Investigation of Solid Phase Microextraction as an Alternative to Dried Blood Spot

Importance of the Topic

Microsampling techniques are transforming bioanalytical workflows by reducing costs, simplifying logistics and minimizing sample volume requirements. Dried blood spot (DBS) sampling has been widely adopted for remote and low-volume collection, but its performance is strongly influenced by hematocrit. Solid phase microextraction (SPME) offers an alternative that combines sampling, cleanup and preconcentration in a single step while potentially mitigating hematocrit effects.

Aims and Study Overview

This study evaluates the performance of functionalized BioSPME fibers as an alternative to DBS media for isolating small-molecule drugs from whole blood. Using carbamazepine as a model analyte, the work compares extraction efficiency, sensitivity and hematocrit dependence of BioSPME versus two common DBS cards across a range of hematocrit levels.

Methodology and Instrumentation

• BioSPME fibers: metal core fibers coated with C18-modified silica particles (45 µm thickness) bound in a biocompatible polymer.
• Sample preparation: whole blood spiked with carbamazepine (50 ng/mL) at hematocrit levels of 20 %, 45 % and 70 %. DBS cards (cellulose- and glass fiber-based) were spotted with 20 µL, dried overnight and desorbed. BioSPME fibers were conditioned in 50:50 acetonitrile:water, extracted for 15 min with agitation, washed in water and desorbed for 30 min in methanol containing internal standard.
• Chromatography and detection: Shimadzu LC-30 pump coupled to an LCMS-8030 triple-quadrupole mass spectrometer. Separation on Ascentis Express C18 (5 cm × 2.1 mm, 2.7 µm) with 5 mM ammonium formate water/acetonitrile mobile phases, 0.3 mL/min, 35 °C. ESI+ MRM detection of carbamazepine transitions.

Main Results and Discussion

• At 45 % hematocrit, BioSPME achieved approximately five-fold higher signal for carbamazepine compared to both DBS media.
• Extraction efficiency with BioSPME decreased as hematocrit increased from 20 % to 70 %, indicating matrix viscosity and diffusional limitations rather than analyte binding to cells.
• Comparison of whole blood versus plasma showed similar recoveries at constant hematocrit, suggesting minimal drug partitioning into red cells.
• Dilution of high-hematocrit blood with saline to a calculated 25 % level restored extraction efficiency to that of native low-hematocrit samples, confirming the dominant role of viscosity.

Benefits and Practical Applications

• BioSPME integrates sampling, cleanup and concentration, eliminating centrifugation and multiple handling steps.
• Enhanced sensitivity and reduced interference enable quantification of low-level analytes in biofluids.
• Compact fiber format permits remote or point-of-care sampling and simplified transport to central laboratories.

Future Trends and Possibilities

Ongoing investigations will focus on freshly prepared blood to avoid hemolysis artifacts, optimization of extraction kinetics across hematocrit ranges and integration of automated workflows. Expansion to other analyte classes and in vivo sampling applications could further extend the utility of BioSPME.

Conclusion

Functionalized SPME fibers demonstrate clear advantages over DBS media for small-molecule isolation from whole blood, delivering higher sensitivity and robustness against hematocrit-related variability. With further method optimization and automation, BioSPME has the potential to become a versatile tool for clinical and bioanalytical sampling.