Qualitative properties and stabilizability of a model for blood thrombin formation

We perform a qualitative analysis of a differential equation that was originally introduced by Stortelder, Hemker and Hemker to model the formation of thrombin, and discuss issues of controllability and stabilizability. Results include a general proof of convergence to equilibrium, and of local exponential stabilizability.     

Determination of polybrominated diphenyl ethers in milk samples. Development of green extraction coupled techniques for sample preparation

Ultrasound‐assisted extraction (UAE), cloud point extraction (CPE), and ultrasound back‐extraction (UABE) techniques have been coupled for lixiviation, preconcentration, and cleanup of polybrominated diphenyl ethers (PBDEs) from milk samples for determination by gas chromatography‐electron capture detection (GC‐ECD). Physicochemical parameters that affect the efficiency of the extraction system were investigated using a design of experiments based on multivariate statistical tools, and considering the sample matrix along the development. The coupling of the leaching step, UAE, enhanced ca. 3.5 times the extraction efficiency of the former sample preparation methodology (CPE‐UABE) leading to cleaner sample extracts suitable for GC analysis. Under optimum conditions, the proposed methodology exhibits successful performance in terms of linearity and precision, with recoveries in the range of 68–70% and LODs within the range 0.05–0.5 ng/g dry weight (d.w.). The proposed sample preparation methodology coupled three green analytical techniques. It expands the application frontiers of CPE for the analysis of biological samples by GC. The optimized methodology was used for determination of PBDEs in powder milk samples, from both commercial and human sources.     

Crosslinking network structure governing particle shape and size distribution by one-step emulsion polymerization in the presence of particle coagulation

In this study, sub-200?nm, crosslinked latex particles with a narrow particle size distribution were prepared by one-step emulsion polymerization in the presence of particle coagulation. The relationship between the particle shape and particle coagulation was investigated by varying the time of crosslinking network structure formation and particle coagulation. Particles with irregular shapes such as doublet, triplet, and ellipsoid were obtained using divinylbenzene (DVB) and ethylene glycol dimethacrylate (EGDMA) as the crosslinking agents, because the crosslinking network structure of particles was formed before the particle coagulation. In contrast, latex particles with a uniform spherical shape were also prepared using triallyl isocyanurate (TAIC) or dihydrodicyclopentadienyl acrylate (DCPA) as the crosslinking agents by delaying the time of crosslinking network structure formation. Alternatively, uniform spherical latex particles were prepared by bringing forward the particle coagulation time using cationic initiator, 2, 2′-azobis (2-methylpropionamidine) dihydrochloride (AAPH). This study presents a new idea that would further broaden the application of particle coagulation in emulsion polymerization.     

Ca~(2+)增敏米诺环素荧光显微成像技术应用于米诺环素的检测

应用固载表面毛细流自组装环荧光显微成像技术,建立了Ca2+增敏米诺环素荧光体系测定牛奶中米诺环残留量的分析方法。将米诺环素溶液与一定量的氯化钙溶液,pH 8.50的氨性缓冲溶液及PVA-124溶液充分混合均匀。反应10 min后,滴在疏水性载玻片表面上,微波加热,溶剂受热挥发后,形成直径约为1.7 mm,环带宽约为45.3μm的自组装环。当点样体积为0.3μL时,线性范围为5.6×10-13~1.8×10-11mol,方法的检出限(3σ)为5.6×10-14mol。应用于米诺环素胶囊中米诺环素和牛奶中残留米诺环素的检测,回收率分别为104.3%~105.0%和96.0%~105.9%,相对标准偏差(n=5)小于3.5%。     

Determination of dimethylselenide and dimethyldiselenide in milk and milk by-products by solid-phase microextraction and gas chromatography with atomic emission detection

A method based on solid-phase microextraction (SPME) followed by gas chromatography with microwave-induced plasma atomic emission detection for determining dimethylselenide (DMSe) and dimethyldiselenide (DMDSe) in milk and milk by-products is proposed. Parameters affecting the SPME, such as sample volume or mass, ionic strength, adsorption and desorption times and temperatures were optimized in the headspace mode. The matrix effect was evaluated for the different samples studied, concluding that standard additions calibration was required for quantification purposes. The detection limits ranged from 70 to 110 pg mL⁻¹ for DMSe and from 80 to 400 pg mL⁻¹ for DMDSe, depending on the sample under analysis. None of the twenty-three samples analyzed contained the studied compounds at concentrations above the corresponding detection limits.     

Determination of phenylurea and triazine herbicides in milk by microwave assisted ionic liquid microextraction high-performance liquid chromatography

The determination of phenylurea and triazine herbicides in milk based on microwave assisted ionic liquid microextraction (MAILME) coupled with high-performance liquid chromatographic separation was described. The experimental parameters of the MAILE, including type and amount of ionic liquid, microwave extraction power, extraction time and salt concentration in sample, were evaluated by a univariate method and orthogonal screening. When 60 μL of [C₆MIM][PF₆] was used as extraction solvent the target compounds can be isolated from the 4 mL of milk. The MAILME is quick (7 min) and simple. The detection limits for isoproturon, monolinuron, linuron, propazine, prometryne, terbutryn and trietazine are 0.46, 0.78, 1.00, 1.21, 1.96, 0.84 and 1.28 μg L⁻¹, respectively. The proposed method was applied to the analysis of milk samples and the recoveries of the analytes ranged from 88.4 to 117.9% and relative standard deviations were lower than7.43%.     

