Dilution procedure

Fiowchart showing the connections among measured quantities in dilution procedures. 

When the adsorption of collagen was allowed to occur overnight at 10°C, and the collagen solution was replaced by buffer still in the cold (10°C) using the dilution procedure, but the viscometer was subsequently transferred to a thermostat at 15°C, the results of Table I are obtained. Raising the temperature from 7.7°C to 15°C has roughly doubled the measured film thickness. 

The parent series of cryptands may be represented by (213) - a stepwise increase in cavity size occurs along this series. High-dilution procedures are employed for the synthesis of these cages. 

The macrotricyclic ligands (240) and (241) may be synthesized by multistep high-dilution procedures (Graf Lehn, 1975). They contain spherical cavities which are able to accommodate suitable guests whether they be cationic, neutral, or anionic. 

What therapeutic measures (e.g., the use of blocking agents or isotopic dilution procedures) have been taken ... 

Another is a so-called serial dilution procedure. In this procedure, the second solution is prepared by diluting the first, the third by diluting the second, the fourth by diluting the third, etc. Once again, volumetric flasks and suitable solution transfer devices are required. 

Reversibility of inhibition can be assessed by dialyzing the inhibited enzyme versus buffer, or by passing the inhibited enzyme down a desalting column, or by a dilution procedure. In each case, an uninhibited (control) sample of enzyme should be treated in parallel with the inhibited enzyme sample, as control enzyme activity often changes to some degree as a result of the experimental procedure. 

A rapid dilution procedure is routinely used in the author s laboratory to assess reversibility, and it is particularly enlightening if enzyme activity is then determined in a continuous spectrophotometric assay. A microplate assay is set up, in triplicate, as outlined in Table 4-3, later. It is assumed, for the purposes of this example, that the for substrate is 10 tM and that the IC50 for the inhibitor in the presence of 10 tM substrate is 200 tM. The concentration of enzyme used in control wells should be at least tenfold greater than the minimum concentration necessary to catalyze a quantifiable increase in product concentration over the duration of the incubation of substrate with enzyme. 

It is critical when performing quantitative GC/MS procedures that appropriate internal standards are employed to account for variations in extraction efficiency, derivatization, injection volume, and matrix effects. For isotope dilution (ID) GC/MS analyses, it is crucial to select an appropriate internal standard. Ideally, the internal standard should have the same physical and chemical properties as the analyte of interest, but will be separated by mass. The best internal standards are nonradioactive stable isotopic analogs of the compounds of interest, differing by at least 3, and preferably by 4 or 5, atomic mass units. The only property that distinguishes the analyte from the internal standard in ID is a very small difference in mass, which is readily discerned by the mass spectrometer. Isotopic dilution procedures are among the most accurate and precise quantitative methods available to analytical chemists. It cannot be emphasized too strongly that internal standards of the same basic structure compensate for matrix effects in MS. Therefore, in the ID method, there is an absolute reference (i.e., the response factors of the analyte and the internal standard are considered to be identical Pickup and McPherson, 1976). 

Description of dilution procedures used to obtain recommended dosage. Was the admixture tested and approved ... 

The classical methods for detection and quantitation of racemization require analysis of the chiral purity of the product of a peptide-bond-forming reaction. For example, the Anderson test is used to explore a variety of reaction conditions for the coupling of Z-Gly-Phe-OH to H-Gly-OEt (Scheme 6). 9 The two possible enantiomeric tripeptides are separable by fractional crystallization, so that gravimetric analysis furnishes the racemization data. This procedure has a detection limit of 1-2% of the epimerized tripeptide. A modification by Kemp,1"1 utilizing 14C-labeled carboxy components, extends the detection limit by two to three orders of magnitude by an isotopic dilution procedure. The Young test 11 addresses the coupling of Bz-Leu-OH to H-Gly-OEt, and the extent of epimerization is determined by measurement of the specific rotation of the dipeptide product. 

Spark source (SSMS) and thermal emission (TEMS) mass spectrometry are used to determine ppb to ppm quantities of elements in energy sources such as coal, fuel oil, and gasoline. Toxic metals—cadmium, mercury, lead, and zinc— may be determined by SSMS with an estimated precision of 5%, and metals which ionize thermally may be determined by TEMS with an estimated precision of 1% using the isotope dilution technique. An environmental study of the trace element balance from a coal-fired steam plant was done by SSMS using isotope dilution to determine the toxic metals and a general scan technique for 15 other elements using chemically determined iron as an internal standard. In addition, isotope dilution procedures for the analysis of lead in gasoline and uranium in coal and fly ash by TEMS are presented. 

Obviously, some procedures take less time than others. For example, sample concentration by the purge and trap technique that precedes VOC analyses takes only about 20 minutes. It is performed immediately prior to analysis on a multisample automated concentrator combined with an analytical instrument. The shortest of all sample preparation procedures is the waste dilution procedure, commonly known as dilute and shoot, which takes minutes. It consists of diluting a known volume of a concentrated waste sample in a known volume of a compatible solvent, followed by an injection into a gas chromatograph. 

