Anupam Giri

Molecular Characterization of Volatiles and Petrochemical Base Oils by Photo-Ionization GC×GC-TOF-MS

The characterization of organic mixtures by comprehensive two-dimensional gas chromatography (GC×GC) coupled to electron impact (EI) ionization time-of-flight mass spectrometry (TOF-MS) allows the detection of thousands of compounds. However, owing to the exhaustive fragmentation following EI ionization, despite the use of mass spectral libraries, a majority of the compounds remains unidentified because of the lack of parent ion preservation. Thus, soft-ionization energies leading to organic compounds being ionized with limited or no fragmentation, retaining the molecular ion, has been of interest for many years. In this study, photoionization (PI) was evaluated as the ion source for GC×GC-TOF-MS measurements. First, capabilities and limitations of PI were tested using an authentic mixture of compounds of several chemical classes. Ionization energy exhibited by PI, equivalent to 10.8 eV, resulted in significant retention of molecular ion information; [M]+• for alkanes, ketones, FAMEs, aromatics, [M-H]+• for chloroalkanes, and [M-H2O]+• for alcohols. Second, considering the potential of PI for hydrocarbons, base oils, complex mixtures of saturated and unsaturated hydrocarbons blended for finished lubricant formulations, were extensively evaluated. Several chemical classes of hydrocarbons were positively identified including a large number of isomeric compounds, both aliphatics and cyclics. Interestingly, branched-alkanes were ionized with lower excess internal energy, not only retaining the molecular ions but also exhibiting unique fragmentation patterns. The results presented herein offer a unique perspective into the detailed molecular characterization of base oils. Such unprecedented identification power of PI coupled with GC×GC-TOF-MS is the first report covering volatiles to low-volatile organic mixtures.

Determination of Thyreostats in Urine Using Supported Liquid Extraction and Mixed-Mode Cation-Exchange Solid-Phase Extraction: Screening and Confirmatory Methods

The application of thyreostats in livestock has been banned in the European Union since 1981, but these drugs are currently in the focus due to the natural occurrence of thiouracil (TU). Studies have been published on TU contamination in urine samples of animal and human origins without any drug administration of it. This paper presents new analytical methods to analyze thyreostats to support the legislation on the recommended concentration (RC) levels of these drugs. Both screening and confirmatory methods are developed for analyzing thyreostats in porcine and bovine urines using a liquid chromatography-tandem mass spectrometry technique. The new methods include a chemical derivatization with 3-iodobenzyl bromide, followed by novel purification approaches using supported liquid extraction and mixed-mode cation-exchange solid-phase extraction (SPE) for screening and confirmatory purposes, respectively. The optimized derivatization in combination with the cation-exchange SPE gives high sensitivity and reducing matrix effect of the analysis. The methods are validated in accordance with the guidelines for the validation of screening methods and European Commission Decision 2002/657/EC. The confirmatory method is used in the national monitoring plan. The detected levels of TU in urine samples are below the currently applicable RC level (10 μg L-1).