x 2.S yo for a single determination. The data and calculations are presented in Table 11. The standard error, calculated from rc,plicatc analyses of one standard, is asslimed to represent the standard error for the analysis specimens. This assumption is not warranted in powder spectrochemical procedures. However, the authors believe that in the solution twhnique discussed here, the standards a r t virtually identical t o the unknowns. Therefore replicate analyses of the 3.0-p.p.m. boron standard are considered to provide as accurate a statement of precision as could have been provided by replicate analyses of one analytical specimen. The boron contents of 34 water samples from the Gulf of hIexico are given by Frederickson and Reynolds ( 2 ) . The salinities were estimated by referring measured water densities corrected
for temperature, to published densitysalinity curves (6). Boron data were taken using the technique described here. The data make it possible to assess the accuracy of the boron determinations. Harvey (5) gives 4.55 p.p.m. of boron as the accepted value for sea water of a salinity of 36.00 parts per mil (%OO). The data of Frederickson and Reynolds ($) indicate a value of 4.65 p.p.m. boron a t 35.00 %OO salinity. Apparently the accuracy of the method is as good as the precision, both providing a standard error of approximately =k 3%. LITERATURE CITED
(1) Ah,yns, L. H., “Spectrochemical Analysis, p. 107, Addison-Wesley Press, Cambridge. 1950. (2) FrederiTkson, A. F., Reynolde, R. C , 0 2 1 a n d Gas J. 5 8 , 154-8 (1960). (3) Harvey, C. E.. “Spectrochemical
Procedures,” pp. 323, 346, Applied Research Laboratories, Glendale, Calif ., 1950. (4) Harvey, H. W., “Chemistry and Fertility of Sea Waters,” p. 3, Cambridge University Press, London, 1955. (5) Ibid., p. 4. (6) Ibid., p. 128. ( 7 ) Ibid., p. 147.
(8) Hatcher, J. T., Wilcox, L. V., ANAL. CHEM.22,567-9 (1950). (I)) Kuemmel, D. F., Mellon, hl. G., Ibzd., 29, 378-82 (1957). (10) Melvin, E. H., O’Connor, R. T., IND.ESG. CHEX.,ANAL. ED. 13, 520 (1941). (11) Russell, R. G., ANAL. CHEIl. 22, 904-7 (1950). (12) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” pp. 264-5, Interscience, New York. 1950. (13) Welche;, F. J., “Organic Analytical Reagents, Vol. 2, p. 336; Vol. 4, pp. 432, 465, 539, Van Nostrand, Princeton, N. J., 1947. RECEIVEDfor review August 4, 1950. Accepted September 23, 1960.
Precise Difference Method for the Spectrophotometric Determination of Cerium(lV) at Micromolar Concentrations 1. A. BLATZ fos Alamos Scientific laboratory, University o f California, 10s Alamos,
b In a cation resin exchange study of the sulfate ion complexes of cerous ion, a precise analytical spectrophotometric method for determination of cerium in the range 5 to 12 X 10-6M was necessary. Existing methods were modified by introduction of a difference method involving reduction of cerium (IV) to cerium(ll1) and studies were made of the factors influencing precision, such as suspended material, presence of organic (reducing) material, purification of reagents and solutions, cell constants, stray light of the spectrophotometer, interfering substances, optimum concentrations of all reagents, time factors, and blank corrections. The molar absorptivities a t 320, 3 4 0 , and 3 6 0 mp were 5.92 X lo3,5.12 X lo3, and 3.52 X lo3. Reproducibility checks revealed a probable error of a single determination of about 0.25% a t each wave length. Iron, thorium, uranium, neodymium, zirconium, nitrate ion, and excess persulfate ion do not interfere. Other possible interferences are discussed. Beer’s law is obeyed within the limits of the precision obtained.
