Phase quantification

Presently, FAB-MS spectra are routinely used to characterize synthetic tyrosine O-sulfate peptides.152,57,63-671 Since partial hydrolysis of the sulfate ester occurs in the gas phase, quantification of the tyrosine O-sulfate residue by mass spectrometry is not possible, but combined with one-peak assignment in HPLC, FAB-MS represents a powerful analytical tool. On the other hand, partial hydrolysis in the gas phase excludes the presence of sul-fonated species which should be perfectly stable. In early studies the presence of such species were excluded by quantitative recovery of tyrosine upon acid hydrolysis or upon hydrolysis with arylsulfatase.1361 Recently, even MALDI-TOF-MS spectra of CCK-peptides1441 and of conotoxins a-PnIA and a-PnlB 138 were reported which show that in the positive-ion mode the [M + H-S03]+ ions represent the base peaks, while in the negative-ion mode, [M-H]-ions consistently correspond to the base peaks. In the CCK peptides intramolecular salt bridging of the sulfate hemi-ester with proximal positive charges of arginine or lysine side chains was found to reduce the extent of hydrolysis in the gas phase significantly.144,1491... 

Asap and Augustin (125) analyzed TBHQ content in frying oil. After solubilization in hexane, TBHQ was extracted into acetonitrile and analyzed on an ODS column using acetonitrile-n-butanol-water as mobile phase. Quantification of TBHQ was achieved at a wavelength of 292 nm. 

In the pharmaceutical community, quantitative analyses has conventionally been based on the intensity of a characteristic peak of the analyte. It is now recognized that phase quantification will be more accurate if it is based on the entire powder pattern.This forms the basis for the whole-powder-pattern analyses method developed in the last few decades. Of the available methods, the Rietveld method is deemed the most powerful since it is based on structural parameters. This is a whole-pattern fitting least-squares refinement technique that has also been extensively used for crystal structure refinement and to determine the size and strain of crystallites. 

In the example above, the phases are such that the chemistry is unambiguous and the phase quantification could have been derived by normative calculation from bulk elemental analysis (XRF). This is not often the case, but it is frequently possible to establish the composition of each phase within a system via electron probe microanalysis or similar and conduct the inverse of a normative calculation to derive the bulk chemistry from the XRD QPA. This can then be compared with the results of a standards based technique such as XRF to obtain a measure of the accuracy of the XRD analysis. Examples of such calculations are given later in the sections dealing with application in mineralogical and industrial situations. Where this is not possible or practical, it is better to consider XRD QPA as a semi-quantitative technique at best. 

Internal Standard Addition. An example of the use of an internal standard for phase quantification is the recent work by Madsen et in their study of the reaction mechanism of pressure acid leaching (PAL) of nickel laterite ores. This was an in situ study in which nickel laterites were reacted with sulfuric acid at elevated temperature and hydrothermal pressure to prevent the boiling of the acid. The purpose of pressure acid leaching is to dissolve any nickel-bearing phases into the acid and subsequently treat this with solvent extraction for the recovery of the nickel. There has been much ex situ work done to the reaction mechanisms of this system, but these studies have relied on the cooling of the system prior to any analytical work. 

As pectenoLoxins have a conjugated diene in the macrolide skeleton, UV detection between 235 and 239 nm is applicable to their detection after LC separation. PTXs can be separated by a C18 or C8 reversed phase column with acetonitrile/water mobile phases. Quantification of PTX2 by isocratic LC-UV detection at 235 nm has been reported [4-7,20,25,26]. The LC-UV detection is not sufh-ciently sensitive or specific for pectenotoxins in bivalve exfracts due to biological matrices, although this approach is useful for algal extracts [4-7,20,25,26]. 

The development and extension of QPA were facilitated by obtaining a large number of standard diffraction patterns of minerals and chemical compounds, thanks to the development of the powder camera by Debye and Scherrer (1916, 1917). Nevertheless, the take-off of phase quantification started in the late 1940s with the design and industrial manufacture of powder diffractometers and the formulation of a theoretical basis for quantitative analysis by Klug and Alexander in 1948. 

