L-Malate Determination in Wines and Fruit Juices by Flow Injection Analysis Adaptation of a Coupled Dehydrogenase/Transferase System

Abstract

A flow injection system for the enzymatic determination of L-malate is described. It is adapted for the analysis of wines and fruit juices by in-line sample dilution. Malate dehydrogenase (MDH) and aspartate aminotransferase (AST) were coimmobilized on controlled pore glass. The NADH generated in the packed bed bienzyme reactor was detected fluorimetrically. Sufficient L-malate conversion could be achieved using the coupled transferase reaction to transform the reaction product oxaloacetate. The linear range of the unmodified flow injection system, 5 – 100 μ M of L-malate, could be increased up to 50 mM by means of zone sampling so that untreated samples could be analyzed directly. From 12 – 20 samples per hour could be analyzed with a standard deviation of less than 2 % depending on variation in the degree of dilution. The activity of the bienzyme reactor decreased less than 4% over an analysis period of 3 weeks with more than 1200 injections.     

A Low Cost Gas Sampling Valve and Gc Set-Up for Analysis of Low Concentration Gas Mixtures

Abstract

A gas sampling valve suitable for on-line injection of low pressure (< 0.5 torr) gas mixtures is described. Its advantages over the commercially available valves are enumerated. An error of < 3 per cent due to non-reproducibility in sample injection was observed. A simple arrangement of column and hot wire detector together with this valve enabled quantitative separation of CO and O₂ with a lower limit of ～ 1 × 10^?7 moles for each component.     

Microprobe sampling—Photo ionization-time-of-flight mass spectrometry for in situ chemical analysis of pyrolysis and combustion gases: Examination of the thermo-chemical processes within a burning cigarette

A microprobe sampling device (μ-probe) has been developed for in situ on-line photo ionization mass spectrometric analysis of volatile chemical species formed within objects consisting of organic matter during thermal processing. With this approach the chemical signature occurring during heating, pyrolysis, combustion, roasting and charring of organic material within burning objects such as burning fuel particles (e.g., biomass or coal pieces), lit cigarettes or thermally processed food products (e.g., roasting of coffee beans) can be investigated. Due to its dynamic changes between combustion and pyrolysis phases the cigarette smoking process is particularly interesting and has been chosen as first application. For this investigation the tip of the μ-probe is inserted directly into the tobacco rod and volatile organic compounds from inside the burning cigarette are extracted and real-time analyzed as the glowing front (or coal) approaches and passes the μ-probe sampling position. The combination of micro-sampling with photo ionization time-of-flight mass spectrometry (PI-TOFMS) allows on-line intrapuff-resolved analysis of species formation inside a burning cigarette. Monitoring volatile smoke compounds during cigarette puffing and smoldering cycles in this way provides unparalleled insights into formation mechanisms and their time-dependent change. Using this technique the changes from pyrolysis conditions to combustion conditions inside the coal of a cigarette could be observed directly. A comparative analysis of species formation within a burning Kentucky 2R4F reference cigarette with μ-probe analysis reveals different patterns and behaviors for nicotine, and a range of semi-volatile aromatic and aliphatic species.     

Improvement on Analyte Extraction by Molecularly Imprinted Polymer Microspheres toward Enrofloxacin

Abstract

A collection of molecularly imprinted polymer microspheres (MIPMs) for Enrofloxacin (ENRO) were for the first time obtained through suspension polymerization in this work. The appropriate MIPMs used as specific SPE adsorbents were selected based on evaluation of binding capacities and morphology characterization. Combined with one simpler MISPE procedure for cleanup and preconcentration of ENRO in milk, further HPLC-UV analysis showed improved sensitivity of 10 µg kg^?1 than those reported in previous studies, with the desirable recoveries of 73.6–101.6%, proving that the developed MIPMs are applicable for extraction of ENRO during the process of sample preparation.     

Use of Solid Phase Microextraction (SPME) with Ion Mobility Spectrometry∗

Abstract

We report the use of solid phase microextraction (SPME) combined with ion mobility spectrometry (IMS) for sampling, screening and identification of organic compounds that are readily detected by IMS. This is a new SPME application. SPME has emerged recently as an excellent sample preparation technique for gas chromatography (GC) and high performance liquid chromatography (HPLC). We have found that SPME can be used very conveniently with IMS. An example of SPME-IMS is described using SPME headspace sampling at room temperature with 0.1 mL vials containing 1.0 microgram or less of either cocaine freebase or cocaine hydrochloride. This is followed by analysis using IMS. A hole, drilled in the IMS sample ticket holder, serves as the SPME-IMS interface.

