aration of mixtures containing these isomers in approsiiiinteiy q u a l concentrations; howl-er, when the ratios vary appreciably, a difference of 1 rninute is not adequate ior a quantitative determination. The minimum detectable concentra:ion :vas determined for each major mmponent in the crude mixture. The \-aiues are given in Table I and xere determined by the proper selection of the instrument sensitivity t o give a peak area of 0.6 to 0.7 sq. cni. using a 0.02-nil. liquid sample. ,Is is evident from Table I, the minimum detect,able concent,ration is related directly t o the retention time and t o the ex?ent of separation of the compounds. The ininiiiium detectable concentration is reinted directly t o the degree of broadening of the peaks, which in turn is related to the retention time. The minimum detectable concentrations of 0.1 and 0.27, for 2,2dinieth~-lpropanal and %butanol, respectivel!., are high because of the poor resolution of these tn-o components. The rather high -\-aiue of 0.07y0 for 1,1.3-trimethoxy-2methylpropane is attributed t o its iong retention time rather than to lack of resolution. All results are reported as the area percentage. Sormally, the area percentage is converted t o weight percentage by the use of conversion factors obtained from the chromatographic analysis of similar samples of knon-n composition; hon-ever, this approach was not feasible because all the identified components were not available as pure Compounds. The errors inherent in the usage of area percentage have been investigated by this laboraton-, and the results nrc in general agreement if-ith those oi other investigator: ( f j . .inai\-ses of other comples-
Tnixtures shon that the area percentage in the first portion of the chrcmatograni (short retention time) is greater than the n eight percentage, whereas the middle portion approximates area percentage very closely, and the area percentage of the compw nents preemt in latter portion of the chroniatograni is less than the weight percenhge. The extent t o nhich the analJses can be in error is probably less than =k5% of the value of the contained component for compounds present in a concentration of greater than 505. Because of the poor separation obtained by distillation, iunctional group analysis would be of little value or, a t any rate, T o d d be considerably in error. The error incurred in the mass spectrometric analysis of the crude product a s well as in the fractions from the distillation would probably exceed the chromatographic error. Less than a n hour is required for the analysis of a n unrefined sample, whereas 3 t o 5 hours would be required by other instrumental and/or chemical techniques. The precision of the chromatographic method was measured by anslyzing a typical sample six times consecutively. The limits of uncertainty at the 957, confidence level are given in Table 11. CONCLUSIONS
Gas chromatography can be applied
to the analysis of complex mixtures containing compounds of different functional groups. The product from the hydroformylation of isobutene can be chromatographically analyzed faster, yet with equal precision and accuracy, than is possible by either chemical or other instrumental techniques. This
method is applicable t o the direct analysis of t’heunrefined material. Chemical and instrumental techniques are used in conjunction with the chromatographic method. T a t e r is determined more accurately by the Karl Fischer method. Xlulticomponent peaks in the chromatogram are analyzed mass spectrometrically. ACKNOWLEDGMENT
The cooperation of the group in the Development Department of Union Carbide under the supenision of J. E. Knap is acknowltdged, particularly the work of W. R. Privette. The cooperation of R. C. Grirnm and J. W. Crandall in supplying samples for calibration is aLw acknowledged. LITERATURE CITED
(1) Broming, L. C., Watts, J. O., .%SAL. Cmu. 29,24 (1957). (2) D. H. Desty, ed., “Vapour Phase ChromatoeraDhv.” Institute of Petroleum, Lonldoh, .kcademic Press, S e w York, 195i. (3) James, h. T., Biochetn. J. 52, 212 (1952). (4) James, -4. T., Martin, -4. J. P., rinolyst 915 (1952). (5) James, A . T., Martin, .4. J. P., Biochetn. J . 50, 679 (1953). (6) James, A . T., Martin, I\. J. P., Smith, G. H., Zbid., 52,238 (1952). (T) James, D. H., Phillips, C. d. G., J . Chem. SOC.1953, 1600. (8) Menapare. H. R., Kyryacos, G., Boord. C. E., .\CS Division of Petro-
leum Chemistry, Symposium on A%dvances in Gas Chromatography, S e a Tork, September 1957, Preprints D 133. (9) Phillips, C. S. G., Disclcssions Faraday SOC.1949, 241.
RECEIVED for review February 18, 1959. -4ccepted J u n e 29, 1959. Division of .-\nalytical Chemistry, 132nd Meeting .\CS,S e w Tork, ?i. Y., September 1957.
