Portable X-ray Fluorescence as a Rapid Determination Tool to Detect Parts per Million Levels of Ni, Zn, As, Se, and Pb in Human Toenails: A South India Case Study

Chronic exposure to inorganic pollutants adversely affects human health. Inductively coupled plasma mass spectrometry (ICP-MS) is the most common method used for trace metal(loid) analysis of human biomarkers. However, it leads to sample destruction, generation of secondary waste, and significant recurring costs. Portable X-ray fluorescence (XRF) instruments can rapidly and nondestructively determine low concentrations of metal(loid)s. In this work, we evaluated the applicability of portable XRF as a rapid method for analyzing trace metal(loid)s in toenail samples from three populations (n = 97) near the city of Chennai, India. A Passing-Bablok regression analysis of results from both methods revealed that there was no proportional bias among the two methods for nickel (measurement range ∼25 to 420 mg/kg), zinc (10 to 890 mg/kg), and lead (0.29 to 4.47 mg/kg). There was a small absolute bias between the two methods. There was a strong proportional bias (slope = 0.253, 95% CI: 0.027, 0.614) between the two methods for arsenic (below detection to 3.8 mg/kg) and for selenium when the concentrations were lower than 2 mg/kg. Limits of agreement between the two methods using Bland-Altman analysis were derived for nickel, zinc, and lead. Overall, a suitably calibrated and evaluated portable XRF shows promise in making high-throughput assessments at population scales.

Insights into Primary Ion Exchange between Ion-Selective Membranes and Solution. From Altering Natural Isotope Ratios to Isotope Dilution Inductively Coupled Plasma Mass Spectrometry Studies

Although ion-selective electrodes have been routinely used for decades now, there are still gaps in experimental evidence regarding how these sensors operate. This especially applies to the exchange of primary ions occurring for systems already containing analyte ions from the pretreatment step. Herein, for the first time, we present an insight into this process looking at the effect of altered ratios of naturally occurring analyte isotopes and achieving isotopic equilibrium. Benefiting from the same chemical properties of all isotopes of analyte ions and spatial resolution offered by laser ablation and inductively coupled plasma mass spectrometry, obtaining insights into primary ion diffusion in the preconditioned membrane is possible. For systems that have reached isotopic equilibrium in the membrane through ion exchange and between the membrane phase and the sample, quantification of primary ions in the membrane is possible using an isotope dilution approach for a heterogeneous system (membrane-liquid sample). Experimental results obtained for silver-selective membrane show that the primary ion diffusion coefficient in the preconditioned membrane is close to (6 ± 1) × 10^-9 cm²/s, being somewhat lower compared to the previously reported values for other cations. Diffusion of ions in the membrane is the rate limiting step in achieving isotopic exchange equilibrium between the ion-selective membrane phase and sample solution. On the contrary to previous reports, quantification of silver present in the membrane clearly shows that contact of the membrane with silver nitrate solution of concentration 10^-3 M leads to pronounced accumulation of silver ions in the membrane, reaching almost 150% of ion exchanger amount. The magnitude of this effect increases for higher concentration of the electrolyte in the solution.

Food Authentication: Species and Origin Determination of Truffles (Tuber spp.) by Inductively Coupled Plasma Mass Spectrometry and Chemometrics

The aim of this study was to develop a protocol for the authentication of truffles using inductively coupled plasma mass spectrometry. The price of the different truffle species varies significantly, and because the visual differentiation is difficult within the white truffles and within the black truffles, food fraud is likely to occur. Thus, in the context of this work, the elemental profiles of 59 truffle samples of five commercially relevant species were analyzed and the resulting element profiles were evaluated with chemometrics. Classification models targeting the species and the origins were validated using nested cross validation and were able to differentiate the most expensive Tuber magnatum from any other examined truffle. For the black truffles, an overall classification accuracy of 90.4% was achieved, and, most importantly, a falsification of the expensive Tuber melanosporum by Tuber indicum could be ruled out. With regard to the geographical origin, for Italy and Spain, one-versus-all classification models were calculated each to differentiate truffle samples from any other origins by 75.0 and 86.7%, respectively. The prediction was still possible according to an internal mathematical normalization scheme using only the element ratios instead of the absolute element concentrations. The established authentication protocol was successfully tested with an external sample set of five fresh truffles. Our results show the high potential of the element profile for the parallel species and origin authentication of truffles.

Chemical Composition of Commercial Cow's Milk

Bovine milk is a nutritionally rich, chemically complex biofluid consisting of hundreds of different components. While the chemical composition of cow's milk has been studied for decades, much of this information is fragmentary and very dated. In an effort to consolidate and update this information, we have applied modern, quantitative metabolomics techniques along with computer-aided literature mining to obtain the most comprehensive and up-to-date characterization of the chemical constituents in commercial cow's milk. Using nuclear magnetic resonance (NMR) spectroscopy, liquid chromatography-mass spectrometry (LC-MS), and inductively coupled plasma-mass spectrometry (ICP-MS), we were able to identify and quantify 296 bovine milk metabolites or metabolite species (corresponding to 1447 unique structures) from a variety of commercial milk samples. Through our literature analysis, we also found another 676 metabolites or metabolite species (corresponding to 908 unique structures). Detailed information regarding all 2355 of the identified chemicals in bovine milk have been made freely available through a Web-accessible database called the Milk Composition Database or MCDB ( http://www.mcdb.ca/ ).

Rare Earth Element Labeling as a Tool for Assuring the Origin of Eggs and Poultry Products

Laying hens were fed terbium and thulium supplemented feed in order to introduce a distinctive rare earth element pattern that allows discrimination of labeled from unlabeled poultry products. Samples of egg yolk, egg shells, meat, bones, liver, blood, and feces were analyzed using either conventional or laser ablation inductively coupled plasma mass spectrometry. Already after a short time of administering supplemented feed, terbium and thulium enrichment could be unambiguously detected in the products, while absolute terbium and thulium contents remained low enough to ensure safety for the customer. This method could potentially be applied to specifically label foodstuffs produced in certain regions or under certain conditions, in order to ensure food authenticity.

Role of Lanthanides in the Traceability of the Milk Production Chain

The traceability and authentication of milk were studied using trace and ultratrace elements as chemical markers. Among these variables, the group of lanthanides resulted in being particularly useful for this purpose as a result of their homogeneous distribution inside milk, which showed on the contrary to be intrinsically inhomogeneous from the elemental point of view. Using in this pilot study milk samples from a factory in Piedmont (Italy), we demonstrated that the distribution of lanthanides can be used as a fingerprint to put into relation the soil of the pasture land on which cows graze and the bottled milk produced in the factory. In fact, the distribution is maintained nearly unaltered along the production chain of milk, apart from the passage into the stomachs of the cows. Using the same variables, it was possible to discriminate between milk produced in the factory and milk samples taken from the large-scale retail trade.