ANALYTICAL CHEMISTRY
1568
to shorten working time and to minimize operating variables between analysts, a series of experiments were performed to determine the effect of various excess quantities of reagent on the stability of the blank and colored solution. STABILITY OF BLANK. The absorbancy of blank solutions versus distilled water were measured a t various time intervals, each blank solution containing a different amount of cupric chloride reagent. The results are shown in Table IV. STABILITY OF COLORED COMPLEX.The effect of excess reagent on the stability of the colored complex was investigated. Table V shows the results obtained. The absorbancy of each colored solution was measured by using in the reference cell a blank prepared simultaneously, and to which was added an equal amount of cupric chloride reagent as indicated in the table.
Table IV.
Effect on Absorbancy at 635 Mg of Varying A m o u n t s of Cupric Chloride
Cupric chloride added, ml. Time in min. after centrifuging 1-5 15 30 Decrease in absorbancyafter 15min. ~
0.7
0.9
2.3
4.1
6.0
6.0
0.053 0.060 0.062
0.053 0.060 0.061
0.040 0.044 0.048
0.032 0.036 0.037
0,038 0.039 0.041
0.041 0,042 0.044
0.007
0.007
0.004
0,003
0,001
0,001
~~
Table V. Effect on Absorbancy at 635 M p of Excess Cupric Chloride Reagent on Stability of Complex Sample 1 2 Glycerol taken, mg. 36 36 Cupric chloride reagentadded,rnl. 0 7 0.9 Equivalent % excess reagent presenta 5 35 Time in min. after centrifuging 1-5 0.430 0.495 15 0.445 0.493 30 0.470 0.492 Variations in absofbancy after 15 min. 0.015 0,002 0 Assuming CaHa(0H)r CuCln.
3 36
4 36
5 36
6 25
7 17
2 3
4 l
6 0
6 0
6.0
248
515
800
1200
1800
0 . 5 0 8 0.482 0.474 0.300 0.171 0.509 0.481 0.475 0.301 0.172 0 . 5 1 4 0 . 4 8 4 0 . 4 7 8 0 . 3 0 1 0 173 0.001
0.001
0.001 0 . 0 0 1
0.001
Under these conditions, little variation, if any, is encountered if readings are taken within the first 15 minutes after centrifugation. In view of the increased sensitivity of the modified method, it can be advantageously applied to those cases where only relatively small quantities of sample are available, or where the glycerol content is too low for determination by other methods. ACKNOWLEDGMENT
CONCLUSIONS
Gilder the conditions prescribed, optimum stability of the blank solution was obtained by the use of 6.0 ml. of cuprir chloride reagent. Optimum stability of the colored complex was observed a t 35 to 1800% excess reagent levels, whereas stability with only a slight escess of reagent wag very poor. According to the modified procedure, 400 to 1800% excesses are encountered, depending on the glycerol concentration. In view of these results, it was not desirable to test the effect of greater quantities of reagent than 6.0 ml.
The author wishes to express his appreciation to hlrs. hl. hi. Agarwal of the Brooklyn Laboratories for her aid in obtaining the experimental data. LITERATURE CITED
Bertram, S. H., and Rutaers, R., Rec. traz. chim., 57, 681 (1938). (2) Reinke, R . C., and Luce, E. N., IND.ENG.CHEM.,ANAL.En.. 18,244 (1946). (3) Schoorl, K.,Pharm. Weekblad, 7 6 , 777 (1939). (4) Whyte, L. K., Oil & Soap, 23, 323 (1946). (1)
RECEIVED for review March 20, 1953. Accepted June 17, 1953.
Determination of Small Amounts of Niobium and Tantalum Using Radioisotope Tracer Technique THOMAS F, BOYD AND MICHAEL GALAN Industrial Test Laboratory, Philadelphia Naval Shipyard, Naval Base, Phihdelphia 12, Pa.
