Spectrophotometers operating conditions

An atomic absorption spectrophotometer (Perkin-Elmer 4000) was used with standard operating conditions to determine dissolved and total Mn, irrespective of oxidation state. Dissolved organic carbon was determined with an organic carbon analyzer (Beckman model 915B TOCmaster). 

The study of the deterioration of the hydroxil groups of the catalyst and the nature of the coke that is being deposited have been studied in situ in a catalytic chamber (Spectra Tech) connected in series with a Nicolet 740 FTIR spectrophotometer. The reaction has also been carried out in an automated isothermal fixed bed integral reactor [6], in cycles of reaction-regeneration, with the aim of obtaining partially deactivated catalyst samples under contrasted operation conditions (time on stream, temperature, contact time and number of regenerations of the catalyst). 

The conclusion is that, for the most accuracy, it is desirable to perform relative error or VFG experiments on the spectrometer used under the desired operating conditions. The importance of carrying out this work increases as the wavelengths approach the extremes of the operating range of the spectrophotometer, in particular the ultraviolet. 

The way to guard against deviations from Beer s law is to construct a calibration curve with your spectrophotometer under fixed operating conditions, showing the measured absorbance over the expected range of analyte concentration. If you operate within this demonstrated range, Beer s law should be valid. 

The determinations of gold are made by an atomic absorption spectrophotometer (Zeeman 5000, Perkin-Elmer) equipped with an electrothermal furnace atomizer (HGA-400) and with Zeeman effect background corrector. The operating conditions and the atomizer program for the spectrometer are listed in Table 3. 

Use of an infrared spectrophotometer in good operating condition does not in itself assure accurate results. The validity of the spectra also depends on the sample-handling techniques, which will be discussed in Chapter 7, and on the selection of proper instrument operating variables, which is a primary concern of this chapter. To aid in understanding the operating variables and their interrelations we shall first examine the basis of operation of one type of widely used infrared spectrophotometer. This will be followed by a discussion of the operating variables and their qualitative and quantitative interdependence. The remainder of the chapter will describe the components and features of infrared spectrophotometers. 

Another method for measuring A is called the point method. The peak used for the analysis is picked in the same manner as in 6-2 and must meet the same criteria. The sample is either scanned over the peak or the monochromator is set to the peak frequency and the transmittance determined at that point. The cell is emptied, cleaned, and refilled with the sample minus the component being determined and, under the same operating conditions, either it is rescanned over the same area, or the transmittance is determined at the same point as above. The true zero of the spectrophotometer must then be determined. Ideally, this is done by replacing the sample with something that is totally opaque at the desired frequency and transparent at all other frequencies. In practice, either a sample with a very high concentration of the desired component is used, or a material that is opaque at the required frequency and transparent at higher frequencies is substituted. 

Weigh out accurately 0.7 g of dried cement into a 250 cm beaker. Disperse in water, add 10 cm cone. HCl and 150 cm hot water. Bring to the boil and keep hot for 5 minutes. Cool and transfer quantitatively to a 250 cm volumetric flask and make up to the marie. Dissolve in a 100 cm aliquot 0.191 g purest KCI and in another 100 cm aliquot 0.254 g purest NaCl. These chlorides are added as ionisation suppressors. Use the atomic spectrophotometer in the emission mode and measure the readings for the two solutions, using the manufacturer s recommended operating conditions. Use calibration standards to find [K] and [Na]. Calculate from the results of spectrophotometry the percentages of oxides of the elements determined. 

Note 2—The spectrophotometer used must be clean and in first-class operating condition. The instrument should be calibrated in accordance with the instructions given in the Standards for Checking the Calibration of Spectrophotometers (200 to 10(X) nm). ... 

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.,... 

Characterization method SEM was carried out on a Zeiss DMS 982 Gemini field emission scanning electron microscope at 4.0 kV. TEM was performed using a JEOL 21 OOF electron microscope operated at 200 kV. The UV/Vis absorption spectra were measured using a Shimadzu UV-I650PC spectrophotometer. N2 adsorption-desorption isotherms were obtained on Nova 2000 pore analyzer at 77 K under continuous adsorption condition. The ionic concentration of the solution was analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES Varian Co., USA). 

To investigate this matter of precision further, as well as the limit of detection, two other types of burners and various hollow cathode lamps were tested under similar conditions. The primary objective was to compare a new single flame total consumption burner, operated on a hydrogen-air fuel mixture, with a premix burner using acetylene and air for fuel. The total consumption burner is the Hetco type, and was used with the Jarrell-Ash spectrophotometer. The premix burner is the Perkin-Elmer type and it was tested as a part of the Perkin-Elmer Model 290 Atomic Absorption Spectrophotometer. Synthetic standards for Ca, Mg, Fe, Pb, and Cu were analyzed in varying concentrations. The data was assessed on both a short-term (daily) basis, where new standard curves were prepared daily, and on a long-term basis, where the shift in the calibration curve was included in the data. 

Set up the atomic absorption spectrophotometer for the air/acetylene flame analysis of cadmium according to the SOP (5.8.) or the manufacturer s operational instructions. For the source lamp, use the cadmium hollow cathode or electrodeless discharge lamp operated at the manufacturer s recommended rating for continuous operation. Allow the lamp to warm up 10 to 20 min or until the energy output stabilizes. Optimize conditions such as lamp position, burner head alignment, fuel and oxidant flow rates, etc. See the SOP or specific instrument manuals for details. Instrumental parameters for the Perkin-Elmer Model 603 used in the validation of this method are given in Attachment 1. 

Describe how you could experimentally determine whether a spectrophotometer was operating under Case I. Case II, or Case III conditions. 

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