Filtering sample solutions

A known quantity of sample is added to a known volume of a universal buffer solution of sufficient capacity and of known pH. The amount of sample must be sufficient to cause precipitation to occur in the formed saturated solution. After waiting for a period of time to allow the saturated solution to reach the desired steady state, the solution is filtered to remove the solid and obtain a clear solution, whose spectrum is then taken by the UV spectrophotometer. Mathematical treatment of the spectral data yields the area-under-the-curve of the filtered sample solution, AUQ. 

The sample solutions injected into an ion chromatographic system must be free of particulate matter to avoid plugging of the capillary connecting tubing and the frits at the head of the analytical column. Even samples that appear to be clear may contain unsuspected fine particles. It is more or less standard procedure to filter sample solutions prior to their injection. Disposable membrane filters with a pore diameter of... 

Decolorisation by Animal Charcoal. It sometimes hap pens (particularly with aromatic and heterocyclic compounds) that a crude product may contain a coloured impurity, which on recrystallisation dissolves in the boiling solvent, but is then partly occluded by crystals as they form and grow in the cooling solution. Sometimes a very tenacious occlusion may thus occur, and repeated and very wasteful recrystallisation may be necessary to eliminate the impurity. Moreover, the amount of the impurity present may be so small that the melting-point and analytical values of the compound are not sensibly affected, yet the appearance of the sample is ruined. Such impurities can usually be readily removed by boiling the substance in solution with a small quantity of finely powdered animal charcoal for a short time, and then filtering the solution while hot. The animal charcoal adsorbs the coloured impurity, and the filtrate is usually almost free from extraneous colour and deposits therefore pure crystals. This decolorisation by animal charcoal occurs most readily in aqueous solution, but can be performed in almost any organic solvent. Care should be taken not to use an excessive quantity... 

Dichloranrine-T (p-toluenesulphondichloramide). Prepare about 200 ml. of a saturated solution of calcium hjrpochlorite by grinding a fresh sample of bleaching powder with water and filtering with shght suction. Dissolve 5 g. of p-toluenesulphonamide in as small a volume of the calcium hypochlorite solution as possible (about 150 ml.) and filter the solution if necessary. Cool in ice, and add about 50 ml. of a mixture of equal volumes of glacial acetic acid and water slowly and with stirring until precipitation is complete. The dichloramine T separates out first as a fine emulsion, which rapidly forms colourless crystals. Filter the latter... 

This analysis is an example of a concentration technique. Once the original sample is brought to volume in the 100-mL volumetric flask, any portion of the sample solution, even that obtained on filtering, may be used for the analysis. 

Procedure. Transfer the almost neutral sample solution of beryllium (containing 5 to 80jug of the element in a volume of about lOmL) to a 25 mL graduated flask, add 2.8 mL of 2.0M sodium hydroxide (or more if much aluminium is present), 5.0 mL of 0.64M boric acid solution, and 6.0 mL of the dye solution (see Note), dilute to the mark with distilled water, and mix well. Measure the transmittance at 520 nm, or with a green filter preferably using a 2 cm cell. 

Procedure. Dissolve a weighed portion of the substance in which the amount of iron is to be determined in a suitable acid, and evaporate nearly to dryness to expel excess of acid. Dilute slightly with water, oxidise the iron to the iron(III) state with dilute potassium permanganate solution or with a little bromine water, and make up the liquid to 500 mL or other suitable volume. Take 40 mL of this solution and place in a 50 mL graduated flask, add 5 mL of the thiocyanate solution and 3 mL of AM nitric acid. Add de-ionised water to dilute to the mark. Prepare a blank using the same quantities of reagents. Measure the absorbance of the sample solution in a spectrophotometer at 480 nm (blue-green filter). Determine the concentration of this solution by comparison with values on a reference curve obtained in the same way from different concentrations of the standard iron solution. 

Procedure. Transfer the neutral sample solution (<100 gMg), free from calcium and other metals, to a 100 mL graduated flask with calibrated neck. Add 25 mL of the buffer solution, dilute to just below the 90 mL graduation mark, and shake. Add 10.0 mL of the solochrome black solution carefully. Shake to mix and dilute to the 100 mL mark with water. Measure the absorbance immediately at 520 nm (green filter) against that of a blank solution, similarly prepared but containing no magnesium. 

Add to the sample solution (containing 1 -25 g of Mo) 4 mL of 1 3 sulphuric acid, 3 drops of 85 per cent phosphoric(V) acid, and 0.5 g of citric acid. Dilute with water to 20 mL and add 2 mL of dithiol solution. Allow to stand at room temperature for 2 hours. Extract the molybdenum complex with 13 mL and 10 mL portions respectively of re-distilled butyl acetate, and make up to 25.0 mL with this solvent in a graduated flask filter through glass wool if not entirely clear. Determine the absorbance of the solution at 670 nm. Prepare a calibration curve as detailed in Section 6.14. 

Procedure. To 100 mL of the neutral sample solution (containing not more than 0.4 mg nitrite) add 2.0 mL of solution A and, after 5 minutes, 2.0 mL of solution B. The pH at this point should be about 1.5. Measure the absorbance after 10 minutes in the wavelength region of 550 nm (yellow-green filter), in a spectrophotometer against a blank solution prepared in the same manner. Calculate the concentration of the nitrite from a calibration plot prepared from a series of standard nitrite solutions. 

