Photometric reproducibility

A simpler determination of photometric reproducibility is often carried out with the aid of a... 

General. Cahn discussed photometric reproducibility and presented data on the precision of conventional spectrophotometry. He found that with the Cary Model 11 and Beckman DU, error in absorbance does not depend upon absorbance magnitude, at least up to A = 1. 

The use of peroxyacids, including PMSA, makes it possible to improve photometric method of nickel determination - to increase selectivity, accuracy and reproducibility of measurements. Peroxyacids as oxidants ai e used for nickel determination in aluminium and copper alloys, natural waters, stomatological products. 

Figure 3.14 Dual-flane photometric detector (Varian). A, Schematic diagram of the dual-flame burner B, Schematic diagram showing the relationship between the burner and the photometric viewing components. (Reproduced with permission from ref. 177. Copyright American Chemical Society).

As a test of reproducibility of spot printing and staining, a 10 spot by 10 row array (100 spots total) were printed on three slides. All slides were stained in a single staining run, using the same secondary detection chemistry with DAB as a chromogen. While DAB cannot provide accurate photometric measurements, it can provide relative comparisons from one spot to another on the same slide. When the stained control slides were analyzed in this... 

We present here the results of abundance measurements of iron, calcium and nickel in four open clusters, from UVES spectra of solar type stars. A code developed by one of the authors (Francois) performs line recognization, equivalent width measurements and finally obtains the abundances by means of OSMARCS LTE model atmosphere [4]. Temperature, gravity and microturbulence velocity have to be input to the program. This is made in an automatic way for a grid of values chosen on photometric basis. Those that best reproduce excitation and ionization equilibria are selected and used, namely when no significant trend of the computed abundances is seen, neither versus the excitation potential of the line nor versus its equivalent width, and for which the abundances obtained with lines of different ionization stages of the same specie give equal results within the errors. This check is made with iron lines, we have in fact at least thirty Fe I lines in each star, and six Fell lines. 

Several methods are available for analyzing disulfoton in biological media some of the commonly used methods are reported in Table 6-1. A variety of detectors may be used for the gas chromatographic analysis of disulfoton, but flame photometric detectors are superior because of low background interference and good reproducibility (Holstege et al. 1991). Mass spectrometric detectors show high specificity (Kawasaki et al. 1992) and may also be used to confirm detection by other methods. 

The paH response is tested by means of the paH values as determined by the indicator method the electromodve force of the cell immersed in buffer solutions whose pan is known is measured and the pan is spectro-photometrically determined and then plotted against E (Fig. 11). It can be seen that for this ethylene glycol-glass electrode the practical response is in good agreement with the theoretical one between pan 2 and 9 and for -1-21, -Hi, and — 19°C. The reproducibility of the determinations, estimated by the use of two different assemblies of electrodes, is better than 1.0 mV and the uncertainty of the pon determination is estimated at 0.1 pan unit. 

The AOAC alkalimetric ammonium molybdophosphate and photometric molybdovanadate methods for animal feed are described by Padmore (1990, pp. 87-88), and for plants by Isaac (1 990, p. 56). A spectrophotometric molybdovanadate procedure is also described in MAFF/ADAS (1986, pp. 181-182). The official Bran-rLuebbe AutoAnalyzer method for phosphate in soil, plant and fertilizer extracts is reproduced with permission in Appendix 6. 

Figure 4.4 — (A) Flow-through cells for spectrofluorimetric sensors (a) fused silica tube (1.5 mm ID) packed with 1 mg of CM-Sephadex C-25 (b) micro-cell holder (c) side and (d) front view of a commercially available sensor. (Reproduced from [62] and [64] with permission of the Royal Society of Chemistry and Elsevier Science Publishers, respectively). (B) Flow-through cells for photometric sensors. Side and front views of two commercially available designs. For details, see text. (Reproduced from [80] and [83] with permission of Elsevier Science Publishers and the Royal Society of Chemistry, respectively).

Figure 4.6 — Manifold used and recording obtained with the flow-through photometric sensor for the determination of formaldehyde. PRA />-rosaniline q flow-rate P peristaltic pump M mixing point R reactor SV switching valve IV injection valve D detector W waste. (Reproduced from [89] with permission of Marcel Dekker, Inc.).

Figure 5.13 — Irreversible-reusable flow-through sensor for the kinetic multidetermination of phosphate and silicate based on integrated sorption of a reaction product, reaction (/ situ reduction) and photometric detection. (A) Microsensor block (1) and components (2). (B) Continuous-flow configuration coupled on-line to the sensor. P peristaltic pumps SV switching valve W waste. For details, see text. (Reproduced from [39] with permission of the American Chemical Society).

Wavelength accuracy and reproducibility, stray light, resolution, photometric accuracy and reproducibility, noise, baseline flatness, stability, and linearity... 

Figure 26-8 Indirect spectrophotometric detection of transparent ions. The column was eluted with I mM sodium phthalate plus 1 mM borate buffer, pH 10. The principle of indirect detection is illustrated in Figure 26-30. [Reproduced tram H. Small, Indirect Photometric Chromatography, Anal Chem. 1982,54,462]...

Castro et al. [64] reported a comparison between derivative spectro-photometric and liquid chromatographic methods for the determination of omeprazole in aqueous solutions during stability studies. The first derivative procedure was based on the linear relationship between the omeprazole concentration and the first derivative amplitude at 313 nm. The first derivative spectra were developed between 200 and 400 nm (A/ = 8). This method was validated and compared with the official HPLC method of the USP. It showed good linearity in the range of concentration studied (10—30 /ig/ ml), precision (repeatability and interday reproducibility), recovery, and specificity in stability studies. It also seemed to be 2.59 times more sensitive than the HPLC method. These results allowed to consider this procedure as useful for rapid analysis of omeprazole in stability studies since there was no interference with its decomposition products. 

Standards of typical meat flavor sulfur aliphatics and heterocyclics were made from 5 ng/pl to 500 ng/pl in hexane to determine response factors as well as reproducibility in the flame photometric detector. Background sulfur compounds were checked in concentrated reagent blanks. 

This is the most useful technique for screening pesticides since it has wide applicability and sensitivity, and utilises equipment which is readily available in most laboratories. Over 95% of all pesticides may be chromatographed intact or as a simple derivative in some cases there is a clearly defined decomposition product although quantification may be difficult if the extent of decomposition is not reproducible. The sensitivity of the method is high using a flame ionisation detector when specific detectors are used, e.g. electron capture, alkali flame ionisation, or flame photometric detectors, even lower concentrations in body fluids may be detected. 

Determination of Nerve Agents In contrast to those rather unusual methods, GC coupled to diverse detection systems, e.g. flame ionization detector (FID), nitrogen-phosphorus detector (NPD), flame photometric detector or mass spectrometer, as well as liquid chromatographic (LC) methods, represent the most common techniques for OP determination especially for biological samples. These methods offer high resolution, sufficient limits of detection, good reproducibility, and robust hardware devices. For more detailed information readers are referred to recent review articles (Hooijschuur et al, 2002 John et al, 2008). 

---