Chromatography of Mixtures of Lactaldehyde, Acetol, and Pyruvaldehyde on Bisulfite Ion Exchange Columns ESKiN
HUFF
Laboratory of Ct’inicol Investigation, National Jnstitute o f Allergy and lnfectious Diseases, Notional Institutes o f Heolth, Beihesdo, Md.
+
A method has been developed for separating mixtures of carbonyl comsounds on Cowex ; (HSOI-) columns employing increasing concentrations of sodium or potassium bisulfite for elu:ion. Micromole amounts of (I mixture or acetol, lactaidehyde, pyruvic ocid, 2nd avruvaldehyae have been sepa!.area from each other by such chromatography, and each peak has been rxcurately quantitated by means of
1626
ANALYTICAL CHEMISTRY
bisulfite uptake. Neutral carbonyl compounds may b e recovered from bisulfite present in the eluted fractions if potassium bisulfite is used as eluent.
HO--Ci‘--PO?-
It‘
C
compounds absorb reversibly onto ion exchange resins in the bisulfite form by forming the corresponding a-hydroxysulfonic acid salts (f-.$. ARBOSYL
8-1 0) :
However. usc of such a roiumn for the separation of niivturrs of carbonyl compounds has been limited (8, IO). Use of bisulfite solutions for elution has allowed the separation of acetol, lactalde-
hyde, and pyruvaldehyde, and improved on the existing methods, making possible use as a general procedure for separation of carbonyl compounds. EXPERIMENTAL
Apparatus. Chromatography tubes (Scientific Glass Co., Bloomfield, N. J., No. e-4189 X) 10 X 300 mm., extended to 850 mm. using 9.5-mm. (inside diameter) borosilicate glass tubing. These tubes have a sealed-in sintered-glass disk of coarse porosity to support the resin, and were calibrated 45 ml. above the sintered-glass disk. Microburet, 5.004. volume, graduated every 0.01 mi. Reagents. Acetol was prepared by the procedure of Perkin (6) or by hydrolysis of acetol phosphate with prostatic acid phosphatase (5). Lactaldehyde was prepared from threonine by reaction with ninhydrin (5). Pyruvaldehyde was prepared by the method of Thornton and Speck (11). Glyceraldehyde and dihydroxyacetone (Concord Laboratories, Cambridge, Mass.). Glyceraldehyde solutions were dedimerized before use (7). Pyruvic acid, reagent grade (Nutritional Biochemical Co., Cleveland, Ohio). Dowex 1-XI0 (Cl-, 200 to 400 mesh) and Dowex 50-Xl2 (H+, 200 to 400 mesh) (The Dow Chemical Co.) were resieved and the 100 to 200 wetrmesh material was used. Both resins were washed in 6N hydrochloric acid and 6N sodium hydroxide before conversion to the ionic form desired. Iodine solutions were prepared by dilution of 1 N iodine (in 2% potassium iodide). Bkulfite solutions 0.1 to 1.6M were prepared from the reagent grade sodium or potassium salt on the day of use and had a pH of 4.7 or were adjusted to p H 2.5 with concentrated hydrochloric acid. When recovery of the carbonyl compounds was desired, potassium bisulfite was used. Otherwise, the sodium or potassium salts were wed interchangeably. Preparation of Column. Dowex 1-X10 (Cl-, resieved to 100 to 200 wet mesh) was washed with a saturated solution of sodium bisulfite until the chloride had been removed. Excess bisulfite was removed by washing with a small volume of water. The resin should be prepared in the bisulfite form on the clay of use or stored in a glassstoppered bottle filled to the neck with a bisulfite solution to avoid oxidation by air. The resin should not be airdried; oxidation is almost complete as indicated by a decrease in the iodine uptake for 1 gram of wet resin from (3 0.67 to 0.12 mmole after drvine: " hours at 37" C . ) . A slurrv of Dowex 1 (HSO,-l " , in water waiallowed to settle in a chromatography tube (9.5 mm. in inside diameter). When the resin had settled to form a column of 45 ml. (length approximately 600 mm.), excess resin was poured off and a small disk of filter u
,
