Direct determination of melamine in dairy products by gas chromatography/mass spectrometry with coupled column separation

A coupled capillary column system was developed for the qualitative and quantitative determination of melamine with isotope internal standard in dairy products by gas chromatography/mass spectrometry (GC/MS) without derivatization. A 30 m of DB-5ms ((5%-phenyl)-methylpolysiloxane, 0.25 mm i.d., 0.25 μm df) coupled with a 1.5 m of Innowax (polyethylene glycol, 0.32 mm i.d., 0.25 μm df) by a quartz capillary column connector was introduced as separation column. Three advantages were discussed for the coupled system. The sample was fortified with a ring-labeled ¹³C₃¹⁵N₃-melamine as an isotope internal standard and extracted by 1% of trichloroacetic acid aqueous solution. 2.2% of lead acetate solution was then added to deposit protein in the sample matrix. After purification by cation exchange cartridge, the sample solution was directly injected and detected by GC/MS. A six-point calibration curve ranging from 0.05 to 2 mg kg⁻¹ of melamine in sample was used to establish instrument response. The recovery was 93.9-102% with relative standard deviation from 3.1 to 8.7% when isotope internal standard used. The calculated method detection limit was 0.01 mg kg⁻¹.     

Quantification of fructo-oligosaccharides based on the evaluation of oligomer ratios using an artificial neural network

The application of an internal standard in quantitative analysis is desirable in order to correct for variations in sample preparation and instrumental response. In mass spectrometry of organic compounds, the internal standard is preferably labelled with a stable isotope, such as ¹⁸O, ¹⁵N or ¹³C. In this study, a method for the quantification of fructo-oligosaccharides using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI TOF MS) was proposed and tested on raftilose, a partially hydrolysed inulin with a degree of polymeration 2-7. A tetraoligosaccharide nystose, which is chemically identical to the raftilose tetramer, was used as an internal standard rather than an isotope-labelled analyte. Two mathematical approaches used for data processing, conventional calculations and artificial neural networks (ANN), were compared. The conventional data processing relies on the assumption that a constant oligomer dispersion profile will change after the addition of the internal standard and some simple numerical calculations. On the other hand, ANN was found to compensate for a non-linear MALDI response and variations in the oligomer dispersion profile with raftilose concentration. As a result, the application of ANN led to lower quantification errors and excellent day-to-day repeatability compared to the conventional data analysis. The developed method is feasible for MS quantification of raftilose in the range of 10-750 pg with errors below 7%. The content of raftilose was determined in dietary cream; application can be extended to other similar polymers. It should be stressed that no special optimisation of the MALDI process was carried out. A common MALDI matrix and sample preparation were used and only the basic parameters, such as sampling and laser energy, were optimised prior to quantification.     

An overview of analytical methodologies for the determination of antibiotics in environmental waters

The widespread occurrence of antibiotics as contaminants in the aquatic environment has increased attention in the last years. The concern over the release of antibiotics into the environment is related primarily to the potential for the development of antimicrobial resistance among microorganisms. This article presents an overview of analytical methodologies for the determination of quinolone (Qs) and fluoroquinolone (FQs), macrolide (MLs), tetracycline (TCs), sulfonamide (SAs) antibiotics and trimethoprim (TMP) in different environmental waters. The analysis of these antibiotics has usually been carried out by high-performance liquid chromatography (HPLC) coupled to mass spectrometry (MS) or tandem mass spectrometry (MS/MS) and to a lesser extent by ultraviolet (UV) or fluorescence detection (FD). A very important step before LC analysis is sample preparation and extraction leading to elimination of interferences and prevention of matrix effect and preconcentration of target analytes.     

Determination of thyreostats in urine and thyroid gland by ultra high performance liquid chromatography tandem mass spectrometry

Thyreostatic compounds could be illegally administered to animals in order to obtain a weight gain due to a higher retention of water in the edible tissue and the gastro-intestinal tract. In the European Union their use for animal production is banned since 1981. Recently a highly sensitive method exploiting the determination of thyreostats with 3-iodobenzylbromide prior to purification to determine thyreostats in urine and other matrices was reported. For the first time, the UPLC instrumentation was used to separate the 3-iodobenzyl derivatives of various thyreostats. The deuterated internal standards tapazole-d₃ and propylthiouracil-d₅ were for the first time used for the quantification of tapazole, thiouracil, methylthiouracil, propylthiouracil, phenylthiouracil and mercaptobenzimidazole. The confirmative quantitative liquid chromatographic tandem mass spectrometric (LC–MS/MS) method was validated according to Commission Decision 2002/657/EC. The decision limit (CCα) and the detection capability (CCβ) were found to be for all compounds below the recommended value of 10 μg kg⁻¹.     