A
for the spectrophotometric determination of cerium (IV) was suggested by Sandell (4) in 1944. It was later developed by PROCEDURE
N. M.
Freedman and Hume (1) and then, with modifications, by Medalia and Byrne (a). I n this paper the procedure has been further developed and modified to give a highly reproducible and precise method for the spectrophotometric determination of cerium in the micromolar concentration range. MATERIALS AND APPARATUS
Absorption measurements were made Kith a Beckman Model DU spectrophotometer that had a n exit slit width of 0.3 mm., a hydrogen lamp, and 10-em. silica cells. The distilled water used throughout was 0.1 to 0.3 expressed as “p.p.m. as NaC1,” as measured by a Barnstead Model PM-2 uuritv meter. Analytical grade, concentrated sulfuric acid was heated with sodium dichromate for about 1 day, distilled under reduced pressure, and stored in previously cleaned bottles. Analytical grade 70% perchloric acid was heated for 2 days and distilled under reduced pressure. The analytical grade concentrated nitric acid was used as received. Cerous perchlorate was prepared as described (3, 8). The final stock solution was 0.3M in perchloric acid and 0.1265 rfi 0.0003M in cerous perchlorate as determined by precipitation from measured volumes with saturated ammonium oxalate and heating to a constant weight of ceric oxide over Meker
burners. All solutions were prepared from this stock solution by dilution using 50-ml. Greiner, Teflon plug burets, precision Norniax pipets, and volumetric flasks. The stock sodium perchlorate solution was obtained by neutralization of Mallinckrodt analytical grade sodium carbonate with 70y0perchloric acid. Baker analyzed reagent grade ammonium persulfate was used. Generally, 250 ml. of a stock solution containing 0.20 gram per milliliter were prepared every 2 months, since it could be stored in a refrigerator a t 4’ C. for this length of time with practically no change in concentration. Solutions were purified by the use of the absorbent carbon Spheron Grade 6 (Godfrey L. Cabot, Inc., Boston, bIass.) from which fine particles mere removed by 30 to 40 swirlings with distilled water. This carbon was first tested with both distilled and conductivity water. Tests indicated that all the optical absorbers whichcould be removed by the carbon were removed in the first hours and that the Spheron-6 itself did not contribute any optical absorbance. The same results were obtained with a very pure (6) graphite, special spectroscopic graphite grade SP-1 (National Carbon Co., New York, N. y.)) which has a much smaller surface area (6) per gram than Spheron-6 and removed the optical absorbing impurities more s l o ~ l y . The stock salt solutions were usually kept in contact with the Spheron-6, VOL 33, NO. 2, FEBRUARY 1961
249
about 1 gram per liter of solution, for 48 to 72 hours and then dripped without pressure, first through a fine frit and then through a Corning ultrafine frit. Later, some of the ammonium persulfate stock solutions were dripped through a Selas microporous porcelain filter which had a maximum pore opening of 0.30 micron ( S o . 0.06 porosity). However, results obtained with this filter did not differ from those obtained with the ultrafine frit. After filtration, more Spheron-6 was added to some of the salt solutions, but in all cases no further changes in transmittances (I,'Iojin the 240- to 400-mp range were observed. The absorbances (log I o / I ) of the carbon-treated ammonium persulfate stock solutions were 30 to 40% smaller than those of the untreated salt in the 320- to 360-mp range, and they gave molar absorptivities (liters per mole cm.) of 8.4, 5.0, 1.8, and 0.7 a t 310, 320, 340, and 360 mp, respectively. Repeated recrystallization of several salts of analytical reagent grade quality in all cases resulted in a negligible to small fraction of the decrease of absorbance attained by one treatment with Spheron-6. Hydrogen peroxide, 0.37,, was prepared every week from the 30% analytical grade reagent and refrigerated. The absorbance of this solution Tvas 0.25, 0.07, and 0.04 a t 320, 340. and 360 m,u, respectively. RECOMMENDED PROCEDURE
