Endpoint determination

Turbidimetric titration has also been applied to one-phase titration of alcohol sulfates and other anionic surfactants. The titration is carried out with hyamine 1622 in aqueous solution without the organic phase and indicator and the endpoint is taken as the point of maximum turbidity. The presence of nonionics and inorganic salts at high concentration interfere with the endpoint determination [243]. 

Applications Potentiometry finds widespread use for direct and selective measurement of analyte concentrations, mainly in routine analyses, and for endpoint determinations of titrations. Direct potentiometric measurements provide a rapid and convenient method for determining the activity of a variety of cations and anions. The most frequently determined ion in water is the hydrogen ion (pH measurement). Ion chromatography combined with potentiometric detection techniques using ISEs allows the selective quantification of selected analytes, even in complex matrices. The sensitivity of the electrodes allows sub-ppm concentrations to be measured. 

The British Pharmacopoeia [2] describes a potentiometric titration method for the determination of penicillamine as the pure drug substance. The method is performed by dissolving 100 mg of the substance in 30 mL of anhydrous acetic acid. The mixture is titrated with 0.1 M perchloric acid, and the endpoint determined potentiometrically. Each milliliter of 0.1 M perchloric acid is equivalent to 14.92 mg of C6HnN02S. 

Figure 14 Some examples of endpoint determination in titrations using chemiluminescent indicators. (A) Acid-base titration the endpoint is detected by the emission of light (B) complexometric titration the endpoint is detected by disappearance of light. M, metal acting as a catalyst X, excited state from the CL precursor acting as indicator.

The two main online applications of hyperspectral imaging are blending endpoint determination (Figure 19) and capsule control (Figure 20). Other applications may be possible, such as content uniformity, determination of dissolution properties, and water quantification, but are not described in this chapter. 

The C02 gas is totally driven off by gentle heating, so that it will not interfere with the endpoint determination The unused portion ofthe H2S04 is tben titrated The back titration reaction is... 

Different experimental approaches are possible with the same endpoint detection method. For example, the titration curve can be plotted and the endpoint determined graphically. First and second derivative curves can be plotted or the derivatives obtained electronically. Another approach is to titrate to a predetermined endpoint signal. This technique is very useful with coulometric titrations, and many examples, especially those involving potentiometric endpoint detection, are found in the literature. The most widely applicable way... 

The endpoint determination, while subjective was found to give values of max to within .02. This procedure was taken from the thesis work of G. Williams at Lehigh University. (H)... 

LTF uses laboratory sublethal toxicity data and biological field observations ranked on the same scale to examine the strength of their relationship. The LTF rating scheme can use all endpoints determined for biota (fish and invertebrates) in field observations, and allows for the addition of further endpoints and indices as they are developed. LTF has the potential of linking a specific effluent source to a measured field effect in indigenous organisms. 

The Microplate algal toxicity test, another popular small-scale bioassay, is equally employed for WASTOXHAS applications (see Chapter 3, volume 1 of this book). In our case, rapid endpoint determinations of growth (72h-IC50s) are made with a microplate fluorescence reader, where algal biomass is indirectly measured via chlorophyll a fluorescence (excitation filter 440 nm - emission filter 640 nm). 

Procedure. Product-Determining Studies. In a typical productdetermining run 10 mmoles of organomercurial were dissolved in ca. 50 ml of CH2C12 and placed in the reaction vessel. After the vessel was cooled to the proper temperature, the 03-02 flow was started. In all cases an immediate white precipitate appeared. This precipitation was constant throughout the entire ozonolysis procedure and in fact was used as an endpoint determinant in certain cases. 

This approach uses power as a function of molecular weight to locate the endpoint. Many viscous polymerization reactions do not lend themselves to either online endpoint determinations or rapid laboratory analyses. 

Power consumption of the mixer motor for endpoint determination and scale-up is widely used (Leuenberger and subsequent work, HoW and subsequent work, Landin et al. Faure et and many others because the measurement is economical, does not require extensive mixer modifications, and is well correlated with the granule growth. 

Whether the application is drying a slurry, powder or granulation, the ultimate goal is achievement of some solvent level appropriate for transfer of the dried material to a subsequent process step. Thus, a method of endpoint determination is crucial to the economic success of the drying step as well as to the endowment of the proper physical characteristics on the dried material. For example, over-drying may result in unwanted static charge or reduced particle size due abradement of particles. 

Perhaps the be.st known method of endpoint determination is thermogravimetric analysis or loss on drying analysis. This method requires an operator to stop the process and gather a representative sample for analysis. The drying process resumes while the sample is analyzed po.sing the po.ssibility that the material may exceed the acceptable endpoint while the analysis is made. Loss on drying is not specific to a particular component as all volatile components are driven off in the analysis. 