Reproducible chemical shifts of a secondary reference and substrate as well can be obtained at sufficient dilution even in a protic donor solvent21. This dilution procedure is not always practical for sensitivity reasons, but when a polarization transfer provides... 

In the laboratory, the isotope dilution procedure involves adding a known amount of spike of known isotopic composition to a known amount of sample of known isotopic composition the mixture of spike and sample is equilibrated the ratio of the sample isotope to the spike isotope is then measured and the resulting R is inserted into the equation. For replicate analyses, this is the only parameter... 

The preparation of the first examples of mixed S,Te-macrocycles, such as 1,4-dithia-7-telluracyclononane, 14-dithia-8-telluracycloundecane, 1,5-dithia-ll-tellurocyclotetradecane, and 1,4,7-trithia-11-telluracyclotetradecane, via a disguised dilution procedure (not therein defined) was reported <02CC427>. 

For the analysis of iron, steel, and ferro compounds, therefore, standards are always used whose chemical composition is very similar to the sample. These standards undergo the same dissolution and dilution procedure as the sample. In special cases they are fused as for the sample. Therefore, the standard solutions differ neither in their physical characteristics nor in their concentration of acid or total salt. Any effects that occur will be the same for sample and standard measurements. They are easily eliminated by including them in the calibration. 

Petroleum oils often contain suspended or colloidal inorganic materials. In the case of used lubricating oils small particles of metals are present. In many cases these suspended solids are of sufficiently small particle size that efficient breakdown occurs in the flame and a simple dilution procedure may be used. However, where it is suspected that this is not the case then it is recommended that an ashing technique is used to prepare the sample. 

Alkyl Pb compounds, mainly tetramethyl and tetraethyl Pb, are added to gasoline as anti-knock agents. The amount added varies from country to country but is generally in the range 200—1500/igml-1 Pb and this may be present as one or both of the Pb alkyl species mentioned. Unfortunately, it has been found that the Pb response in atomic absorption spectroscopy is dependent on the particular alkyl with which it is associated. Thus, unless it is known that only one particular Pb alkyl is present in a gasoline sample, it is not possible to employ a simple dilution procedure. Since the exact nature of the Pb species is seldom known for sure, then a general analytical method must ensure that the response from the various Pb alkyls is equalised in some manner. This is achieved by stabilisation with iodine and a quaternary ammonium salt. 

Dilutions. The quality of your results depends on accurate dilutions and scrupulous care in avoiding contamination of the dilute solutions by stray electrolytes. Follow the dilution procedure described below. 

A dilution procedure typically involves two types of glassware a pipet and a volumetric flask. A pipet is a device for accurately measuring and transferring a given volume of solution. There are two common types of pipets measuring pipets and volumetric pipets, as shown in Fig. 4.10. Measuring pipets are used to measure out volumes for which a volumetric pipet is not available. For example, we would use a measuring pipet as shown in Fig. 4.11 to deliver 28.6 milliliters of 17.5 M acetic acid into a 500-milliliter volumetric flask and then add water to the mark to perform the dilution described above. 

This relationship can also be used to establish the accuracy of the Se spike concentration, which Is most conveniently added as a solution. Employing accurately prepared samples of natural selenium (Sen known) spiked with known amounts of the 2se solution, R is then measured and Equation 4 solved for Sega This is basically an inverse Isotope dilution procedure. When performed on the same Instrument to be used for subsequent measurements. It has the added advantage of cancelling out any mass discrimination by the Instrument. 

Much effort has been devoted to find inexpensive formulations compatible with an economical process. To obtain an inverse monophasic microemulsion, special conditions have to be met. Their main parameters are as follows surfactant concentration, HLB of the surfactant(s), temperature, nature of the organic phase and composition of the aqueous phase. A preferred class of surfactants are those forming microemulsions without any added cosurfactant (alcohol). The presence of an alcohol is indeed liable to favor chain transfer reactions, limiting the range of attainable molecular weights (19,20) In addition, the dilution procedure of these microemulsions containing alcohols is not trivial since the continuous phase consists of a solvent mixture of unknown composition. 

X 2S-cm neutral alumina column (activity grade 1) loaded using acetonitrile. The mixture is eluted slowly with acetonitrile, and the deep yellow band is collected. The eluate is concentrated to 25 mL and diluted with an equal volume of methanol. Repetition of this concentration-dilution procedure leads to crystallization of the bridged product, IV, which is collected by suction filtration, washed with methanol, and dried in vacuo over P4O10. Yield 3.5 g (62%). 

The culture showing the best results from an EIA assessment designed to detect the presence of picloram specific antibodies was selected for the limiting dilution procedure to acheive the clonality of the hybridoma cells. A dilution was calculated to yield one cell per well of a 96 well microtitration plate. The wells of the plate were checked daily for the presence of a single colony. Once a colony was visible, it was fed with 125 uL of RPMI medium. 

---