Quantification and Quality Control

Commonly used techniques for this purpose are chromatography and hyphenated methods, mostly coupled with element-specific detection, for example, GC-AED,221 GC coupled with atomic absorption detection (GC-AAS),222 or ICP-MS. The last mentioned provides superior sensitivity as well as the possibility of using isotopically labeled standards for quantification and quality control.223... 

Vibrational Spectroscopy [Infrared (mid-IR, NIR), Raman]. In contrast to X-ray powder diffraction, which probes the orderly arrangement of molecules in the crystal lattice, vibration spectroscopy probes differences in the influence of the solid state on the molecular spectroscopy. As a result, there is often a severe overlap of the majority of the spectra for different forms of the pharmaceutical. Sometimes complete resolution of the vibrational modes of a particular functional group suffices to differentiate the solid-state form and allows direct quantification. In other instances, particularly with near-infrared (NIR) spectroscopy, the overlap of spectral features results in the need to rely on more sophisticated approaches for quantification. Of the spectroscopic methods which have been shown to be useful for quantitative analysis, vibrational (mid-IR absorption, Raman scattering, and NIR) spectroscopy is perhaps the most amenable to routine, on-line, off-line, and quality-control quantitation. 

A series of unknown samples is usually measured together with two sets of calibration standard samples (covering the concentration range for the assay, usually two sets of six or more calibration standards) and two or more sets of quality control samples. The calibration standard samples will be used to establish the calibration for the unknowns. Quality control samples (usually at least 5 % of number of unknowns) are matrix samples of known concentration, which are equally distributed over the analytical run (usually two sets of three different concentration levels 2-3 times the LOQ, mid concentration range and close to the upper limit of quantification). They establish a set of control samples in order to verify the assay performance within the run. Typically, the calibration standards and quality control samples should be within +/-15% of the nominal value. However, in typical assays, it is considered to be acceptable, if 75 % of the standards are within the +/-15 % criteria. Outliers will not be used for the calculation of the calibration curve. Not all standards at one concentration should be excluded. A similar criteria is applied for the quality control samples 2 out of 3 of the quality control samples should be within +/-15 % of their nominal value. 

In addition to the mass spectral aspects of these assays, which are outlined below, there may also be extensive requirements to be met by the analyst with respect to compliance with good laboratory practice, which governs the operations of analytical laboratories and includes sampling regimes, assay validation procedures (e.g., limits of detection, limits of quantification, accuracy, reproducibility, and ruggedness), and laboratory accreditation (e.g., staff training, laboratory equipment, documentation, quality assurance, and quality control).142-145... 

Use of quantitative 2D NMR spectroscopy is still quite rare in food analysis and quality control. A possible reason can be that experimental set-up, acquisition and processing of 2D NMR experiments are considered to be too difficult or time-consuming compared to ID NMR experiments. Also, restrictions and regulations from the laboratory environment (quality systems, standards) can hinder application of new methodology in quantification. Considering the challenging sample matrices the 2D NMR methods would be excellent tools in quantification. 

In this article we have introduced the Bruker SGF Profiling method for the authentication, verification and quality control of fiuit juices. In addition to tihe quantification of a large array of characteristic compounds, this fully automated NMR screening technique uses statistical models for the estimation of fhiit content or the origin of the juice. This analysis tool can show known and unknown deviations from normality. Currently, routines are under development to identify unknown deviations by constructing spectral patterns which can be compared to an existing reference compound database. ... 

Routine analytical methods typically include micro (graphite furnace) atomic absorption spectrometry and electrochemical approaches such as anodic-stripping voltammetry. More complex, expensive and nonroutine/ research approaches are inductively coupled plasma-mass spectrometry and definitive methods such as thermal ionization-mass spectrometry. These methods have the requisite sensitivity, specificity, and record of reliability for quantification across the range of environmental exposures that humans presently encounter. Combining current instrumental methods with carefiil quality assurance and quality control protocols permits adequate proficiency for even low Pb concentrations, values of 1—2 pg/dl. 

Raman spectroscopy has been used to characterize organic fibers and films since the 1960s. Initially, Raman spectroscopy was used primarily to identify the material in the same way that infrared (IR) spectroscopy was used. Chemical identification and quantification are still used extensively to determine the type of polymer, the type and amount of comonomers, and the type and amount of pigments, dyes, or other additives. This has been used in forensic science, archaeology, competitive analysis, and quality control. The techniques are nearly identical to those used for the identification of other solids and liquids, with minor modifications required by the fibrous or filmlike nature of the materials. This application will be discussed in Section II,... 

Quantification of the Microarray Signai intensities and Quality Control... 

