Articles

Extraction of Aerosol Defence Pepper Spray Residues on Clothing and Analysis by GC–MS
Gino Van Vaerenbergh and Jab Verstraeten
The use of aerosol defence pepper sprays for self-defence and as an assault weapon has increased globally. The residue of these sprays is often left behind as physical evidence on a victim’s clothing or personal belongings. A rapid and accurate method was developed for the qualitative determination of capsaicin and its most important analogues: dihydrocapsaicin and nordihydrocapsaicin on clothing.

Trace Metabolic Profiling and Pathway Analysis of Clomazone Using Liquid Chromatography Coupled with Triple Quadruple-Linear Ion Trap Mass Spectrometry in Predictive Multiple Reaction Monitoring Mode
Wei Zou, Hagai Yasuor, Albert J. Fischer, and Vladimir V. Tolstikov
Detection, analysis, and characterization of low-abundant metabolites remain an unresolved problem in metabolic studies. In the present study, we report a novel approach addressing this challenge. This current methodology derived from the predictive multiple reaction monitoring (pMRM) mode available on triple quadruple-linear ion trap mass spectrometers. pMRM mode could offer the highest sensitivity among various acquisition modes in studying trace levels of metabolites of herbicide clomazone in plants. In addition, pMRM mode allowed identification of positional isomers of metabolites. Unknown metabolites were further identified and validated by obtaining accurate masses and isotopic ratios using selected ion monitoring (SIM) and data-dependent MS-MS scans on high resolution LC–MS.

Columns

LC Troubleshooting: Locating Precision Problems
John W. Dolan
Too much variability in your LC method? This month’s column looks at how to track down the problem source.

GC Connections: Valves for Gas Chromatography: Fluidic switching applications
John Hinshaw
Previous installments in this series covered the basics of valving and its applications in gas chromatography. This month, John Hinshaw discusses the use of fluidic switching devices for open-tubular column manipulations such as heart-cutting and comprehensive multidimensional GCXGC.

Practical Data Handling: Variable Selection and Reduction in Multivariate Calibration and Modelling
Yvan Vander Heyden
Multivariate calibration and modelling are often used in the pharmaceutical industry to build predictive models. Many different modeling techniques can be used for that. However, each of these techniques usually requires either a variable selection step to limit the number of variables to built the model, or creates so-called latent variables to built the simple models. Many variable selection methods have been applied. An overview of these will be discussed In cases where latent variables are used, the models based on the entire data set usually are not as good as when first information-less variables are eliminated. In such cases different possibilities exist to reduce the number of variables used to calculate the latent variables.

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