Kurze Mitteilungen

k

---• F I D e

6 g lO

k

m P ~ r

mlr~

Abb. 1. Gas-Chromatogramme eines derivatisierten Bakte- rienfettsfiuregemisches aufgenommen mit Elektronenein- fangdetektion (ECD) und Flammenionisationsdetektion (FID). Alle Sfiuren als Methylester, Hydroxyfetts~iuren zu- sMzlich als Heptafluorbutyrate: a 2-Hydroxydecansfmre; b Dodecans/iure; c 2-Hydroxydodecans/iure; d 3-Hydroxy- d0decans~iure; e Tetradecansfiure; f 2-Hydroxytetradecan- s~ure; g 3-Hydroxytetradecansfiure; h Palmitoleins/iure; i Palmitins~iure; k 2-Hydroxyhexadecans~iure; l M-Methyl- hexadecans/iure; rn Heptadecans~iure; n C)ls/iure; o Stearin- sfiure; p 2-Hydroxystearins/iure; q Nonadecans~iure; r Ara- chinsfiure. Die Probe wurde ftir ECD 1:100 verdtinnt

127

nenden hohen Selektivitfit des Nachweises yon Hydroxyfett- s/iurederivaten mit dem ECD ist besonders die betrfichtliche Steigerung der Nachweisempfindlichkeit hervorzuheben. Un- ter den angegebenen gas-chromatographischen Bedingungen wurden noch 10 pg des Heptafluorobutyrates des 12-Hydro- xystearinsfiuremethytesters nachgewiesen. Fiir den sicheren Nachweis von Hydroxyfettsfiuren in unbekannten biologi- schen Proben haben wir gas-chromatographisch-massen- spektrometrische Verfahren mit verschiedenen Ionisationsbe- dingungen und mit Auswertung sowohl der positiven Ms auch negativen Massenspektren vorgeschlagen [4-6]. Ffir den Routinebetrieb ist das bier beschriebene einfache gas-chro- matographische Verfahren jedoch gut geeignet. So lassen sich beispielsweise aufgrund der hohen SelektivitM noch kleinste Mengen yon Hydroxyfetts~iuren in belasteten Fetten nach- weisen (Stan, Scheutwinkel-Reich, unver6ffentlicht).

Literatur

1. Grob, K., Grob, G., Grob, K. : J. High Res., Chromatogr. & Chromatogr. Comm. 1, 149 (1978)

2. Pardun, H. : ttandbuch der Lebensmittelchemie, Bd. 4, S. 667. Berlin, Heidelberg, New York: Springer 1969

3. Schlenk, H., Gellerman, J. L. : Anal. Chem. 32, 1412 (1960) 4. Stan, H. J., Scheutwinkel-Reich, M. : Vortrag, 6th Inter-

nat. Symposium on Mass Spectrometry in Biochem. and Medicine, 21. 6 , -22 . 6. 1979 in Venedig (Italien), Pro- ceedings (im Druck)

5. Stan, H. J., Scheutwinkel-Reich, M. : Fresenius Z. Anal. Chem. 296, 400 (1979)

6. Stan, H. J., Scheutwinkel-Reich, M. : Vortrag, AOCS-ISF World Congress, 27. 4 . -1 . 5. 1980 in New York, Pro- ceedings (im Druck)

Eingegangen am 13. Mai 1980

Fresenius Z. Anal. Chem. 303, 127-128 (1980) - (�9 by Springer-Verlag 1980

An Improved System for Anaerobic Stability Investigations in Solutions at Increased Temperatures

D. Dekker and J. H. Beijnen

Dept. of Anal. Pharmacy, Fac. of Pharmacy, State Univ. of Utrecht, Catharijnesingel 60, NL-3511 GH Utrecht, The Netherlands

Verbessertes System fiir anaerobe Stabilit~itsuntersuchungen in L6sungen bei erh6hter Temperatur

Key words: Untersuchung der Stabilit/it von Substanzen; anaerob, erh6hte Temperatur, verbesserte Vorrichtung

Introduction

Stability investigations under anaerobic conditions in so- lutions are usually performed in weU closed vessels, after oxygen has been removed by flushing each of them with nitrogen. At desired time intervals the content of the flask is then analyzed.

