89

2Yachweis der o-Diphenolgruppierung

a) Ammoniummolybdat nach Pridham [17]: Eine 0,1 m-LSsung yon (NI{~)~Mo~O~a • 4 H20 ,,Merck" gibt mit Kaffees~ure und dem reduzierten Spaltprodukt eine tiefe gelbe Farbe. Die Reaktion ist fiir o-Diphenole spezifisch.

b) Titan(III)-chlorid nach Weygand [18]: 1 ml der w~13rigen LSsung der reduzierten Spalt- produkte f~rbt sich mit einigen Tropfen 5%iger w~Briger Titan(III)-chloridl5sung (eisenfrei ,,Merck") orangerot. Wird das Spaltprodukt in 1 ml Methanol gelSst und mit 1 ml Pyridin ver- setzt, so entsteh¢ mit Titan(III)-chloridlSsung an tier Luft ein orangeroter Niederschlag. Kaffee- si~ure gibt mit Titan(III)-chlorid einen ziegelroten Niedcrschlag.

Li teratur

1. Ladd, J.N., Brisbane, P.G. : Australian J. Soil. Res. 5, 161 (1967). 2. Burges, N.A., Hurst, H.M., Walkden, B. : Geochim. Cosmochim. Acta 28, 1547 (1964). 3. Flaig, W. : Suomen Kemistilehti A 33, 229 (1960). 4. Homer, L, Geyer, E.: Chem. Ber. 98, 2009, 2016 (1965). 5. Akabori, S., Ohno, K., Narita, K. : Bull. Chem. Soc. Japan 25, 214 (1952). 6. Pierpoint, W.S. : Biochem. ft. 112, 609 (1969). 7. Brieskorn, C. H., Mosandl, A. : Tetrahedron Letters 1970, 109. 8. Kestner, O. :Chemie der Eiwei~k5rper. Braunschweig: Vicweg-Verlag 1925. 9. Pigman, W. : The Carbohydrates, Chemistry, Biochemistry, Physiology. New York: Academia

Press Inc. 1957. 10. Bnjard, E.L., Mauron, J.: J. Chromatog. 21, 19 (1966). 11. Moffat, E., Lytle, R.: Anal. Chem. 31, 926 (1959). 12. Nomoto, M., Narahashi, Y., 1Kurakami, ~ . : J. Biochem. (Tokyo) 48, 593 (1960). 13. Thompson, A.R. : Australian J. Sci. Res. 3 A, 128 (1950). 14. Lechner, H., Hofmann, J. : Ber. Deut. Chem. Ges. 55, 912 (1922). 15. Bock, H.: Z. Anorg. Allgem. Chem. 293, 264 (1958). 16. Brauer, G. : Handbuch der pr~parativen anorganischen Chemic, S. 360 (Hydrazin). Stuttgart:

Encke 1954. 17. Pridham, J.B. : g. Chromatog. 2, 605 (1959). 18. Weygand, F., Csendes, E. : Chem. Ber. 85, 45 (1952).

Prof. Dr. C. H. Brieskorn Inst. fiir Pharmazie u. Lebensmittelehemie der Universit~t D-8700 Wiirzburg, Landwehr

Rapid Spectrophotometric Determination of Quinine in Tonic Waters

W. F. vA~¢ GILS and GERDA G. HIDSKES

Provinciale Keuringsdienst van Waren, Assen (The Netherlands)

Received November 7, 1971

Summary. The quinine content of tonic water, after rendering it carbondioxide free, can rapidly be determined by measuring 50 ml of the liquid, adding 20 ml 1.0 n-HCl/25°/o-phosphorie acid (1 : 1) and water to 100 ml. The absorbance at 347.5 nm in 1 em euvettes against a reagent blank is a measure for the quinine content read from a calibration graph. The method is reliable, reproducible, rapid and simple and therefore suitable for routine analysis.

Zusammen/assung. Die Chiningehalte yon ,Tonic Waters' k6nnen sehr sehnell bestimmt wer- den in kohlens~urefrei gemaehten Getrgnken, wenn 50 ml der Flfissigkeit, 20 ml 1.0 n-HC1/25%- Phosphors~ure (1 -{- 1) und Wasser bis 100 ml zugesetzt werden. Die Extinktion wird gemes- sen bei 347,5 nm, 1 cm Schichtdicke, gegen die Reagen~ien als Referenz. Der Chiningehalt wird einer Eichkurve entnommen. Die Methode ist zuverl/issig, reproduzierbar, schnell und einfach und ist deshalb schr geeignet fiir Routine-Analysen.

