Spectrophotometers commercial models

In this paper we will first describe a fast-response infrared reactor system which is capable of operating at high temperatures and pressures. We will discuss the reactor cell, the feed system which allows concentration step changes or cycling, and the modifications necessary for converting a commercial infrared spectrophotometer to a high-speed instrument. This modified infrared spectroscopic reactor system was then used to study the dynamics of CO adsorption and desorption over a Pt-alumina catalyst at 723 K (450°C). The measured step responses were analyzed using a transient model which accounts for the kinetics of CO adsorption and desorption, extra- and intrapellet diffusion resistances, surface accumulation of CO, and the dynamics of the infrared cell. Finally, we will briefly discuss some of the transient response (i.e., step and cycled) characteristics of the catalyst under reaction conditions (i.e.,... 

The model immunoassay is the enzyme-linked immunosorbent assay (ELISA) in which a non-specific capture antibody is bound to a surface, such as a multi-well plate or small tube [13]. In the basic form of ELISA, a second antibody tagged with an enzyme interacts specifically with the analyte. The enzyme assay produces a colored product that is read with a spectrophotometer. There are many variations on the basic immunoassay format that serve to increase sensitivity, specificity, linear range, and speed. Many commercial instruments have been developed to take advantage of various technologies for reporter molecules. The immunoassay may be coupled to an electronic sensor and transducer, such as a surface acoustical wave (SAW) sensor. Electrochemiluminescence (ECL) is a method in which the detector antibody is tagged with a ruthenium-containing chelate [13-15]. When the tag is... 

Hb and Ni-reconstituted Hb were prepared according to reported methods (13). Mb was made by the method of Alston and Storm (14) Solutions of the proteins in 0.05 M phosphate buffer at pH 7.5 were used for obtaining spectra. The proteins are stable in air and do not photodecompose. Ni protoporphyrin IX (Ni(ProtoP)), Ni uroporphyrin I (Ni(UroP)), and Ni octaethylporphyrin (Ni(OEP)) were obtained from Porphyrin Products and used without further purification. All solvents were of highest purity obtainable from commercial sources. All materials showed the literature uv-visible absorption spectra. Absorption spectra were obtained on a Perkin-Elmer Model 330 spectrophotometer. 

The output of a lamp may be monitored by chemical actinometry. The standard method remains the irradiation of potassium ferrioxalate which is useful in the range 254 to 480 nm. The method is described in detail by Calvert and Pitts (1966) and by Murov (1973). But perhaps, the most convenient way to check the lamp output is to keep a stock solution of a model compound or the reagent itself, if it is readily available, and determine its rate of photolysis periodically by irradiation in a spectrophotometer cuvet. In this way the output of the lamp in the region of interest can be rapidly checked. An alternative is to use one of many radiation measuring instruments that are commercially available, a thermopile and voltmeter, for example (see Appendix for a list of manufacturers). 

Many commercial visible-UV spectrophotometers are suitable for this experiment. These instruments range from simple single-beam devices such as the Spectronic model 20 to high-performance double-beam scanning spectrophotometers such as various Varian-Cary models. The components and operational principles of these instruments are... 

The combination of rapid mixing and fast detection systems allows cationic polymerisations to be followed on an even shorter time scale than with adiabatic calorimetry. Recent commercial stop-flow spectrophotometers have a dead time of about 15 msec, an improvement of more than one order of magnitude over previous home-made models. This implies that reactions with half lives of less than 100 msec can be analysed kinetically with a good degree of accuracy. Hi -vacuum techniques are not compatible with these instruments and all operations are therefore carried out in an inert atmosphere. 

The first commercially available flame photometer was introduced in the 1940s by the Perkin-Elmer Corporation. In 1948, Beckmann Instruments, Inc., introduced a flame attachment that could be used with their popular model D.U. spectrophotometer. By the late 1950s, instruments had been developed that used lithium as an internal standard to maximize precision. Autodilution features and microprocessor-controlled operations became widely used options in the 1970s. The most recent significant development was the introduction of cesium as the internal standard, by Instrumentation Laboratory, Inc. (Figs. 1-3). This development makes concurrent lithium determinations more practical. 

Serum copper analysis was performed using a Perkin-Elmer atomic absorption spectrophotometer. Model 308. The previously described method by Prasad (136) was used after slight modification. For protein precipitation we used 7.5% trichloroacetic acid instead of 2N HCl used by Prasad. Analytical sensitivity for copper with this method was 0.2 jxg/ mL for 1% absorption and a relative detection limit of 0.005 fig/mL, Recovery studies done by adding known amounts of copper to the serum ranged between 96-104%. Analysis for ceruloplasmin was made by using commercially available immunodiffusion plates (Hyland, Inc. normal range, 20-35 mg/100 mL). Precision of the method has been tested by running 20 determinations for both copper and ceruloplasmin on one aliquot. CoeflBcient of variation did not vary by more than 3-5%. All samples were run in duplicates. 

It is worth noting that, because of the enrichment of reaction-center components in the ether-extracted PS-I particles as prepared by Ikegami and Ke , it has been possible to measure the difference spectrum of a component of low concentration such as Aq directly in a conventional commercial instrument (Hitachi model 557 dual-wavelength spectrophotometer) as illustrated by the results in Fig. 2 (B) above. Ordinarily, such difference spectra are obtained from flash-induced transients measured with specially-built, high-sensitivity instruments. 

Automation of sample preparation of pharmaceutical solids has been quite successful. A variety of instrumentation is commercially available from several vendors. The instruments are capable of handling a dosage form, placing it into a vessel, adding solvent, and mechanically homogenizing the sample until the analyte is dissolved. Typically, the instrument can then dilute to the desired concentration. Some models are also capable of transferring the prepared solution to a HPLC injector or an ultraviolet spectrophotometer for measurement. These instruments use accurate balances to control the accuracy of solvent additions and dilutions. 

Rates of reduction were followed spectrometrically using a Hitachi model 220A spectrophotometer. The increase of reduced cytochrome c was followed at 550nm. All rates were determined using 3ml quartz cells with a 1cm light path, under anaerobic conditions. The reaction were carried out in pH 7.0( 0.01) phosphate buffer solutions at 25 C, and initiated by addition of 3-CD-NAH dissolved in DMF. All reagent were purchased from commercial suppliers and were used without further purification. 

---