     

Sampling and Sample Homogeneity as Introductory Topics in Analytical Chemistry Undergraduate Courses

This work deals with the development of an experiment to evaluate the effect of sample characteristics on precision and accuracy of the sampling step. Parameters such as sample homogeneity, particle sizes, and sample mass were evaluated by analyzing the standard deviations (n = 3) obtained for Ca, Fe, Mg, Na, P, S, and Zn determinations in a breakfast cereal sample by inductively coupled plasma optical emission spectrometry. The proposed experiment can improve the assimilation of important concepts such as sampling, sample representativity, precision and accuracy by undergraduate students in analytical chemistry laboratory courses.     

Determination of Trace Elements in Biological Standard Reference Materials by Graphite Furnace Atomic Absorption Spectrometry with Solid and Slurry Sampling

Compared to conventional dissolution methods, solid and slurry sampling methods offer advantages which include speed, improved sensitivity, a reduced risk of contamination, and a reduced risk of analyte loss. Most successful graphite furnace atomic absorption spectrometry (GFAAS) results have been obtained by the use of modern furnace technology, which includes Zeeman background correction, platform atomization, and matrix modifiers. In this work, solid and slurry sampling were investigated for the determination of Ag, Cu, Fe, Mn, Pb, and Zn in biological National Institute of Standards and Technology (NIST) standard reference materials (SRMs) with the use of vintage (1980) GFAAS instrumentation, aqueous calibration, and deuterium arc background correction. Although reasonable accuracy was obtained with solid sampling, the relative standard deviation was between 13 and 53%, which was probably caused by the inability of the furnace to reproducibly vaporize the sample and the inability of deuterium arc background correction to account for the high background signals. Good accuracy and precision (3–13%) were obtained with slurry sampling, with the exception of the determination of copper in citrus leaves. This low result (three times below the certified value) and high precision (RSD = 31%) were probably caused by irreproducible atomization of the sample matrix.     

Linear quantification calibration of crystallinity based on a simple univariate analysis of binary chemical images by selecting a threshold to define the sampling depth in Raman mapping

It is common belief that in Raman mapping, the sampling depth from which Raman signal is collected originates from a probe laser spot size of approximately 1–5 µm³. Actually, the active pharmaceutical ingredient (API) crystals detected by mapping on the sample surface distribute from surface to over a few tens to hundreds of microns into the sample, as determined by z‐slices mapping in this context. It was also found that the score of API crystals detected in a chemical image decrease with their depth into the sample. Therefore, a larger threshold of the binary chemical images can be used to restrict the sampling depth and consequently eliminate the problem of ‘saturation’ by quantifying merely the amount of API crystals within a sampling volume equivalent to a smaller sampling depth rather than the overall detected crystalline API in the chemical images. Eventually, one single linear quantification calibration was established over the crystallinity from sub‐percent (<1%) to over 20% w/w of a model sample by using a simple univariate analysis of binary chemical images method. Copyright © 2013 John Wiley & Sons, Ltd.     

Current Status of Direct Solid Sampling for Electrothermal Atomic Absorption Spectrometry—A Critical Review of the Development between 1995 and 2005

Abstract

The literature about direct solid sampling (SS) and slurry sampling atomic absorption spectrometry (AAS) over the past decade has been surveyed critically. It became apparent that a very significant change had occurred, particularly in the relation between the two major techniques used for that purpose. In the 1990s, slurry sampling was typically considered the technique of choice, combining the significant advantages of the solid and the liquid sampling methods, at least in part because of the availability of a commercial accessory for automatic slurry sampling. The situation is completely inverted now, as the above accessory has been discontinued and rugged and reliable accessories for direct SS became available. Direct SS electrothermal (ET) AAS has been shown to provide the best limits of detection because of the absence of any dilution and a minimal risk of contamination. Calibration against aqueous standards appears to be feasible after careful program optimization. The absence of any significant sample handling makes SS ET AAS ideally suited for fast screening analyses. The introduction of high‐resolution continuum source AAS appears to open additional attractive features for SS ET AAS because of the significantly simplified optimization of furnace programs and the visibility of the spectral environment, which makes it easy to avoid spectral interferences. New calibration strategies make a “dilution” of samples unnecessary, which used to be one of the major limitations of SS ET AAS. Finally, direct SS analysis is an important contribution to clean chemistry, as practically no reagents are used.     

Speciation Analysis of Mercury in Aquatic Environment

Abstract

This review considers methods for mercury speciation with low limits of detection that can be applied to real aquatic environmental samples (waters, sediments, biological tissues). Special attention is given to the necessity of clean sampling procedures and the proper storage of the samples. In this review, different extraction techniques for sediments and biological tissues are considered. The performance of different separation techniques, like liquid chromatography and off‐line and on‐line gas chromatography, are compared for their environmental applications.