Directed dilution

Dilute Polymer Solutions. The measurement of dilute solution viscosities of polymers is widely used for polymer characterization. Very low concentrations reduce intermolecular interactions and allow measurement of polymer—solvent interactions. These measurements ate usually made in capillary viscometers, some of which have provisions for direct dilution of the polymer solution. The key viscosity parameter for polymer characterization is the limiting viscosity number or intrinsic viscosity, [Tj]. It is calculated by extrapolation of the viscosity number (reduced viscosity) or the logarithmic viscosity number (inherent viscosity) to zero concentration. 

Sometimes the reaction mixture, especially when chosen for a low conversion and with a high ethoxylation grade, implies a mixture with a relatively low NaCl content, directly diluted with water. But mostly with this type of ether carboxylate a washing step is introduced in order to remove NaCl and other... 

Other workers have determined zinc in serum by direct dilution 87> 88). McPherson and George 89) determined total copper and zinc of red cells and the free copper and zinc of plasma and dialysis fluids of patients undergoing regular hemodialysis, using atomic absorption spectroscopy. Spry and Piper 90) determined zinc in whole blood and plasma in blood cells of iron deficient rats. The zinc concentrations were raised in the iron deficient rats. 

Matsumiya etal. 91) determined zinc in both serum and urine by direct dilution. Dawson and Walker92) diluted plasma 20-fold with 0.1 AT hydrochloric acid, in whole blood diluted 100-fold, and in urine diluted 10-fold. Suppression of up to 15 % of the absorbance by inorganic components was overcome by adding the appropriate amounts of those ions to the standards. Willis93) determined zinc in urine by direct aspiration. Other workers have also determined zinc in urine 79>94) and in blood and urine 9S). 

A medication order calls for 400 mg of Kefzol (cefazolin sodium) to be administered IM to a patient every 12 hours. Vials containing 250 mg, 500 mg, and 1 g of cefazolin sodium are available. According to the manufacturer s directions, dilutions may be made as follows ... 

Protein A chromatography yields inununoglobulins in very concentrated form. Therefore, the absorbance of the solution should not be measured directly. Dilute the sample into PBS, and take areading using PBS as a blank. The optical density of the diluted sample should not be above 1-1.5 to fall within the range of linearity. 

Filtration injection of sample directly dilution and injection elution from reverse-phase HPLC column with methanol/water... 

Oils and fats Direct dilution Tracer Extrasil ODS-2 UV... 

In this application, the samples were extracted using pure methanol, which was then directly diluted in the assay buffer. 

Electrolyte pH 4.5, 0.1M acetate buffer solution prepared using analytical grade reagents and purified water from a Millipore Milli-Q system (conductivity < 0.1 iS/cm). DNA solutions obtained by direct dilution of the appropriate volume in acetate buffer. 

Direct Dilution of a Certified Solution. When standard tracer solutions are purchased from commercial sources, detailed certificates must accompany them (see Section 11.2.6 in Radioanalytical Chemistry). Because the activity of the certified tracer solution usually is greater than needed for tracing individual samples, one or several sequential dilutions must be performed meticulously to produce the solution from which an aliquot will be pipetted into the samples. Dilutions should be prepared in a chemical form identical to the original solution with regard to type and concentration of acids and reagents to assure tracer solubility and stability. The analyst should perform dilutions by weight rather than by volume for precise work. The final dilution is usually planned to obtain a solution from which about 0.05 Bq is pipetted into a sample that contains that amount or less of plutonium analyte. 

Some 20 years ago Schramel [85] reported the analysis of milk by ICP-AES just by diluting the samples in water and using direct nebulization. It was eventually proved, though, that in ICP-AES the direct dilution of milk samples with... 

Trichloracetic acid (TCA) has been used to release Fe from serum proteins for many years, yet it is only recently that this kind of preparation has been used for the analysis of other metals. A comparison of TCA precipitation with simple dilution as preparation for serum Zn analysis was reported by Boyde and Wu [23] and by Kelson and Shamberger [24], Both groups found that Zn was quantitatively recovered from serum using TCA and that the concentrations found were consistently higher than those obtained by direct dilution. The former group found a mean positive bias of +20% for the TCA preparation, but the latter found more consistent... 

Several papers deal with magnesium determination in blood and urine. Willis (WIO) analyzed serum in the air-acetylene flame and found no effect from the presence of sodium, potassium, calcium, or phosphate, but states that an enhancement was seen in serum diluted with water only, probably due to serum proteins. This interference was controlled by addition of strontium or EDTA. Sensitivities were the same in the eoal gas-air and air-acetylene flame, indicating complete atomization of magnesium. In urine (W13) no interference was encountered and determinations were performed on samples directly diluted with water. 