During removal of the nitrogen flushing-equipment and during the closing-time of the vessel, some oxygen may enter the system (especially when ampoules are used). Particularly in solutions, in which the compound under investigation is present in small concentrations, this may lead to undesired oxidation of the studied product. To study efficiently anaer- obic decomposition of prednisolone in aqueous solution, we therefore developed a system consisting of only one bottle. Using this technique we are now able to flush with nitrogen at temperatures up to 100~ and to remove the oxygen effec- tively. Since our system is closed under nitrogen pressure, no oxygen may leak into it. At desired time intervals samples are taken by opening a tap. Collecting, cooling and storage of the samples proceeds under a nitrogen atmosphere. The proposed device is time-saving and specially useful for anaerobic decomposition studies at elevated temperatures of com~ pounds in low concentrations.

Using this system we did not observe any oxidative decomposition products as described in our studies on anaerobic decomposition of prednisolone in aqueous solution.

Description of the Apparatus. The system consists of two main parts, the reaction vessel (Fig. 1 G) and the sample-collection compartment (Fig. 1 P).

128 Fresenius Z. Anal. Chem., Band 303 (1980)

The reaction vessel is a commercially available infusion bottle with a specially developed screw cap. The collection part is a commercially available bag, which can be filled with nitrogen (Glove Bag Model X-27-17; 12R, Instruments for Research and Industry, Cheltenham USA). The screw cap is made of Teflon (Fig. 2). Part of it is milled, in order to simplify its connection with the bottle. Three Teflon taps are fitted in the cap. Silicone rings are placed between the taps and the cap in order to improve a good connection.

At the inside of the cap, two taps are connected with small silicone tubes (Fig. 1 E and F). The ends of the small tubes are sticking out about I cm above the bottom of the bottle. At the outside of the cap these two taps are also connected with small fitting tubes (Fig. 1 H a n d K), ending in the Glove Bag and at a nitrogen gas supply tank, respectively. Between the bottle and the cap a stopping silicone rove is placed in order to improve a good connection. A cooling system (Fig. 1 N) is fixed in the Glove Bag, to cool the samples.

Operation. Directions for use of the Glove Bag are enclosed in the commercially available packing. When the Glove Bag is pumped up, tube L is closed by pinching. The operator puts tile stop-ring inside the cap and screws it on the bottle (all taps are closed) (Fig. 1).

Tap A and B are opened (tap C remains closed) and nitrogen is flushed into the bottle. After a while the bottle is opened and a solution, flushed with nitrogen, is put into the bottle (tap A and B remain opened). The bottle is dosed again and put in a warm bath at constant temperature. Nitrogen is flushed through the solution, during its warming-up and also

Fig. 1. Illustration of the system during collecting and cooling of a sample. A Exhaust tap; B nitrogen inlet tap: C sample exhaust tap; D Teflon screw-cap; E inner nitrogen inlet tube; F inner sample exhaust tube; G reaction vessel; H outer nitrogen inlet tube; K outer sample exhaust tube; L nitrogen tube for pumping up the Glove Bag; M sample vessel; N cooling system; O cooling tubes; P Glove Bag

SQUARE THREAD.D=36 P I T C H = 5 STOPPING ROVE

I , I 20MM Fig. 2. Parts of the screw cap

for some time at the equilibration temperature. The time needed to obtain equilibrium of temperature between the solution in the bottle and the constant temperature bath is measured, using a thermocouple which is pushed through a rubber infusion-bottle cap into the solution. (It is necessary to measure the temperature of the solution in a closed bottle.) After sufficient nitrogen is flushed through the solution, tap A is dosed and after about 1 s tap B is closed. Tap C is opened and in the Glove Bag samples are collected in cooled vessels. For collecting the samples, pressure is obtained by opening tap B every now and then. Before collecting a new sample a few milliliters have to be discarded (dead volume in tube K). The concentration of the drug in the first sample is regarded

as the initial concentration, in the anaerobic decomposition process. The samples are stored in the Glove Bag until they are analyzed. Decomposition during storage can be verified by comparing the analytical results of samples collected at the initial concentration, and of those which have been stored at different times.

Acknowledgements. We thank Prof. Dr. R. A. A. Maes and Dr. A. W. M. Indemans for critical reading of the manuscript, the technical staff for the technical drawings and construction of the device and Dr. P. M. C. Parel for the illustration.

Received February 13, 1980