Photometric determination accuracy

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-... 

Ganshirt [66] uses this method also for the quantitative spectro-photometric determination of caffeine (accuracy 12%). Cyclohexane-acetone (40 60) was used with silica gel G. 

Liquid absorbance standards provide a theoretically perfect way of checking the linearity of the photometric scale of an instrument because absorbance is directly proportional to concentration or path length. However, technical imperfections in instruments, cuvets, and filter solutions limit the accuracy of absolute photometric determinations (60). Liquid standards should be prepared for each calibration session. Solid samples should be checked and recertified periodically by an accredited standards testing laboratory. Color standards that change with temperature or light exposure such as the National Bureau of Standards red glass filter No. 2101 that is doped with selenium (50) must be used cautiously as recommended by the standards issuing laboratory. 

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. 

The influence of temperature, solution s pH and other parameters in formation of ionic associate is investigated. As a result, optimal conditions of determination are established pH 4,0 volume of acetate buffer - 0,5 ml volume of 0,1% aqueous solution of CV - 0,3 ml extraction time - 3 minutes. The ratio of aqueous and organic phases is 1 1. Photometric measurement of toluene layer is carried out at = 606,0 nm. The accuracy of procedures checked by the method of additives. 

The infrared ellipsometer is a combination of a Fourier-transform spectrometer (FTS) with a photometric ellipsometer. One of the two polarizers (the analyzer) is moved step by step in four or more azimuths, because the spectrum must be constant during the scan of the FTS. From these spectra, the tanf and cosd spectra are calculated. In this instance only A is determined in the range 0-180°, with severely reduced accuracy in the neighborhood of 0° and 180°. This problem can be overcome by using a retarder (compensator) with a phase shift of approximately 90° for a second measurement -cosd and sind are thereby measured independently with the full A information [4.315]. 

Gravimetric, photometric, chromatographic, enzymatic, and microbiological methods for the determination of amino acids are reviewed and discussed. Marked advances have been made during the present decade in methods applicable to the determination of amino acids, and with the development of new analytical methods it should soon be possible to determine all the amino acids of biological importance with a degree of accuracy sufficient for practical as well as many theoretical purposes. 

Photometric accuracy is determined by comparing the difference between the measured absorbance of the reference standard materials and the established standard value. Many solid and liquid standards are commonly used to verify the photometric accuracy of a spectrophotometer. An optically neutral material with little wavelength dependency for its transmittance/absorbance is desirable because it eliminates the spectral bandwidth dependency of measurements. The advantages and disadvantages of various commonly used photometric accuracy standards are summarized in Table 10.6. Even for a relatively stable reference standard, the intrinsic optical properties may change over time. Recertification at regular intervals is required to ensure that the certified values of the standards are meaningful and accurate for the intended use. 

Note that instruments 1-4 were photometric devices with less then 0.01 absorbance accuracy evaluated against reference neutral filters at 546 nm and A = 1.000, traceable to INM. The bandwidth provided by the interference filters equipping the absorption photometers was within the range of 4-10 nm. Instrument 5 was a 10 nm bandwidth photometric device with less than 1.0% absorbance linearity, evaluated at 405 nm and 500 nm, against liquid absorbance RMs type 16.02 and 16.03 [5], Enzymatic colorimetric methods for determination of glucose and urea were used. The o-cresoftalein colorimetric method was used for calcium determination. 

Calibration solutions of cadmium and lead have been prepared from high purity (higher than 98%) cadmium and lead nitrate dissolved in nitric acid. A high accuracy titration method (EDTA complexometry reaction with photometric detection) was used to determine the final... 

Optical Considerations. The objective of this investigation was to determine the amount of water in coexisting phases of the C10PO system. The value of the data is therefore determined by the instrument s photometric accuracy. Several factors which contribute to photometric inaccuracies in infrared microspectroscopy include sample geometry, spherical aberrations caused by the introduction of... 

Over the last decade both the speed and accuracy of data acquisition and the sensitivity of the LEED experiment have been significantly improved. In most structure determination experiments the LEED patterns are displayed on a phosphor screen. LEED I-V curves are then measured by photometric or photographic means. Fast data acquisition systems have been developed that record LEED patterns with video cameras interfaced to computers and generate I-V curves during the experiment./3,4/ The sensitivity of LEED is also being greatly increased with the development of instruments that can detect single... 

A new way to form a microscopic foam film in the middle of a biconcave drop (Fig. 2.2) has marked the further improvement of the microinterferometric technique. The increase in accuracy and reliability of the photometric and registering devices contributed to this improvement. The experimental details and the metrological characteristics of the microinterferometric technique for determination of foam film thickness has been the object of numerous studies [e.g. 16,23,39-43,58],... 

Photometric accuracy is determined by comparing measured absorbance to a certified absorbance of accepted standards. Solutions of potassium dichromate... 

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. 

Janssen (Jl) suggested that spectral analysis, until then used only for qualitative observations, was suitable also for quantitative work. He felt that such a development would be particularly advantageous in the case of elements like sodium which were difficult to determine by classic procedures. His suggestions bore fruit 3 years later when Champion et al. (Cl) constructed an instrument for the determination of sodium in plant ash. A solution of plant ash was introduced into the flame by means of a platinum wire and the emission intensity measured by comparing it by means of a visual photometric attachment with light from a reference constant-intensity sodium flame. This spectronatrometre was the first flame photometer and when one considers that it was capable of an accuracy of between 2 and 5 %, it is interesting that it was not for more than 70 years that the method was applied to clinical problems. 

The qualification of a Raman spectrometer is described in USP chapter < 1120>. In particular, the tests for the operational and performance qualification of a Raman spectrometer are described x-axis precision, photometric precision, laser power precision and accuracy. The x-axis of the Raman spectrometer is the Raman shift measured in wavenumbers. Before the Raman shift can be determined, both the laser wavelength and spectrophotometer calibration must be determined. The precision of the Raman shift can then be measured using an American Society for Testing and Materials (ASTM) Raman standard material [20]. A commonly used Raman standard material is acetaminophen. The peak position of the known reference peaks can be determined visually, but is better done with a peak location algorithm. The USP chapter on Raman specifies that the peak location should not vary more than... 

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