Quantification of Calcium Sulfate Phase Transformations In order to quantitatively describe the progress of phase conversion ratios of absolute intensities of characteristic peaks of each phase s XRD pattern were compared. This method is generally considered suitable for quantitative phase analysis of mixtures [35]. To aid phase quantification, calibration curves based on prepared mixtures with known composition were used and the respective intensity ratios calculated. The intensity ratios were calculated from the intensity of peaks at 26 29.10725.43°, 29.71°/25.43° and... 

It is stressed that true crystallinity bands have only been proved for a small number of polymers, and so the majority of measurements that actually correlate intramolecular conformation with crystallinity should be interpreted with caution. For example, in the Raman spectrum of highly oriented PET it is possible to observe a high level of trans glycol conformers which are nonetheless located in amorphous material [235]. In this case, correlation of con-former content with crystallinity would be misleading, and the carbonyl bandwidth actually gives a better measure. As well as phase quantification, characterisation of phase transitions in response to temperature or mechanical changes has also received considerable attention [236-240]. 

Upon identifying the list of potential hazards and its contributing factors, which could be achieved by several methods including HAZard and OPerability studies (HAZOP) (Villemeur (1992)), Failure Mode and Effects Analysis (FMEA) (Military Standard (1980)), Fault Tree Analysis (FTA) (Henley and Kumamoto (1992)), etc, the next step is to quantify these events for the risk estimation phase. Quantification of risk considers two parameters, namely,... 

In the external standard approach, phase quantification is carried out through the comparison of the phase scale factors of a sample to the scale factor of a well-characterised standard material measured under identical diffractometer conditions. In this procedure only the constant parameter K is cancelled out and the different MACs of the sample, jJL , and the standard, Ps, need to be taken into account. The following expression can be developed from Equation 4.5 (Man Suherman et al. 2002 O Connor and Raven 1988) ... 

The assay of ethyleneamines is usually done by gas chromatography. Compared to packed columns, in which severe tailing is often encountered due to the high polarity of the ethyleneamines, capillary columns provide better component separation and quantification. Typically, amines can be analyzed using fused siUca capillary columns with dimethyl silicones, substituted dimethyl silicones or PEG Compound 20 M as the stationary phase (150). 

With this mobile phase colour compounds and carotenoids separated with 15 ml of chloroform (first fraction) and the second fraction with 20ml chloroform contained total petroleum hydrocarbons. At the end Spectrofluorophotometry was employed for quantification of analytes. 

Phase 3 - Process Planning. The important design characteristics from Phase 2 are ranked with key process operations, where quantification yields actions to improve the understanding of the processes involved and gain the necessary expertise early on. The critical process operations highlighted are then carried forward to the next phase. 

Modern materials have a complex three-dimensional internal structure with many different phases. Although for these samples quantification is not possible, technologists are often interested in relative differences between several samples, or they already know the bulk concentrations and are only interested in the element distribution. 

In Raman spectroscopy the intensity of scattered radiation depends not only on the polarizability and concentration of the analyte molecules, but also on the optical properties of the sample and the adjustment of the instrument. Absolute Raman intensities are not, therefore, inherently a very accurate measure of concentration. These intensities are, of course, useful for quantification under well-defined experimental conditions and for well characterized samples otherwise relative intensities should be used instead. Raman bands of the major component, the solvent, or another component of known concentration can be used as internal standards. For isotropic phases, intensity ratios of Raman bands of the analyte and the reference compound depend linearly on the concentration ratio over a wide concentration range and are, therefore, very well-suited for quantification. Changes of temperature and the refractive index of the sample can, however, influence Raman intensities, and the band positions can be shifted by different solvation at higher concentrations or... 

