Intracellular contents reflect the specific history of a cell including innate physiological heterogeneity as well as differing levels of exposure to environmental influences. A method capable of analyzing a variety of species from within a single human erythrocyte is demonstrated. Guided by a microscope, individual cells can be drawn into open capillaries of 10-microns i.d. On contact with a low ionic strength buffer solution, the cell lyses and releases its intracellular fluid. The ionic components are then separated by capillary electrophoresis. For glutathione, microderivatization with a fluorescent reagent can be accomplished in vitro with monobromobimane. The effects of extracellular oxidizing and reducing agents on the glutathione levels can thus be followed. For sodium and potassium, or any other ionic species, charge displacement of a fluorescent cation results in indirect fluorescence detection. The two detection modes are suitable for intracellular components present at low-attomole and sub-femtomole levels, respectively.

Microdialysis sampling has become an important means of continuously monitoring reactions in vivo. This sampling technique places a constraint on the analysis method because of the very small sample volume provided. On the other hand, microdialysis provides the advantage of clean samples that do not require cleanup prior to analysis. An on-line coupling of microdialysis sampling to capillary electrophoretic (CE) analysis is described that uses the advantages of microcolumn separations to overcome the small volume limitation. An interface was designed which converts the continuous microdialysis sample stream into discrete 60-nL sample plugs and then injects a portion of this plug into the CE system. The on-line interface provided precision of 2.6% with minimal band broadening or peak height loss relative to off-line sampling. Using a high-speed micellar electrokinetic chromatography (MEKC) separation, resolution of the investigational antineoplastic SR 4233 from its main metabolite SR 4317 was achieved in less than 60 s. This allowed the on-line system to achieve a 90-s temporal resolution for determining the pharmacokinetics of SR 4233 in vivo.

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The most widely used in vivo sampling technique, microdialysis sampling, provides important data on the extracellular concentration of low molecular mass (<1000-5000 Da) species. However, biological macromolecules of much greater mass (>20-90 kDa) have key in vivo roles as chemical messengers or are currently under consideration as biopharmaceuticals. Microdialysis, which utilizes a sampling process based upon analyte diffusion, is largely ineffective at monitoring the local, transient extracellular concentrations of important macromolecular species. Ultrafiltration sampling is an in vivo sampling technique utilizing a convective, rather than diffusive, sampling mechanism. This paper demonstrates the effective recovery (>90%) of model proteins with molecular weights up to 68 000 from in vivo and in vitro sites through the use of miniature ultrafiltration sampling probes. Selectivity in the sampling process can be achieved through alteration of the membrane structure. In vivo ultrafiltration sampling in conjunction with slab gel electrophoresis and silver staining detects three recovered proteins (MW 9100-26 800) present in the extracellular space of a series of rats.