EA-IRMS

Whereas conventional methods for analysing sulphur isotope compositions need >10 mg of physically separated sample and long analytical times, in contrast, the EA-IRMS technique uses small samples (1-2 mg) and has short analysis times. This achieves the high physical resolution and large sample populations needed for adequate study of biological variation in Archaean sulphide-rich organic sediments. 

The isotopic characterisation of organic compounds by classical elemental analysis with isotope ratio mass spectrometry (EA-IRMS) demands milligram amounts of pure compounds, which can not always easily be provided. Most analytes in flavour characterisation are volatile, and therefore, after their extraction, coupling of (capillary) gas chromatography (cGC) with IRMS would be an ideal tool for the isotope ratio analysis of the individual substances. For C- ]127, 128] and N-analysis ]179, 180] this has been realised for a long time by combining GC to IRMS via a combustion (C) unit (GC-C-IRMS), even for polar substances after their derivatisation ]181, 182]. 

Most flavourings are complex mixtures of many compounds. As IRMS makes only sense with pure analytes, a strict purification of individual substances is indispensable. Therefore GC-IRMS has been further developed and optimised to multi-compound isotope ratio analysis by its coupling IRMS to capillary (c) and multidimensional (MD) gas chromatography (see 6.2.2.2.2). This methodology demands a strict intrinsic control and standardisation [340] apart from the international standards (see Table 6.3) also secondary standards like the polyethylene foil IAEA-CH7 or the NBS22 oil are available from the IAEA in Vieima. However, as these substances are also not suitable for the direct standardisation of data from a coupled GC system for flavour isotope analysis, certificated tertiary laboratory standards for hydrogen have been developed by parallel analysis of flavour compounds by TC/EA-IRMS and MDGC-P-IRMS [210]. 

Organic matter content was estimated by combustion of the samples on an elemental analyzer (EA-IRMS) coupled to a DeltaPlus-XL Finnigan mass-spectrometer. None of the samples contained more Aan 0.2% organic carbon. 

BSIA The BSIA technique is based on the use of an automated sample preparation instrument for the conversion of the sample of interest into simple gases for IRMS analysis. This instrument is called an elemental analyzer (EA), which is coupled to the IRMS (elemental analyzer-isotope ratio mass spectrometer, EA-IRMS). The isotopic values obtained from analysis utilizing EA-IRMS represent the isotopic composition of the entire sample (i.e., if the sample consists of a complex mixture, then the isotopic composition will be of the combined mixture as opposed to the isotopic composition of the individual components in the mixture). 

Jasper et al. [44] address the potential for the use of EA-IRMS to characterize conunerdally available analgesic drugs as they leave the manufacturer for distribution. These data could be used to assist in the differentiation of production batches and assist in the identification of counterfeit materials on the market. Jasper et al. [45] reported on the analysis of the isotopic compositions of four different active pharmaceutical ingredients (APIs) from different manufacturers and different batches. Samples from different sources (manufacturers and/or batches) could be readily differentiated using EA-IRMS. Phillips et al. [23] also reported on research conducted by Jasper on differentiating pharmaceutical products from different batches using EA-IRMS. 

Paint and Varnish Finnigan Mat [86] analyzed the carbon and nitrogen isotope values in paint and varnish samples using an EA-IRMS. Differentiation of these samples was achieved based on a combination of the isotope values of the two elements. Farmer et al. [87] provide an overview of research conducted to determine the stable isotope composition of 51 white architectural paints. Carbon, oxygen and hydrogen isotope values were measured and likehhood ratio analysis applied to the data. While samples originating from different sources were differentiated, a false-positive rate of 2% was observed. 

Carter et al. [90] demonstrate the ability of EA-IRMS to link samples of pressure-sensitive adhesive tapes originating from the same batch. The majority of tape samples in the project could be discriminated based on the carbon isotopic composition of the intact samples. In cases where the samples could not be differentiated, analysis of the carbon isotopic composition of the polymer backing provided further discrimination. Additional classification could be achieved based on the hydrogen and oxygen isotopic composition of the intact tapes and the hydrogen isotopic composition of the backing materials. 

Soil Croft, as dted by Phillips et al. [23], and Croft and Pye [97] discuss research on the analysis of soil samples by EA-IRMS. The studies demonstrate that carbon and nitrogen isotope data can be useful when trying to differentiate different soil types and samples from different origins. Pye et al. [98] also measured the bulk carbon and nitrogen isotope values of different soil samples. Two different sites of interest could be discriminated based on the stable isotope data however, the need for a multitechnique approach was emphasized. 

Finnigan Mat [86] report that different lots of explosives can be distinguished from each other based on carbon and nitrogen isotope ratios. Lots of explosives generally refer to explosives that are manufactured by a continuous process as opposed to batches which are made in discrete groups with set quantities of starting materials. TNT samples were collected from three different sources, analyzed by EA-IRMS, and the results compared. The authors highlighted that further research was needed to determine whether the isotope ratio values were a result of different production sites, different lots of substrate in the production process, or postproduction adulteration. 

Beardah [105] summarizes the final year of the PEL, DSTL project, reporting on results that confirmed that EA-IRMS would generally be able to discriminate between samples from different batches from the same manufacturer. Preliminary results on the analysis of triacetone triperoxide (TATP) samples were also addressed. The overall need for further work and collaboration in specific areas was addressed. 

Belanger, as cited by Phillips et al. [23], discusses the analysis of the isotopic composition of various explosives (including AN, gunpowder, TNT, cyclotrimethyl-enetrinitramine [RDX], and nitroglycerine [NG]). The work confirmed that there was a range of carbon and nitrogen isotope ratio values in the samples when analyzed with EA-IRMS. The analyses of oxygen and sulfur isotope ratios in various samples were also discussed. 

IRMS can be used to assist in the determination of the origin of oil spills and other forms of contamination in the environment. Philp [116] provides an overview of the application of IRMS (both GC-IRMS and EA-IRMS) in environmental and forensic geochemistry. 

Ehleringer et al. [148] report on the analysis of carbon and nitrogen isotopes in heroin and cocaine using EA-IRMS. 

Casale et al. [151] discuss the important issue of isotopic fractionation of carbon and nitrogen isotope values that may occur during the illicit synthesis of cocaine and heroin. Casale et al. [152] also discuss a case study where EA-IRMS and GC-IRMS were utilized to determine that heroin samples seized from the merchant vessel Pong Su were isotopically distinct from the known origin/process classihcations of Southwest Asian, Southeast Asian, South American, and Mexican. 

Idoine et al. [155] cover the use of GC-IRMS and EA-IRMS for the measurement of C, N, O, and H isotopes in heroin and cling film. The authors report that a combination of the C, N, O, and H results from EA-IRMS is able to distinguish between most samples of bulk heroin and also cling films grouped according to seizure. GC-IRMS was utilized to successfully analyze sample impurities. 

Denton et al. [157] analyzed the carbon and nitrogen isotopic composition of C. saliva L. using EA-IRMS to try and determine the country of origin of seized cannabis leaves. The authors also evaluated how growing conditions influenced the isotopic composition of samples. The isotopic composition of plants from Australia, Papua New Guinea, and Thailand did not allow differentiation between... 

Dautrarx et al. [24] discuss the successful analysis of carbon isotope values in heroin samples containing acetaminophen (a cutting agent used as an adulterant) using EA-IRMS and GC-IRMS. Potential isotopic fractionation effects during sample handling, preparation, and analysis were discussed. 

Figure 4.24 Reproducibility and accuracy of P T-irm-GC-MS. Plotted are the differences from the pure liquid standards measured by EA-IRMS and the horizontal bars correspond...

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