Karl Fischer titrimetry is another endpoint determination method requiring collection of samples from the dryer. This analytical method is more sophisticated than simple loss on drying. It is also more costly, more time consuming and exposes employees to dangerous chemicals. Expenditures are also necessary for the chemical reagents and the safe disposal of these reagents. 

The following endpoint determination methods do not generally require a physical sampling to be taken from the dryer and could be termed non-destructive methods. 

Additionally, near-infirared spectroscopy has been utilized to monitor moisture for endpoint determination (155,156), though this technique is limited to detecting only moisture at the bed surface. The FBRM is a technique for panicle size determination in a study by Dilworth et al. (157), comparing power consumption. FBRM, and acoustic signals, these measurements were found to be complimentary. Thermal effusivity is a material propeny that combines thermal conductivity, density and heat capacity. Fariss et al. (158) used at-line samples and found colinearity between power consumption and thermal effusivity. 

Most experiments requiring assessment of growth or toxicity involve comparison of experimental treated cultures with control untreated cultures. If such comparisons are to give an accurate measurement of growth stimulation or inhibition, then control and experimental wells should still be in exponential growth phase at the time of assay endpoint determination. Also, the cell number in all wells should be in the linear position of the graph of optical density versus cell number per well. To ensure that these conditions apply, each assay method should be characterized for ... 

Landis, W.G., G.B. Matthews, R.A. Matthews, and A. Sergeant. 1994. Application of multivariate techniques to endpoint determination, selection, and evaluation in ecological risk assessment. Environ. Toxicol. Chem. 13 1917-1927. 

If the flasks containing turbid solutions, after endpoint determination, were allowed to stand for 20 to 30 min, they would slowly clarify and could then be titrated with more CEES. It is... 

These systems are designed for the endpoint determination of substrate concentrations, and do not provide a straightforward means for making kinetic measurements. Stopped-flow enzyme reactor systems have been designed for automated kinetic assays. A diagram of a stopped-flow reactor that uses a postcolumn chemical indicator reaction is shown in Figure 4.12.31 In this system, the flow rate of the... 

Every in vitro method should be detailed in the developer laboratories using Standard Operating Procedures (SOPs) covering all essential components and steps of the method. The SOP(s) should be sufficiently defined and described and should include the rationale for the test method, a description of the materials needed, such as specific cell types, a description of what is measured and how it is measured, a description of how data will be analyzed, acceptance and decision criteria for evaluation of data, and what are the criteria for suitable test performance. All limitations, e.g., lack of metabolic competences (presence of phase 1 and phase 2 biotransformation activities) or absence of critical transporters, should be included in the in vitro method description. In general, the in vitro method should not require equipment or material from a unique source. This may not be always possible for particular in vitro test systems or other components of the method in which case a license agreement between the provider and a recipient/user may be required. For complex and/or specialized equipment, the equipment specifications and requirements should also be described. Acceptance criteria for measurements carried out on the equipment should also be provided where applicable (e.g., for analytical endpoint determinations, linearity and limits of detection should de detailed) [2],... 

Prake P, Greenhalgh D, Grierson SM, Hempenstall JM, Rudd DR. Process control and endpoint determination of a fluid bed granulation by application of near infra-red spectroscopy. Inti J Pharm 1997 51 75 -80. 

The enzyme 3a-hydroxysteroid dehydrogenase (EC 1.1.1.50), which is isolated from Pseudomonas testosteroni, catalyzes the conversion of all 3a-hydroxycholanic acids to 3-ketochoIanic acids, with the concomitant reduction of NAD to NADH. The NADH formed in the reaction is then determined spectrophotometrically at 340 nm. To ensure complete reaction, hydrazine is usually added to bind the 3-keto products (P2). The optimum conditions for enzymatic assay include a pH of 9.0 to 9.5 and reaction temperature in the range 20 to 40 C (T13). Reaction rates for individual bile acids may not be identical, but the assay is normally carried out as an endpoint determination. Alternatively, the addition of bovine serum albumin appears to overcome the problem of variable aflinity of 3a-hy-droxysteroid dehydrogenase for different bile acids if reaction rates are to be measured (S13). 

Previously, we tested a manual method using antibiotic-mediated lysis of nontarget cells followed by immuno-magnetic separation with an adenylate kinase (AK) bioluminescence endpoint determination. This 4 h assay for patient swabs was carried out on a limited number of samples. The work reported here was to introduce automation into the assay and to carry out tests on a larger number of samples in a hospital setting. Initial assay development was done in a non-clinical laboratory using spiked samples. The assay was then adapted to fit in with the standard hospital test. Modifications were introduced as testing in the hospital laboratory proceeded. 

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