Stable isotopic analysis of pyrogenic organic matter in soils by liquid chromatography–isotope‐ratio mass spectrometry of benzene polycarboxylic acids

Pyrogenic organic matter (PyOM), the incomplete combustion product of organic materials, is considered stable in soils and represents a potentially important terrestrial sink for atmospheric carbon dioxide. One well‐established method of measuring PyOM in the environment is as benzene polycarboxylic acids (BPCAs), a compound‐specific method, which allows both qualitative and quantitative estimation of PyOM. Until now, stable isotope measurement of PyOM carbon involved measurement of the trimethylsilyl (TMS) or methyl (Me) polycarboxylic acid derivatives by gas chromatography–combustion–isotope ratio mass spectrometry (GC‐C‐IRMS). However, BPCA derivatives can contain as much as 150% derivative carbon, necessitating post‐analysis correction for the accurate measurement of δ¹³ C values, leading to increased measurement error. Here, we describe a method for δ¹³ C isotope ratio measurement and quantification of BPCAs from soil‐derived PyOM, based on ion‐exchange chromatography (IEC‐IRMS). The reproducibility of the δ¹³ C measurement of individual BPCAs by IEC‐IRMS was better than 0.35‰ (1σ). The δ¹³ C‐BPCA analysis of PyOM in soils, including at natural and artificially enriched ¹³ C‐abundance, produced accurate and precise δ¹³ C measurements. Analysis of samples that differed in δ¹³ C by as much as 900‰ revealed carryover of <1‰ between samples. The weighted sum of individual δ¹³ C‐BPCA measurements was correlated with previous isotopic measurements of whole PyOM, providing complementary information for bulk isotopic measurements. We discuss potential applications of δ¹³ C‐BPCA measurements, including the study of turnover rates of PyOM in soils and the partitioning of PyOM sources based on photosynthetic pathways. Copyright © 2011 John Wiley & Sons, Ltd.     

Trace Determination of Domoic Acid in Sea Water and Phytoplankton by High-Performance Liquid Chromatography of the Fluorenylmethoxycarbonyl (FMOC) Derivative

Abstract

A method is presented for the trace determination of domoic acid, a neurotoxic amino acid responsible for cases of Amnesic Shellfish Poisoning resulting from the consumption of contaminated shellfish. The method involves pre-column derivatization with 9-fluorenylmethylchloroformate to form the FMOC derivative followed by reversed-phase HPLC with fluorescence detection. The detection limit for domoic acid in seawater and aqueous extracts is 15pg/mL (50 pM) using gradient elution, a 20μL injection volume, and a 2.1mm I.D. microbore column. Use of dihydrokainic acid as an internal standard improved quantitation. The method was applied to the detection of domoic acid in seawater, in phytoplankton cultures (Nitzschia pungens forma multiseries), and in natural mixed phytoplankton assemblages in estuarine waters.     

Selecting wave function states in open quantum dots

We study how wave function scarring in an open quantum dot is influenced as the strength of its environmental coupling is varied and show evidence for groups of wave function scars that recur periodically with gate voltage. The precise form of these scars is found to evolve with gate voltage, which we discuss in terms of the properties of the semi-classical orbits that give rise to the scars. We also provide convincing experimental evidence for a correlation between the scars and the oscillations observed in the conductance when the gate voltage is varied.     

Reveal for Salmonella test system.

The Reveal for Salmonella (RSS) test system is a presumptive qualitative test that detects the presence of Salmonella organisms in foods within 21 h total testing time, allowing the user to release negative products 24 h earlier than when using other rapid test kits. Foods are enriched with a proprietary resuscitation medium called Revive and then selectively enriched with either Selenite Cystine or Rappaport-Vassiliadis selective media. The enriched culture is used to inoculate the RSS detection device, which initiates a lateral flow through a reagent zone containing anti-Salmonella antibodies conjugated to colloidal gold particles that capture antigens present in the culture. The antigen-antibody complex migrates farther and is captured by an additional anti-Salmonella antibody, causing the colloidal gold to precipitate and form a visual line, indicating a positive result. A procedural control line also will form regardless of the presence of Salmonella organisms to indicate the test is working properly. Existing AOAC Official Methods for Salmonella organisms require a 48 h enrichment before testing. Hence, a food product has to be held before release, adding extra cost to the company and the consumer. The RSS test system was evaluated by quantitative spiking studies. Although AOAC encourages inclusion of naturally contaminated foods, almost all microbiological AOAC validation studies have been performed with artificially contaminated foods for absolute control over the study. The RSS test system is designed to test many food types for Salmonella organisms and has a limit of detection of 5-10 colony-forming units (cfu)/25 g with a false-negative rate of < 1% and a false-positive rate of < 5.0%. It showed an 81% overall agreement with the traditional procedure of the U.S. Department of Agriculture's Food Safety Inspection Service.     

A kinetic theory for polymer melts VI. calculation of additional material functions

The Curtiss-Bird constitutive equation is used to analyze three flows: large-amplitude oscillatory shearing; superposition of steady shear flow and small-amplitude oscillations; and eccentric disk rheometer flow. The corresponding Doi-Edwards theory results can be obtained as a special case by setting the link-tension coefficient equal to zero.     

Some stereochemical aspects of the pellizzari rearrangement

Variable temperature nmr spectroscopy and X-ray crystallography have been employed to study the stereochemistry of 2-cyano-3,3-dimethyl-1-phenylpyrazolidin-5-one which thermally rearranges to 2,3-dihydro-2,2-dimethylpyrimido[1,2-a]benzimidazol-4(1H)-one.     

A study of the thermal rearrangements of pyridine n-arylimines and of 5-aryl-4-hydroxypyrones,by differential scanning calorimetry

The rates of rearrangement of selected 2-methyl-4,6-diphenylpyridine N-arylimines and 5-aryl-3-carbomethoxy-4-hydroxy-6-methoxypyrones have been measured using differential scanning calorimetry and the energies and entropies of activation deduced. The mechanistic relevance of these observations is discussed.     

Interactions between two spheres falling along their line of centers in a viscoelastic fluid

An experimental investigation is presented in which the distance between two identical spheres falling along their line of centers in a viscoelastic fluid is determined as a function of time. It is found, for all five experimental fluids, that for small initial separations of the spheres, the two spheres eventually converge. However, for large initial separations, the two spheres eventually diverge. This leads to the definition of a critical initial separation distance. From this quantity a characteristic time can be derived for the two sphere fluid system which depends solely upon fluid properties. The implications of this study for suspension rheology are discussed.