Unfortunately these and other existing quality control procedures do not answer aU problems. There remains a clear need for development of PCR reference materials that win provide information both on quality and quantity levels. For quality the reference materials should be host-specific and PCR primers, for positive control, may correspond to host specific house keeping genes e.g. b-actin. For quantitative analysis, fluorescence dyes in specific primers might be used in order to measure accurately the amount of DNA present. Such practices, and other as yet un-realized procedures, will be needed to achieve reliable results in the quantification of DNA analysis. 

Typical applications at Polysar included the quantification of residual solvents and monomers in finished rubber products (e.g. styrene in SBR), quality control of feedstocks such as benzene or ethyl benzene as impurities in styrene monomer, and the analysis of samples collected from environmental monitoring programs. 

Another RP-HPLC technique has been applied for the determination of synthetic food dyes in soft drinks with a minimal clean-up. Separation of dyes was obtained in an ODS column (150 x 4 mm i.d. particle size 5 pm). Solvents A and B were methanol and 40 mM aqueous ammonium acetate (pH = 5), respectively. Gradient conditions were 0-3 min, 10 per cent A 3-5 min, to 25 per cent A 5-8 min, 25 per cent A 8-18 min, to 75 per cent A 18-20 min, 75 per cent A. The flow rate was 1 ml/min and dyes were detected at 414 nm. The separation of synthetic dyes achieved by the method is shown in Fig. 3.35. The concentrations of dyes found in commercial samples are compiled in Table 3.21. The quantification limit depended markedly on the type of dye, being the highest for E-104 (4.0 mg/1) and the lowest for E-102 and E-110 (1.0 mg/1). The detection limit ranged from 0.3 mg/1 (E-102 and E-110) to 1.0 mg/ml (E-104 and E-124). It was suggested that the method can be applied for the screening of food colourants in quality control laboratories [113]. 

In commercial formulations, phospholipids are not available as pure products. Mostly they are obtained as a by-product of the process of refining vegetable oils, during the so-called degum-ming step (3,4), from which a liquid-to-pasty product is obtained that is referred to as lecithin. Lecithin contains about 65% phospholipids plus about 30% residual neutral lipids and minor amounts of glycolipids. For historical reasons, most commercially available lecithins are derived from soybean oil, but lecithins of other oils could be used as well. From this discussion it follows that the determination and quantification of phospholipids is of importance both to control how efficiently the phospholipids have been removed from vegetable oils and to control the quality of the lecithin. For this purpose it is important to know not only the total amount of phospholipids but also the amount of the different types of phospholipids present, because it is well known that the functional properties of the various phospholipids differ widely (2-8). 

A selective, sensitive, and rapid hydrophilic interaction liquid chromatography with electrospray ionization tandem mass spectrometry was developed for the determination of donepezil in human plasma [32], Donepezil was twice extracted from human plasma using methyl-ferf-butyl ether at basic pH. The analytes were separated on an Atlantis HILIC Silica column with the mobile phase of acetonitrile ammonium formate (50 mM, pH 4.0) (85 15, v/v) and detected by tandem mass spectrometry in the selective reaction monitoring mode. The calibration curve was linear (r = 0.9994) over the concentration range of 0.10-50.0 ng/ ml and the lower limit of quantification was 0.1 ng/ml using 200 /d plasma sample. The CV and relative error for intra- and inter-assay at four quality control levels were 2.7% to 10.5% and —10.0% to 0.0%, respectively. There was no matrix effect for donepezil and cisapride. The present method was successfully applied to the pharmacokinetic study of donepezil after oral dose of donepezil hydrochloride (10 mg tablet) to male healthy volunteers. 

Murakami et al. [82] developed and validated a sensitive HPLC technique to quantify omeprazole in delayed release tablets. The analysis was carried out using a RP-Cig column with UV-VIS detection at 280 nm. The mobile phase was diluted with phosphate buffer (pH 7.4) and acetonitrile (70 30) at a flow-rate of 1.5 ml/min. The parameters used in the validation process were linearity, range, quantification limit, accuracy, specificity, and precision. The retention time of omeprazole was about 5 min with symmetrical peaks. The linearity in the range of 10-30 ng/ml presented a correlation coefficient of 0.9995. The excipients in the formulation did not interfere with the analysis and the recovery was quantitative. Results were satisfactory and the method proved to be adequate for quality control of omeprazole delayed-release tablets. 

Whether the monitoring of endoxifen plasma concentrations in breast cancer patients would constitute a valid approach to optimize individual dosage and improve treatment efficacy is under scrutiny and remains to be demonstrated. In that purpose large prospective studies relating endoxifen plasma levels to clinical outcomes are as yet needed. In this perspective, it is critical to settle analytical and selectivity discrepancies between methods and laboratories and to ensure reproducible quantification results between laboratories. These concerted harmonization efforts can be carried out within the frame of an international external quality control program, which as yet, remains to be organized. 

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