September 2010

Antioxidants are added to polyolefins to improve the stability of the resin from oxidation and degradation during processing of the finished article and to increase product lifetime. Without antioxidants, polyolefins would quickly degrade during and after the extrusion or thermoforming process, which would cause inferior appearance and physical properties. The proper level must be added to protect the polymer and to minimize cost. Antioxidants are usually extracted from the resin and the extract is analyzed by RPLC, GC, or Fourier transform infrared spectroscopy. Unfortunately, many of these procedures require significant manual labor, time, and solvent, rendering them impractical for high-throughput work processes. In addition, they may not provide complete extraction of the additives depending upon the type of resin. A validated analytical method was needed for the determination of three common antioxidants, Irganox® 1010, Irganox® 1076, and Irgafos® 168 in polyolefin resins. This paper shows the determination of these antioxidants using dissolution followed by precipitation with o-xylene and methanol. Direct analysis of the solution is achieved in 8 min using RPLC.

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This review describes the utility of flow field-flow fractionation coupled with multiangle light scattering and differential refractive index (FlFFF-MALS-DRI) detection methods for the separation of ultrahigh molecular weight sodium hyaluronate (NaHA) materials and for the characterization of molecular weight distribution as well as structural determination. The sodium salt of hyaluronic acid (HA), NaHA, is a water-soluble polysaccharide with a broad range of molecular weights (105–108) found in various naturally occurring fluids and tissues. Basic principles of FlFFF-MALS using field programming for the separation of the degraded products of NaHA prepared by treating raw materials with depolymerization or degradation processes such as membrane filtration, enzymatic degradation, ultrasonic degradation, alkaline reaction, irradiation by γ-rays, and thermal treatment for the development of pharmaceutical applications are introduced. Changes in molecular weight distribution and conformation of NaHA materials due to external stimuli are also discussed.

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Hyaluronic acid (HA) was extracted in a relatively large scale from rooster comb using a method similar to that reported previously. The extraction method was modified to simplify and to reduce time and cost in order to accommodate a large-scale extraction. Five hundred grams of frozen rooster combs yielded about 500 mg of dried HA. Extracted HA was characterized using asymmetrical flow field-flow fractionation (AsFlFFF) coupled online to a multiangle light scattering detector and a refractive index detector to determine the molecular size, molecular weight (MW) distribution, and molecular conformation of HA. For characterization of HA, AsFlFFF was operated by a simplified two-step procedure, instead of the conventional three-step procedure, where the first two steps (sample loading and focusing) were combined into one to avoid the adsorption of viscous HA onto the channel membrane. The simplified two-step AsFlFFF yielded reasonably good separations of HA molecules based on their MWs. The weight average MW (Mw) and the average root-mean-square (RMS) radius of HA extracted from rooster comb were 1.20×106 and 94.7 nm, respectively. When the sample solution was filtered through a 0.45 μm disposable syringe filter, they were reduced down to 3.8×105 and 50.1 nm, respectively.

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We describe a new CE method with UV-detection for the quantification of histidine (His) and its methylated forms 1-methylhistidine and 3-methylhistidine, both in plasma and urine. Analytes were basically resolved using a 60 mmol/L Tris-phosphate run buffer pH 2.2 in less than 12 min. The use of a mixture of ACN/ammonia (80:20) for protein precipitation allows the quantitative recovery of all His from plasma. The optimization of the sample volume injection permits to reach an LOD of 20 nmol/L, thus improving the sensitivity of about hundred times in comparison to the previous described assays. Moreover, the opportunity to also measure creatinine in the same run makes it possible to evaluate the renal function contemporarily, thus avoiding further dosages with significant time saving. The application method has been proved by measuring His, 1-methylhistidine and 3-methylhistidine in 44 healthy subjects. In conclusion, our new method seems to be an inexpensive, fast and specific tool to assess large numbers of patients for routine analysis both in clinical and research laboratories.

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Publication year: 2010Source: TrAC Trends in Analytical Chemistry, In Press, Corrected Proof, Available online 28 September 2010[No author name available]

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