m. y P.p.m.' 21.2 1.06 20 8 1.04 21.1 1.06 20.9 1.04 21.3 1.06 20.9 1.04 21.4
1.07
20.8
1.04
Corrected for preceding resin blank and apiment B A S . blank of 0.9 y boron. 1438
ANALYTICAL CHEMISTRY
fact that the same behavior was observed when a Tygon plastic column was employed. If the regenerated anion exchange resin were allowed to stand in a solution containing appreciable quantities of boric acid and equilibrated, excessive amounts of rinsing were required to reduce the boron content of the rinse to a low constant value. The explanation for these phenomena appears to be a slow equilibrium governed by the rate of diffusion of boric acid in the resin phase. When thc resin is rinsed a t a constant rate, and the liquid phase is being continuously displaced, a relatively constant rate of elution of boron is found in the rinse water which would depend on the amounts originally present in the resin and the rate a t which diffusion to the liquid phase occurs. When the columns are allowed to stand, equilibration between the liquid and resin phases occurs and higher concentrations of boron are found in the first rinses of such a resin bed. APPLICATIONS
I n view of the fact that elution of boron from the resin as obtained from the manufacturer could be brought to a low constant value by rinsing a t a given flow rate, i t appeared feasible to rinse a resin bed and pass a sample through the column without interruption of flow, and correct the boron found in the sample by the amount found in the preceding rinse. This procedure was used for all samples described. Ion Exchange Separation Procedure. 4 50-ml. buret equipped Tvith three-way stopcock and containing approximately 40 ml. of mixed resin [60 t o 100 mesh Nalcitc HCR (8% cross Iinked) in t h e acid form and Amberlite IR-45 in the free base form] was rinsed continuously with 1 liter of distilled water a t a flow rate of 2.5 t o 2.8 ml. per minute. The final 250 nil. of rinse was collected in a 250-ml. volumetric flask. The sample was added t o the column and rinsed with distilled water until 250 ml. of effluent were collected. The boron content of both flasks was determined by the carminic acid procedure, and the boron content of the sample was corrected by subtracting th::t amount of the rinse sample. Determination of Boron in Synthetic Blood Ash Solution. A synthetic blood ash solution (B.-4.S.) was prepared using the published average composition of Yoe and Grob ( 5 ) . The boron content of the solution was 1.05 p.p.m. by using the sanic standard boric acid solution used to standardize the carminic acid colorimetric analysis procedure. The solution was analyzed prior to the addition of boron to determine the apparent
reagent blank, and after the addition of the boron to test recovery. The lonionic strength of the samples allon-cd several successive ones to be passed through the same 40-ml. resin bed (Table 11). The detailed data on the reagent blank illustrate the procedure and shon the reproducibility of the blank obtained by rinsing of the resin. All results fall within the limit of 1 0 . 3 y of boron which is claimed for the colorimetric analysis. The recoveries of boron in blood ash solution (Table 111) compare favorably with the 93.6% average recovery obtained by Yoe and Grob ( 5 ) using a methxl borate distillation procedure for separation, and tetrabroniochrysazin as the colorimetric rr-. agent. The apparent reagent blank I\ 111 be discussed in a later section. Determination of Boron in Steels. Tn o Sational Bureau of Standaids sterls 11 hich contained boron weie analyzed by t h e above proceduie. T n o to 5 grams of steel turnings r\cre dissolved under reflux n i t h 24 nil. of dilute aqua regia (1 to 1). After solution was complete, 30% hydrogcn peroxide \vas added in 1-ml, portions a t the top of t h e condenser. Evolution of gas from each portion was a1lowed to subside before the addition of the next. This technique reduced the total ionic content of the samplc by oxidizing some of the chloride content to chlorine gas. This permitted tlic use of 50-ml. resin beds without exhausting the bed capacity. The trcatment mas continued until hydrolysis products were observed to precipitatc. One milliliter of concentrated hyclrochloric acid was added and the sample refluxed until the precipitated matvri: 1 dissolved. The acid-insoluble fraction was recovered by an ASTM procedure ( I ) . The two fractions were combinrd mid diluted t o 250 ml. in a volumPtric flask. Each sample was run in triplicate from aliquot portions using individual resin columns for each samplc aliquot. The results (Table IT.') shon that the precision obtainable on replicate samples varies only t o 0.0003% boron. However, accuracy is pnnr and subject t o determinate error. Effect of Total Salt Content of Samples on Recoveries of Boron. Thc iqcrrase in the positive e r m in boron iccovery found in using signifirantly l . i r g t ~samples of steel indicatrs a dtpcntlenee upon total salt c n n t m t of the sample and thcreforc the amount of ion eucliange resinexhausted by t h t samplc. This relationship n tis cqwrinientally verified as shon-n in Figure 1 , in vhich the boron found in the effluent is plotted us. salt content of boron-frce sodium chloride samples. -1ftcr this relationchip \vas established, the boron content of the blood ash solution reagents was redeterruined ithout pas-ing the sample through the ion cwThange columns, and found t o bc
zeio. The boron blank which previously was attributed t o boron contamination of reagents was shown actualiy to be a salt elution of boron from the resins. Expressing the salt content of the blood ash solution sample< used in terms of milliequivalents of sodium chloride and using the slope of tlic line in Figure 1, the calculated amount of boron eluted b y such samples is 0.97 y of boron. The close agrccnient nith the experimental value of 0.9 y of boion is perhaps a fortunate occurrencc. but is nevertheless ncll within cupcriniental error and of the propcr orrlcr i f magnitude.
Table
Wt. of Steel, Gram
Determination of Boron in National Bureau of Standard Steels
Boron, y Present Resin blank
-_
.-
Found7
I3oron, TC
SBS Steel S o . 51, 0.0027% Boron 0 5000 0.5000
1
0 1349
DISCUSSION OF RESULTS
l‘hic work establishes the fact that thil mixed resin bed ion exchange procedure as originally proposed for the separation of milligram quantities of boron provides recovery of boron well within limits of titrimetric analytical procedures, using a fully repeneratctl anion exchange resin as obtained from the nimufacturer in the free h s e form. Rcqcntation and re-use of m . h rriins are not recommended, although tlic exact rimon why such fully reqcm’iatcd rrsiiiq will retain small amountq of boron has not becn clearly t-t:ihlished. The separatory procedwe, :is applie(1 t
