Photometric determination precision

In this development of a flow injection method for the determination of nitrate andnitrite, Anderson [168] chose the Shinn [155] method to reduce nitrate and nitrite because of its high sensitivity and relative freedom from interferences. Anderson [168] used flow injection in the photometric determination of nitrite and nitrate with sulfanilamide and N-( 1-naphthyl) ethylenediamine as reagents, as discussed next. The detection limit is 0.05 xm for nitrite and 0.1 xm for nitrate at a total sample volume of 200 iL. Up to 30 samples can be analysed per hour with relative precision of about 1%. 

Among the analytical methods presently used for the characterization of natural and synthetic peptides and proteins, the primary value of amino acid analysis is the determination of absolute peptide and protein content in solids and solutions and the quantitation of their amino acid composition and stoichiometry. It involves two steps, i.e. complete hydrolysis of peptides and proteins, followed by photometric determination of the released amino adds. The steps are laborious and time-consuming, and there is a continuous need for improvement of the techniques to increase precision and sensitivity. 

Melphalan has been determined spectrophotometrically at 262 nm in methanol solution [65]. The assay is linear in the 3 to 15 pg/ml range, with precision of 2%. In contrast with the above mentioned colorimetric methods, the procedure is not stability-indicating the major contaminant and degradation product, the bis(2-hydroxyethyl)derivative, has a UV spectrum very similar to that of Melphalan [48]. Ultraviolet spectro-photometric determinations in aqueous solution were also reported [66]. 

The control of the chemical operations like deprotection, deprotonation, coupling, blocking, washing, and detachment in future instruments has to proceed continuously parallel to the operations. From the author s point of view this will only be possible with flow photometry on circulating reaction solutions, though this method lacks [95] the highest accuracy [195] desired. Since the precision [195] of photometric determinations is well established in analytical chemistry, the deviation of up to 0.4% in the measurements from the true values can be compensated by electronic comparisons of the course of kinetics in repeated reactions. In other words The future computer control of peptide synthe-... 

Pyridine-2,6-dicarboxylic acid and pyridine-2,4,6-tricarboxylic acid are valuable reagents for the precise photometric determination of iron. ... 

Several instrument manufacturers supply flame photometers designed specifically for the determination of sodium, potassium, lithium, and sometimes calcium in blood serum, urine, and other biological fluids. Single-channel and multichannel (two to four channels) instruments are available for these determinations. In the multichannel instruments, each channel can be used to determine a separate element without an internal standard, or one of the channels can be reserved for an internal standard such as lithium. The ratios of the signals from the other channels to the signal of the lithium channel are then taken to compensate for flame noise and noise from fluctuations in reagent flow rate. Flame photometers such as these have been coupled with flow injection systems to automate the sample-introduction process (see Section 33B-3). Typical precisions for flow-injection-analysis-based flame photometric determinations of lithium, sodium, and potassium in serum are on the order of a few percent or less. Automated flow injection procedures require l/KIO the amount of sample and 1/10 the time of batch procedures. -... 

A method for the determination of hydroxy group in polyethylene glycols has been described by Fritz and co-workers [4]. The method consists of substituting the hydroxyl group with a chromophoric siloxy group, purification of the silylated polymer, and a photometric determination of the chromophor concentration. The silanisation of the primary hydroxyls with dimethylaminosilanes proceeds quantitatively under very mild conditions and elimination of the excess reagent by precipitation is easy. The precision of the method is 4.5% (95% confidence level) down to 5 x 10 mol/kg. The method has about the same precision as acylation methods, but yields a 100-fold gain in sensitivity. 

The worked out soi ption-photometric method of NIS determination calls preliminary sorption concentration of NIS microamounts from aqueous solutions on silica L5/40. The concentrate obtained is put in a solution with precise concentration of bromthymol-blue (BTB) anionic dye and BaCl, excess. As a result the ionic associate 1 1 is formed and is kept comparatively strongly on a surface. The BTB excess remains in an aqueous phase and it is easy to determinate it photometrically. The linear dependence of optical density of BTB solutions after soi ption on NIS concentration in an interval ITO - 2,5T0 M is observed. The indirect way of the given method is caused by the fact the calibration plot does not come from a zero point of coordinates, and NIS zero concentration corresponds to initial BTB concentration in a solution. 

