Molecular Vibrations Are Not Asymmetric.

There is considerable confusion when naming vibrations in infrared and Raman spectra. One of the most common errors is the identification of some stretching and bending vibrations as "asymmetric". There are no asymmetric vibrations as such vibrations incur rotations and translations. The correct term is antisymmetric and it is demonstrated, through molecular symmetry operations, why this is the correct term.

An unusual clandestine laboratory synthesis of 3,4-methylenedioxyamphetamine (MDA).

An unknown compound from a putative clandestine laboratory was analyzed by GC-MS, GC-IRD, IR (ATR), and NMR and found to be α-methyl-3,4-methylenedioxyphenylpropionamide (MMDPPA), an unusual precursor for the synthesis of 3,4-methylenedioxyamphetamine (MDA), a Schedule I controlled substance. A portion of this precursor was subjected to the Hofmann Degradation (i.e., Hofmann Rearrangement) reaction using a sodium hypochlorite solution (bleach) to produce the expected compound, MDA. When excess hypochlorite was used in the reaction, a second, unexpected, compound was formed. Use of the listed instrumentation identified the new material as 2-chloro-4,5-methylenedioxyamphetamine, a compound not previously identified in the forensic literature.

Novel search algorithms for a mid-infrared spectral library of cotton contaminants.

During harvest, a variety of plant based contaminants are collected along with cotton lint. The USDA previously created a mid-infrared, attenuated total reflection (ATR), Fourier transform infrared (FT-IR) spectral library of cotton contaminants for contaminant identification as the contaminants have negative impacts on yarn quality. This library has shown impressive identification rates for extremely similar cellulose based contaminants in cases where the library was representative of the samples searched. When spectra of contaminant samples from crops grown in different geographic locations, seasons, and conditions and measured with a different spectrometer and accessories were searched, identification rates for standard search algorithms decreased significantly. Six standard algorithms were examined: dot product, correlation, sum of absolute values of differences, sum of the square root of the absolute values of differences, sum of absolute values of differences of derivatives, and sum of squared differences of derivatives. Four categories of contaminants derived from cotton plants were considered: leaf, stem, seed coat, and hull. Experiments revealed that the performance of the standard search algorithms depended upon the category of sample being searched and that different algorithms provided complementary information about sample identity. These results indicated that choosing a single standard algorithm to search the library was not possible. Three voting scheme algorithms based on result frequency, result rank, category frequency, or a combination of these factors for the results returned by the standard algorithms were developed and tested for their capability to overcome the unpredictability of the standard algorithms' performances. The group voting scheme search was based on the number of spectra from each category of samples represented in the library returned in the top ten results of the standard algorithms. This group algorithm was able to identify correctly as many test spectra as the best standard algorithm without relying on human choice to select a standard algorithm to perform the searches.

Semiautomated depositor for infrared microspectrometry.

The measurement of minute samples is desirable in many areas of research and analysis, including biological, environmental, and forensic sciences. The use of manual solution direct deposition, combined with surface evaporation, is a very useful and convenient method for the transfer of many analytes to a spectroscopic sampling window. For Fourier transform infrared (FT-IR) spectrometric analysis, high quality attenuated total reflection (ATR) and transmission analyses are possible with suitable solution deposits. If the sample area is very small, placement of the analyte deposit on the active area of the sampling accessory must be done carefully. To achieve this, a novel direct deposition system has been developed. This system, a series of valves attached to a glass nebulizer, generates deposits that are reproducible, and placement of the deposits is precise. The valves allow the sample to be loaded, helium airflow to expel the sample, and the nebulizer to be cleaned after deposition. To help contain the sample to a small area once deposition has taken place, a vacuum line is attached to the nebulizer. This simple semiautomated deposition system allows for higher sensitivity and run-to-run reproducibility for minute sample analysis.

A metal nebulizer capillary electrophoresis/Fourier transform infrared spectrometric interface.

A capillary electrophoretic (CE) system has been successfully interfaced to a Fourier transform infrared spectrometer. The advantage of such an interface is that analytes may be detected and often unequivocally identified without analyte derivatization. The interface consists of a stainless steel tube in which the CE capillary is placed and the two are held in contact with the use of a metal tee. A solvent elimination approach is used with the interface, so that analytes are deposited onto an infrared transparent window, that is, CaF2, and measured with the use of an infrared microscope. A critical component of this design is to provide an electrical connection at the end of the CE column to permit stable separations that allow for efficient transport of the sample onto the window. The interface produces an aerosol that is directed at the surface of the infrared transparent window. The use of a volatile electrolyte, along with the flow of helium, allows for partial evaporation of the electrolyte in flight and complete evaporation of the solvent and electrolyte on the surface of the window to produce a "dry", or neat, analyte deposit.

Glass nebulizer interface for capillary electrophoresis-Fourier transform infrared spectrometry.

A capillary electrophoresis system has been successfully interfaced to a Fourier transform infrared spectrometer. The design of the interface is a custom-designed glass microconcentric nebulizer. Typical deposit characteristics include reproducible circular deposits of uniform thickness that lack any splatter as found in earlier designs. Interface performance is demonstrated in that there is no loss of electrical current during operation and spectra of analytes can be readily produced. Furthermore, it has been shown that the interface maintains the plug flow characteristic of capillary electrophoresis.