Use between 0.03 and 0.10 mg. of cerium to obtain mavimum precision with the 10-em. silica cells. To the solid which results from the sulfuricnitric acid treatment, add 25 ml. of distilled witer, 1.40 nil. of distilled concentrated sulfuric acid (except as changed later), 0.15 ml. of 0.01JI silver perchlorate, and 5.0 ml. of ammonium persulfate (0.20 gram per milliliter) in 100-nil. beakers. Cover the beakers with watch glasses and place in boiling water a t 92" C. for 15 minutes & l o seconds or less. (Probably the time should be shorter a t nearly 100" (2.). Place the beakers in ice water for about 5 minutes and then filter under positive pressure through a very finepore filter into 50-id. volunietric flasks, After three 5-ml. washings of first the beakers and then the filters, dilute to 50 ml. Mix thoroughly, let the solutions stand for 12 to 18 hours, and transfer to 10-em. silica cells. After a t least 1 hour read transmittance a t 320 mp, shake thoroughly, and read transmittances a t 320, 340, and 360 nip, taking four readings a t each wave length. (If the settling of suspended material, which n-as usually 0.1 to 0.3% in transmittance, is greater, more frequent shaking is indicated.) Add the equivalent of 0.06 ml. of 0.3% hydrogen peroxide, shake thoroughly, and read transmittances. Take care not to touch the cell nindows during a complete reading, since cleaning the cell windows with lens paper often changes their transmittances. If greater precision for a single sample is required, repeat
250
ANALYTICAL CHEMISTRY
the above spectrophotometric process 12 to 24 hours later. DEVELOPMENT OF PROCEDURE
The method of Medalia and Byrne ( 2 ) was tried initially. Fifty milliliters of a solution containing cerium were 1 N in sulfuric acid, 3 X 10-4LlIin silver nitrate or perchlorate, and initially 9 X 10-3V in potassium persulfate. After being boiled (92°C.) for 10 minutes in a beaker with watch-glass cover, cooled in ice mater for 5 minutes, and made up to volume with distilled water in 50-nil. volumetric flask., the samples were immediately transferred to 10-em. silica cells, and their transmittances measured against a reference solution made from the same batch of water with the saine concentrations of sulfuric acid and silver salt. The resulting absorbances drifted downward continuously, and the average deviations of sets of absorbance measurements w r e frequently 57c or more. These erratic results and drift were traced mainly to the settling of suspended material and the reduction of cerium(1V). This indicated the need for filtration through very fine-pore filters and purification of all reagents, Large supplies of the necessary glassmare were cleaned in a concentrated sulfuric acid-sodium dichromate mixture and stored in distilled water until netded. For a more complete oxidation of organic material. a greater concentration of persulfate was tried through the substitution of ammonium for potassium persulfate and use of a longer heating period. Hov ever, as shon n by lledalia and Byrne ( 2 ) ,ammonium ion is oaidized to nitrate ion under these conditions and contributes to the absorbance around 320 niF. The fact that the molar absorptivities of ccriuni(II1) are 6, 2. and 1 a t 320, 340, and 360 mp, respectively, or about 0.1% or less than those of cerium(1T') a t the same wave lengths. suggested that cerium be determincd by the difference of the absorbances bcforc and after reduction of eerium(1T.'). Dilute hydrogen peroxide was chosen as the reducing agent. It does not reduce nitrate ion iior many other ions under these conditions; it reduces cerium(1V) to ccrium(II1) practically instantaneouslj ; and in the amounts required it contributes only a negligible absorbance. Errors in transmittances because of settling of suspended material are cancelled out, and this permits each cell and solution to be its own reference. Determination or use of cell constants is not required if care is taken not to touch or dirty the cell windows during a complete reading. For convenience the other cell in the spectrophotometer was filled with distilled water.
Six samples, two each 2.534 x lo+, 5.068 X and 7.062 X 10-6V in cerium(IV), were analyzed, using untreated chemicals directly from their containers, and boiled for 90 minutes. The resulting absorbances obeyed Beer's lam in this concentration range, with average and maximum deviations from the mean of 0.5 and 1% a t 320 mp and 0.9 and 1.770, respectively, a t 340 my. The molar absorptivities obtained were 5.84 X lo3 and 5.02 X l o 3 a t 320 and 340 nip, respectively. TJpon standing for several days, these solutions did not change their absorbances after the hydrogen peroxide treatment-that is, all the ammonium persulfate was destroyed effectively in the heating process. Later, it was discovered that this procedure occasionally gave results that \!