Dilution method

Dilution susceptibility testing methods are used to determine the minimal concentration of antimicrobial required to inhibit or kill the microorganism. This can be achieved by dilution of an antimicrobial in either agar or broth media [20]. 

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For this kind of case, a modification of the dilution method is being developed. Instead of using an external fixed-geometry measurement chamber, a suitable part of the process, e.g. a stretch of pipe, is used. A radiation detector is mounted on the outside of the pipe, and a tracer emitting sufficiently hard gamma radiation is used. As sufficient mixing can be achieved by injecting upstream the separator the radiation level found will be strictly proportional to the concentration and thus inversely proportional to the true flow rate. 

The plaque assay is desirable because it is very sensitive and only detects infectious viral particles. However, there are viral agents which cannot be supported by cell lines. In these cases other methods must be used. The polymerase chain reaction (PGR), which amplifies DNA or RNA from viral agents, can be used to detect the presence and quantity of viral agents. The amount of RNA or DNA target in the initial sample can be determined by competitive PGR where the quantity of amplified product is compared to a control PGR product where the initial amount of target is known. Quantification is also possible by an end-point dilution method similar to that used to determine a tissue culture infections dose. PGR methods can be very sensitive however. 

As a disiafectant or antiseptic, phenol [108-95-2] (carboHc acid) is mosdy of historical iaterest. However, its extensive use continues ia both iavestigative and analytical microbiology, eg, as ia the AO AC phenol coefficient and use-dilution methods. 

Tuberculocidal Test. The tubercle bacillus is resistant to disinfectants because the cells are protected with a waxy coating that is not readily penetrated. The tuberculocidal test is a use dilution practical type test that employs porcelain cylinders. The bacteria are different from those in the use dilution method (Table 10), the incubation time is longer, and the details of the procedure are different. For example, in the tuberculocidal test the test is divided into two parts, a presumptive test and a confirmatory test. The former employs Mycobacterium smegmatis and the latter employs Mycobacterium bovis (BCG). For the presumptive test the incubation time is 12 days, as against 48 hours for other bacteria used in the use-dilution method. For the confirmatory test the incubation time is 60 days, with an additional 30 days in case there is no growth. As shown in Table 10, the concentrations of the phenol standard are higher than used with other bacteria. 

This method is highly sensitive (detection limit achieves 5T0 M), reproducible and simple in implementation. The accuracy of the results was verified by the added—found and dilution methods. 

The sensory technique used for assessing human perception of odors is called olfactometry. The basic technique is to present odorants at different concentrations to a panel of subjects and assess their response. The process favored by the U.S. National Academy of Sciences is dynamic olfactometry (16). This technique involves a sample dilution method in which a flow of clean, nonodorous air is mixed with the odorant under dynamic or constant... 

Solution A dilution method was employed to achieve correct antifoam concentration. An injection... 

C. Dilution method. The sample and standard solution are contained in glass tubes of the same diameter, and are observed horizontally through the tubes. The more concentrated solution is diluted until the colours are identical in intensity when observed horizontally through the same thickness of solution. The relative concentrations of the original solutions are then proportional to the heights of the matched solutions in the tubes. This is the least accurate method of all, and will not be discussed further. 

Solid dilution method 8 Appendix British Standards... 

Data corrected for recovery using isotope dilution method. Tobacco data are reported per dry weight. 

API Serial Dilution Method. The API serial dilution method is the most widely used method for the detection of microorganisms. Field test methods for estimating bacterial populations have been standardized. A standard method dealing with the dose-response (time-kill) testing for evaluating biocides has been established. Sampling methods are of special importance because effective sampling is essential to any successful analysis. 

In most alpha and mass spectrometric methods for which sample preparation is extensive and chemical recoveries can vary considerably from sample to sample, precise elemental concentrations are determined by isotope dilution methods (e.g., Faure 1977). This method is based on the determination of the isotopic composition of an element in a mixture of a known quantity of a tracer with an unknown quantity of the normal element. The tracer is a solution containing a known concentration of a particular element or elements for which isotopic composition has been changed by enrichment of one or more of its isotopes. 

