Evaluation of Amount of Blood in Dry Blood Spots: Ring-Disk Electrode Conductometry

• Published in: Analytical chemistry (Washington) 2016-06, Vol.88 (12), p.6531-6537
• Main Authors: Kadjo, Akinde F, Stamos, Brian N, Shelor, C. Phillip, Berg, Jordan M, Blount, Benjamin C, Dasgupta, Purnendu K
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Blood; Blood tests; Conductance; Conductivity; DBS; Electrodes; Mathematical models; Methyl alcohol; Sodium; Spots
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/acs.analchem.6b01280

A fixed area punch in dried blood spot (DBS) analysis is assumed to contain a fixed amount of blood, but the amount actually depends on a number of factors. The presently preferred approach is to normalize the measurement with respect to the sodium level, measured by atomic spectrometry. Instead of sodium levels, we propose electrical conductivity of the extract as an equivalent nondestructive measure. A dip-type small diameter ring-disk electrode (RDE) is ideal for very small volumes. However, the conductance (G) measured by an RDE depends on the depth (D) of the liquid below the probe. There is no established way of computing the specific conductance (σ) of the solution from G. Using a COMSOL Multiphysics model, we were able to obtain excellent agreement between the measured and the model predicted conductance as a function of D. Using simulations over a large range of dimensions, we provide a spreadsheet-based calculator where the RDE dimensions are the input parameters and the procedure determines the 99% of the infinite depth conductance (G 99) and the depth D 99 at which this is reached. For typical small diameter probes (outer electrode diameter ∼