edited by WALTER A. WOLF Eisenhower College
chern ed compact/
Seneca Falls, NY 13148
Price in US. $/kg
Are All Those Sugars Really Important?
a
Hugh Akers
Lamar Umversity Beaumont, TX 77710
Sugar
After reading a number of organic texts that referred to various sugars as the "most prestigious or famous." an attempt was madeto rank the "imiortanie" of the monosaccharidks based on the extent of their distribution, occurrence, or use. Two measures of this idea, the price1 and the number of references2 to a particular sugar, are listed in the table below. An ohvious feature is the inverse relationshin between the cost of the natural D-form and the numher of publications involving the different sugars. The sugars fall into two categories. The first nine listed are expensive in the D-form, are normallv unavailable commerciallv in the L-form. and are prepared from other sugars or isolated from unusual materials. The occasional uawer that mentions these sunars is concerned mainly with biooiganic chemistry (conformation analysis) versus conventional biochemistry. The second nine sugars include the "common" monosaccharides, are referenced most frequently, and are generally available in the D and L-forms. Some apparent exceptions to this pattern require explanation. L-Arahinose, a plant polysaccharide component,3 is the most orevalent form of that suear in nature. D-Arahinose.~ an in" -~ significant sugar in nature, is relatively inexpensive because i t can be obtained from a D-glucosederivative.4~-Sorbose,an uncommon sugar in nature, is readily available because i t is a precursor of vitamin C.5 ~
~
o-form
Psicose
form
NA
NA 400,000
600.000 600.000 350.000 272.000 240,000 58,000 23,000 12,400 2.700 NA 265 144 89 71 23 8.4
Gulose Xylulose ldose Ribulo~e
Allrose Allose
Tagatose Talose Lyxose Sorbose Ribose Arabinose Mannose Xylose Galactose Fructose Glucose
References in Chem. Ab~t.~
NA NA NA NA
24 32 12
NA NA NA 4.720 24 39,600 86 17,800 1,230
90,000 NA
1.0
30
8,400
16 8 30
26 30 101
215 580 621
820 904 1607 2333 11330
Prices auoted were derived from the 1980 Adams Chemical Co., Calbiochem-Behrina Carp.. ICN ~harmaceufaals.Inc, Sigma Chemical Company. or Vega Biochemicals c b
~~~
~~
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"Chem Sources-U.S.A.,"Directories Publishing Co., Inc., Ormond Beach. Florida. 1980. Chemical ~ i x t r x t sNmth . Co!/cc!,vc lnmw ,Voi 76 851 Cnemca Substance Index. American Cncm cal Soc cly. Co1.mo.s. On o 432 10. 1978
Hudson, C. S., J. Amer. Chem. Soc, 73,4039 (1951). Fletcher, H. G., et al., J. Amer Chem. Soc., 72, 4546 (1950) EDUC., 36, 60 (1959). Perirnan, D., J. CHEM.
.
.
are not commercially availeble. /See footnote 1.1 b ~ h number e of references listed are those in the Chemical Substances Index of the ninth collective index of (See footnote 2.1 Derivatives were not conhowever, references to all a. o. i,as well as furanase. and pyranore ring forms were included in the tabuiafion.
chemical ~bstracb.
sidered:
8.
.,
Separating Copper and Cadmium in QualitativeAnalysis Don W. Hayden University of Wisconsin Center-Fox 1478 Midway Road Menasha WI 54952
Valley
Richard L. Hunt
Instrumental Analysis Laboratory Experiments Jeffrey A. Hurlbut Metropol~tanState College, Denver. CO 80204
The instrumental analysis lahoratory is a difficult course to teach because of several factors. The students have varied backgrounds, the equipment and chemicals are expensive, the instruments are in constant demand. the class sizes are laree. and there are few instrumental lahoratory manuals. ~ e c a i s e of these factors we devised our own instrumental analysis laboratory scheme. This lahoratory scheme consisted of over 20 experiments from which the students selected any six or seven during the semester; they performed those experiments which interested them: and thev worked in small zrouws. Five or six experiments wer;available in eachbf the following areas: chromatography, absorbance, electrochemistry, and miscellaneous. We would like to make a copy of our 35page laboratory manual availahle to those who are interested. We have had excellent results with this approach, and the use of the ten to fifteen instruments was evenly spread out over the semester.
Morehead State University Morehead. KY 40351
We suggest a different method for the separation of copper and cadmium in qualitative analysis which is based on the reductive precipitation of copper(I1) as copper(1) thiocyanate, using an iodide-thiocyanate solution.' This procedure eliminates the hazards of the cyanide ion used in the traditional method, and it is less delicate than the dithionite method often used as an alternative. An outline follows for the procedure, to be modified dewendent on samwle size. The traditional method for crronw.I1 is followed up tothe separation of hismuth(II1) using an excess of 6 M NHs after checking for completeness of precipitation. After centrifugation and removal of the hismuth(II1) precipitate, the traditional decision, based on the color of the decanted solution is made. Cadmium(I1) is tested for directly by the addition of ammonium sulfide if no blue color is ohserved. If a blue coloration is present, copper(I1) is removed before the test for cadmium is made. Hammock and Swift, Anal. Chem., 21,975 (1949). Volume 59
Number 1 January 1982
59
T o remove copper(II), add 3 M H2S04 until the deep blue color has disappeared and no further color change is noted. Add 2 drops in excess. Now add 2 M KI-2 M KSCN mixture dropwise with frequent shaking until no further changes occur. The solution will be a yellow to red-orange color due to the presence of 12, with a light colored CuSCN precipitate. Centrifuge and decant, discarding the precipitate. Add a drop of the KI-KSCN mixture to the decantate to test for completeness of precipitation. Add 0.5 MNazSz03(stabilizedwith 0.1% Na2C03)dropwise to just discharge the color of the solution. Then add 6 M NHBuntil the solution is just barely basic to litmus. Now add several drops of ( N H M solution to test for cadmium(I1). A white or tan-colored milky suspension due to sulfur should be regarded as a negative test. A black precipitate indicates the presence of metals other than cadmium(I1); this means the previous steps have not been carried out correctly and must be repeated on a new sample. A positive test for cadmium(I1) is indicated by a large amount of a yellow to orange precipitate of CdS.
60
Journal of Chemical Education
We have found this procedure gives around 60% correct cadmium results for beginning students with less than five lab periods of college labwork. Results from second semester students were over 90% correct. Identification of Bi3+, Cu2+ and CdZ+ Notes to the instructor 1) This experiment uses 6M NH3, 3M H2S04,10% Na&03 eontaining about 0.1% NazCOs, and saturated (NH&S solutions. The KI-KSCN solution is 2M in each salt. The CdZ+and CuZ+were 0.1 M while the Bi3+ was 0.04 M. 2) In the new procedure given above, the solution must he strongly acidic when the CuSCN is removed. This procedure is not affected by chloride ion. The solution becomes slightly cloudy when the NazSrOs is added, hut if the NHBis added immediately a colorless solution that is only faintly cloudy is obtained. 3) The CdS precipitates as an orange solid if Cu2+ wag originally present hut will be yellow if Cu2+is absent, even if the solution is treated as described. A white precipitate here indicates either sulfur due to reaction of (NH&S with an acidic solution or eontarnination with zinc ion. I n the latter case CdZ+can he missed.