Multi-method for the determination of antibiotics of different substance groups in milk and validation in accordance with Commission Decision 2002/657/EC

The presented method is able to analyse 47 substances of the antibiotic groups tetracyclines, quinolones, macrolides, sulfonamides, diamino-pyrimidine derivatives and lincosamides simultaneously in a single analytical run. Applying an in-house validation concept, the validation of the multi-method was successfully accomplished with a low number of experiments. Each substance was validated at least at the concentrations 0.5, 1.0 and 1.5 MRL (maximum residue limit), or respectively, at concentrations as low as possible for substances without MRL. The calculated relevant validation parameters, e.g. the decision limit CCα, the detection capability CCβ, the repeatability, the within-laboratory reproducibility and the recovery, are in an acceptable range and in compliance with the requirements of Commission Decision 2002/657/EC. A proficiency test and the implementation of the method by other laboratories were performed successfully.     

Application of ultra-high-pressure liquid chromatography–tandem mass spectrometry to the determination of multi-class pesticides in environmental and wastewater samples: Study of matrix effects

An ultra-high-pressure liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) method for the determination of 37 pesticides (herbicides, insecticides and fungicides) in environmental and wastewater has been developed. To efficiently combine UHPLC with MS/MS, a fast-acquisition triple quadrupole mass analyzer was used. This analyzer (minimum dwell time, 5 ms) allows acquiring up to three simultaneous transitions in the selected reaction monitoring mode for each compound assuring a reliable identification without resolution or sensitivity losses. A pre-concentration step based on solid-phase extraction using Waters Oasis HLB cartridges (0.2 g) was applied with a 100-fold pre-concentration factor along the whole analytical procedure. The method was validated based on European SANCO guidelines using surface, ground, drinking and treated water (from an urban solid residues treatment plant) spiked at two concentration levels (0.025 and 0.1 μg/L), the lowest having been established as the limit of quantification objective. The method showed excellent sensitivity, with instrumental limits of detection ranging from 0.1 to 7 pg. It was applied to environmental water samples (ground and surface water) as well as to samples of urban solid waste leachates (raw leachate and treated leachate after applying reversed osmosis) collected from a municipal treatment plant. Matrix effects have been studied in the different types of water samples analyzed, and several isotope-labelled internal standards have been evaluated as a way to compensate the signal suppression observed for most of the compounds studied, especially in wastewater samples. As a general remark, only those pesticides which response was corrected using their own isotope-labelled molecule, could be satisfactorily corrected in all type of samples, assuring in this way the accurate quantification in all matrix samples.     

Effect of stability of internal standard on quantification of 15 flavonoids in Epimedium using CZE

A CZE method was developed for the simultaneous determination of 15 flavonoids, including epimedin B, epimedin A, hexandraside F, epimedin C, icariin, sagittatoside B, sagittatoside A, hexandraside E, 2′′‐O‐rhamnosyl icariside II, baohuoside VII, baohuoside I, caohuoside C, epimedoside C, baohuoside II, and kaempferol‐3‐O‐rhamnoside, in different species of Epimedium, and the effect of stability of internal standard (IS) on quantification was also investigated. As a result, rutin was not available for use as an IS because of its unstable property in sample solution, which suggested that the stability of IS both in standards and sample solution should be considered for the analysis. Using stable daidzein as IS, the analysis was performed within 35 min by using 50 mM borax buffer containing 20% ACN as a modifier (pH 10.0), while separation voltage was 25 kV and temperature was at 30°C. The method was validated to be accurate, simple, and repeatable, and was successfully applied to the analysis of 36 samples from 17 species of Epimedium.     

Quantitative determination of 16 polycyclic aromatic hydrocarbons in soil samples using solid‐phase microextraction

A method for the determination of polycyclic aromatic hydrocarbons (PAHs) in soil samples using ultrasonic‐assisted extraction with internal surrogates combined with solid‐phase microextraction and GC‐MS has been developed. Five kinds of commercial solid‐phase microextraction fibers, 100 μm PDMS, 30 μm PDMS, 65 μm PDMS/DVB, 50 μm DVB/CAR/PDMS and 85 μm PA, were compared to choose the optimal SPME fiber for extraction of PAHs. One hundred micrometers of PDMS fiber was found to be more suitable for the determination of PAHs due to its wider linear range, better repeatability, lower detection and more satisfactory efficacy than the other fibers. Under the recommended conditions, 100 μm PDMS fiber could provide low nanogram level detection limits with correlation coefficient greater than 0.98. The method was also applied to determine PAHs in a spiked soil sample, obtaining recoveries higher than 79.3%. A field study with naturally contaminated samples from local contaminated sites was carried out. The proposed method was found to be a reliable, inexpensive and simple preparation method for quantitative determination of 16 PAHs in soil samples.     

A note on neutral elements in posets

Neutral elements and central elements are characterized in different classes of posets such as sectionally semi-complemented posets, atomistic posets etc.      

常见连续型统计分布的一点注记

正态分布是概率论与数理统计中最重要的一个分布,本文讨论了常见的连续型统计分布与标准正态分布间的关系,结果表明:几乎所有的常见连续型统计分布都是标准正态分布的函数.