Spectroscopy-07-01-2016

In the “Molecular Spectroscopy Workshop” column, we have been trying to provide hands-on advice and easy-to-implement tips to start using spectroscopic tools for the analyst who has the responsibility to derive answers to questions as quickly as possible. Very often the identity of an unknown is of ultimate importance, and very few analytical chemists coming out of graduate programs have been taught to systematically analyze spectra to infer identity of the source. In addition, it is rare that an industrial environment will provide resources for the analyst to be educated in this field. Thus, the availability of any means to provide spectral identification will make the difference between success and failure; that is, acquiring a spectrum is useless if one cannot identify it. In this column, I discuss some of the fundamentals of spectral interpretation, illustrate the use of searching software, including mixture analysis, and show how sometimes the software can provide spectral interpretation.

This month’s column will describe a novel ED-XRF system, which utilizes a combination of a Bragg polarizer, used simultaneously with a direct excitation source, together with a novel, highly annealed pyrolytic graphite (HAPG) crystal as a band-pass filter. By selection of the optimum configuration, it will allow for high precision of minor and major elements across a wide wavelength range and/or lower detection capability for smaller groups of elements from potassium to manganese. To show the practical benefits of this technology, this study will focus on these performance metrics for the determination of titanium in polymer samples, together with the multielement analysis of high purity graphite using the ashing sample preparation method. In particular, it will be shown that the improved performance for graphite will allow for lower sample weights to be used resulting in significantly shorter ashing times, which is a requirement for high sample workload laboratories and process control applications.

This article verified the Brill transition in nylon 6,6 by Raman spectroscopy through heating and cooling processes of the sample. When nylon is heated at around 160 C a crystalline phase transition occurs from a triclinic structure at room temperature to a pseudohexagonal structure above that temperature. This phase transition is known as the Brill Transition. With temperature-dependent Raman scattering measurements, it was possible to determine the vibrational behavior of nylon 6,6 during the Brill transition, and consequently to identify the main Raman bands associated with the Brill transition.

This installment begins with a needed discussion on the theory behind the three different types of infrared bands, how to recognize them, and how to use them to help you interpret spectra. Continuing on from the last column, this knowledge is used to help better distinguish mono- and di-substituted benzene rings from each other.

Several leading scientists discuss recent developments and trends in XRF and XRD techniques.

Click the title above to open the Spectroscopy July 2016 regular issue, Vol 31 No 7, in an interactive PDF format.