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MCAL Spectrophotometry

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MCAL Spectrophotometry MCAL Spectrophotometry Instruments include: Cary 50 UV-vis Spectrophotometer Eclipse Spectrofluorometer HPLC Diode Array and Fluorescence ICP-OES with CCD detection Spectrophotometry • The instruments all have in common that they use the absorption or emission of light, in the form of electromagnetic radiation (EMR) as a means of measuring the presence and/or concentration of material in a solution. Cary 50 and Eclipse Cary 50 Spectrophotometer Mainly used to measures concentration of an analyte in solution Concentration based on absorption of light (incident minus final light beam) by analyte (Beer-Lambert law) at specific wavelength Need standards due to different extinction coefficients of different analytes. Concentration • Based on Beer’s Lambert Law that concentration is proportional to the absorption of certain energy in the form of light A(absorbance) = εcd ε = extinction coefficient (constant for each compound) d = path length of cuvette =1cm c = concentration of analyte Cary 50 Uv-Vis spectrophotometer (measures absorption at specific wavelength) Detector diodes Mirrors Cuvette holder Grating Xenon light Beam splitter Czerny-Turner monochromator In the common Czerny–Turner design,[1] the broad-band illumination source (A) is aimed at an entrance slit (B). The amount of light energy available for use depends on the intensity of the source in the space defined by the slit (width × height) and the acceptance angle of the optical system. The slit is placed at the effective focus of a curved mirror (the collimator, C) so that the light from the slit reflected from the mirror is collimated (focused at infinity). The collimated light is diffracted from the grating (D) and then is collected by another mirror (E), which refocuses the light, now dispersed, on the exit slit (F). In a prism monochromator, a reflective prism takes the place of the diffraction grating, in which case the light is refracted by the prism. At the exit slit, the colors of the light are spread out (in the visible this shows the colors of the rainbow). Because each color arrives at a separate point in the exit-slit plane, there are a series of images of the entrance slit focused on the plane. Because the entrance slit is finite in width, parts of nearby images overlap. The light leaving the exit slit (G) contains the entire image of the entrance slit of the selected color plus parts of the entrance slit images of nearby colors. A rotation of the dispersing element causes the band of colors to move relative to the exit slit, so that the desired entrance slit image is centered on the exit slit. The range of colors leaving the exit slit is a function of the width of the slits. The entrance and exit slit widths are adjusted together. Grating Scan Grating motor Varian Cary® 50 UV-Vis spectrophotometer • Dual beam (split beam), Czerny-Turner monochromator, 190–1100 nm wavelength range, approximately 1.5 nm • Lamp full spectrum Xe pulse lamp single source • quartz overcoated optics, room light immunity, central control by PC with Windows® interface. • Grating holographic, 27.5 x 35 mm, 1200 lines/mm, blaze angle 8.6° at 240 nm • Beam splitting system • Detectors 2 silicon diode detectors . Xenon Flash Lamp Advantages • The maximum scan rate is 24,000 nanometers (nm) per minute. • Scan190–1100 nm in less than 3 seconds. • Measure samples up to 3 Abs • The Xenon lamp has a very long lifetime— 3 x 109 flashes • Room-light immunity Uv-Vis Experiment • The analysis involves solving a set of simultaneous equations which describe the absorbance behavior of a mixture of vitamins; B1 (thiamine) and B6 (pyridoxine) at different wavelengths. • The number of equations, and likewise the number of wavelengths, equals the number of components in the mixture Scan of Vitamin B1 and B6 B6 B1 Simultaneous Equations Mixture of B1 and B6: A245 = εB1(245)CB1 + εB6(245)CB6 A290 = εB6(290)CB6 + εB1(290)CB1 Spectrofluorometer • Mainly used to measure the concentration of fluorescing compounds. • Advantage - high sensitivity • Disadvantage - low number of compounds fluoresce • But - can make compounds fluoresce by binding a fluorescent compound Motors Grating Sample holder Grating Drive Filter Xenon lamp Detector