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

An automated technique for the determination of analytes in an ultrasonically levitated sample of 2 to 5 microL volume has been developed. Contactless dosing of reagents or solvents into an ultrasonically levitated drop was realized via piezoelectric micropumps. Drop size was continually controlled with 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 hydroxide added via a piezoelectric micropump in five successive titrations with 18 nmol of sulfuric acid inside a levitated drop (indicator bromothymol blue) had a relative standard deviation of 0.7% and differed only by 0.2% from the expected value.

Use of erythrocyte ghosts for preconcentration in element speciation.

A totally new biosorption concept has been tested. It involves the use of a biological membrane with given transport characteristics that encloses a reaction compartment chosen to bind incorporated substances irreversibly. Such a system is an erythrocyte ghost: erythrocytes that are hypotonically lysed can be filled with the desired media and resealed by warming up for 1 h. The transport system exploited is the predominant one in erythrocytes, i.e., the anion transport system with 10(6) channels/cell. Erythrocyte ghosts (in the following simply called ghosts) filled with ascorbate or cysteine as intracellular reductants were compared to unmodified human erythrocytes with regard to their ability to accumulate chromate specifically. Furthermore, the lifetime and behavior of the ghosts with respect to the influence of extracellular Cr(III) were tested. The great similarity found between the ghosts tested and unmodified erythrocytes clearly shows the general applicability of this new biosorption concept which offers possibilities for the biosorption of analytes that cannot be accumulated by unmodified erythrocytes.