-ere too low. Klien reducible material, such as 5 ml. of distilled water nhich had been soaked for a IT cek with the resin Don ex 50, v a s added to any sample just before the 90-minute heating period, the resulting absorbances were aln ays low, sometimes as much as 50 to loo%, and erratic. Hence this procedure is not recommended, especially if considerable organic material is present or if better precision and reproducibi'ity are desirt.d. Since the molar absorptivity of 5.84 X l o 3 a t 320 mp differs considerably from the 5.58 X l o 3 given by hIedalia and Byrne ( 2 ) or the 6.3 X lo3 given by Freedman and Ilunie ( I ) , an investigation n a s made. Generally, higher niolar absorptivities were obtained by boiling for only 10 minutes or by using silver perchlorate or ammonium persulfate in greater concentrations. and lo!\ er molar absorptivities n ere obtained 11hen organic material \\ as added to the sample. To renioic organic material samples !\ere evaporated to dryness, 2 nil. of concentrated sulfuric acid and 0.5 nil. of concentrated nitric acid nere added, and thc \\ztvh glasscovered beakers mere placed on a hot plate (protected by plastic covers) and heated a t 125" to 150" C. for about 48 hours. The watch glasses nere then reniowd, the temperaturc wa? raised to 180" C. for about 15 minutes, and finally the acids were evaporated a t 200" C. This usually requircd up to 6 hours. The samplcs were then stored until needed. K i t h i . 1 ~standard cerium solutions, if the sulfuric-nitric acid treatment n as omitted, results averaged 1.27, laxer than those obtained n i t h this treatment. Another objection to the above procedure is that it is difficult to filter, store, and transfer the solutions obtained after the heating process nithout contamination from organic or other reducible material. If the solutions were heated for 15 minutes, some residual ammonium persulfate concentrate was
left. The initial absorbances, as determined by difference, were always reestablished with speeds that were greater the larger the silver perchlorate and/or ammonium persulfate concentrations and the lower the sulfuric acid and/or sodium perchlorate concentrations ( 7 ) . If, immediately after filtration, the samples were put into the 10-cm. silica cells, the absorbances decreased steadily for the first few hours (frequently 10% or more) and then gradually increased t o constant values after an additional several hours. T h a t this was due mainly to incomplete removal of reducible material during the heating process was demonstrated by permitting the solutions (after dilution to 50 ml.) t o stand for 12 to 18 hours. Then, whm these solutions were transferred to the silica cells and Ivhen the final silver perchlorate concentration was 3 x ~ o - ~ the N , drift in absorbance did not exceed about 1%. This always occurred in less than 1 hour. Finally, the effects of silver perchlorate and ammonium persulfate concentrations on the molar absorptivities w r c investigated. Three blanks 2 x 10-4X in silver perchlorate were made 0.0035, 0.0088, and 0.08831 in ammonium persulfate. Aftcr +~nding a t room temperature 18 hours, abqorbances of 0.035, 0.039, and and 0.29, respectively, were obtained a t 320 mp. Other experiments confirmed t h a t grcater ammonium persulfate concentration aln-ayi: gave increased absorbanc’s a t all three wave lengths, whether cerium was present or not. Aftcr thp hydrogen peroxide treatment, rxidual absorbances were 0.1, 0.04, :md 0 02 a t 320, 340, and 360 nip, indicating. by comparison with absorbances after 90-minute boiling a residual persulfate concentration of roughly 0.001M. The time of boiling at nearly 100’ C. can be adjusted to give approxiinntc.lv these residual absorbances and this residual persulfate concentration. Probably a standard time chosen in the 10- to 13-minute interval would b r adrquatts. At thi- rrsidual persulfate concentration, for blanks which were 3 to 60 X 10-6M in silver perchlorate, the absorbance of silver(II1) ( 7 ) was, roughly, directly proportional to the silver perchlorate conccntration. The silver (111) absorbance a t 320 mp increased about 0.025 for Pach increase of 2 x l O - 4 M in si1vr.r perchlorate. This same increment was obtained for numerous samples with cerium present in the range’ 4 to 10.5 x 1 0 - 6 W and silver perrhloratc in the range 3 to 20 X 104-11. At 1.0 X 10-5-11 silver perchlorate, the sample absorbances were always low and continually decreased toward the limit which indicated complete reduction of cerium(1V). A t 2 x 10-5M
Table
I.
Blank Determinations and Their Precision Indices
Blank adsorbances Deviation from mean Average Maximum Standard Table ( I .
