Sequential measurement of 13 C, 15 N, and 34 S isotopic composition on nanomolar quantities of carbon, nitrogen, and sulfur using nano-elemental analysis/isotope ratio mass spectrometry.

RATIONALE: We report modifications to a commercial elemental analyzer-isotope ratio mass spectrometer that permit high-precision isotopic analysis of nanomoles of carbon (C), nitrogen (N), and sulfur (S) on a single sample without chemical or cryogenic trapping of gases. The sample size required for measurement by our system is about two orders of magnitude less than that for conventional analyses. METHODS: Our system builds on the analytical advancements offered by the EA IsoLink IRMS System and employs simple modifications to reduce the diameter of the flow path (reactors, water trap, and transfer lines), enhance peak separation (gas chromatography capillary column), and improve sample transfer to the ion source of the mass spectrometer (reduced flow rates). RESULTS: Conventional precision (<0.2‰) can be achieved down to c. 500 nmol C, N, and S for samples analyzed without modification of the commercial system. Further reduction in sample size (<50 nmol C, N, and S) was achieved with minor modifications. There is a significant carbon blank and a small nitrogen blank that can be measured directly and a sulfur blank that can be calculated using regression. Only 30 nmol of N, 22 nmol of C, and 12 nmol of S are needed to achieve better than 1‰ precision (1σ) from a single measurement. Larger samples and more replicate measurements provide better precision. CONCLUSIONS: The nano-EA method described here reduces sample size requirements by two orders of magnitude compared to traditional approaches and improves the accuracy and precision of isotope measurements on sample sizes less than 1 µmol. These advancements simplify the analytical technique and broaden the range and type of samples amenable to EA analysis.

Tracing the Geographical Origin of Roasted and Green Coffee Using Isotope Fingerprints.

Background: Coffee is one of the most popular beverages worldwide, sourced from different geographical regions. To ensure that coffee beans come from labelled locations, laboratories need an analytical solution that can discriminate geographical origin. Coffee beans have a fingerprint, a unique chemical signature that allows them to be identified: Isotope fingerprints of carbon, nitrogen, sulfur, hydrogen, and oxygen have been reliably used for origin claim verification. Objective: Show that hydrogen and oxygen isotope fingerprints from green and roasted coffee beans can determine the origin of coffee beans. Methods: The coffee beans were initially ground to as fine as possible a powder using a cryo-mill. Following, samples were weighed into tin capsules and introduced to the Thermo Scientific EA IsoLink™ IRMS System via the Thermo Scientific MAS Plus autosampler, where they were pyrolyzed at 1450°C, and converted to H2 and CO for analysis. Results: The hydrogen and oxygen isotope fingerprints of the coffee beans show that they can be clearly differentiated at the continent scale. Conclusions: It is evident that measuring the isotope fingerprint of coffee beans helps support legislation on food integrity and labelling (EC Reg. No. 1169/2011) and product geographical indication/origin (EC Reg. No. 510/2006), therefore protecting consumers and brands. The origin of a coffee bean can be determined using their hydrogen and oxygen isotope fingerprints. Highlights: Hydrogen and oxygen isotope fingerprints can help determine the origin of coffee beans, allowing the label claim to be verified.

A stable isotope approach for the quantification of sewer infiltration.

Extraneous flows in wastewater collection systems are conventionally evaluated solely on the consideration of discharge hydrographs, which often involves a great degree of subjectivity and oversimplification. To obtain reliable information on the material fluxes within the urban environment, the use of intrinsic tracers can be the optimal choice. We demonstrate the successful use of naturally occurring stable isotopes of water (18O/16O and D/H) to accurately quantify extraneous discharge of groundwater in a combined sewer network. Fresh water supply from a distant hydrological regime provided usable isotopic separations between drinking water (proxy for real foul sewage) and local groundwater (proxy for sewer infiltration) of 1.8 per thousand in delta18O and 11.7 per thousand in 62H. Diurnal variation of wastewater isotopic composition reflected both the varying rates of foul sewage production and irregular dispersion effects in the pipe network. The latter suggest the existence of larger cumulative backwater zone volumes, which have not been attended to yet. Infiltrating groundwater contributed 39% (95% confidence interval = +/- 2.5%) of the total daily dry weather wastewater discharge. This paper discusses all relevant aspects for practical application of the method. It presents a comprehensive framework for uncertainty analysis and details on the detection and discrimination of possibly interfering effects.

Estimating sewer leakage from continuous tracer experiments.

Direct measurements of sewer leakage with continuous dosing of tracers are often considered too imprecise for practical applications. However, no mathematical framework for data analysis is reported in literature. In this paper, we present an improved experimental design and data analysis procedure together with a comprehensive framework for uncertainty assessment. Test runs in a 700 m-long watertight sewer showed no significant bias and a very high precision of the methodology. The standard error in the results was assessed to 2.6% of the labeled flow with a simplified model. It could be reduced to 1.2% when a dynamic data analysis procedure was applied. The major error contribution was caused by transient transport phenomena, which suggests that careful choosing of the experimental time is more important than the choice of a very specific tracer substance. Although the method is not intended to replace traditional CCTV inspections, it can provide complementary information for rational rehabilitation planning.