an investigation of a colorimetric method ( 1 ) for the D determination of niobium and tantalum in austenitic steel, i t was desirable to know how completely these elements were preT
RixG
cipitated a t various steps of the analyeis. An outline of the method investigated which is essentially a modification of that of Thanheiser (2) follows. ANALYTICAL PROCEDURE
Two grams of sample are dissolved in a mixture of concentrated hydrochloric and nitric acids. Thirty milliliters of perchloric acid (70%) is added, and the solution is boiled until the chromium is oxidized t o chromic acid. Two-hundred milliliters of hot water, 10 ml. of concentrated hydrochloric acid, and 50 ml. of saturated sulfurous acid are added, and the solution is boiled for 3 minutes. Paper pulp is added, and after standing 15 minutes on the steam bath, the solution is filtered through S o . 40 Whatman paper. The paper is mashed 15 times with hydrochloric acid (2%). The paper and precipitate are ignited a t a low temperature in a platinum crucible until the precipitate is free of carbon. Three milliliters of concentrated hydrofluoric acid and 5 ml. of 1 to 1 sulfuric acid are added, and the solution is heated t o fumes of sulfur trioxide until the volume is about 1.5 ml. (Tungsten and molybdenum interfere with the subsequent colorimetric determinations and are removed if present.) The contents of the
cooled crucible are washed into the original beaker containing 5 ml. of boric acid (4%) by a stream of hot hydrochloric acid (2y0), using about 100 ml. Fifty milliliters of saturated sulfurous acid is added, and the solution is boiled 10 minutes. Paper pulp is added, and after standing 15 minutes on the steam bath, the solution is filtered through Xo. 40 Whatman paper and washed 15 times with hot hydrochloric acid (2%). The paper and precipitate are ignited a t a temperature of 1000" to 1050" C. The melt is fused with potassium bisulfate and dissolved in saturated ammonium oxalate solution. The niobium is determined colorimetrically in a portion of the solution, after adding dehydrated phosphoric and sulfuric acids and hydrogen peroxide (30%). The tantalum is determined colorimetrically on another portion, after adding phosphoric and pyrogallic acids. APPLICATION O F RADIOISOTOPE TECHNIQUES
Niobium Loss in First Hydrolysis and Precipitation. The steps of the operations described are shown in Figures 1 and 2. Triplicate 2-gram samples of Bureau of Standards sample 1234 (containing 0.75% niobium and 0.02% tantalum) were dissolved and taken to fumes as in the analytical procedure. Two tenths milliliter of a solution of niobium sulfate, containing niobium-95 (V.S. Atomic Energy Commission No. 41F), equivalent to 1 mg. of niobium with an activity of approximately 0.06 microcurie was added, The niobium sulfate solution was made by fusing niobium oxide (NbzOs)with a small amount of potassium bisul-
V O L U M E 2 5 , NO. 1 0 , O C T O B E R 1 9 5 3 fate and dissolving in concentrated sulfuric acid. The solution was refumed to ensure thorough mixing of all soluble niobium. The niobium was precipitated and filtered as in the procedure, the filtrate being reserved. The precipitates were ignited and xfter cooling were transferred to slightly cupped aluminum planvhets, l l / r inches in diameter. The precipitates were dispersed as uniformly as possible over the surface of the lanchets, using a etirring rod and a small amount of absolute agohol, to prevent dusting and facilitate dispersion. Care was taken not to spread the material to the edge of the planchet as more material tended to collect in a thicker layer a t the small fillet where the cupped edge was formed than over the rest of the surface. After drying in an oven for 10 minutes the samples were counted (PI, Nb,. in Figure 1) in a windowless flow counter by means of a Radiation Counter Laboratories RCL nucleometer. To determine the wtivity, counts were made with and without covering the sample with a lead foil, 0.002 inch thick. The difference is the activity (lue to hetas. SAMPLE 123 A
SAMPLE
123A
RADIOACTIVE Nb or To
SOLUTION AND PRECIPITATION
