tion as before. Both membrane preparations are then washed once with lysis buffer, collected by centrifugationat 27,000 X g, assayed for orotein3.and frozen for later use. SDS-Polyacrylarnide Gel Electrophoresis Labeled and unlabeled erythrocyte membrane proteins are electrophoresed on 10%polyacrylamide slab gels (at pH 8.6) in the presence of SDS, according to a procedure modified from Studier.2Other SDS gel procedures are also suitable.
Membrane samples are prepared for electrophoresis by diluting 1mgof sample protein toa tatalaf 900 ~1with water andadding 100 d of eleetroohoresissamole buffer. The eel wells are loaded with 25 r for a12h. orat0.5 .hl of oreoared samole. and run at 1.5 m ~ o ewell mA per well overnfght.After electrophor;sis, the gel is stored in 50% methanol until visualized with a UV viewbox at 302 nm in the dark.
. .
The fluorescentgels may be stored indefinitely in 50%methanol, hut are not stable to acid fixatives. Fluorescent gels may be photographed with Polaroid type-57 high-speed film using a green high-contrast filter and a UV blocking filter.
An Improved Calcium Flame Test Robert S. Pearson University of Arkansas at Monticello, Monticello, AR 71655 Flame tests make interesting and attractive demonstrations. Viewrrs of all ages enjoy &e vivid colors and are struck by the variety of flame colors ohtained from seemingly similar colorless solutions. Fairly large groups of viewers can easily see flame colors if strips of absorbent paper arc dipped part wov into the solution hrinr demonstrat~dand then held at the lo&er edge of a burner fiame. We use approximately 2- X 10-cm strios of chromatoeraohv - . oaoer cut from laree rectangular sheets. The strips are creased lengthwise i e f o r e dinoine to eive some mechanical streneth. Strios of filter " paper also work well. When usine,. oaDer . . s t r i ~ sit is imoortant t o show what a "blank" looks like. If a strib of paper is dipped inw pure water and held in a burner flame. it will rventuallv Droduce the orange flame color characteristic of hot solid pakicles. Viewers need to recognize this orange coloration as a feature of the paper strip method. It will appear sooner or later during the course of any flame test performed with paper strips. Our freshman chemistry students use flame test wires t o detect the presence of several ions, but even when usina wires it is often ;lifficult or impossible to prevrnt complet& the This diffiwlty is appearance or an orange flame n~lori~tion. rsprcially acute whrn testing for calcium ion. Wr use the calcium prorcdure described hy Sorum and Lagowskit in which (:a" is seoaratrd t'rcm other ions as Ca(:d)~oreciuitate. The CaCaOa is ihen dissolved in a few drops i f HCI soiution and flame tested. In a high percentage of cases the flame color is orange rather than red. The true red flame color of calcium is revealed. however. if the calcium ion solution is mixed with roughly an equal vd~umeof saturated ammonium bromide solution and tested again. During the appropriate laboratory period the instructors carry a 30-ml dropper bottle filled with saturated NHaBr to add to calcium ion test solutions. T h e improvement is usually quite dramatic. Ammonium bromide is extremelv soluble in water so one should start with about 15 ml of water when preparing asolution to fill a 30-ml dropper bottle. For most flame tests a 1 M aqueous solution of the metal chloride gives a very satisfactory test solution. Two important exceptions are boron and lead. "
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A
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The green boron flame test is easily demonstrated with the paper strip method if the test so~utidnused is asaturated solution of boric acid in methanol. T h e nonluminous flame of the methanol dues not interfere with the green flame color. A 95%ethanol solution can he substitnted for the methanol. but some orange flame coloration will he present. Lead(I1) chloride has a low water solubility so a 1 M solution of the nitrate or acetate are the logical choices for a test solution. Placing a drop or two of HCI solution on the moistened test strio will . oreci~itate . PbClv and eive a somewhat better flame t&t than the plain lead(1i) nit& solution. Good ventilation in the demonstration area is es~eciallv . imoortant . when vaporizing heavy metals such as lead. The table lists elements eivine r)rominenr flame colors alnne to use for dem; with a suggested convenient c ~ e m i c a form l onstratine flame colors. Colorrd fireworks' rely on several of the elements listed in the table, whereas active metals such as Mr and Al -orovidc the intense white light present in some fireworks. Flame colors which are simple to produce are virtually confined to metals, but aqualitative test for halides also employs a flame color. The Beilstein test for organic halides3 is conducted by heating a copper wire in a flame until it no longer imparts color and then dipping the wire in a suspected halide and repeating the heating. Organic halides usually cause the copper flame color to reappear whereas most nonhalide organic compounds do not. Flame tests provide a captivating i h s t r a t i o n of the diversity of properties possessed by the elements. Even very young children can be painlessly introduced to the concepts of analysis and identification via the flame tests. Early encounters with chemistry should leave the beginner filled with wonder rather than dread.
Flame Colors of Elements Element Li
Na K
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Sorum, C. H.. and Lagowski, J. J., "introduction to Semimicro QualitativeAnalysis," 6th ed., Prentice-tLall,Englewwd Cliffs,NJ, 1983, p. 257. McLain, Joseph Howard. "Pyrotechnics," The Franklin Institute, Philadelphia. 1980, pp. 143, 144. Shriner. Ralph L., Fuson. Reynold C., Curtin. David Y., and Morrill. Terrance C., "The Systematic Identification ot Organic Compounds," 6th ed., Wiley, New York, 1980, pp. 81, 82. 622
Journal of Chemical Education
Rb CS
Ca Sr
Ba Cu B Pb
Flame Color
Chemical Farm
red yellow violet violet violet
1 MLICl
red red
1 MCaC12 I M SrCI2 I MBaCIz 1 M CUCI~
yellow-green blue-green green
bluewhite
1
MNaCI
1 MKCI 1 MRbCl
1 MCsCI
saturated H&iO, in methanol I M Pb(NOs)2-add HCI to the test paper
