Centrifugation spectrophotometric

Different extraction-spectrophotometric procedures were proposed for the P(V) and As(V) determination as ionic associates (lA) of polyoxometalates with basic dyes. Main disadvantage is difficulty in separation of reagent excess. Flotation, centrifugation or extraction does not allow to create sufficiently sensitive procedures due to worsening of reproducibility. 

An area worthy of study is the development of systems of increasing sample throughput beyond the single column operation. Scott has introduced a prototype multicolumn system based on the centrifugal analyzer principle (53). In this set-up a series of LC colimns is rotated on a disc, with sample delivery at the center of the disc and elution and spectrophotometric analysis on the outside. He has suggested using affinity columns for rapid serum protein analysis by this approach. Of course, other principles, such as segmented flow, could be envisioned in an automated LC system as well. Undoubtedly, we can expect to see the availability of such systems in the next few years. 

In another spectrophotometric procedure Motomizu [224] adds to the sample (2 litres) 40% (w/v) sodium citrate dihydrate solution (10 ml) and a 0.2% solution of 2-ethylamino-5-nitrosophenol in 0.01 M hydrochloric acid (20 ml). After 30 min, add 10% aqueous EDTA (10 ml) and 1,2-dichloroethane (20 ml), mechanically shake the mixture for 10 minutes, separate the organic phase and wash it successively with hydrochloric acid (1 2) (3 x 5 ml), potassium hydroxide (5 ml), and hydrochloric acid (1 2) (5 ml). Filter, and measure the extinction at 462 nm in a 50 mm cell. Determine the reagent blank by adding EDTA solution before the citrate solution. The sample is either set aside for about 1 day before analysis (the organic extract should then be centrifuged), or preferably it is passed through a 0.45 xm membrane-filter. The optimum pH range for samples is 5.5 - 7.5. From 0.07 to 0.12 p,g/l of cobalt was determined there is no interference from species commonly present in seawater. 

From spectrophotometric or centrifugal measurements it will often be possible to deduce Kgi° and AV2l. Assume that a fraction a of the total concentration of A is dissociated into At,... 

The mean sizes obtained were 500 150, 350 77, 192 25, and 100 16, for 0.6, 0.4, 0.2, and 0.1pm liposomes, respectively. Drug concentration was determined by spectrophotometric assay of chromophoric complex between the BP and copper (II) ions (63) or by high performance liquid chromatography (HPLC) (64). Lipid concentration was determined by Bartlett method (65). Stability of the liposomes was determined by examining drug leakage. Then 400 pL of liposomal formulations were centrifuged... 

To prepare DQAsomes or vesicles composed of dequalinium derivatives, the appropriate amount of bola-lipid (10 mM final) was dissolved in methanol, dried using a rotary evaporator, suspended in 2.5 mL 5mM N-2-hydroxyethylpiperazine-N -2-ethane sulfonic acid (HEPES), pH 7.4, bath sonicated for about one hour followed by probe sonication for 45 minutes (10 W). The sample was then centrifuged for 30 minutes at 3000 rpm, the clear, or in some cases, opaque supernatant collected and the remaining non-solubilized residue lyophilized. The concentration of solubilized bola-lipid can be determined spectrophotometrically or can be inferred from the amount of recovered compound after lyophilization. 

A stock solution of DNA was prepared by dropping a 10 nM solution of NaClO on the DNA fibers to give an approximate concentration of lmgml This solution was gently agitated at 4 °C for 48 h, centrifuged at 8000 r.p.m. for 10 min and its concentration determined spectrophotometrically. 

Add 24.3 g solid ammonium sulfate per 100 ml EDTA-filtrate (yields a 40% saturation) and stir at 4 °C for 30 min. Collect the precipitate by centrifugation. Wash the pellet once with 30% saturated ammonium sulfate (3 vol. Soln. E -i- 7 vol. ddH20), spin down again and dissolve the precipitated IgY in a small volume of Soln. A (about 1/10 of the original yolk volume). Dialyze against TBS and determine the IgY content spectrophotometrically. 

Determination of Emulsion Stability and Oil Droplet Size. A combination of centrifugation and spectrophotometric techniques was used for the evaluation of emulsion stability. Solutions... 

Problems that may arise with spectrophotometric assays may be due to turbid samples, inadequate mixing, or poor design of controls/blanks. Turbid samples should be clarified by centrifugation (a simple benchtop centrifuge at -5000 x g should be adequate) before reading the absorbance of the clear supernatant. 

Sampling and Measurements. The determination of dissolved actinide concentration was started a week after the preparation of solutions and continued periodically for several months until the solubility equilibrium in each solution was attained. Some solutions, in which the solubilities of americium or plutonium were relatively high, were spectrophotometrically analyzed to ascertain the chemical state of dissolved species. For each sample, 0.2 to 1.0 mL of solution was filtered with a Millex-22 syringe filter (0.22 pm pore size) and the actinide concentration determined in a liquid scintillation counter. After filtration with a Millex-22, randomly chosen sample solutions were further filtered with various ultrafilters of different pore sizes in order to determine if different types of filtration would affect the measured concentration. The chemical stability of dissolved species was examined with respect to sorption on surfaces of experimental vials and of filters. The experiment was performed as follows the solution filtered by a Millex-22 was put into a polyethylene vial, stored one day, filtered with a new filter of the same pore size and put into another polyethylene vial. This procedure was repeated twice with two new polyethylene vials and the activities of filtrates were compared. The ultrafiltration was carried out by centrifugation with an appropriate filter holder. The results show that the dissolved species in solution after filtration with Millex-22 (0.22 ym) do not sorb on surfaces of experimental materials and that the actinide concentration is not appreciably changed with decreasing pore size of ultrafilters. The pore size of a filter is estimated from its given Dalton number on the basis of a hardsphere model used in the previous work (20). 