FILTRATE DISCARD
SOLUTION AND p R E CI P I TAT1 ON
I
PRECIPITATE
,
1569
Five tenths milliliter of a solution of tantalum sulfate, containing tantalum-182 (U. S. Atomic Energy Commission No. 73), equivalent to 1 mg. of tantalum with an activity of approximately 0.03 microcurie was added, and the mixture was refumed. The tantalum sulfate solution was made by igniting tantalum to the oxide (Tanoh),fusing the oxide with a small amount of potassium bisulfate, and dissolving in concentrated sulfuric acid. The tantalum (and niobium) were precipitated, filtered, and ignited exactly as when radioactive niobium was present instead of radioactive tantalum. The filtrates (PI,Ta, in Figure 1) was fumed and reserved. The activity of the ignited precipitate ( P I , Ta, in Figure 1 ) was determined as before except that a thicker covering of lead foil (0.004 inch) was used. Three additional two-gram samples of standard 1234 were dissolved, and approximately 1 mg. of nonradioactive tantalum as tantalum sulfate in sulfuric acid was added to each. The sohtion was fumed, hydrolyzed, and filtered as in the analytical procedure. The paper and precipitate were dissolved in a mixture of 25 ml. of nitric acid (sp. gr., 1.42), 5 ml. of sulfuric acid (sp. gr., 1.84), and 1 ml. of perchloric acid (70%). This mixture was evaporated to fumes, and the evaporation continued until the volume was approximately 1.5 ml. The resulting solution was added to the reserved fumed filtrate (8'1, Ta, in Figure 1) from the original precipitation. This mixture was refumed, diluted, hydrolyzed, and filtered. The precipitate (Pz, Ta, in Figure 1 ) was ignited, and the activity was determined as before. The per cent of tantalum lost w'as calculated in the same manner as for niobium. Practically all of the tantalum n-as precipitated. SAMPLE l 2 3 b
SAMPLE l23A
I
PR E C l P l T A T E PI( Nb. To ) COUNT
F"AyYaI
I
SOLUTION IN0 PREClPl TbTlOH
SOLUTION
SOLUTION AND PRECIPITATION
PREC IPlTATlOW
1
FILTRATE
FILTRATE OtSCARD
PI ( N b , T o
FILTRATE F, (m,Tai DISCARD
I
SOLUTION
1
I
PRECIPITATE
9 (*.Tal
' II SOCUTION AND PRECIPITATION
AND
COUNT
Figure 1.
I
I
P R E C l P lTATE
DISCARD
I
PRECIPITATE
PREClPlTATlON
Flow Sheet for First Hydrolysis and Filtration MSCARO
Three additional samples of standard 123A were dissolved :md approximately 1 mg. of nonradioactive niobium as niobium sulfate in sulfuric acid solution was added to each. The solution was fumed, hydrolyzed, and filtered as in the analytical procedure. The paper and precipitate were dissolved in a mixture of 25 ml. of nitric acid (sp. gr., 1.42), 5 ml. of sulfuric acid (sp. gr.. 1.84), and 1 ml. of perchloric acid (70%). This mixture was evaporated to fumes, and the evaporation was continued until the volume was approximately 1.5 ml. The resulting solution was added to the reserved fumed filtrate (8'1, Nb, in Figure 1) hom the original precipitation. This mixture was refumed, diluted, hydrolyzed, and filtered as in the case of the original samples. The precipitates ( P z , Kb, in Figure 1) were ignited, :tiid the radioactivity was determined as before. The additional niobium was added to the reserved filtrates to provide carrier material for small amounts of niobium which might not have been precipitated originally, and also to furnish about the same weight of ignited precipitate in both the first and second set of samples, so that when their respective activities were compared, vorrertions due to self absorption would be minimized. The amount of niobium lost during the f i s t hydrolysis and precipitation is found as follows: Let A = counts per minute of ignited precipitate of niobium oxide ( P I ,Kb) and let B = counts per minute of ignited precipitate of niobium oxide ( P 2 ,Nb) obtained from filtrate (F1,S b ) ;
B
t'hen the per cent of niobium lost = A __ + B X 100. The per cent ofniobiumcontent lost wason theorderof l % ( l . l , l . l , a n d 1.2y0). Tantalum Loss in First Hydrolysis and Precipitation. Two grams of Bureau of Standards sample 123A were dissolved in triplicate and taken to fumes as in the analytical procedure.
I
FILTRATE D IS CAR 0
Figure 2.