320 hIp 0 0041 f 0 . 0 0 0 7 (17%) 0.0014 (3470) hO.0003 (7700)
340 M p 0.0036 f0.0006 (17%) 0.0011 (3170) f 0 . 0 0 0 3 (8%)
360 ?vir 0.0034 &0.0006 (18%) 0.0014 (41%) k 0 . 0 0 0 3 (970)
Precision Indices of Determinations for 21 and 12 Standard Solutions
(Sets I and 11) Deviation from mean Average Maximum Standard Probable error of a single sample
Percentage 340 mp
320 mp 0 . 3 3 (0.28) l.0S(0.59) 0 09 (0.10)
0 . 2 8 (0.19) 0.81(0.59) 0.08 (0.07)
360 m y 0.39(0.40) 0.94(0.98) 0.10 ( 0 . 1 4 )
0.29(0.23)
0.25(0.16)
0.32(0.33)
all samples were stable; hence the procedure was standardized at 3 X 10-5V silver perchlorate. Larger concentrations were avoided because the large percentage variations in silver (111) absorbance resulted in poorer precision. The use of untreated chemicals and about a tenfold smaller persulfate concentration may explain, in part, the 6% smaller molar absorptivity obtained by Jledalia and Byrne ( 2 ) . The use of higher silver ion concentration (2.5 X 10-4Jf) may explain, in part, the 6% higher molar absorptivities obtained by Freedman and Hume as compared with the final values given in this work of 5.92 X lo3, 5.12 X lo3, and 3.52 X lO3at 320. 340, and 360 nip, respcctivel>-. RESULTS AND DISCUSSION
The standard deviations from the arithmetic mean. u, were calculated for these samples from u = [ S ( A t j 2 / n(n - l)]l/*,and the probable error ( n 1)]1’2, fromP. E. = 0 . 6 7 4 5 [ 2 ( A ~ ) ~ / where the A t ’ s are the deviations from the mean and n is the number of samples. Table I lists the results obtained for a set of eight zero cerium blanks as determined by the Recommended Procedure, \\-hich includes second determinations made 24 hours after the reoxidation. The absorbance contributions of the hydrogen peroxide are a t most 0.0005,0.0002, and 0.0001. Twenty-one standard samples (Set I) were determined over a period of 13 months, and later a Set I1 of 12 standard samples was determined. These solutions were 6.000 X ’7.000 X 10-6, and 10.50 X 10-6M in cerium (IV). Set I absorbances did not change during the stated period. Table I1 lists the precision indices of Set I and, in parentheses, of Set 11. If, for either set, the results at each cerium concentration and a t all three
wave lengths 1% ere averaged, these composite numbers obeyed Beer’s law with a n average deviation of nearly 0.1% for each set. During the resin experiments, 298 samples were analyzed, including 28 re-analyses, thus affording ways of checking the reliability of this procedure. Three averages for 28 samples at each of the three wave lengths gave a grand mean with a n average deviation of nearly 0.1%. When 28 samples were re-analyzed and compared in groups of four with the original analyses, a grand average deviation of 0.12% and a maximum deviation of o.2970 were obtained. There was no trend between the first and second spectrophotometric determinations. For 12 standard samples, averages for the two determinations agreed to within less than 0.1%. Third determinations performed 2 days later on some samples which had been equilibrated with Dowex 50 also showed no trend. Effect of Sulfuric Acid. Two standard samples were made 0.5N and two 1.25.V in sulfuric acid. These tn-o pairs each differed less than 0.1% from t h e general average. However, re-oxidation is considerably faster with 0.5.V and some\That slower with 1.253’ acid (‘7). At either 2.ON sulfuric acid or 1.651%- sodium perchlorate, the absorbances of the standard samples decreased continually after the 15-minute heating. Most solutions analyzed were unaroidably 0.15M in sodium perchlorate, although this varied from 0.075 to 0.25M in some samples n i t h no difference in results. Since the success of this procedure depends in part upon oxidizing cerium(II1) t o cerium (IV) faster than cerium(1V) is reduced, i t might be better to use 0.5N acid or less and zero sodium perchlorate. The following 10 samples were treated VOL. 33, NO. 2, FEBRUARY 1961
251
Table 111.
Interference of Cations and Anions
6.000 X
Th(SOa)J
2
7.000 X
CozS01
2
7.000 x 10-6 7.000 X 7.000 X 7.000 X
1.8 X 2 . 3 x 10-4 2.2 X 2.5
Fe(KH4),(S04)z K2Cr20i
2 1
ZrOS04
1 2
NdS(S01)a
as described in the Recommended Procedure, except as noted. Effect of Length of Time of Heating. Two samples, one 6 X 10+ and one 10.5 x 10-631 cerium(IV), were heated for 10 minutes and two were heated for 20 minutes. The first two averaged 0.30% high, and the latter, 0.45% low. The residual ammonium persulfate concentration for the former !%-asabout 2 x 10-3M and for the latter, about 6 x 10-4~. Effect of Ammonium Persulfate Two samples of the Concentration. same concentration were heated with twice as much (10 ml.) ammonium persulfate and two with half as much (2.5 ml.). The former averaged 2.4y0 high and t h e latter 1.7y0low. The residual ammonium persulfate concentration was about 3 X 10-3M in the former case and about 2 X 10-4M in the latter. Effect of Use of Nonpurified Chemicals. Two samples were given the
sulfuric-nitric acid treatment but 11ere heated with undistilled sulfuric acid and ammonium persulfate which was not treated with the carbon Spheron6. They averaged 0.67y0 low and the residual ammonium persulfate concentration was about 3 X 10-4M. Since blanks for these last 10 samples described were not known, the results were compared with the sum of the standard plus blank absorbances.