paper applied to the top to prevent disruption when eluent wm added. Absorption and Elution. The caybony1 compounds were absorbed onto the column from a small volume (10 to 100 ml.). The flow rate both for absorption and elution was 0.20 ml. per minute. Up to 200 pmoles of carbonyl compounds can be handled on a column with a resin bed volume of 45 ml., depending somewhat on the degree of separation. Sjostrom (10) has been able to separate 5-mmole quantities of compounds which separate widely. Elution was carried out a t 24" C . with 0.1, 0.2, 0.4, 0.8, and 1.6M bisulfite solutions applied successively with a pipet to the top of the resin bed 3.00 ml. at a time. Each aliquot was allowed to drain completely by gravity before the next aliquot ww added. Fractions (3 ml.) were collected in 12 X 77 mm. test tubes, stoppered to avoid oxidation, and stored a t 5" to IO" C. prior to analysis. Two resin volumes (resin volume = volume of chromatography tube occupied by resin column) of each solution were passed through the column. The entire o p eration was performed manually and took about 4 days. Of this time only about 40 hours were necessary for elution, as the column was stoppered tightly and allowed to stand overnight. Continuous flow and automatic control of the column were not attempted, but should be possible if exposure of eluent and eluate to air can be minimized. If the bisulfite solutions are prepared daily to avoid air oxidation to bisulfate, excellent reproducibility of the peak effluent volumes for various compounds is obtained. Analysis of Eluate. For fractions less than 0.4M with respect to bisulfite a 1 .OO-ml. aliquot containing 10 pmole of carbonyl compound was mixed in a small (12 X 77 mm.) stoppered test tube with enough 0.8M sodium bisulfite to make the final concentration approximately 0.4M. After reaction for 1 hour or more at room temperature, the tubes were cooled and stored at 5" to 10" C. For fractions 0.4M or greater a 0.50- to 1.00-ml. aliquot was acidified to approximately pH 2.5 with hydrochloric acid and 1.644 sodium bisulfite (pH adjusted to 2.5 with hydrochloric acid) added to a final concentration of about 0.8M. The tubes were stoppered and allowed to react at 24" C. for 2 hours or more. Just prior to titration the contents of the stoppered test tube were washed into a 50-ml. Erlenmeyer flask with 20 ml. of 0" C. water. While the solution was stirred by bubbling air through it, IN iodine (0" C.) was added until in slight exdess. These steps must be in a cooled solution to prevent breakdown of the a-hydroxysulfonic acid salts. As soon as the excess bisulfite w w destroyed, the following solutions (at 0" C.) were added successively to the starch-iodine end point: 0.1N sodium thiosulfate, 2 ml. of 1% starch, 0.01N iodine, 0.01N thiosulfate, and 0.005N iodine. The end point should be within
Table I. Loss of Sulfite after Addition of Sodium Bicarbonate to AcetolBisulfite Complex
Time between Total Addition Iodine of Sodium Added Bicarbefore bonate and Sodium Bi- Start of Gassing carbonate, Titration, Bisulfite % Seconds Loss, Mixture Air 99 ... 1: 88 ... 0 91 ... 2 0
>
I)
I
1
Nt
76
0
0 60
2 10
Table 11. Reaction of Some Carbonyl Compounds with Sodium Bisulfite and Stability of Complex Formed . Yo of,
Theoretical Bisulfite Bound at Indicated Times
Final Conon. of NaHSOa,
Compound Acetol'
Mmole Final
1
47
99 101
103 102
4.7
99
101
0.4
4.7
99
100
0.4 0.4
0.8
4.7 4.7 2.5
100 93 95
100 99 07
0.4 0.8
4.7 2.5
96 99
100 100
0.4 0.4 0.8
4.7 2.5 2.5
56 72
83 83
81
81
/M1.
0.4
Lactaldehydea 0 . 4 Acetol phosphate5 0 . 4 Glvceraldehydeb
Dihydroxyacetoneb Acetoneb Sodium pyrUVateb Pyruvaldehyde'
after
Mixing pH 4.7 4.7
hour days
"Periodate uptake used to calculate amount of carbonyl compound. Pyruvaldehyde is considered to be 100% reacted when 2 moles of NaHSOs are bound per mole of periodate uptake. b Weight used to calculate amount of carbonyl compound. Reaction between carbonyl compound and bisulfite carried out at 24' c. for first day and thereafter at 5" to 10' C. 1drop of 0.005N iodine. If the solution is not aerated, sulfur dioxide present in the atmosphere will be reabsorbed after the end point is reached, causing a gradual fading of the starch-iodine color. Finally, an excess of solid SOdium bicarbonate was added to raise the pH and release the bound sulfite, which was then titrated with 0.005M standard iodine as rapidly as possible. In an experiment (Table I) 1.WmI. aliquots of a solution containing, in equilibrium, 11 pmoies of acetol an$ 400 moles of sodium bisulfite per m. were removed and added to 20 ml. of VOL 31, NO. 10, OCTOBER 1959
1622
Table 111.
