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CHEM237L Lecture Notes - Diabetes Mellitus Type 1, Blood Sugar, Chromophore

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15 Jul 2014

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The absorptivity coefficient will be the same between the standards (s) and the unknowns (u) because we are using the same light absorbance species (glucose). Therefore, the absorbance equation will be a = l c. The path-length should also stay constant between the standards and the unknowns because we are using the same volume in each of the wells, therefore: l s = lu. Now we can set the standards and unknowns equal to each other and solve for the concentration of the unknown as follows: Q3: the absorptivity constant and the concentration are constant. The path length is dependent on volume; therefore we can solve this problem: The absorbance would be 0. 0989 if the volume was 220ul: they would determine the concentration to be this: Two possible interfering substances for this enzymatic method for determining the amount of glucose in your blood would be:

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Related Questions

Spectrophotometric Determination of Iron in a Vitamin Pill Introduction Iron is one of the essential elements in the human diet. In the body, iron is present in the form of dietary iron results in the condition of anemia. Many people take vitamin pills containing iron to supplement their dietary intake ofiron. The technique of is method of instrumental analysis. Many different types spectrophotometers are available that a of the electromagnetic radiation transmit light in different regions spectrum. In is experiment, a visible spectrophotometer will be used. A visible spectrophotometer of a measures the amount of light that a colored solution absorbs. When a beam o the sample depends on wavelength passes through a colored solution, the amount of light absorbed by the concentration of what the substance is that is absorbing the light. The absorbance also depends on the the path through the light passes. The relationship between absorbance, concentration, and pathlength is expressed by the equation known as Beers la gte where A is the al of the solution, E is a constant called absorptivity, which is a characteristic of the substance and the wavelength of the absorption, c is the concentration of the absorbing substance in is a unitless the solution, and e is the length of the path through which the light passes. Abe quantity, concentration can be expressed in any convenient concentration unit, and the pathlength is measured in centimeters. The units of absorptivity depend on the concentration units used. In this experiment concentration is measured in mg/mL Therefore, the units of e are mL/mg cm To determine the absorptivity of a particular substance, a calibration curve is constructed. A series of standard solutions in which the concentration of the absorbing species is known are prepared and their absorbances absorbance as a function concentration is made. If the absorbin species obeys Beer's law, the plot will be a straight line, y mr b. When the pathlength is 1.0 cm, the slope of the line is the absorptivity. The absorbance of a solution of unknown concentration can be read and its concentration determined from the calibration curve. In this experiment, a commercial vitamin pill will be analyzed for its iron content. The form of iron present in the vitamin pill, most likely iron(T) sulfate, has a negligible visible absorbance. The iron(T) will be converted to a species that has a large absorbance, allowing the absorbances of solutions of low iron(T) concentration to be measured. The reagent 1.10-phenanthroline, Figure 1, reacts with is red-orange and absorbs visible ligh most strongly at 508 nm. Iron(ll) is easily oxidized to iron(TI) in aqueous solution. A reducing agent, hydroquinone, is added to the solution to prevent this oxidation from occurring. In addition, the acidity of the solution must be controlled to ensure the formation of the complex. In this experiment, sodium citrate is added to maintain the proper pH of the solution A series of standard solutions with known iron concentrations is prepared, the absorbances of the solutions are read, and a calibration curve constructed. From the calibration curve, the concentration of iron in a solution made from the dissolved vitamin pill will be determined and the total amount of iron in the vitamin pill calculated.

