Identifying Fenton-Reacted Trimethoprim Transformation Products Using Differential Mobility Spectrometry.

A transformation product of trimethoprim, a contaminant of emerging concern in the environment, is generated using an electro-assisted Fenton reaction and analyzed using differential mobility spectrometry (DMS) in combination with MS/MS techniques and quantum chemical calculations to develop a rapid method for identification. DMS is used as a prefilter to separate positional isomers prior to subsequent identification by mass spectrometric analyses. Collision induced dissociation of each DMS separated species is used to reveal fragmentation patterns that can be correlated to specific isomer structures. Analysis of the experimental data and supporting quantum chemical calculations show that methylene-hydroxylated and methoxy-containing phenyl ring hydroxylated transformation products are observed. The proposed methodology outlines a high-throughput technique to determine transformation products of small molecules accurately, in a short time and requiring minimal sample concentrations (<25 ng/mL).

Signal enhancement in laser diode thermal desorption-triple quadrupole mass spectrometry analysis using microwell surface coatings.

Laser-diode thermal desorption (LDTD) is an ionization source usually coupled to triple quadrupole mass spectrometry (QqQMS) and specifically designed for laboratories requiring high-throughput analysis. It has been observed that surface coatings on LDTD microwell plates can improve the sensitivity of the analysis of small polar molecules. The objective of the present study is to understand and quantify the effect of microwell surface coatings on signal intensity of small organic molecules of clinical, environmental, and forensic interest. Experiments showed that the peak areas of diclofenac, chloramphenicol, salicylic acid, and 11-nor-9-carboxy-Δ9 -tetrahydrocannabinol obtained by LDTD-QqQMS increased by up to 3 orders of magnitude when using microwells coated with ethylenediaminetetraacetic acid (EDTA). Tests with different chelating agents and polytetrafluoroethylene as microwell surface coatings showed that nitrilotriacetic acid gave significantly higher peak areas for five out of the nine compounds that showed signal enhancement using chelating agents as coatings. Scanning electron microscopy studies of EDTA-coated and uncoated microwells showed that analytes deposited in the former formed more uniform and thinner films than in the latter. The enhancement effect of surface coatings in LDTD-QqQMS was explained mainly by the formation of homogenous and thinner layers of nanocrystals of analytes that are easier to desorb thermally than the layers formed when the analytes dry in direct contact with the bare stainless-steel surface. Chemisorption of some analytes to the stainless-steel surface of the microwell plate appeared to be a minor factor. Surface coatings widen the number of compounds analyzable by LDTD-QqQMS and can also improve sensitivity and limits of detection.

Impact of water stagnation in residential cold and hot water plumbing on concentrations of trihalomethanes and haloacetic acids.

This study demonstrates that levels of trihalomethanes (THMs) increase considerably when cold water stagnates in residential pipes and, more significantly, when water remains in the hot water tank. Levels of haloacetic acids (HAAs) increase as well in both cases, but less significantly in comparison to THMs. The study also demonstrates that in both the plumbing system and residential hot water tank, chlorinated and brominated DBP species do not behave in the same manner. Finally, the study shows that sustained use of water in households helps to maintain THM and HAA levels close to those found in water of the distribution system. The results are useful to identify methods of indoor water use that minimize population exposure to DBPs and improve DBP exposure assessment for epidemiological studies.