Experimental setup for the determination of analytes contained in ultrasonically levitated drops

An automated technique for the determination of analytes in an ultrasonical ly levitated sample of 2 to 5 mu L volume has been developed. Contactless d osing of reagents or solvents into an ultrasonically levitated drop was rea lized via piezoelectric micropumps. Drop size was continually controlled wi th a programmed CCD camera. A diode array spectrometer designed for the use with optical fibers was used for absorption and fluorescence measurements. Determinations via direct absorption measurements following the method of standard addition and acid-base titrations with an absorption indicator and a fluorescent indicator were carried out. The mean consumption of sodium h ydroxide added via a piezoelectric micropump in five successive titrations with 18 nmol of sulfuric acid inside a levitated drop (indicator bromothymo l blue) had a relative standard deviation of 0.7 % and differed only by 0.2 % from the expected value.