90

Introduction

The increasing use of quinine in soft drinks, such as bit ter lemon and tonic waters has often caused warnings in medical circles, since excessive use of quinine m a y cause allergic reactions to people who are sensitive to it. Quinine should be observed as a medicin. I n most countries, however, its use in soft drinks is allowed between fixed limits. I n the Netherlands only a lower limit of 40 mg quinine as hydrochloric acid salt per liter is prescribed, the opinion being tha t an upper limit is set b y the natura l bitterness of quinine. For control laboratories of public health services it is of importance to have at their disposal a rapid method for the determinat ion of quinine.

Of the various methods reported in literature only a few are applied to soft drinks. Schr5der [1] applied a potentiometrie titration with perehloric acid in non-aqueous solution. Strache [2] developed a fluorimetric method, tIadorn and Zfircher [3] compared various extraction methods [4, 5] and recommended the ether extraction at room temperature from an alkaline solution. For non-eoloured drinks, such as tonic waters we have developed a direct spectrophotometric method which is very simple, rapid, reliable and therefore suitable for routine analysis. The results have been compared with those obtained by ttadorn's method [3]. The latter method should, however, be preferred when dealing with eoloured drinks.

Experimental Prel iminary experiments were carried out with pure quinine solutions in distilled

water. The influence of sugars, citric acid, lactic acid and tar tar ic acid upon the ab- sorbance of quinhle at 347.5 n m in 0.1 n-HC1 solution was found to be negligible. The addit ion of preservatives, such as sorbic acid and benzoic acid, likewise did not exert any influence. An exception was salicylic acid, but in all tonic waters invest igated no salicylic acid could be detected. Wi th pure quinine solutions and the above men- t ioned additions no discrepancies were found when comparing the results of the spectrophotometrie me thod with those of Hadorn ' s method [3]. I n subsequent ex- periments with about 20 tonic waters of varying origin, however, the absorbances at 347.5 n m in 0.1 n-HC1 solutions yielded much higher quinine contents t han corres- ponded with the amounts found by Hadorn ' s method. On further examinat ion it appeared tha t all tonic waters investigated contained traces of iron, which were responsible for the discrepancies found. For this reason phosphoric acid was added to mask this iron-effect.

The amount of phosphoric acid added was based upon the results obtained with quinine solutions to which ferric ions have been added up to the relatively high content of 2 mg Fea+/litre, this being the highest amoun t found by us in natura l mineral waters.

To s tudy the reproducibil i ty of the method the quinine content of a tonic water was determined in duplicate by 6 analysts according to bo th the spectrophotometr ic method and Hadorn ' s method. The results are given in table 1.

Table 1. Quinine content of tonic water in mg/litre

10 ml × % I-I3PO~ added Hadorn's x = 25 × = 37.5 × ~ 75 method

Number of determinations Minimum value Maximum value l~Iean value Standard deviation

9 6 12 6 65.6 64.2 64.7 64.7 67.4 65.8 66.7 65.6 66.3 65.4 65.5 65.0 0.38 0.33 0.45 0.36

Procedure Apparatus. Spectrophotometer, Unieam SP 500. - - Graduated flasks, 10- and 100 ml capa-

cities. - - Reagents. Hydrochloric acid. - - 25%ig Phosphoric acid. Acid mixture: mix equal volumes of n-hydrochloric acid and 250/0 phosphoric acid.

91

Standard quinine solution: Dissolve 50 mg of pure basic quinine in 20 ml acid mixture and make up to 100 ml with distilled water. Shake the solution thoroughly and transfer by pipette 10.0 ml of it into a 100 ml graduated flask. Add 18.0 ml of the acid mixture and make up to the mark with distilled water. Shake well. This solution contains 50 ~g/ml of basic quinine.

Procedure Expell the carbon dioxide from about 60 ml of tonic water by gentle heating on a water bath.