Recovery of Carbonyl Compounds from Bisulfite Ion Exchange Column
Peak I'olume,
so. Resin 1-01s.
Compound Acetol Lactaldehyde Pyruvate Pyruvaldehyde
3.8 f 0.1 4 5 f 0.2 6.7 f 0.1 7.4 f 0.1
Table IV. Recovery of Carbonyl Compounds from Potassium Bisulfite Solution
Compound Lactaldehyde Pyniva1deh.de .icetone
70
99*4
3.5-1.1 1.2-4.8 6.6-6.9 7.1-8.0
loo f 3
102 98 f 6
v
I
covery
p0,md IiHs01
Mix-
Recovery,
Re-
ComIn
Range of Elution, so. Resin 1-01s.
these conditions the bisulfite comples IS broken without the solution's becoming alkaline enough to cause hypoidite 06dation in the subsequent treatment with iodine. Iodine was added in solution until there was a slight excess. which was removed with 0.1-Y thiosulfate solution. A volume of 3.4V perchloric acid equal to the potassium hydroxide followed by 10 mmoles of bsr-
in
(by Bisulfite
Mix-
Binding
35.0 4.0
89 70
ture, Aliquot), pmoles Mmoles yo 140 8.0 83 ture, 89 4:
0" C. aater. Excess bisulfite waa removed and iodine added, followed by sodium bicarbonate. After varying lengths of time: titrat.ion was carried out to the starch-iodine end point. The very rapid loss of 2% of the sulfite after release from the acetol-bisulfite complex can be avoided if 99% of the required amount of standard O.OO5N iodine is added before the bicarbonate, followed by immediate and rapid titration to the end point (Table I). I second aliquot of the sample solution is used when further accuracy is desired. Accuracy was checked by a comparison of the observed bisulfite uptake to the amount of compound by weight or by periodate uptske. Except for acetone, pyruvate, and pyruvaldehyde (where 0.8-11 bisulfite was used a t p H 2 3 , the bisulfite uptake for the compounds tested was close to theoretical in the presence of 0.411 bisulfite (pH 4.7) after reaction for 1 hour a t 2 4 ° C . (Table 11). Pyruvate and acetone gave approximately theoretical uptake of bisulfite, but pyruvaldehyde was only 81% reacted. Therefore, a correction factor must be applied in calculating the amount of pyruvaldehyde from bisulfite uptake data. The stability of the carbonyl compounds in the presence of 0.4 and 0.831 bisulfite is apparent from Table 11. Bisulfite uptake is quantitative even after storage of the mi.xture for 47 days in a stoppered test tube. Separation of Mixtures of Carbonyl Compounds. Complete separation of a misture of acetol, lactaldehyde, pyruvic acid, and pyruvaldehyde has been achieved (Figure 1). These compounds were absorbed as a mixture of 10 pmoles of acetol, 30 pmoles of lactaldehyde, 40 pmoles of sodium pyruvate, and 44 pmoles of pyruvaldehyde in a final volume of 82 ml. and eluted as described above. The average range of elution and peak volume for these compounds in several runs are given in Table IIT.
= O
I
2 3 4 5 6 7 8 NUMBER OF RESIN VOLUMES
9
Figure 1. Chromatography of some 3-carbon carbonyl compounds on Dowex 1 in bisulfite form
. ....
