Analysing Sr isotopes in low-Sr samples such as single insects with inductively coupled plasma tandem mass spectrometry using N2 O as a reaction gas for in-line Rb separation.

RATIONALE: Strontium isotopes are valuable markers of provenance in a range of disciplines. Limited amounts of Sr in low-mass samples such as insects mean that conventional Sr isotope analysis precludes their use for geographic origins in many ecological studies or in applications such as biosecurity. Here we test the viability of using inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) with N2 O as a reaction gas for accurately determining Sr isotopes in insects with Sr < 100 ng. METHODS: Strontium isotopes were determined in solution mode using ICP-MS/MS with 0.14 L/min N2 O as a reaction gas to convert Sr+ into SrO+ for in-line separation of 87 Sr from 87 Rb. The Sr isotope reference standards NIST SRM 987, NIST SRM 1570a and NIST SRM 1547 were used to assess accuracy and reproducibility. Ten insect species collected from the wild as a proof-of-principle application were analysed for Sr concentration and Sr isotopes. RESULTS: Using ICP-MS/MS we show for the first time that internal mass bias correction of 87 Sr16 O/86 Sr16 O based on 88 Sr16 O/86 Sr16 O works to give for NIST SRM 987 a 87 Sr/86 Sr ratio of 0.7101 ± 0.012 (RSD = 0.17%) and for NIST SRM 1570a a 87 Sr/86 Sr ratio of 0.7100 ± 0.009 (RSD = 0.12%), which are within error of the accepted values. The first 87 Sr/86 Sr ratio of NIST SRM 1547 is 0.7596 ± 0.0014. Strontium analyses were run on 0.8 mL of 0.25-0.5 ppb Sr, which equates to 2-4 ng of Sr. Strontium isotope analysis with a precision of >99.8% can be achieved with in-line separation of 87 Sr from 87 Rb at least up to solutions with 25 ppb Rb. CONCLUSIONS: A minimum of 5 mg of insect tissue is required for Sr isotope analysis. This new ICP-MS/MS method enables Sr isotope analysis in single insects, allowing population-scale studies to be feasible and making possible applications with time-critical uses such as biosecurity.

Pre-cleaning of hair is not beneficial in LA-ICP-MS studies of chronic metal exposure.

Chronic exposure to toxic metals is a serious global health concern. However, population-wide biomonitoring is costly and carries several sampling constraints. Though hair sampling can be a useful way to assess environmental exposure, external contamination is a long-standing concern, and a pre-cleaning step prior to metal quantification has long been recommended despite a lack of evidence for its efficacy. In this study, we quantified the spatial distribution of 16 elements in unwashed human hair samples using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), then tested how two common pre-cleaning treatments (Triton-ethanol, Triton-nitric acid) affected metal content in external and interior layers of hair using LA-ICP-MS. We show that elements differ in their spatial distribution across hair and that pre-cleaning is not consistent in its effect on element concentrations and decreases interior concentrations of some elements. We demonstrate that differences among individuals can be quantified reliably with LA-ICP-MS analysis of interior concentrations of unwashed hair. Our study tests the widespread notion that pre-cleaning is essential in analyses of hair for environmental exposure to metals, and examines the benefits of a unified approach to analysis of metals in hair using LA-ICP-MS.

Changes in plasma and oral mucosal lycopene isomer concentrations in healthy adults consuming standard servings of processed tomato products.

The consumption of tomato products is associated with a reduced risk of cardiovascular disease and several cancers. It is hypothesized that lycopene, the major carotenoid in tomato products, may mediate this relationship. We designed a study to examine changes in plasma and buccal mucosal cell (BMC) lycopene concentrations in healthy adults consuming standard daily servings of processed tomato products: spaghetti sauce, tomato soup, or vegetable juice. Thirty-six healthy subjects consumed a lycopene-free diet for 2 wk and were then assigned to one of three (n = 12) intervention groups consuming daily, single servings of sauce (21 mg lycopene per (1/2) cup), soup (12 mg lycopene per 1 cup), or juice (17 mg lycopene per 8 oz) for 4 wk. Fasting blood and BMC samples were evaluated by high-performance liquid chromatography analysis for carotenoids and lycopene isomers. Total plasma lycopene concentrations (Mean +/- SEM) decreased from 1.05 +/- 0.07 to 0.54 +/- 0.05 micromol/l (49%, P < 0.0001) during the 2-wk washout period. Following intervention, plasma lycopene concentrations increased significantly for those consuming sauce, soup, and juice (compared with washout baseline) to 2.08 (192%, P < 0.0001), 0.91 (122%, P < 0.0001), and 0.99 (92%, P < 0.0001) micromol/l, respectively. Plasma isomer concentrations show a 61:39 ratio of cis:all-trans at the start of the study. During the 2-wk washout the decrease in plasma all-trans-lycopene was greater than that for pooled cis isomers (70:30 cis:trans ratio, P < 0.001). After 2 wk of dietary intervention isomer ratios returned to those observed at the start of the study. Total BMC lycopene concentrations did not significantly change during the brief washout. During the 4-wk intervention period, BMC total lycopene concentrations increased (P < 0.005) by 165, 42, and 48% nmol/mg protein for those consuming sauce, soup, and juice, respectively. This study demonstrates that plasma lycopene decreases by 50% after approximately 2 wk on a lycopene-free diet with a decrease in the ratio of all-trans compared with cis isomers. Single, daily servings of processed tomato products significantly increase blood and BMC lycopene for 2 wk. Additional studies of lycopene bioavailability, isomerization, metabolism, and bioactivity will provide greater insight into the potential health benefits suggested by epidemiological studies and laboratory investigations.