After cooling to room temperature, transfer by pipette 50.0 ml of the solution into a 100 ml graduated flask. Add 20 ml of the acid mixture and make up to the mark with distilled water. Shake thoroughly and measure the absorbance in a 1 cm cuvctte at 347.5 nm against a reagent blank, l~ead the concentration from a calibration graph.

Calibration graph Transfer by pipette 0, 1.0, 2.0, 4.0, 6.0, 8.0 and 10.0 ml each of the standard quinine solution

into 10 ml graduated flasks. Make up to 10.0 ml with a dilute acid mixture in water (1 + 4) and mix thoroughly. Measure the absorbance at 347.5 nm in 1 cm cnvettes against the reagent blank and construct a calibration graph by plotting the absorbances found as a function of the corres- ponding concentrations in micrograms per 10 ml final solution.

Calculation Calculate the amount of quinine from the following equation.

W ~ 10 -3 • a . b • M i / M , " C nag quinine, ttC1/litre where W is the amount of quinine expressed as its hydrochloric salt in the starting material, mg/litre; a the dilution factor; b the ratio of the volumes of the solution to be measured and of the final solution used for the calibration; 2//i and M, the respective tool • wts of quinine-t{C1 and of quinine (360.5 and 324.0 respectively); C the amount of quinine found from the calibration graph, ~g per 10 ml of final solution.

Re fe rences

1. SchrSder, H. : Mineralwasser-Ztg. 10, 630 (1957). 2. Strache, F. : Deut. Lebensm. Rundschau 55, 153 (1959). 3. ttadorn, H., Ziircher, K. : Mitt. Gebiete Lebensm. Hyg. ~ , 194 (1964). 4. Pritzker, J., Jungkunz, R.: Pharm. Acta ttelv, l l / l~ , 223 (1939). 5. - - - - Mitt. Gebiete Lebensm. Hyg. 4~, 232 (1951).

W. F. van Gils, G. G. ttidskes Provinciale Keuringsdienst van Waren Assenflqetherlands

Nachweis und Identifizierung kiinstlicher wasserlSslicher Farbstoffe H E I ~ WoIDIc~t u n d H~LGA G~CAU~R

Mitteilung aus dem Forschungsinstitut der Ernihrungswirtschaft, Wien (0sterreich)* **

Eingegangen am 29. November 1971

D e t e c t i o n a n d I d e n t i f i c a t i o n o f Ar t i f i ca l W a t e r - S o l u b l e Dyes tu f f s

Summary. 197 synthetic dyestuffs in food and cosmetics are detected by isolating 5 groups of dyestuffs by means of the wool-dyeing technique and separation by paper chromato- graphy using 6 distinct solvents. Certain characteristics of the isolated dyestuffs are discussed, allowing a safer estimation of colouring agents in various samples than so far possible.

Zusa~nmen]assung. Es wird ein Arbeitsgang zum Nachweis yon 197 synthetischen l%rbstoffen in Lebensmitteln und Kosmetika beschrieben. Bei der Isolierung mittels Wollfaden erfolgt bereits Auftrennung in fiinf Farbstoffgruppen. Die Trennung wird papierchromategraphisch mit sechs nach bestimmten Gesichtspunkten ansgew~hlten Fliel]mittelgemischen durchgefiihrt. Die Vorteile des neuen Verfahrens liegen darin, dab sowohl dutch die groBe Anzahl der berficksich- tigten ~'arbstoffe als auch dureh die Identifizierung mittels zahlreicher charakteristischer Eigen- schaften die Beurteilung yon Proben mit grSf]erer Sicherheit als bisher mSglich ist.

* Vorgetragen yon Dr. H. Gnauer am 15. 4. 1971 anl~131ich der Internationalen Lebensmittel- chemischen Fachtagung des Vereines 0sterreichischer Chemiker in Wien.

** Wegen des groBen Umfanges der erarbeiteten Daten konnte die Drucklegung nicht in einer Fachzeitschrift erfolgen, sondern wurde im Eigenverlag in Form einer Broschiire herausgebracht. Sie kann auf Anforderung gegen Erlegtmg einer Schutzgebiihr vom Forschungsinstitut der Er- n~hrungswirtschaft, Blaadstrate 29, A-1190 Wien, bezogen werden.