Cdumn size 9.5 X 600 m m Elution carried out with 0.1, 0.2,. 1.6M potassium bisuulf)teadded at points indicated by arrows at top of figure
On a similar column it has been possible to separate acetaldehyde (peak a t 4.5 resin volumes) and formaldehyde (peak at 5.2 resin volumes). I n a run nith a mixture of glyceraldehyde, dihydroxyacetone, and acetone all three compounds were recovered (101% yield) without separation in the range 3.9 to 4.5 resin volumes. KOdifference in the position of elution of the compounds studied was observed if sodium bisulfite solutions were used instead of potassium bisulfite. Recovery of all compounds studied n-as very good (94 to 103%, Table III). Recovery of Compounds from Eluate. Removal of bisulfite from pooled fractions for recovery of isolated carbonyl compounds proved to be difficult, because there was often a 500- to 1000-fold molar excess of bisulfite salt present. If recovery was desired, it was necessary to use potassium bisulfite for elution and the following standard procedure. Finely powdered iodine was added to a solution (20 ml.) containing 10 mmoles of potassium bisulfite and 10 to 100 pmoles of a carbonyl compound until the presence of an excess of iodine in solution indicated the free sulfite had been oxidized to sulfate. The solution was quickly decanted from the solid iodine, iodine destroyed Kith a dilute potassium bisulfite solution, phenolphthalein added, and 3 . W potsssium hydroxide added to a faint pink color. If the p H is allowed to rise above 9, a ioss of lactaldehyde occurs. Enough sodium bicarbonate was added just to decolorize the phenolphthalein. Under
ium carbonate (for remol-a1 of sulfate) was added with stirriig, and the mixture was cooled to 0" C. to precipitate potassium perchlorate. .An excess of silver carbonate (15 mmoles) n-as added to remove iodide and stirred for 5 minutes. Fire millimoles of barium carbonate n-as added to precipitate any residual sulfate, and after stirriig the entire mixture R-BS centrifuged at 0" C. The precipitate was washed nith 20 ml. of 0" C. water and recentrifuged. The combined supernatants were treated with 7 grams of Dowes I (HC03-) to remove anions, and the resin was removed by filtration. Dorrex 50 (H+, 7 grams) was added to remove cations, carbon dioxide removed by evacuation, and Dowex removed by filtration. By using this procedure several compounds were recovered in good yields (Table IV). DISCUSSION
The choice of bisulfite solutions for elution of mi.xtures of carbonyl compounds from a bisulfite ion eschange column has markedly improved the usefulness of the separative procedure originally described by Gabrielson and Samuelson (3). Initial attempts using sodium hrbonate-bicarbonate solutions for elution allowed some separation of acetol and lactaldehyde, but peaks were often asymmetric, irregular, and of excessive volume. Recovery of compounds, particularly in the case of pyruvaldehyde, was often low. When bisulfite is used for eluent, peaks are symmetrical, reproducible, shsrp, and of little volume. Analysia of the eluate by bisulfite uptake is quantitative and
provides a very sensitive assay, allowing a peak of only 1 or 2 pmoles of carbonyl compound to be readily detected. The presence of 0.13f (or greater) bisulfite in all fractions and throughout the resin bed stabilizes carbonyl compounds as the bisulfite complex. This allows separation and quantitative recoveF of volatile compounds as a-ell as ones which tend to polymerize or oxidize readily. The method described should be useful for stabilizing, separating, and q u a -
titating micromole amounts of nldehydes and ketones fornied in biological systems. particularly where it is clesirable to recover these compounds for isotopic degradative studies or for further characterization. LITERATURE CITED
(1) GabrielJon, G., Samuelson, O., .J& C h m . Sm@, 6 , 7‘29 (19.52). (2) Zbid., p. 138.
(3) Gabrieleon, G., Samuelson, 0..S w m k . K ~T &~k . 62, , 211 ( 1 9 j ~ ) , (4) Zbid., 64, 150 (19.52).
( 5 ) Huff. E., Rudney, H.. J . R i d . Ciirr i i
,
2 3 4 ~low (lgjY’,
(6) Perkin. K. H., J. C‘hsui. SOC. 59, 766 (1691). ( 7 ) Rudnej-, H., .irch. Biociienl. 23, 67 (1949 j. ( E ) Samuelson, O., Pjostrom. E., Sr,t t i $ / ; . Kem. Tidskr. 61, 305 (1952). (9) Pamuelson. O., Westtin, .\.. Ihid., 5 9 , 2 U (1947). (10) Sjostrom, E.. Trans. C h n i f w r s Zlnir. 136, 8 (195311. (11) Thornton. B. J., Speck, J. C., .\SAL, CHEU.22, S99 (195Oj. RECEIVED for reiiew Soveniber 10. 1958. -1ccepted July 16, 1959.
X-Ray Fluorescence Analysis of Stainless Steel in Aqueous Solutions R. W. JONES and R. W. ASHLEY Chemistry and Metallurgv Division, Chalk River Project, Atomic Energy o f Canada Ltd., Chalk River, Ontario, Canada
b Nickel, chromium, molybdenum, and niobium have been determined in aqueous solutions of stainless steels by x-ray fluorescence spectrometry. Nickel, chromium, and molybdenum are determined directly in solution, while niobium is separated by conversion to NbzOj and determined after briquetting with cellulose powder. The method is considerably faster than conventional wet-chemical techniques and gives results which are more precise and accurate than those from previously reported x-ray methods. The standard deviation for all four elements is better than 1% of the amount present in the concentration range of interest. Agreement between chemical and x-ray fluorescence results on standard steel samples is within 1%.