CHE 169 Exp. #3 The Determination of an Equilibrium Constant hemical reactions occur to reach a state of cquilibrium. The equilibrium state can be characterized by uaively delining its equilibrium constant, K In this experiment, you will determine the value of Ke or the reaction between iron (III) ions and thiocyanate ions, SCN Fe (aq)+ SCN (aq)FesCN (aq) he equilibrium constant, Kng, is defined by the equation shown below. To find the value of Ky, which depends only upon temperature, it is necessary to determine the molar oncentration of each of the three species in solution at equilibrium. The concentration will be determined by neasuring light that passes through a sample of the equilibrium mixtures. The absorbance of the colored olution is proportional to its concentration. The red pectrometer, an appropriate wavelength for maximum absorbance will be determined. FeSCN solution absorbs blue light. Using the n order to successfully evaluate this equilibrium system, it is necessary to conduct three separate tests First, a series of standard solutions of FeSCN will be prepared from solutions of varyin concentrations of SCN and constant concentrations of H' and Fe". The Fe concentration will be in side reactions (to form FeOH, for example). The excess of Fe" ions will make the SCN ions the limiting reagent, thus all of the SCN used will form FeSCN ions. The FesCN complex forms slowly, taking at least one minute for the color to develop. It is best to record absorbance readings no ter a specific amount of time has elapsed, between two and four minutes after preparing the equilibrium mixture. Do not wait much longer than four minutes to take readings, however, because the mixture is light sensitive and the FeSCN-ions will slowly decompose. series of solutions will prepared that have varied concentrations of the Fe' ions and Second, a new series of solutions will prepared that have varied concentrat the SCN ions, with a constant concentration of H ions. The concentrations o be comparable in concentra results of this test equilibrium constant for this reaction. f Fe" and SCN will tion with neither species in vast excess over the other. You will use the to accurately evaluate the equilibrium concentrations of each species, and thus the

Topic: spectroscopy: examination of the absosorption spectrum and determination of the extinction coefficient for Flavin mononucleotide

2) in part 2 of the experiment, you are asked to prepare 5.0 mL of 2.0 x10-5M FMN starting with a 1.0 x 10 -4 solution of FMN? Calculate the amounts of 1.0 x 10-4 M FMN solution and water needed.

ice POT Il. Experimental Procedure 1) Examination of the absorption spectrum of FAIN. Prepare 5.0 mL of 1 x 10 4 MI FMN by luting 0 10 ml of 5.0 x 103 M FMN into 4.90 mL of water. Place about 3 mL in a plastic cuvette and take absorbance readings every 10 nm between 340 nm and 600 nm. (Use water as the blank and be sure to re-zero the blank every time you change the wavelength.) Tabulate the absorbance readings in Table l. Inspect the data and determine where the absorbance is maximal for use in the next part. Plot absorbance (y) vs. wavelength (x) in Excel. Be sure to label the axes correctly 2) Prepare 5 0 mL of 2.0 x 10-5 M FMN by diluting the 1.0 x 10-4 M FMN from part #1 appropriately. Place part of the new FMN sample you prepared in a quartz cuvette provided by the TA Collect an absorbance spectrum of the sample between 190 nm and 1100 nm using the Shimadzu UV1800. (Use water as your blank in the reference cuvette). Export your data to a thumb drive for later analysis in Excel. (Note- everyone in the lab must share the 4 Shimadzu spectrophotometers, so you may need to wait for your turn to complete this part. If so, proceed to parts 3 and 4 and return to this when one of the instruments is free.) 3) Construction of a calilbration curve. Prepare 4.0 mls of 5x104 M FMN by diluting the 5 x103 M FMN appropriately. Prepare 6 test tubes as indicated in the table below. Calculate the concentration of FMN present in each of the 6 tubes and enter concentrations in Table II. Set the wavelength on the Genesys to the wavelength where the absorbance of FMN is maximal in the visible region and measure the absorbance of each of the 6 test tubes. Record these values in Table II. (At the wavelength where the absorption is maximal we will get the greatest response and inaccuracies in setting the monochromator will be the smallest, since the slope of the absorbance spectrum at this point is the least.) Plot the absorbance vs, concentration in Excel. In Excel, add a linear regression trendline that goes through (0,0) and determine the slope of the line. This slope gives the extinction coefficient for the FMN under these conditions. Tube # 6 mL of 5x 104 M FMN0.1 02 04 0.6 0.8 1.0 4.9 48 4.644 42 4.0 mL of water 4) Determination of unknown. Dilute 1.0 mL of the FMN solution with unknown concentration into 4.0 ml of water. Measure the absorbance and record it in Table IlI Repeat this three times and average your results