I
PRECIPITATE lNb,Ta) CWNT
5
Flow Sheet for Second Hydrolysis and Filtration
Niobium and Tantalum Loss in Second Precipitation and Filtration. The same techniques described above were used t o determine how much niobium and tantalum were lost during the second precipitation and filtration. Six 2-gram samples of Bureau of Standards sample 123A (three for niobium and three for tantalum) were dissolved. The same amounts of radioactive niobium and tantalum were added as before, and the samples were carried through the steps of the analytical procedure through the second hydrolysis, qrecipitation, and filtration. The paper and precipitate were ignited as in the procedure, and the activityof theignited precipitates (Pz, Kb, Ta, in Figure 2) was determined. The filtrates (8'2, Nb, Ta, in Figure 2) in the second precipitation were fumed and reserved. Six additional samples of sample 123A were dissolved, and the same amounts of nonradioactive niobium and tantalum were added as when the radioisotopes were used. The niobium and tantalum (plus niobium) were precipitated and filtered as before. The paper and precipitate were dissolved in a mixture of 25 ml. of nitric acid (sp. gr., 1.42), 5 ml. of sulfuric acid (sp. gr., 1.84), and 1 ml. of perchloric acid (70%). The mixture was fumed until the volume was 1.5 ml., and the resulting solution was added to the reserved filtrate (F?, Nh, Ta,
ANALYTICAL CHEMISTRY
1570 in Figure 2) from the second precipitation. The mixture was refumed, diluted, hydrolyzed, precipitated, and filtered as in the Nb, Ta, in case of the original solution. The precipitates (P!, Figure 2) were ignited, and the activity was determined as usual. The amount of niobium lost was very low (1.1, 0.4, and 0.6%); practically all the tantalum was precipitated. The weight of the second ignited precipitate (approximately 25 mg.) is lessthan that of the first (approximately 45 mg.) due to a smaller amount of impurities. However, the material added as carrier is also precipitated twice in the procedure used so that the weights of the ignited precipitates, whose counts are compared, are about the same.
remained insoluble. Only the soluble portion was taken into consideration in the calculations, as this was the only part which was carried through exactly the same procedure as the radioactive niobium. The amount of tantalum in soluble form in the steel was insignificant and was neglected in the calculations.
Effect of pH on Precipitation. In addition, studies were made of the completeness of precipitation of 1.0 mg. of niobium and of tantalum in 250 ml. of solution buffered with sodium sulfate (137') a t pH of 9.5 and from 0.8 to 6.8 in steps of approximately one pH value. S o sulfurous acid was used a t 6.8 and 9.5. The solutions contained 50 ml. of saturated sulfurous acid a t the other pH values. The pH was adjusted on the acid side with hydrochloric acid and on the alkaline side with ammonia. The solutions were boiled, let stand 15 minutes, and filtered. The precipitates rvere ignited and the activity was determined. The activity was determined in the filtrate, following the techniques described before. Practically all of the niobium and tantalum w'as precipitated (98% or more) from pH of 2.0 to 9.5 inclusive. The effect of increasing the concentration of niobium and tantalum a t pH of 0.8 at which relatively high losses were found was determined. The results are shown in Table I.
Sample 1 2 3 4 5
Sample 1 2
3 4 5 a
A
+
Precipitation of Niobium Counts/Min. Due t o Betas Niobium A. ignited B. Present, Mg. precipitate filtrate 1.0 14743 4169 2.0 14606 1267 587 3.9 14227 5.9 13713 284 277 7.8 13178 Precipitation of Tantalum Counts/Min. Due t o Betas Tantalum A , ignited B, Present, M g . precipitate filtrate 1 2060 16008 1402 15780 4 11588 10424 10386 10631 10 14111 5292 13117 5013 16 17119 1013 16655 1155 20 14972 580 14314 452
* x 100.
