Volumetric dried blood spot microsampling: A sustainable, patient-friendly, and practical approach for retinol and α-tocopherol analysis in a clinical setting.

Dried blood spot (DBS) technique has gained significant attention due to the growth of decentralized diagnostics. This technique reduces the number of hospital visits for patients and the workload for personnel in specialized hospitals. This microsampling method provides an environmentally friendly (green) and patient-friendly alternative to conventional phlebotomy. Challenges related to sample heterogeneity in traditional DBS cards have been overcome by the volumetric DBS sampling using new types of commercially available devices. Due to the unstable nature of the analytes, commercial volumetric DBS devices allow blood sampling at primary care units in remote settings and facilitate transport it via temperature-controlled systems. Blood sample stability has improved from 24 h at 4-8 °C to 30 days at -80°C. DBS also requires over 1000 times less shipping and storage space than liquid blood. We optimized the DBS method to require only 10 µL of blood and achieve extraction efficiencies of over 90 % for retinol when the result from validated method is the reference value. However, α-tocopherol recovery varied from 53 to 75 % depending on the filter paper type used. Furthermore, we successfully developed a liquid-liquid extraction method for both analytes from whole blood, with over 90 % recovery. Our approaches eliminate the need for separate serum and erythrocyte extractions, simplify sample preparation, and reduce reagent use and energy consumption. Both devices enable reliable volumetric collection. Our approach makes micronutrient monitoring more accessible and enables sample collection in decentralized settings. This aligns with the objectives of green analytical chemistry and universal health coverage.