Synchronous fluorescence measurement of enrofloxacin in the pharmaceutical formulation and its residue in milks based on the yttrium (III)-perturbed luminescence

A simple, rapid and sensitive synchronous fluorescence method is put forward for the determination of enrofloxacin (ENRO) in the pharmaceutical formulation and its residue in milk based on the yttrium (III)-perturbed luminescence. When Y³⁺ is added into the ENRO solution, the fluorescence of ENRO is significantly enhanced. The synchronous fluorescence technology is employed in the method to determine trace amount of ENRO residue in milks. The synchronous fluorescence intensity of the system is measured in a 1-cm quartz cell with excitation wavelength of 328 nm, Δλ = 80 nm. A good linear relationship between the fluorescence intensity and the ENRO concentration is obtained in the range of 1.0 × 10⁻⁹ to 2.0 × 10⁻⁶ mol L⁻¹ (r² = 0.9992). The limit of detection (LOD) of this method attains as low as 3.0 × 10⁻¹⁰ mol L⁻¹ (S/N = 3). The selectivity of this method is also very good. Common metal ions, rare-earth ions and some pharmaceuticals, which are usually used together with ENRO, do not interfere with the determination of ENRO under the actual conditions. The proposed method can be applied to determine ENRO residue in milks, and limit of quantification (LOQ) determined in the spiked milk is estimated to be 2.8 × 10⁻⁸ mol L⁻¹ (10 μg L⁻¹). Moreover, this method can be used as a rapid screening for judging whether the ENRO residues in milks exceed Minimal Risk Levels (MRLs) or not. In addition, the mechanism of the fluorescence enhancement is also discussed in detail.     

Construction of a simple optical sensor based on air stable lipid film with incorporated urease for the rapid detection of urea in milk

This work describes the construction of a simple optical sensor for the rapid, selective and sensitive detection of urea in milk using air stable lipid films with incorporated urease. The lipid film is stabilized on a glass filter by polymerization using UV (ultra-violet) radiation prior its use. Methacrylic acid was the functional monomer, ethylene glycol dimethacrylate was the crosslinker and 2,2′-azobis-(2-methylpropionitrile) was the initiator. Urease is incorporated within this mixture prior to the polymerization. The presence of the enzyme in these films quenched this fluorescence and the colour became similar to that of the filters without the lipid films. A drop of aqueous solution of urea provided a “switching on” of the fluorescence which allows the rapid detection of this compound at the levels of 10⁻⁸ M concentrations. The investigation of the effect of potent interferences included a wide range of compounds usually found in foods and also of proteins and lipids. These lipid membranes were used for the rapid detection of urea in milk.     

Raman spectroscopic quantification of milk powder constituents

Raman spectroscopy has significant potential for the quantification of food products. Milk powder is an important foodstuff and ingredient that is produced on large scale (over 20 million tonnes per annum). Raman spectroscopy, unlike near- and mid-infrared spectroscopies, has not been used extensively to quantify milk powder constituents. The effect of sample presentation on spectroscopic calibrations of protein and fat for 136 New Zealand milk powders was assessed using Raman spectroscopy. Prediction models were produced to quantify a protein concentration range of 32.19-37.65% w/w for skim milk powder, and a protein concentration range of 23.34-25.02% w/w and a fat concentration range of 26.26-29.68% w/w for whole milk powder (where ratios of prediction to deviation exceeded 2.6 with one exception). The resultant calibrations were not influenced by sample orientation; the sample temperature during data collection did affect the calibrations. Calcium fortification in the form of calcium carbonate was identified within a sub-set of samples, reinforcing the efficacy of Raman spectroscopy for identifying both crystalline and non-crystalline constituents within milk powder.     

Estimating Aluminum leaching from Aluminum cook wares in different meat extracts and milk

A method of estimating Al leaching from Al cook ware in some meat extracts and liquid milk was investigated. In the present work four kinds of Al cook wares from four countries were chosen from the local market. Extracts of boiled meat (lamb, chicken, and fish) were used to make 10–50% (w/v) concentrations. In addition liquid fresh milk and long life milk were diluted to make 10–50% (v/v) concentrations. Weight loss (WL) method, atomic absorption, polarization method, and surface study were applied. The “estimated” Al intake per person from WL in 30% meat extract and milk range from 8.16 to 12.75 mg/h with fish extract having the highest leaching and chicken extract having the lowest leaching. Atomic absorption gave comparable results to that of WL. Comparing the present results with the Provisional Tolerance Weekly Intake of Al approved by the FDA/WHO shows that Al leaching from Al cook wares may add high doses of Al into the diet.