Spectrophotometric Methods: The Determination of Iron
The goal of this laboratory experiment was the quantitative spectrophotometric determination of Fe (II) by using a calibration plot, which obeyed the Beer-Lambert Law. In order to determine the Fe (II) concentration, a series of solutions of known concentrations were made. The solutions were analyzed by the Ocean Optics spectrophotometer in order to determine their absorbance. The concentration of the unknown Fe (II) was determined by the “eye-ball” method from the Beer’s Law plot of the series of solutions. In this experiment, bipyridine method was used to measure the total iron concentration of an aqueous solution and the reduced iron content in a mineral-enriched cereal. In a similar manner, the concentration of the iron in the cereal was determined from the Beer’s plot by using the “eye-ball” method. Ocean Optics Spectrophotometric Block Diagram
Source: Is a tungsten-halogen lamp, which emits radiation in the visible region (as well as the near the infrared and long wavelength end of the UV). Sample Holder: the sample holder that is also called the cuvette is a rectangular tube with two transparent faces. Pyrex glass or plastic cuvettes are transparent to visible light, but fused silica is needed for UV work. Fiber Optic: it is a flexible cable specifically designed to transmit light to a remote site. These devices are commonly used in telephone transmission lines and for ultra-high speed data transfer in computers. Special miniatures versions are used by physicians to view internal body organs. Slit: the entrance slit determines the spatial width of the light beam striking and grating. Grating: disperses the light, which means that the component wavelengths are spread out in space (much like the rainbow effect of a prism). 2048 Miniature Detectors: Each of these detectors has a charged-coupled device. The dispersed bean is passed from the granting projects onto the detector array. Each CCD receives only a narrow wavelength band, determined by the relative positions of the CCD and the granting. Charged-coupled device (CCD): The CCD array measures the intensity of each wavelength band and has the ability to acquired the entire spectrum with a single reading. Analog-to-digital converter (A:DC): changes each CCD level (in volts) to a binary number. Computer Interface: The main function of the computer interface is to translate the information obtained from the CCD into a usable format to be sent to the computer. Computer: stores the PD and PB at the beginning of the experiment and after the P is measured the computer calculates absorbance.
Spectrophotometric analyses are performed using a narrow wavelength band centered at λmax because: •
Because the sample only absorbs a small section of the source wavelength so to have significant change one must the use the wavelengths that interact with the sample. •
The slope of the Beer’s Law plot is steepest at λmax providing the maximum sensitivity, so that small concentrations can be detected and give a measurable signal. •
To have a linear Beer’s Law plots the absorbance is read at λmax because Beer’s Law is obeyed best at λmax. Purpose of the following commands:
Store Reference: Storing a reference spectrum is required before the software can calculate absorbance measurements. The blank contains everything found in the sample solution except the substance you are trying to analyze or measure. Store Dark: Storing the dark spectrum is a required before the software can calculate absorbance measurements. A beam block is placed into the cell holder to completely block the light path going to the spectrometer.
Calculation of the concentration in ppm Fe of the standard iron solution
Calculation of the concentration in ppm Fe of the diluted standards for the Beer's Law plot.
Calculation of the...
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