TuP-09


AN EVALUATION OF THE TURBO-IONSPRAY INTERFACE FOR THE QUANTITATION OF TACROLIMUS IN WHOLE BLOOD

CE Jones1, A Jones2, PJ Taylor1, and SM Pond1,3

Departments of 1Clinical Pharmacology and 3Medicine, Princess Alexandra Hospital, Qld 4102.
2Centre for Drug Design and Development, The University of Queensland, Qld 4067.


Turbo-ionspray is a recently developed interface which allows the introduction of flow rates of upto 1 ml/min directly into the source of the mass spectrometry. In this study the performance of turbo-ionspray, in terms of compound stability and sensitivity, was evaluated against ionspray for the quantitation of tacrolimus (an immunosuppressant drug) in whole blood.

Initially, the turbo-ionspray temperature (250, 350, and 550 °C) was evaluated using a standard solution of 10 ng/mL tacrolimus in methanol. A standard curve of whole blood samples (0.1, 0.5, 1.0, 5.0, 10, 20, and 50 µg/L) were prepared by the method of Taylor et al. [1] Chromatographic separation, for this assay, was achieved with a 2 mm i.d. x 100 mm C8 Brownlee column (Activon), at ambient temperature, using a mobile phase of 80 % methanol/20 % 0.05 M ammonium acetate buffer (pH 5.1). Both interface systems used a flow rate of 400 µL/min which gave a run time of less than 3 min. For the ionspray interface, the flow was split post column 1:5 into the mass spectrometer. Detection was in positive ion mode using multiple reactant monitoring (Tacrolimus m/z 821.5-->768.4, internal standard m/z 809.5-->756.4) at an orifice potential of 65 V.

The table below illustrates the effect of turbo-ionspray operating temperature on compound response normalised against ionspray response.

Ionspray
Turbo-ionspray Operating Temperature (°C)
 
250
350
550
1.0
4.4
7.0
13.8


For the whole blood standards, linearity was observed for both interface systems (r >= 0.998). Overall the response, using turbo-ionspray, for tacrolimus and the internal standard was increased 800 % and 900 %, respectively.

In conclusion, turbo-ionspray produced a linear response for tacrolimus extracted from whole blood, with an 8 fold increase in response compared with ionspray. The ability of the turbo-ionspray interface to allow high flow rates and produce increased response provides a powerful tool in quantitative drug analysis.

1. Taylor, P.J., Jones, A., Balderson G.A., et al. Clin. Chem., 1996, 42, 279-285.