## 5 Particle Detectors
### Mass Spectrometry
#### 5.2.3 IRMS  
Isotope ratio mass spectrometry (IRMS) enables the measurement of natural isotopic abundance of stable elements in solid, liquid, and gaseous samples, with high degree of accuracy and precision, and is particularly well-suited for light isotopes (C, N, H, O, and S). The typical sensitivity of this technique is in the order of 10\({}^{-4}\) and the sample mass required is very small, in the order of hundreds of milligrams. The potential of this methodology lies in its ability to determine the origin and the pathway of a given substance in the environment, exploiting the natural effect of fractionation. Fractionation is the discrimination between the isotopes of an element as a consequence of the chemical-physical processes of translocation and transformation of the compounds of the element itself, from one environmental compartment to another one. As a result of fractionation, there may be an enrichment or decrease in a heavier isotope in the compound of interest, compared to a lighter one (normally the more abundant in nature) [270]. A typical example where fractionation takes place is the process of water evaporation: the lighter isotopes of H\({}_{2}\)O (\({}^{1}\)H e \({}^{16}\)O) go preferentially into the vapor phase, while the heavier isotopes (\({}^{2}\)H and \({}^{18}\)O) remain in liquid water. Since the differences in isotope abundance are typically very small in nature, by convention, the isotope ratio of a sample to a standard is measured in units per thousand (delta notion \(\delta\)), where the ratio R refers to that of the heavier isotope with respect to the lighter isotope; the most frequently measured isotopes are \({}^{13}\)C/\({}^{12}\)C (carbon), \({}^{15}\)N/\({}^{14}\)N (nitrogen), \({}^{34}\)S/\({}^{32}\)S (sulfur), \({}^{18}\)O/\({}^{16}\)O (oxygen) and \({}^{2}\)H/\({}^{1}\)H (hydrogen). Therefore, the delta notion is: 8(%) = (Rs/Rstd \(-\) 1) \(\times\) 1000, where Rs is the isotopic ratio of the sample and Rstd is that of the reference standard. All isotope ratios are referred to in terms of a primary standard. In the CH field, IRMS is widely exploited, as it provides new information about the diet and migrations of ancient populations, as well as the provenance of the raw materials used in archeological artifacts. Measurements of \(\delta^{13}\)C and \(\delta^{15}\)N [271,272] on bone collagen have allowed reconstructing the type of diet followed by the ancient populations, thus providing a contribution to the social study of our ancestors (for example, it has been possible to establish which individuals had easier access to more valuable foods, with a high protein content, and to identify the different social classes) [273,274]. The analysis of \({}^{13}\)C in fatty acids (C16:0 and C18:0) in the cooking residues of archaeological ceramic finds enables tracing the type of food used by the acients, distinguishing between vegetable and animal fats [275,276]. \(\delta^{13}\)C and \(\delta^{18}\)O on marbles enable tracing their origin, and, further, the quarries from which they were extracted. Again, the carbon isotopic characterization of the mortars is used to identify the carbon source origin [277] and the analysis of the oxygen isotopes can be useful to study the inorganic phase of bones, thanks to the link between the O isotopes relative abundances and the water drunk by an individual, making it possible to trace back its origin [278,279]. IRMS instrumentation is equipped with a multi-collector detection system, which enables continuous and simultaneous measurements. The advantage lies in the measurement of multiple isotopes in a single sample and in a single run. In the framework of INFN-CHNet, at the iCONa lab (isotopic C, O and N analysis laboratory) of the Distabit (Department of Environmental, Biological and Pharmaceutical Sciences and Technologies), University of Campania \"[PERSON]\", an Isotopic Ratio Mass Spectrometer (IRMS Delta V Advantage, Thermo Scientific) enables measuring very small samples, with a typical sensitivity of \(10^{-4}\).