Direct analysis of dried blood spots by femtosecond-laser ablation-inductively coupled plasma-mass spectrometry. Feasibility of split-flow laser ablation for simultaneous trace element and isotopic analysis

Abstract

This work describes a novel procedure based on the use of a 1030 nm femtosecond (fs) laser ablation (LA) device operating at a high repetition rate (30 000 Hz) coupled to a sector field-inductively coupled plasma-mass spectrometer (ICP-MS), enabling the complete ablation of dried blood spot (DBS) specimens in a reasonable time (200 s for samples of 5 μL). The integration of the complete signal obtained, in combination with the use of Pt as an internal standard (which can be added to the clinical filter paper prior to the blood deposition, ensuring compatibility with unsupervised sample collection schemes), permits obtaining an analytical response that is independent of the particular characteristics of every sample. On the basis of this methodology, an analytical method was developed for the direct determination of several elements (Cd, Co, Cu and Pb) in four blood reference materials as well as in three real samples, providing accurate results in all cases evaluated, at concentration levels ranging from 0.1 to hundreds of μg L⁻¹. Detection limits of 0.043 (Cd), 0.42 (Co), 0.54 (Cu), and 0.040 (Pb) μg L⁻¹ are achieved, and precision values most often range between 3 and 9% RSD. Finally, the potential to couple the LA device simultaneously to a multicollector-ICP-MS and a sector field-ICP-MS unit by split-flow is also demonstrated, thus allowing us to obtain both elemental (Co, Cu, Cd and Pb) and isotopic (Cu isotopic composition) information from every particular DBS, and therefore maximizing the amount of information that can be drawn from a single DBS specimen. Still, the precision of the approach is limited at this point, as RSD values of approx. 1500 ppm and delta variations of almost 4‰ were observed for five DBS specimens created from the same blood sample.