The sampling of solution for activity measurement is carried out by filtration with 0.22 pm Millex filter (Millipore Co.) which is encapsuled and attached to a syringe for handy operation. The randomly selected filtrates are further passed through Amicon Centriflo membrane filter (CF-25) of 2 nm pore size. The activities measured for the filtrates from the two different pore sizes are observed to be identical within experimental error. Activities are measured by a liquid scintillation counter. For each sample solution, triplicate samplings and activity measurements are undertaken and the average of three values is used for calculation. Absorption spectra of experimental solutions are measured using a Beckman UV 5260 spectrophotometer for the analysis of oxidation states of dissolved Pu ions. 

Several solid surfaces, such as filter paper, sodium acetate, and silica gel chromatoplates with a polyacrylate binder, have been used in solid-surface luminescence work (1,2). Experimentally it is relatively easy to prepare samples for analysis. With filter paper, for example, a small volume of sample solution is spotted onto the surface, the filter paper is dried, and then the measurement is made. In many cases, an inert gas is passed over the surface during the measurement step to enhance the RTF signal. For powdered samples, the sample preparation procedure is somewhat more involved. Commercial instruments can be readily used to measure the luminescence signals, and a variety of research instruments have been developed to obtain the solid-surface luminescence data (1,2). 

Direct measurement of adsorptive stripping voltaimnetric peaks using HMDE 0.60 V and accumulation potential of -0.40V Dilution in phosphate buffer and water, analyzed in Vis region Ion pair formation with octadecyltrimethylammonium bromide at pH 5.6, extraction of ion pair into n-butanol Sample solution mixed with 1 M HCl, ethanol and purification on Sephadex DEAE 25 gel, gel beads are filtered off, packed into 1 nun cell and absorbance measured... 

Filter samples can be prepared to airborne workplace concentrations by spiking each filter with aqueous solution containing elements with concentrations gravimetrically traceable to ultrapure metals or stoidiiometricaUy well defined oxides. The amormts correspond for some of the materials to current threshold limit values of contaminants in workroom atmospheres provided that the simulated filter has been exposed to one cubic meter of air. The certified values are based on a gravimetric procedure, i.e. weight per volume composition of the primary reference material dissolved in high purity sub-dis-tiUed acids. The National Institute of Occupational Health in Oslo, Norway, has produced several batches of such materials certified for 20 elements. Additionally, information values are reported for four other elements see Table 6.2. 

To 100 mL of the water sample add 20 mL of 0.2 M acetate buffer (pH 4) to acidify the mixture to pH 4. Filter the solution through a Cig extraction disk with suction and rinse the disk with 50 mL of acetonitrile-water (1 19, v/v). Discard the eluate. Collect the bispyribac in a 500-mL round-bottom flask with 100 mL of acetonitrile. Evaporate the eluate to dryness under reduced pressure. Then the residue is processed as described below. 

Precondition a Cig (EC) SPE column (l-g/6-mL) with methanol (5mL) followed by another 5 mL of acetonitrile-water (3 7, v/v). Transfer the sample on to the column and allow it to percolate through the column under vacuum, discarding the column eluate. Wash the column with 5 mL of acetonitrile-water (3 7, v/v). Dry the column under high vacuum for 15 min and wash it with hexane (5 mL). Elute the azoxystrobin from the column with 5 mL of ethyl acetate-dichloromethane (11 9, v/v), and evaporate the eluate to dryness under a stream of air in a heating block at 50 °C. Dissolve the sample in 1 mL of acetonitrile-water (1 1, v/v) and filter the solution through a 0.45-p.m syringe filter, transferring the filtrate to an autosampler vial ready for LC/MS/MS analysis. 

Weigh 50 g (dry weight) of soil sample into a 500-mL Erlenmeyer flask. Add 250 mL of acetone-water (4 1, v/v) and shake vigorously for 1 h and filter the solution by suction through Whatman No. 2 filter paper covered with a 1-cm layer of Hyfio Super-Cel. Rinse the flask and cake with 100 mL of acetone. Combine the filtrate and rinsings and concentrate to less than 40 mL below 40 °C with a rotary evaporator. 

Comparison between the inventories in the collected fractions (the colloidal and ultrafiltered fractions) and in the starting sample often indicate that there are losses of nuclides on to the ultrafiltration cartridge. These are largely recovered by subsequent acid rinses of the ultrafilters and filtration system. It is not clear whether the recovered abundances should be considered part of the colloids retained by the filter, or solutes that have adsorbed in the system (Gustafsson et al. 1996 Andersson et al. 2001), even though test experiments with colloidally-bound " Th showed significant losses in the ultrafiltration system (Baskaran et al. 1992.)... 

The most common method of isolation and sample cleanup involves contacting a filtered aqueous solution with an appropriate immiscible organic solvent in a. aboratory separatory funnel of appropriate size. Some specific examples are discussed later. With multicomponent samples a single solvent or solvent mixture is unlikely to extract all components equally causing discrimination. Ihis discrimination may be useful if the solvent discriminates against the extraction of solutes that are not of interest in the analysis. 

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