Con A Binding Assay. For each binding experiment a number of 60 by 15 mm Petri dishes containing 3.0 ml PBS and 1.5 ml of a 3 mg/ml Con A solution were adjusted to the required conditions of temperature or pH. A volume of 0.6 ml of a well-mixed 1 1 (v/v) suspension of dextran gel spheres was added with a 1 ml plastic pipet to each dish, followed by incubation with shaking. Control samples contained methyl a-D- glucopyranoside (a-MG) at a final concentration of 0.1 M. At various intervals the contents of a sample and a control dish were centrifuged quickly and the supernatant withdrawn for UV spectrophotometric analysis at 280 nm... 

Table 1. The effect of 1 mM NaF + 20 pM A1C13 on the acetylcholinesterase activity (AChE) in freshly prepared intact RBC and in hemolysate of patients with AD (mean age 72.5 5.1 years), age-matched healthy controls (AM-HS) (72.1 1.6 years), and the group of young healthy subjects (YS) (35.9 8.5 years). Whole venous blood samples were drawn from each subject after overnight fasting., always at 07 30 AM. Red blood cells (RBC) were isolated from the blood of patients with AD, AM-HS, and YS by centrifugation [68], RBC AChE activity was evaluated in intact freshly prepared RBC or hemolyzate following the spectrophotometric method [45] with modifications. Buffer was Tris-HCl, pH 7.5 in the solution of 154 mmol L 1 NaCl, acetylthiocholine iodide was a substrate. Measurement of enzymatic activity was performed in fluorimeter polystyrene cuvettes for 3 min (UV/VIS spectrophotometer Shimadzu, Japan). The effects of 1 mmol L-1 NaF in the presence of 20 pmol L 1 A1C13 were measured. Data are expressed in percentage of the AChE activity in the absence of aluminum and fluoride ions. No differences between the AChE activity were found between the investigated groups...

Whey protein concentrate. The whey protein used was prepared by ultrafiltration and spray drying. Protein content (N x 6.55) was 68% (dry weight). Lipid content was 7.1% (dry weight). In order to study heat induced aggregation by spectrophotometric methods the turbidity of the dilute protein dispersions was too high. The turbidity of whey protein dispersions is caused by lipids associated with proteins probably in the form of emulsified oil droplets. This fraction was removed by precipitation at pH 4.5 from dispersions made in dist. water and separated by centrifugation at 40 000 xg. 

Procedure. Aqueous phases were prepared from samples of cerium (IV), cerium (III), berkelium, and acid and diluted by distilled water to the proper concentrations. Samples of cerium were chosen in order to obtain dijSerent cerium (IV)/cerium (III) ratios. The solutions were allowed to stand for six hours to reach the oxidation equilibrium. A 2 cc. sample of the solvent was added to the same volume of aqueous solution and mixed for 15 minutes. After separation by a centrifuge, samples of both phases were taken for the beta counting of berkelium and the spectrophotometric determination of cerium (IV). In addition, one aliquot of the loaded solvent was taken for determining the distribution coefficient of berkelium (IV). 

The experiments were carried out in 250-mL graduated cylinders with ground joints at room temperature (20—22 °C). Centrifuge K24 (Janetzki, GDR) was used for the centrifugation of 25 mL samples. The minimum" and the maximum diameters of its angle rotor were 5 and 14 cm, respectively. At 17,000 r.p.m. the g value for the 7-cm diameter was 15,350 g. Aluminium concentrations were determined colorimetrically with aluminon . Colour was determined spectrophotometrically at 387 nm with the correction for turbidity at... 

After incubation for the desired time interval, remove medium with test agent and incubate cells with fresh medium containing 40 xg ml NR dye. (An aqueous stock solution of 4 mg mH, shielded from light by foil, can be kept for several weeks.) This medium should be prepared earlier and incubated at 37°C overnight to allow for precipitation of small dye crystals. Centrifuge medium for 10 min at 1500 g before use and add 0.2 ml of decanted super-nate to each well. The first two wells on each plate should receive medium without NR and serve as blanks for spectrophotometric analysis. 

In PAH solubilization tests with soil, batch-test soil-aqueous samples with nonionic surfactant and 14C-PAH were rotated on a tube rotator periodically to maintain the soil in suspension during equilibration. The samples were centrifuged, and aliquots were expressed through preconditioned 0.22- xm Teflon filters to reduce soil-derived colloidal substances. The extent of PAH solubilization in nonionic surfactant solution without soil was assessed in batch tests as a function of surfactant dose to confirm the value of PAH aqueous solubility (S) and to determine the values of Scmc and MSR. Nonionic surfactant sorption onto soil was evaluated for sub-CMC (or sub-CAC) aqueous-phase concentrations by surface-tension measurements. Supra-CMC sorption of nonionic surfactant to determine or supra-CAC isotherm was assessed either with azo dye solubilization and spectrophotometric analysis, or by measurement of chemical oxygen demand, from which the amount of surfactant in bulk solution could be inferred (10). 

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