Measurement of longitudinal sulfur isotopic variations by laser ablation MC-ICP-MS in single human hair strands

Abstract

A new method for the measurement of longitudinal variations of sulfur isotope amount ratios in single hair strands using a laser ablation system coupled to a multicollector inductively coupled plasma mass spectrometer (LA-MC-ICP-MS) is reported here for the first time. Ablation parameters have been optimized for the measurement of sulfur isotope ratios in scalp human hair strands of 80-120-microm thickness and different washing procedures have been evaluated. The repeatability of the method has been tested and the ability to measure sulfur isotopic variations in 1,000-microm-long hair segments has been evaluated. A horse hair sample previously characterized for carbon and nitrogen isotope ratios in an interlaboratory study has been characterized by LA-MC-ICP-MS to be used as an in-house standard for the bracketing of human hair strands. (34)S/(32)S isotope amount ratios have been measured and corrected for instrumental mass bias adopting the external standardization approach using National Institute of Standards and Technology (NIST) RM8553 and full uncertainty budgets have been calculated using the Kragten approach. Results are reported as both (34)S/(32)S isotope amount ratios and deltaS(V-CDT) values (sulfur isotopic differences relative to a reference sample expressed in the Vienna Canyon Diablo Troilite (V-CDT) scale) calculated using NIST RM8553, NIST RM8554, and NIST RM8556 to anchor results to the V-CDT scale. The main advantage of the new method versus conventional gas source isotope ratio mass spectrometry measurements is that longitudinal variations in sulfur isotope amount ratios can be resolved. Proof of concept is shown with human scalp hair strands from three individuals, two UK residents and one traveler (long periods of time abroad). The method enables monitoring of longitudinal isotope ratio variations in single hair strands. Absolute ratios are reported and delta(34)S(V-CDT) values are plotted for comparison. Slight variations of <1.2 per thousand were detected in the hair strands from UK residents whereas the traveler presented a variation of >5 per thousand. Thus, the measurement of sulfur isotopic variations in hair samples has potential to be an indicator of geographical origin and recent movements and could be used in combination with isotope ratio measurements in water/foodstuffs from different geographical locations to provide important information in nutritional and geographical studies.

Stable Isotope Ratios as Biomarkers of Diet for Health Research

“…Interestingly, hair δ 13 C and δ 15 N values did not achieve equilibrium with the new diet during that period, indicating a relatively slow isotopic turnover rate for the amino acid pool supplying hair synthesis (63). An exciting 2009 paper described an approach using laser-ablation to measure variation in δ 34 S values continuously along a single strand of human hair (134); however, such approaches are not yet widely available.…”

Inductively Coupled Plasma Mass Spectrometry

“…These changes could be related to short and long-distance journeys of the corresponding individual. 509 The method presented may thus be of use in future forensic or archaeological studies.…”

Determination of low‐level (sub‐microgram) sulfur concentrations by isotope dilution multi‐collector inductively couple plasma mass spectrometry using a 33S spike and internal normalization for mass bias correction

“…Measurement of sulfur by quadrupole ICP‐MS are also complicated by the generation of interfering ions that cannot be resolved from the sulfur peaks of interest (Table ). High‐resolution sector field ICP‐MS instruments, in contrast, are capable of resolving many of these interferences when operated in medium resolution (3000) mode …”

“…[7,[9][10][11][12][14][15][16][17][18] The majority of researchers employing isotope dilution sector field ICP-MS for sulfur determinations have used a 34 S-enriched spike material. To correct for mass bias, the isotopes of silicon [7,[9][10][11]15,16,18] or the sample-standard bracketing approach [8,12,13,16,17] have been used: the first requires the assumption that silicon behaves identically to sulfur in the plasma and the second that a correction that is often not matrix-matched and external to the sample is accurate. An alternative approach to using 34 S as the spike material is to use a highly enriched 33 S spike and then quantify the sulfur by measuring the ( 33 S/ 32 S) ratio.…”