Fats, oils, and lipids are common components of meats, nuts, and dairy products and manufactured goods, such as potato chips, cookies, and chocolate. They are soluble in nonpolar solvents, such as hexane and methylene chloride. The analyte, of course, should also be soluble in the extraction solvent. Typically normal-phase SPE would be used to retain a compound from this extraction solvent. A solid fat may be homogenized in a blender with hexane, filtered or centrifuged, then the solvent would be passed through a normal-phase column for retention of the solute. Another approach is the use of matrix solid-phase dispersion, where the solid would be ground into the silica and C-18 directly, then the analyte eluted directly from the ground mixture with either hexane or methylene chloride. The hexane or methylene chloride extract could then be applied directly to a normal-phase sorbent for separation. Liquid oils may be directly diluted with hexane or methylene chloride and applied to the normal-phase sorbent. Other lipid substances may be handled either as solids or liquids depending on their form. 

Should a compound II, in which R2 signifies NH2 or the radical of an alkylamine or hydroxyalkylamine, having from 1 to 4 carbon atoms inclusive in the alkyl portion, be used, then the reaction mixture, after heating with hydrazine, may be directly diluted with water and extracted with a water-immiscible solvent, e.g. chloroform, if desired, after the addition of ammonia. 

Pharmaceutical liquids require very minimal sample preparation they can be injected directly, diluted in mobile phase or other suitable diluent, or extracted into an organic solvent. A diluent is chosen to maintain solubility of the analyte as well as compatibility with the chromatographic system. Pharmaceutical suspensions must be pretreated to dissolve the drug prior to analysis. Another liquid dosage form is an emulsion, in which the liquid is suspended in a second immiscible liquid such as polydimethylsilicone. The sample preparation must break the emulsion. In the analysis of a polydimethylsilicone suspension, a liquid-liquid extraction is generally used to break the emulsion and prepare the sample for simethicone measurement. 

Sample pretreatment, like dilution, neutralization, and filtration, may sometimes be necessary prior to injection of a sample into a FIA system, although highly concentrated, very acid (basic) or viscous samples may be directly diluted by injecting microliter volumes into confluence-type manifolds. Filtration cannot be avoided if suspended solids are present initially, yet precipitates may also be formed during the analytical procedure. Not only can the presence of solid particles lead to possible blocking of the tubes, but they can equally well interfere with the transducers, especially in optical systems. Although sample cleanliness is usually easy... 

In this work, several approaches such as direct dilution, wet-ashing, and a newly developed microwave digestion technique were used to prepare and analyze petroleum samples for the purposes of method and result comparison. The samples used for this study were a NIST lubricant additive Standard Reference Material (SRM) 1848, Residue Fuel oil SRM 1634B, 1634C, and a polymer resin. 

For direct dilution organics ICP, USP/FCC grade mineral oil and reagent made O-xylene from Fisher Scientific are used. Organoraetallic standards from Conostan are used for calibration and internal standard. 

For direct dilution organics ICP approaches, modified ASTM D 5185 and D 4951 methods were used in our laboratory. O-xylene is the solvent of choice, and intemal standard is used for all organic ICP applications. 

In Table 1, the direct dilution ICP approach gave lower results because the short residence time (2-3 milli-seconds) of sample aerosol in the ICP plasma was not able to fully decompose the large dry aerosol generated by the nebulization of the used oil. Contrary to direct dilution ICP, microwave digestion dissolved and converted all analytes into aqueous solution prior to ICP analysis. Thus, the results are much better and reliable. Different from samples 1 and 2, ... 

TABLE I—Comparison of microwave digestion and direct dilution ICP for used/fresh oils... 

Element Certified Value Microwave Digestion Wet Ashing Direct Dilution... 

The direct dilution approach works well for lubricant additives and fresh oils. However, this approach caimot handle used oils containing particulate or volatile compounds. Accurate analysis for sulfiir by ICP can be problematic if the samples contain volatile sulfur such as in sulfide form. There is a vapor enrichment phase separation that occurs during the pneumatic nebulization process in ICP. Hence, the use of closed vessel, high-pressure microwave digestion can be used to accurately prepare samples containing volatile sulfides. ICP can be used to determine the accmate sulfur result. 

As another example, a certified fuel residue SRM 1634 C was used to validate the microwave digestion with other proven methods. Thus, microwave digestion is still able to produce better results than other traditional methods, such as wet ashing or direct dilutions. In Table 4, the microwave data is able to achieve better results than wet ashing for both 1634B and 1634C SRMs. However, the direct dilution data are just about the same as microwave digestion data. 

The ultraviolet absorption spectrum obtained either by direct dilution or preliminary treatment with resin (see section 2.3) may be used for determining purity. 

Table 9.6 An example of a preparation scheme for a calibration curve in solution prepared by direct dilution from a stock solution using three sub-stocks each of which was ...

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