Serum replacement method

The adsorption of fully and partially hydrolyzed (88%) polyvinyl alcohol (PVA) on 190-1lOOnm monodisperse polystyrene latex particles was investigated. The effect of molecular weight was investigated for 190 nm-size particles using the serum replacement adsorption and desorption methods. The adsorption density at the adsorption-isotherm plateau followed the relationships for the fully hydrolyzed... 

The determination of adsorption isotherms at liquid-solid interfaces involves a mass balance on the amount of polymer added to the dispersion, which requires the separation of the liquid phase from the particle phase. Centrifugation is often used for this separation, under the assumption that the adsorption-desorption equilibrium does not change during this process. Serum replacement (6) allows the separation of the liquid phase without assumptions as to the configuration of the adsorbed polymer molecules. This method has been used to determine the adsorption isotherms of anionic and nonionic emulsifiers on various types of latex particles (7,8). This paper describes the adsorption of fully and partially hydrolyzed PVA on different-size PS latex particles. PS latex was chosen over polyvinyl acetate (PVAc) latex because of its well-characterized surface PVAc latexes will be studied later. 

Adsorption Isotherms. The adsorption isotherms were determined using the serum-replacement adsorption or desorption methods (7). For the adsorption method, the latex samples (50 or 100 cm 2% solids) containing varying amounts of PVA were equilibrated for 36 hours at 25°C, placed in the serum replacement cell equipped with a Nuclepore membrane of the appropriate pore size, and pressurized to separate a small sample of the serum from the latex. For the desorption method, the latex samples (250 cm 2.5% solids) were equilibrated for 36 hours at 25°C and subjected to serum replacement with DDI water at a constant 9-10 cm /hour. The exit stream was monitored using a differential refractometer. The mean residence time of the feed stream was ca. 25 hours. It was assumed that equilibrium between the adsorbed and solute PVA was maintained throughout the serum replacement. For both methods, the PVA concentration was determined using a An-C calibration curve. 

Polystyrene latexes have been prepared using persulfate initiator for many years, but only recently have methods been developed to determine the number and loci of the sulfate surface groups. To determine these surface groups, the latex is cleaned to remove the adsorbed emulsifier and solute electrolyte, then the surface sulfate groups in the H+ form are titrated conductometrically with base. The latexes can be cleaned effectively by ion exchange (2-5) or serum replacement (6) dialysis is not effective in removing the adsorbed emulsifier and solute electrolyte (3,5,6). +... 

Seven polystyrene latexes prepared with persulfate initiator and bicarbonate buffer were characterized to demonstrate the efficacy of this method (6). Three were monodisperse latexes prepared using conventional emulsifiers four were prepared using sodium styrene sulfonate or sodium vinyltoluene sulfonate as canan-omeric emulsifiers. Each latex was subjected to serum replacement with... 

Table IV shows the results of these experiments. Serum replacement with water gave low values for the surface charge because of incomplete replacement of the Na+ and K+ ions by H+ ions. However, serum replacement with water, hydrochloric acid, and water gave values equal to, or slightly less than, those obtained by ion exchange, demonstrating the efficacy of this new cleaning method. The values for the dialyzed samples were also significantly lower than those obtained by ion exchange.

The results obtained with ISEs have been compared several times with those of other methods. When the determination of calcium using the Orion SS-20 analyser was tested, it was found that the results in heparinized whole blood and serum were sufficiently precise and subject to negligible interference from K and Mg ([82]), but that it is necessary to correct for the sodium error, as the ionic strength is adjusted with a sodium salt [82], and that a systematic error appears in the presence of colloids and cells due to complexa-tion and variations in the liquid-junction potential [76]. Determination of sodium and potassium with ISEs is comparable with flame photometric estimation [39, 113, 116] or is even more precise [165], but the values obtained with ISEs in serum are somewhat higher than those from flame photometry and most others methods [3, 25, 27, 113, 116]. This phenomenon is called pseudohyponatremia. It is caused by the fact that the samples are not diluted in ISE measurement, whereas in other methods dilution occurs before and during the measurement. On dilution, part of the water in serum is replaced by lipids and partially soluble serum proteins in samples with abnormally increased level of lipids and/or proteins. 

Quest Diagnostics use an LC-MS/MS panel for diagnosing cortisol-related disorders by urine analysis. This panel was designed to diagnose Cushings syndrome and the hypertensive conditions AME and GRA. The panel quantifies cortisone, cortisol, 6/j-hydroxycorlisol and 18-hydroxycortisol (18-OHF). The Quest analysis uses 2H4 cortisol as an internal standard and HTLC for on-line extraction. This panel has replaced the RIA and HPLC methods previously used by this commercial laboratory. Another recent publication describes MS/MS of cortisone and cortisol in serum using APPI and similar conditions and MRM transformations to those listed above [43]. 

The TSH radioimmunoassays procedures have replaced other methods for the quantitative assessment of changes in pituitary responsiveness after repeated dose treatment, test compounds which enhance the secretion of thyroid hormones lead to a suppression of the serum TSH concentrations, a clinical example being hyperthyroidism (Connors et al. 1981, Pekary et al. 1980). On the other hand, a reduction in circulating concentrations of thyroid hormones (T3 and T4) will release the pituitary gland from feedback inhibition, and the serum concentration of TSH may arise in an exponential manner. 

Synthetic method 26 A variety of growth factors is added to the existing basal media to replace the serum s functions. 

We have developed a thermal ionization method for use in a standard quadrupole mass spectrometer (1) The method uses a modified solids inlet probe Figure in conjunction with replacable filament assemblies The rhenium filaments are coated with calcium salts precipitated from biological materials in a basic ammonium oxalate solution Calcium is precipitated directly from urine and serum first made basic with ammonium hydroxide fecal samples and aliquots of diet are homogenized with a 9 1 water/nitric acid mixture, centrifuged, made basic and... 

---