Quantitative analysis using FAB is not straightforward, as with all ionisation techniques that use a direct insertion probe. While the goal of the exercise is to determine the bulk concentration of the analyte in the FAB matrix, FAB is instead measuring the concentration of the analyte in the surface of the matrix. The analyte surface concentration is not only a function of bulk analyte concentration, but is also affected by such factors as temperature, pressure, ionic strength, pH, FAB matrix, and sample matrix. With FAB and FTB/LSIMS the sample signal often dies away when the matrix, rather than the sample, is consumed therefore, one cannot be sure that the ion signal obtained represents the entire sample. External standard FAB quantitation methods are of questionable accuracy, and even simple internal standard methods can be trusted only where the analyte is found in a well-controlled sample matrix or is separated from its sample matrix prior to FAB analysis. Therefore, labelled internal standards and isotope dilution methods have become the norm for FAB quantitation. 

For destructive measuring methods, a CRM would serve as a reference to check the recovery of a particular matrix removal procedure. This is especially important for open destructions at atmospheric pressure. Alternatively, isotope dilution methods may be used once isotopic equilibrium is established, loss of analyte does not affect the analysis result. Isotope dilution techniques are only available in a few specialised laboratories. Another type of problem is encountered in pressurised methods oxidising the matrix in a closed vessel or bomb. Due to the large amounts of gas (CO2, NO, SO2) evolving from samples with a high organic matrix content, an excessive pressure build-up occurs that prohibits the use... 

The isotope dilution method can be used for the measurement of molecules or elemental species (about 60 elements have stable isotopes). This approach allows ultratrace analysis because, contrary to radioactive labelling where the measurement relies on detecting atoms that decay during the period of measurement, all of the labelled atoms are measured. 

A mass-isotope dilution method for determining the gamma isomer of benzene hexachloride, in which gamma-hexadeuterobenzene hexachloride is used as a tracer molecule and the dilution is determined by use of infrared spectrophotometry, has been developed by Trenner et al. (52). Impurities have no effect on the accuracy of this method. 

Hawkins, A., et al. (1997). Comparison of plasma vims loads among individuals infected with hepatitis C vims (HCV) genotypes 1,2, and 3 by quantiplex HCV RNA assay versions 1 and 2, Roche monitor assay, and an in-house limiting dilution method. J. Clin. Microbiol. 35,187-192. 

A reference solution is prepared by a dilution method. A known quantity of sample is dissolved in a known volume of the system buffer of known pH the amount of sample is X times less than in the above case in order to avoid precipitation in the formed solution. The spectrum is immediately taken by the UV spectrophotometer, to take advantage of the possibility that solution may be supersaturated (i.e., solid should have precipitated, but because not enough time was allowed for the solid to precipitate, the solution was temporarily clear and free of solid). Mathematical treatment of the spectral data yields the AUC of the reference sample solution, AUQ . The ratio R = AUCS/AUCS is used to automatically recognize the right conditions for solubility determination when the reference has no precipitate, and the sample solution is saturated with precipitate. Under these conditions, solubility is determined from the expression... 

Animal infectivity methods Some viruses do not cause recognizable effects in cell cultures but cause death in the whole animal. In such cases, quantification can only be done by some sort of titration in infected animals. The general procedure is to carry out a serial dilution of the unknown sample, generally at ten-fold dilutions, and samples of each dilution are injected into numbers of sensitive animals. After a suitable incubation period, the fraction of dead and live animals at each dilution is tabulated and an end point dilution is calculated. This is the dilution at which, for example, half of the injected animals die. Although such serial dilution methods are much more cumbersome and much less accurate than cell culture methods, they may be essential for the study of certain types of viruses. 

The compound 7-(4-chloro-benzyl)-2-(4-chloro-phenyl)-3,8a-dihydro-pyridazino[4,3-( ][l,3,4] thiadiazin-8-one 42 has been reported to be active against Bacillus Escherchia coli, Staphylococcus aureus, and Pseudomonas aeruginosa by a serial dilution method <2001IJB475>. Triazino-thiadiazines 24f, 25b, 25c, and 25f <2002IJH287> have been reported to be active against S. aureus-, sydnone derivatives of triazino-thiadiazine 24f <2002IJH287> are more reactive than coumarin derivatives. 

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