Theoretical representation of the behaviour of a hydrocyclone requires adequate analysis of three distinct physical phenomenon taking place in these devices, viz. the understanding of fluid flow, its interactions with the dispersed solid phase and the quantification of shear induced attrition of crystals. Simplified analytical solutions to conservation of mass and momentum equations derived from the Navier-Stokes equation can be used to quantify fluid flow in the hydrocyclone. For dilute slurries, once bulk flow has been quantified in terms of spatial components of velocity, crystal motion can then be traced by balancing forces on the crystals themselves to map out their trajectories. The trajectories for different sizes can then be used to develop a separation efficiency curve, which quantifies performance of the vessel (Bloor and Ingham, 1987). In principle, population balances can be included for crystal attrition in the above description for developing a thorough mathematical model. 

J. A. Pascual and J. Sanagustin, Eully automated analytical method for codeine quantification in human plasma using on-line solid-phase extraction and high-perfomance liquid clrromatogi aphy with ulti aviolet detection , 7. Chromatogr. B 724 295-302 (1999). 

The knowledge of these adsorption isotherms allows quantification of the respective affinity for the stationary phase with respect to the different solutes. Many different isotherm equations have been described in the literature, and experimental methods allowing their determination are reviewed by [58]. As a first approximation, modified competitive Langmuir isotherms can often he used ... 

The amorphous orientation is considered a very important parameter of the microstructure of the fiber. It has a quantitative and qualitative effect on the fiber de-formability when mechanical forces are involved. It significantly influences the fatigue strength and sorptive properties (water, dyes), as well as transport phenomena inside the fiber (migration of electric charge carriers, diffusion of liquid). The importance of the amorphous phase makes its quantification essential. Indirect and direct methods currently are used for the quantitative assessment of the amorphous phase. 

Mathematical techniques allow us to quantify total displacement caused by all vibrations, to convert the displacement measurements to velocity or acceleration, to separate this data into its components using FFT analysis, and to determine the amplitudes and phases of these functions. Such quantification is necessary if we are to isolate and correct abnormal vibrations in machinery. 

A sensitive determination of alkanesulfonates combines RP-HPLC with an on-line derivatization procedure using fluorescent ion pairs followed by an online sandwich-type phase separation with chloroform as the solvent. The ion pairs are detected by fluorescence. With l-cyano-[2-(2-trimethylammonio)-ethyl]benz(/)isoindole as a fluorescent cationic dye a quantification limit for anionic surfactants including alkanesulfonates of less than 1 pg/L per compound for a 2.5-L water sample is established [30,31]. 

Castro and Canselier [114] similarly used reverse phase HPLC with methanol-water containing a low concentration of nitric acid as eluent. Quantification was made possible by using a moving-wire flame ionization detector. 

Factors may be classified as quantitative when they take particular values, e.g. concentration or temperature, or qualitative when their presence or absence is of interest. As mentioned previously, for an LC-MS experiment the factors could include the composition of the mobile phase employed, its pH and flow rate [3], the nature and concentration of any mobile-phase additive, e.g. buffer or ion-pair reagent, the make-up of the solution in which the sample is injected [4], the ionization technique, spray voltage for electrospray, nebulizer temperature for APCI, nebulizing gas pressure, mass spectrometer source temperature, cone voltage in the mass spectrometer source, and the nature and pressure of gas in the collision cell if MS-MS is employed. For quantification, the assessment of results is likely to be on the basis of the selectivity and sensitivity of the analysis, i.e. the chromatographic separation and the maximum production of molecular species or product ions if MS-MS is employed. 

A dansyl-containing lysine analogue, monodansylcadaverine (MDC), was used in initial TGase linking, because the dansyl UV absorption peak allowed quantification by reverse-phase HPLC using the absorbance at 280 nm. The reacted Qll was dissolved in TFA along with a known dansyl standard. Peak areas of the standard were then compared with product to establish the amormt of MDC present into Qll. Six Qll peaks were measured and ascribed to Qll with zero to five MDCs attached (Fig. 33). 

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