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H a r o l d T. M c K o n e Saint Joseph College West Hartford, Connecticut 061 17
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Identification of FD&C Dyes by Visible S P ~ C ~ O S C O P ~ A consumer-oriented undergraduate experiment
The c u r r e n t controversy over the safety of some FD&C certified colors (1 c o u d e d with o u r recentlv described facile method of separation a n d chromatographic identification of s o m e FD&C food colors 12)encuuraeed u s t o d e v e h a~n u n dergraduate experiment involving t h i identification dl FI)&C dyes bv visible SDectrosroDv. In addition tr, heine "relevant." t h i s iivestigatidn has o t h e r advantages over many typical freshman experiments in that it serves a s a good introduction t o recording spectroscopy, is relatively simple to perform, requires minimal quantities of chemicals and equipment, a n d can he accomplished, with good planning, in t w o 2-hr labor a t o r y periods. As of the present, FD&C certified colors fall into two categories: permanent and provisional. In the first category are: Yellow 5, Red 3, Blue 1, Red 40, Orange B (only allowed in casings of sausage and similar meats), and Citrus Red 2 (only allowed on orange skins). In the second categoryare Yellow 6, Blue 2, Green 3, and Red 4 (the latter allowed only in maraschino cherries). Although Red 2 is presently banned (3),i t must be considered since foods produced before February 12,1976 may contain the dye. Adetailed history and discussion of food colors is found in references (4) and (5).The structures ofthese 11 dyes are shown in the figure. At present, manufacturers of materials containing FD&C dyes are not required to list an the label the spefifie dyeor dyes used. They may simply use the term "artificial color." Hence, there is high student interest in determining the nature of the color additives in foods. Also, since foods processed hefore February 12,1976 may contain Red 2, there isstudent curiosity as t o whether or not aspecific food contains this additive. A w r m t nrticle in this Journol, deacrrheua farile method of separating some FD&C dyer from Cuds (21.Although colors from wnous kinds of fwd product; mav he ~solntedand examinrd rhrough this procedure, we have determined that this method works best on the following: sodas (diet and regular), flavored gelatin-type products, juices from pickles, olives, and cherries, certified food colors, canned, frozen. and ~ackaeed .. fruit drink mixes. and anv other liouid or easilv liquified prrdurt. Fat omtaining suha&cac such as pr&swd me&. :cr rrmm, and salad d r r w n g s are mme difficult to examme but ran also be used. ~
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Experimental About 25 ml of the artificially colored "food" is treated in the manner of McKone and Nelson (2). A drop of the treated extract is chromatographed on a small Silica Gel plate' using 50:25:25:10 nhutanol-ethanol-water-eoncdammonia as the developer. If the chromatogram indicates only one colored component, the visible spectrum is run on the treated sample with no additional work-up. If more than one dye isshownto he present by tlc, the entire treated extract isspotted on a large Silica Gel tlc plate and developed as above. The colored fractions are then m a p e d off of the dry, developed plate, dissolved in water, filtered through a small piece of cotton to remove Silica Gel particles, and the visible spectrum run as before. In Table 1are listed the absorption maxima (nm) of the 11FD&C dyes. Discussion For clarity, the dyes in Tnhle 1 have been arranged intu three mtpgmer: the"yel1uws." thc"reds."and the"blucr." Sinre Orange H Is I L W ~exdwively inn orange skins, onlv Yellow 5 and Yellow 6 need to be differentiated in the "y&w" category. The absorption maxima for Yellow 5 and Yellow 6 (422 and 480 nm, respectively) are suffi'Silica must be handled with -re. For a discussion of some hazards resulting from prolonged exposure t o silica dust see Ref. (6). 376 1 J m l of ChemicalEducation
Table 1. Abrormian Maxima lnml of FD&C Dvss
Dve Yellow
Orange
Yellow Red Red Red Citrus Red Red Blue Green Blue
Solvent
System
water water water water water water chloroformb water was6
water
Absorption Maxirnaa i n m l
422 437
480 495 500
515 515 527 610 625
630
water
aTheSe maxima may vary rligntly depending upon the sample and tne rDectroDhOtOmeter used. bcitrur Red 2 is insoluble in water. CBlue 2 fader somewhat rapidly when in solution and exuored to
light.
ciently.separated that characterization of the specific artificial dye or dyes in most "yellow" containing products is unambiguous. The "reds" present a somewhat more complex situation. Red 4 is allowed only in maraschino cherries. I t is relatively easy t o confirm its presence in this product (absorption maxima 495 nm) and it is reasonable to exclude it from consideration in other orcdueh. Citrus Red 2, foundonly insausage meat ond related prud&acan hpehminnted from consideration if the " f o d " analy~edare of the types previously described. Our students have had minimum difficulty distinguishing among Red 40 (absorption maximum 500 nm), Red 2 (absor&ion niximuri 515 nm), and Red 3 (absor~tionmaximum 527 nm). Although Blue 2, Green 3, and Blue 1 have relatively close absorption maxima (610,625, and 630 nm, respectively), our students ~
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Table 2.. Student A n a l y s i s of "Foods" for FD&C D y e 5 F D & C D y e s as D e t e r m i n e d b y Visible S p e c t r o r c o ~ v
"Food" Red fruit drink D i e t raspberry soda ~ i e s tt r a w b e r r y s o d a Red gelatin j u i c e f r o m r e d maraschino cherries j u i c e f r o m green maraschino cherries nrtificiai butter tiavor extract
Red Red Red Red Red Blue yellow
2 2 2 2 4 1 5
Yellow
6
Yellow
5
in some food products. No attempts were made to analyze these dyes quantitatively. Over the past three years, approximately 100 undergraduates have performed this and related food dye experiments. Student response has been very favorable. Several students developed keen interest in food additives and transformed this academic curiosity into a continuing concern over the nature of the foods they are consuming. In addition, students take from this unit some basic concepts of bonding, molecular structure and properties, and have applied these in investigations of other complex organic molecules such as are found in over-the-counter drugs and pesticides. Note added in proof: After this article was accepted for publication, the FDA hanned further use of Red #4. However, Red # 4 may still be found in maraschino cherries purchased before late 1976. Literature Clted
have been able ta differentiate among them. The f a d that Blue 2 fades quite rapidly in aqueous solution aided our differentiation. It must he admitted, however, that it is difficult todistinguish Green 3 from Blue 1.This difficulty . may be an advantage in that it emphasizes the fact that experiments may yield inconclusive results. Tahle 2 lists the FD&C dyes found by our students to he present ~
111 C ~ ~ n s u m m R s p u ~38,191 tr, 119781. (2) MeKone, H.T., and Nelson, G.,J. CHEM. EDUC., 53,722 (1976). 181 Csrwin,E., and Pinel. W. L..FDA Cirnrum~r.I R [April 19761. 14) F U P ~ ~ .E.. T . 1EditorI. "Hsndbuok of Fuod Additives: 2nd Ed..The Chemical R u i r i m Cw. Cleveland, Ohio. 1972. 15) Nat. Acsd. Sei.. "Fond Colors." NaL. Acad. Sri. Puhlieaticm W a s h i n ~ t m i. ) C . 1971. (6) Sax. N. Irving, IEdilorl, "Dangerous Properties of industrial Materiair." :lrd Ed.. Val> Nustrand Co..New Yurk, 1968,~.1088.
Volume 54, Number 6, June 1977 1 377