photomultiplier Emmission monochromator Excitation monochromator Gratings Sample PMT Reference Xenon lamp PMT Beam splitter Sample holder (cuvette) Emmission Scan Eclipse Spectrofluorometer 398.00 , 248.736 , 398.00 250 200 150 100 Intensity (a.u.) 50 0 300 400 500 600 Wavelength (nm) HPLC with Diode Array Detector Fluorescence detector Diode Array Detector Diode Array • The diode array uses a broad emission light source • two diode arrays and dual-pathlength flow cells. • All the light is allowed to pass through the sensing cell • and subsequently the light is dispersed by means of a holographic grating and • the dispersed light allowed to fall on an array of diodes. Diode Array Diode Array • The light (photons)generated electric charge carriers discharges the diode capacitor • The amount of charge needed to recharge capacitors is proportional to number of photons detected by each diode, which is proportional to light intensity. HPLC Experiment • Identification of unknown compounds by their retention time. • Determination of concentration by use of 1) external standard curve, 2) internal standard or standard 3) or standard addition. Cary 50 Scan Caffeine 204 273 Diode Array Screen Four view display shows the chromatogram, 3D, absorbance and spectrum plots Quinine and Caffeine 140,000 µV TH4 mix 11_11_17_2011 3_19_57 PM.DATA [STAR 800 - 363] 135,000 130,000 125,000 120,000 115,000 110,000 105,000 Fluorescence detection Quinine 100,000 95,000 90,000 85,000 80,000 Exc λ = 347, Em λ = 448 rt = 12.1 75,000 70,000 65,000 60,000 55,000 50,000 45,000 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 -5,000 -10,000 RT [min] 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 42 mAU TH4 mix 11_11_17_2011 3_19_57 PM.DATA [335 Ch 2 ] 40 38 36 Uv detection λ = 213, 273 34 32 30 Caffeine 28 26 24 rt = 9.6 22 20 18 16 14 12 10 8 6 4 2 0 -2 -4 -6 RT [min] 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 HPLC Experiment - Light Sources • Fluorescence detector uses Xenon lamp which has wavelength region of 250-600 • The HPLC Diode Array uses two lamps a deuterium lamp with wavelengths from 160 to 380 and tungsten halogen lamp which covers wavelengths from 240 to 2500. HPLC Experiment Concentration Determined by External Standard EXTERNAL STANDARD 6 5 4 3 AREA 2 1 0 0 2 4 6 8 10 12 CONCENTRATION 700-ES Series Simultaneous ICP’s ICP-OES Experiment • Determine the mineral content of solid samples of: – Grains – Mining rock – Water – Feeds and foods – Surfaces Radial Plasma Central Channel Viewing Volume Fireball Viewing Height Work coil Spraychambers Sturman-Masters Glass Cyclonic -double pass - smaller volume Aerosol To Plasma to Torch Sample Sample Inlet Flow To Drain Pump to Drain Need source of excitation Need way of measuring light emission Varian Simultaneous ICP Optics Detector Chip Prism Cross- disperser Echelle Grating Light from Plasma Echelle Grating Varian Simultaneous ICP Optics Torch Echelle Grating Detector Chip Prism Cross- disperser 720-ES Series CCD Detector VistaChip CCD detector • The CCD (charge coupled device) 70 000 pixels, arranged to exactly match the two dimensional image from the echelle optics. • continuous wavelength coverage from 167–785 nm. • trace and major concentrations can be measured simultaneously, Charged Coupled Device (CCD) A charge coupled device (CCD) is an integrated circuit etched onto a silicon surface forming light sensitive elements called pixels. Photons incident on this surface generate charge that can be read by electronics and turned into a digital copy of the light patterns falling on the device 720-ES Series CCD Detector Order 88 167 nm Order 19 785 nm ICP Experiment • Determination of mineral content in commercial products (product labelling, nutrient requirements, mining). – Dry ashing of sample • Burns off organic material leaving ash (minerals) – Acid digestion of sample • Dissolves minerals or can dissolve total sample including organic material (wet ashing) • Concentration determined by external standard,standard addition, and internal standard. Concentration of unknown Standard Addition 7000 0.5 2621.76 1 4633.48 1.5 5991.37 6000 5000 4000 3000 2000 Intensity 1000 0 -1.5 -1 -0.5 0 0.5 1 1.5 2 -1000 -2000 -3000 Concentration EXTERNAL STANDARD 6 5 4 3 EMMISSION 2 1 0 0 2 4 6 8 10 12 CONCENTRATION.
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