Investigated is the influence of the purity degree and concentration of sulfuric acid used for samples dissolution, on the analysis precision. Chosen are optimum conditions of sample preparation for the analysis excluding loss of Ce(IV) due to its interaction with organic impurities-reducers present in sulfuric acid. The photometric technique for Ce(IV) 0.002 - 0.1 % determination in alkaline and rare-earth borates is worked out. The technique based on o-tolidine oxidation by Ce(IV). The relative standard deviation is 0.02-0.1. 

The total cerium content in the single crystal samples on the basis of rare-earth elements is determined by photometry after Ce(III) oxidation by ammonium persulfate. The Ce(III) content is calculated from the difference. Comparison of the determination results of the total cerium content obtained by photometric and atomic emission methods for Li GdlBO ljiCe demonstrated the elaborated procedure precision and systematic error absence. 

Jagner [28] has also described a semi-automatic titration for high-precision determination of chlorine in seawater, where it has been used for the potentiometric determination of total halides (silver electrode) and alkalinity (glass electrode), and for the photometric titration of total alkaline-earth metals. Several titrations can be effected simultaneously. 

Jagner [150] used computerised photometric titeration in a high-precision determination of calcium in seawater. 

Jagner and Kerstein [654,655] used computer-controlled high-precision complexiometric titration for the determination of the total alkaline earth metal concentration in seawater. Total alkaline earths were determined by photometric titration using EDTA with eriochrome Black as indicator. The method yielded 63.32 (xmolekg-1 for the total alkaline earth concentration in standard seawater of 3.5% salinity. The precision was about 0.01%. 

The results obtained with ISEs have been compared several times with those of other methods. When the determination of calcium using the Orion SS-20 analyser was tested, it was found that the results in heparinized whole blood and serum were sufficiently precise and subject to negligible interference from K and Mg ([82]), but that it is necessary to correct for the sodium error, as the ionic strength is adjusted with a sodium salt [82], and that a systematic error appears in the presence of colloids and cells due to complexa-tion and variations in the liquid-junction potential [76]. Determination of sodium and potassium with ISEs is comparable with flame photometric estimation [39, 113, 116] or is even more precise [165], but the values obtained with ISEs in serum are somewhat higher than those from flame photometry and most others methods [3, 25, 27, 113, 116]. This phenomenon is called pseudohyponatremia. It is caused by the fact that the samples are not diluted in ISE measurement, whereas in other methods dilution occurs before and during the measurement. On dilution, part of the water in serum is replaced by lipids and partially soluble serum proteins in samples with abnormally increased level of lipids and/or proteins. 

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. 

When experimental data are available for k as a function of [H+], three unknown coefficients have to be evaluated for a process for which k is given by eqn. (5) and five unknown coefficients for one when k is given by eqn. (6). It is advisable to carry out separate determinations of the ionization constants K, or K, and K2, respectively, (concentration constants valid for the ionic strength of the kinetic experiments) whenever possible with a reasonable precision. These determinations should be done with the aid of appropriate potentiometric or photometric methods [8,9] independent of the kinetic measurements. As soon as the ionization... 

As with calcium, AAS methods provide greater accuracy and precision for magnesium measurements than do photometric methods however, they are not frequently used for routine determination of magnesium by clinical laboratories. AAS is used as a reference method for magnesium. 

In 1926 Bruce (17) of the National Bureau of Standards reported upon one of the first attempts to improve the precision of hiding power measurements. A thin film was uniformly spread over a black and white glass plate by spinning, and the contrast ratio was determined photometrically. This method was improved upon by Haslam (18). who... 

The absorption of dye was determined from the change in concentration of the dyebath during the dyeing process, which was measured spectro-photometrically. Because of the phototropic character of the dye, each solution was illuminated for 10 min with a 100-W bulb at a distance of 6 in, through 2 in. of water. The results obtained in this way were found to be more precise than those obtained using a 10-min illumination at a distance of 1 in., which was used by previous workers. These latter conditions were shown to cause heating of the solution, which was thought to be a source of error. 

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