x . 10-4 _
16
7
-0.06
92
26
6
-0.32
28 14 60 88 Segligible Segligible
-0.34 -1.7 -0.04 -0.5
~~
1X 1 x 10-6 1 x 10-6
1
22
x 10-6
38 31
Effect of Larger Cerium Concentrations. Four samples were deter-
mined at a cerium concentration of 2.380 X 10-6M and four more a t precisely half this concentration, The former set gave initial absorbances of around 1.5, 1.2, and 0.86 and the latter set about half these values a t 320, 340, and 360 mp. Since the average deviation between the two sets was 0.18%, i t seems likely that stray light of the spectrometer had a negligible effect on the results. Interferences. The effects of various cations and anions present in small amounts are discussed by RIedalia and Byrne (2) and by Smith ( 5 ) . Table I11 gives some cases studied which had higher concentrations than the cerium, and which in some instances had appreciable absorbances relative to the cerium(1V). For example, a t 320 mp the thorium nitrate samples had an average absorbance which was about 22% of the absorbance of the cerium (IW. The potassium dichromate was added after the sulfuric-nitric acid treatment, since it is converted to a n insoluble oxide by this treatment. The cerium(1V) was reduced with 0.03M sodium azide. I n the amounts used the sodium azide had less absorbance than the hydrogen peroxide. Of three dichromate-free cerium(1V) samples reduced with sodium azide. one gave about the same
result and the other two were about 1% below the values obtained with hydrogen peroxide reduction. Other reducing agents for cerium(1Vj are discussed by Yost. Russell, and Garner (8). Ruthenium salts need not be considered, since volatile ruthenium tetroxide will be driven off in the sulfuricnitric acid treatment and in the persulfate treatment ( 5 ) . Tantalum chloride was insoluble under the conditions of the procedure uscd. Halide ion in excessive concentration will interfere with the silver ion-persulfate oxidation. Halides can be eliminated by fuming down two or three times with concentrated sulfuric arid (6). ACKNOWLEDGMENT
The author acknowledges the interest and helpful criticisms of J. F. Lemons. under whose general direction this work was done. He is grateful to J. E. Jordan, who prepared the cerous perchlorate, and Henry Crew, who helped with the purification of salt solutions. LITERATURE CITED
(1) Freedman, -1. J., Hume, D. S . , ANAL.CHEM.22, 932 (1950). 12) Medalia, A. I., Byrne, B. J., Ibid., 23,453 (1951). 1 3 ) Newton. T. W.. Arcand. G. 11..J. Aril. Chem. So;. 75, 2449 (1953). (4) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” p. 251, Interscience, Yew York, 1944 (2nd ed.. 1950). ( 5 ) Smith, M. E., Los Alamoe Sci. Laboratory Rept. LA-1995 (January 1956). (6) Smith, R. K.,Pierce, C . , Joel, C. D., J . Phys. Chem. 58,298 (1954). (7) Yost, D. LI.,Russell, H., Jr., “Systeniatic Inorganic Chemistry of the Fifthand Sixth-Group Nonmetallic Elements, pp. 379 ff., Prentice-Hall, S e w York. 1944. (8) Post, D.’M., Russell, H., Jr., Garner, C. S., “The Rare-Earth Elements and Their Compounds, p. 60, New Pork, 1947. ~
\ - ,
I
RECEIVEDfor review April 28, 1960. .Iccepted October 6, 1960. Work carried out under the auspices of the U. 8. Atomic Energy Commission.
A Two-Dimensional System of Paper Chromatography of Some Sugar Phosphates EDWARD J. WAWSZKIEWICZ Department o f Biochemistry, University of California, Berkeley 4, Calif.
b A two-solvent system of considerable differentiating ability, for the separation and identification of phosphate esters of some sugars, is described. The use of acid-washed 252
ANALYTICAL CHEMISTRY
DaDer and the addition of (ethylene. , dinitrilo)tetraacetic acid aid in the
I
,
by ghosting.
largely
eliminating
OEPARATION and identification of phosphate esters of the sugars are of great importance in studies of carbohydrate metabolism. A number of methods have been devised for the sep-