Niobium Lost, %" 22.0 8.0 4.0 2.0 2.1
Tantalum Lost, %" 88.6 91.8 47.4 50.6 27.3 27.7 5.6 6.5 3.7 3.1
I
20 30 40 so SAMPLE WEIGHT O N PLANCHET ( MG. Nbl 0 , / 8 . 5 CM')
Figure 3. Table I. Effect of Concentration of Niobium and Tantalum on Their Precipitation at pH of 0.8
I
1
IO
Absorption Curve for Betas from Niobium-95
Where only small amounts of niobium and tantalum are lost, errors due to self absorption are small, because the weights of the samples whose counts are compared will be approximately the same. The self absorption curves shown in Figure 3 and Figure 4, for niobium and tantalum, respectively, indicate theorder of the error which may be expected for differences in weights between samples listed under column A with corresponding samples under column B in Table I. The curves were prepared to correspond to the conditions of this investigation. Thus a mixture of niobium and tantalum oxides was used to obtain the data for one of the curves shown in Figure 4, corresponding to the operations conducted under the analytical procedure, while tantalum oxide alone was used to correspond to the studies made when only tantalum was present. Corrections for absorption, however, were not made for the data of this report, as variations due to other causes were usually considerably larger than those due to absorp-
B
DISCUSSION OF RESULTS
The results indicate that only very small amounts of niobium and tantalum are lost during the first precipitation and filtration, following the given procedure. I n no case was the loss greater than O.Olyobased on a 2-gram sample. When only niobium and tantalum were present, precipitation was complete except for traces, over a wide pH range, except a t pH of 0.8. The pH of the solution a t the time of the first precipitation is about 0.8. The complete precipitation obtained is apparently due to the coprecipitating effect of the relatively large amounts of other elements present. Where only niobium or tantalum are present, precipitation a t low p H values should be avoided. A portion of the niobium and tantalum in chromium-bearing austenitic steels usually exists in a form which is insoluble after the acid treatment of the analytical procedure. For the particular steel used in this study, approximately 85% of the niobium
z2
\
In -
3 0
0
P
>
c
2
c U 0
I 10
I
I
I
20 30 40 SAMPLE WEIGHT O N PLANCHET ( M Q . i e . 5 CY' 1
I
Figure 4. Absorption Curve for Betas from Tantalum-182
V O L U M E 25, N O . 10, O C T O B E R 1 9 5 3 tion. Counts for samples under column A were made for 1 minute. Sufficient counts were made under column B to reduce t,he standard error, due t o the random nature of decay, to less than 3%.
1571 sored by the Bureau of Ships, Department of the Navy. The views expressed by the authors are their own and are not t o be considered &a representing the officialviews of the Department of the Navy.
ACKNOWLEDGMENT
Acknowledgment is made to Kenneth Proctor for advioeinreference to analytical procedures. Thanks are expressed to Lt. Comdr. Harry 0. Kulberg, James. E. MoCambridge, and Leonard Zoole for their continued intereat,. This investigation was spon-
73.
LITERATURE CITED
proctar,K, L,,
work,
(2) Thmheiser. G., and Mitteilungen, K. W.. Institut Eisenfmachuw, 22, 260 (1940). R~~~~~~~for Deaember5 , 1952. Aaoepted .rune 25. 1953.
Erythromycin Hydroiodide Hydrate
Contributed by HARRY A. ROSE, Eli Lilly & CO., Indianapolis, Ind.
hydroiodide hydrate was used to determine the E molecular weight of erythromycin base by x-ray methods. RYTHROMYCIN
The compound appears to be a dihydrate. Calculatious based on the analysis of the iodine content indicate a molecular Neight of 905,while the x-ray method indicates 901.8, Crystals suitable for optical and x-ray work may be obtained by crystallizing from aqueous potassium iodide solution.
eter of 114.59 mm. the calculation.
A Nave-length
value of2.2896 A. was used in
Principal Lines d
I/&
Face Symbol"
d
I/Ii
Face Symbol
CRYSTAL MORPHOL~CY Crystal System. Orthorhombic. Form and Habit. The crystals are elongated dong the c axis and show the prism (110)and macrodame (101). Axialgatio. a : b : c = 0.925:1:0.786. Interfacial A n g k (I'olnr). l O l n l O l = 80'48'. 110AliO = 94"28'. a Other reflections might contribute to these lines. and the indicated faae symbols a m suggested only as poasible contributing resections.
FUSION DATA. Erythromycin hydroiodide hydrate melts with decomposition in the range 193-195' C. (Kofler hot stage). On cooling, the melt solidifies as a glass which does not orystalliee.
e-b CI
-b
--a
Figure 1. Typical Crystalsof Erytbmmyein IXydroiodide Hydrate OPTICAL PROPERTIES
,
Refractive Indices (5893 A,; 25' C.). a = 1.528 zt 0.002. P = 1.536 zt 0.002. 7 = 1.550 zt 0.002, Optic Axial Angles (5893 A,; 25' C.). 2V = 75" (mleulated from a. B. and 7 ) . Optic'AxiaI Plane. 1~). Sign of Double Refraction. Positive. Acute Biwtrix. 7 = c. X-RAYDIFFRACTION DATA Cell Dimensions. a = 16.99 A,; b = 18.37 A,; c = 14.43 A. Formula Weighta per Cell. 4 (3.98calculated from x-ray data). Formula Weight. 905 (from iodine content); 901.8 (x-ray). Density. 1.332 (displacement). The fallowing data were obtained using chromium radiation with a vanadium pentoxide filter. The camera. used had a diam-
~
