Viscous samples

Because the separation is nearly independent of the total amount of protein loaded onto the column, no limitation with respect to the protein concentration exists for concentrations at least up to 60 mg. The high mechanical stability enables the injection of even highly viscous samples with high concentrations of protein. 

Viscous Sample Dilute to reduce processing time... 

Filters even viscous samples with less hand force than ever before possible... 

Eliminate potential pitfalls such as air bubbles in the sampling syringe, tightly sealed vial closures, an overly fast sample dosing speed for viscous samples, sample adsorption, siphoning, sample evaporation, etc. 

Sample line dispersion can be reduced by introducing several air bubbles between samples and the inter-sample wash, using a so-caUed peddng-probe sampler. In practice, this is most useful for viscous samples such as hlood serum. 

Electrothermal vaporization has many appHcations relating to ICP analysis the abihty to vaporize solvents and to handle small soHd or viscous samples are particularly important. In addition, the measurement of the isotopic ratios of lead in various ores provides a unique identification of the ore and its source. Now that commercial systems are available, the technique will undoubtedly become popular. These techniques seem to have found favour, particularly in Japan. 

Many of the robotic manipulations used in this system (designed primarily for non-viscous samples) were adapted, in part, from those developed for a viscous Hquids KF system introduced by Zymark. 

The instruments for polymer HPLC except for the columns (Section 16.8.1) and for some detectors are in principle the same as for the HPLC of small molecules. Due to sensitivity of particular detectors to the pressure variations (Section 16.9.1) the pumping systems should be equipped with the efficient dampeners to suppress the rest pulsation of pressure and flow rate of mobile phase. In most methods of polymer HPLC, and especially in SEC, the retention volume of sample (fraction) is the parameter of the same importance as the sample concentration. The conventional volumeters— siphons, drop counters, heat pulse counters—do not exhibit necessary robustness and precision [270]. Therefore the timescale is utilized and the eluent flow rate has to be very constant even when rather viscous samples are introduced into column. The problems with the constant eluent flow rate may be caused by the poor resettability of some pumping systems. Therefore, it is advisable to carefully check the actual flow rate after each restarting of instrument and in the course of the long-time experiments. A continuous operation— 24h a day and 7 days a week—is advisable for the high-precision SEC measurements. THE or other eluent is continuously distilled and recycled. 

Figure 9.29 Membrane formation by meteoritic amphiphilic compounds (courtesy of David Deamer). A sample of the Murchison meteorite was extracted with the chloroform-methanol-water solvent described by Deamer and Pashley, 1989. Amphiphilic compounds were isolated chromatographically on thin-layer chromatography plates (fraction 1), and a small aliquot ( 1 p,g) was dried on a glass microscope slide. Alkaline carbonate buffer (15 p,l, 10 mM, pH 9.0) was added to the dried sample, followed by a cover slip, and the interaction of the aqueous phase with the sample was followed by phase-contrast and fluorescence microscopy, (a) The sample-buffer interface was 1 min. The aqueous phase penetrated the viscous sample, causing spherical structures to appear at the interface and fall away into the medium, (b) After 30 min, large numbers of vesicular structures are produced as the buffer further penetrates the sample, (c) The vesicular nature of the structures in (b) is clearly demonstrated by fluorescence microscopy. Original magnification in (a) is x 160 in (b) and (c) x 400.

Solids, suspensions, or highly viscous samples can be automatically introduced into the chromatograph. 

Supervisors usually assume that novice analysts joining their group know how to use a micropipettor properly. Usually, this is not the case therefore, some suggestions for accurate pipetting of viscous samples involved in (3-glu-can analysis arc presented here. Do not immerse the pipet tip more than 3 mm into the solution. Deeper immersion usually leads to... 

Viscous samples make mass transfer through the sample slow. Stirring reduces the time for mass transfer. 

In the case of extremely viscous samples or samples with high pectin contents, centrifugation is often employed. The sample is centrifuged for 20 min at 12,000 x g, 4°C, and then the supernatant is filtered. 

Samples are usually placed in 1mm thick quartz spectrophotometer cells sealed with Parafilm or similar. Samples in which the aqueous phase has a very high D to H ratio are sometimes thicker, as the level of incoherent scatter due to H will be low. Samples may be in the scattering apparatus for several hours, and so H20/D20 exchange due to faulty sealing can cause errors. For gel-like samples, it is very important that there are no air bubbles trapped in the sample. Gel or viscous samples can be centrifuged to the bottom of cells, and air bubbles removed, using a Helma Roto-Vette or similar. 

The asphaltene fraction (ASTM D-893 ASTM D-2007 ASTM D-3279 ASTM D-4124 ASTM D-6560 IP 143) is the highest molecular weight and most complex fraction. In any of the methods for determination of the asphaltene content, the sample is mixed with a large excess (usually >30 volumes hydrocarbon per volume of sample) of low-boiling hydrocarbon, such as n-pentane or n-heptane. For an extremely viscous sample, a solvent such as toluene may be used prior to addition of the low-boiling hydrocarbon, but an additional amount of the hydrocarbon (usually >30 volumes hydrocarbon per volume of solvent) must be added to compensate for the presence of the solvent. After a specified time, the insoluble material (the asphaltene fraction) is separated (by filtration) and dried. The yield is reported as a percentage (% w/w) of the original sample. 

Matrix solid-phase dispersion (MSPD) is the extraction method of choice for the analysis of solid samples, such as plant material, foodstuffs or tissue samples [26]. This method has been developed especially for solid or viscous matrices. MSPD is preferable to other extraction techniques, because the solid or viscous sample can be directly mixed with the sorbent material of the stationary phase [27]. As the carotenoid stereoisomers stay bound in their biological matrix until the elution step, they are protected against isomerisation and oxidation [28]. The extraction scheme of MSPD is shown in Figure 5.2.1. 

Measurements of the zero shear viscosity (20 °C) were made with a Bohlin VOR rheometer in the viscometry mode. If a Newtonian region was not found at the lowest measurable shear rates, the samples were characterized with a Bohlin-CS constant stress rheometer, with which it was possible to obtain extremely low shear rates. This approach was especially needed for highly viscous samples exhibiting pseudoplastic behavior on the VOR rheometer. Newtonian regions were found for each sample in this manner, yielding the zero shear viscosities reported. 

Florisil Mg03Si Polar adsorbent Florisil is a magnesium-substituted silica with a highly polar surface typically has a relatively large particle size (approximately 200 pm), and therefore high flow rates are possible even with viscous samples used with many official methods, and in cases where the Lewis acidity of alumina would be problematic... 

Due to the high absorbency in the MIR region and to comply with the Beer-Lambert law, the path-length of the cuvette must be about 10 pm. The development of the attenuated total reflectance (ATR) device allows the sampling problems encountered when collecting spectra from opaque and viscous samples to be overcome (Figure 20.1). 

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