Using 19F-NMR and 1H-NMR for Analysis of Glucocorticosteroids in Creams and Ointments : -Method Development for Screening, Quantification and Discrimination
Topical treatment containing undeclared corticosteroids and illegal topical treatment with corticosteroid content have been seen on the Swedish market. In creams and ointments corticosteroids in the category of glucocorticosteroids are used to reduce inflammatory reactions and itchiness in the skin. If the inflammation is due to bacterial infection or fungus, complementary treatment is necessary. Side effects of corticosteroids are skin reactions and if used in excess suppression of the adrenal gland function. Therefore the Swedish Medical Products Agency has published related warnings to make the public aware. There are many similar structures of corticosteroids where the anti-inflammatory effect is depending on substitutions on the corticosteroid molecular skeleton. In legal creams and ointments they can be found at concentrations of 0.025 ‑ 1.0 %, where corticosteroids with fluorine substitutions usually are found at concentrations up to 0.1 % due to increased potency.
At the Medical Products Agency 19F-NMR and 1H-NMR have been used to detect and quantify corticosteroid content in creams and ointments. Nuclear Magnetic Resonance, NMR, is an analytical technique which is quite sensitive and can have a relative short experimental time. The low concentration of corticosteroids makes the signals detected in NMR small and in 1H‑NMR the signals are often overlapped by signals from the matrix. With 1H‑NMR characteristic signals could be detected in a less crowded spectral window between 5.96 ‑ 6.40 ppm where overlapping signals from the matrix often are absent. Since fluorine is less common in molecules, the option of using 19F‑NMR increases the possibility of finding fluorine-containing corticosteroids in creams and ointments. The corticosteroid signals in 19F‑NMR are detected at -165 ppm and -187 ppm, depending on where fluorine is located on the structure.
Quantifying with 1H-NMR and 19F-NMR gave similar result with an accuracy of 98‑116 % and 89-106 % respectively, and RSD values between 2‑35 %, depending on the kind and amount of corticosteroid. Relations between the structure and some signals in 1H‑NMR were found, making it easier to determine the basic structure of unknown corticosteroids in creams and ointments. Screening experiments were performed on creams and ointments with known concentration corticosteroid in order to find minimum NS for analyzing products which might contain corticosteroids. In order to detect a corticosteroid concentration of 0.05 % 19F‑NMR needed 64 NS with an experimental time of 2 min and 1H-NMR needed 160 NS with an experimental time of 17 min. Concentrations of 0.025 % could for some corticosteroids be detected with these parameters. The possibility of spiking samples in order to discriminate between corticosteroids was also investigated. The corticosteroids available at the MPA could be discriminated from each other with at least one of the methods 1H‑NMR or 19F-NMR, and in most cases with both. A market research was done in order to search for counterfeits and salespersons in different health food stores were asked to recommend the best product to treat eczema or psoriasis. Nine recommended products were bought where one was found illegally containing a corticosteroid. In previous experiments at the MPA there had been occurrences of a split signal in 19F-NMR when analyzing creams. The split 19F‑NMRsignal was shown to be related both to the presence of water and structural effects of the corticosteroid
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