S
steels have been analyzed by s-ra!- florescence spectrometr? for several years I 2 . 4 . 5 ) . Such analvses have been genernliy perfornied on solid samples having a uniform surface area and finish ( 4 ) .and are not readily adaptable t o other s n i p l e fornis such 3 s drillings and turnings. .inother disadvantage of using solid samples is the existence of “absorption-enhancement” effects which often lead to serious errors ( 4 ) . Sherman ( S ) , Soakes (y), and Mitchell (6) have treated the problem mathematically with good results, and Burnham, Hower. and Jones (3) worked out a general scheme of analysis based on the equations of Sherman by altering and extending the Original equations. They were able t o adapt their method t o a great variety of sample shapes and forms. and t o reduce the amount of mathematical computations involved by the use of graphical methods. TAISLESS
Silverman and Houck (9) worked out a scheme for the determination of iron. chromium. and nickel in aqueous solution, but the accuracy was t o onl!- about 3ycof the amount present. The present paper describes a somen-hat different aqueous method which results in greater accuracy. and also permits the deterniination of niobium and niolyhdenuni to be camed out on the same saniple. In this work, which was intended specifically for the analysis of the 1S5; chromium, 8% nickel series of stainless steels, no attempt was made to determine iron. because this element is generally obtained by difference. If required, the method could ensill- be estended t o include the iron deterniination. The method should also be rendily adaptable to anslyses of other steels and alloys. EXPERIMENTAL
Instrumentation. A Philips, threespecimen s-ray 5uorescence spectrograph, Model 52254, with specimen spinner and helium path attachments was used. Conditions were as follows: X-ray tube Philips F.\-60 W target .inalyzing cyatal LiF (L’d = 4.028 -\. Collimation Primary. 5 X 4 inch parallel plnte Secondary, 0.005 X 4 inch parnllel plate Detector Philips. Type 5224.5, scintillation counter (Sa1 crystal I Pulse height .itomic Instrument analyzer Co., Model 510; single channel, modified to allow 3-fold increase in available channel width Chemical Procedures. Becausc niobium is difficult t o maintain completely in solution in the common mineral acids, it was decided t o carry
out a cheniical separntinn of tiitniobium from the ma j o r con s t it u e n t 5 of the steel by the sulfurous aci,! hydrolysis method ( 1 ) . -kn addition:d advantage of this separation is that the concentration of the niobiuni in the niobium fraction is greater than that in t h t original steel sample, thereh;: giving increased sensit.ivity. This is desirablr. because the niobium content of the steels is generally less than 15;.
A O.5-gram s m p l e of eke; is diesolved in 10 ml. of aqua regin. \\-hen solution is complete. ’7 ml. of concentrated sulfuric acid are added and the solution is tnken t.o d y n e s . The s l t s 3re then taken up in about 50 ml. of water. and 25 ml. of 3 saturated solution of sulfur dioxide and n little filter pulp rre added. The solution is heated nearly to boiling and digested for to 1 hour, after which it is filtered and the precipiiste ~ 3 s h e dKith :ipprosimately 200 mi. of distilled n-nter to which 1 to 2 drops of sulfuric wid nre added. The filter paper and precipitnte are ignited a t ahnut SOO” C. :ind the ignited residue is then mixed \ \ i t h 1.00 gram of cellulose powder (\VhAtman ashless cellulose pon-der for c!iromstography. stmdard gnde! nnd hriquetted into n !-inch diameter pellet a t 60,OOO-pound pressure ir: an .kRL briquetting machine (>lode1 44.51 The filtrate is concentmted to t.\;nctl!. 50 nil. and thr m o i ~ ~ h d c n u mvliro. niiuni, and nickel cieterniinntions :ire made on 3 10-ml. aliquot of this solution. Preparation of Standards. Siobiuin standards n-ere prepared by taking aiiquots of a soiution of Johneoi!. Matthey and Co., Ltd.. “spec-pure” niobium and carrying them through the hydrolysis and briquetting steps. A different series of standard solutions prepared for the molybdenum determination than for nickel ana chro’1.
VOL. 31, NO. 10, OCTOBER 1959
.S
1629
