A student researcher performed a chromatographic separation of caffeine and aspartame. The retention time for caffeine, te, was found to be 209.6 s with a baseline peak width, w., of 14.4 s. The retention time for aspartame, ta, was 260.0 s with a baseline peak width, wa, of 21.2 s. The retention time for the unretained solvent methanol was 49.2 s. Calculate the average plate height, H, in micrometers for this separation, given that it was performed on a 22.1 cm long column. Н- µm Calculate the resolution, R, for this separation using the widths of the peaks. R = Calculate the resolution if the number of theoretical plates were to increase by a factor of 2. R2N =

A student researcher performed a chromatographic separation of caffeine and aspartame. The retention time for caffeine, te, was found to be 209.6 s with a baseline peak width, w., of 14.4 s. The retention time for aspartame, ta, was 260.0 s with a baseline peak width, wa, of 21.2 s. The retention time for the unretained solvent methanol was 49.2 s. Calculate the average plate height, H, in micrometers for this separation, given that it was performed on a 22.1 cm long column. Н- µm Calculate the resolution, R, for this separation using the widths of the peaks. R = Calculate the resolution if the number of theoretical plates were to increase by a factor of 2. R2N =

Chemistry

10th Edition

ISBN:9781305957404

Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste

Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste

Chapter1: Chemical Foundations

Section: Chapter Questions

Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...

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The protein concentration of a protein isolate was determined using the Bradford assay. Five dilution of bovine serum albumin (BSA) were prepared from a 5.00 mg/mL BSA stock solution. To these dilutions, 100 µl of Bradford reagent were added. After 5 minutes, the absorbance was taken at 595 nm. Standard # BSA, in mg/mL Volume of Bradford reagent, A595 in mL 1 5.0 0.000 1.00 5.0 0.134 3 2.00 5.0 0.265 4 3.00 5.0 0.388 4.00 5.0 0.497 The supernatant dilution was prepared by mixing 49 µL of the protein isolate with 16 µL water. The absorbance was taken 5 minutes after addition of 100 mL Bradford reagent. Calculate the protein concentration (in mg/mL) of the original isolate if the absorbance at 595 nm was 0.413. Note: Final answer format must be x.xxx (three decimal places). Round off only in the final answer. Do not round off in the middle of calculation.
Chloroform is an internal standard in the determination of the pesticide DDT in a polarographic analysis in which each compound is reduced at an electrode surface. A mixture containing 0.500 mM chloroform and 0.800 mM DDT gave signals of 15.3 µA for chloroform and 10.1 µA for DDT. An unknown solution (10.00 mL) containing DDT was placed in a 100-ml volumetric flask and 10.2 ul of chloroform (MW = 119.39, density = 1.484 g/mL) were added. After dilution to the mark with solvent, polarographic signals of 29.4 and 8.7 µA were observed for the chloroform and DDT, respectively. Find the concentration of DDT in the unknown.
If the standard addition intercept is the major source of uncertainty, find the uncertainty in the concentration of Sr in tooth enamel in parts per million. Find the 95% confidence interval for Sr in tooth enamel.
QUESTION 5 In a chromatographic separation using a polar stationary phase and a mobile phase composed of 60% hexane and 40% ethyl acetate, two compounds, benzene (peak A) and toluene (peak B), are eluted. The width of peak A at its base is 1.2 min, the width of peak B at its base is 1.3 min, and the retention time of peak A is 5.2 min and peak B is 3.5 min. What is the resolution (Rs) between these two peaks and is it acceptable? R = 1.36. It is not an acceptable resolution. R = 0.74. It is an acceptable resolution. R = 1.36. It is an acceptable resolution. R = 0.74. It is not an acceptable resolution.
Which is correct? Random errors affect accuracy and systematic errors affect precision. An accurate result shows agreement with the true or accepted value. Precise results can contain significant random error, but little systematic error. The standard deviation is a good measure of accuracy. Polydimethylsiloxane (PDMS) stationary phases have low polarities. Which of the following statements is TRUE about gas chromatography using PDMS stationary phases? The gas chromatography column is typically packed with silica microparticles. An oven is used to control the column temperature because a constant temperature is always needed in gas chromatography Octane (C8H18, boiling point: 126 ºC) is eluted later than dodecane (C12H26, boiling point: 216 ºC) 3-Pentanone ((C2H5)2CO, boiling point: 102 ºC) is eluted later than propanol (CH3CH2CH2OH, boiling point: 97 ºC)
A young researcher set out to develop a method for quantifying the polycyclic aromatic hydrocarbon (PAH) content in a contaminated soil sample using open tubular gas chromatography. During the initial stages of method development, the researcher was unable to separate the early eluting compounds, anthracene and naphthalene, with baseline resolution. Select the possible modifications the researcher could make to improve the resolution. use a column with a smaller inner diameter decrease the column length increase the stationary phase thickness increase the temperature choose a different stationary phase
A mixture of three components is separated using paper chromatography, and each component is analyzed using absorption. With standards containing 100 ppm of each component run simultaneously, the following data were obtained: cmpd A, 0.72 absorbance; B, 0.55; C, 0.80. For the unknown mixture, the data obtined when run under identical conditions were as follows: cmpd A, .0.15 absorbance, B, 0.84; C, 0.75. a) Calculate the relative percentage composition of the unknown mixture. b) The distances traveled by the three components were 8.5, 6.3, and 5.5 cm, respectively. Sketch the appearance of the paper chromatogram. Label each spot. c) Calculate the Rf values if the solvent front is 18 cm.
A quality-control laboratory analyzes a product mixture us-ing gas-liquid chromatography. The separation of components ismore than adequate, but the process takes too long. Suggest twoways, other than changing the stationary phase, to shorten theanalysis time
As part of an analytical chemistry laboratory course, a student measured the Ca2+ content in two water samples, city-supplied drinking water and well-supplied drinking water, using two different analytical methods, flame atomic absorption spectrometry (FAAS) and EDTA complexometric titration. The results of this experiment are given in the table as the mean Ca2+concentration (?¯) and standard deviation (?) in parts per million (ppm). Each sample was measured five times (n=5) by each method. Method City-Supplied Drinking Water (?¯±?x¯±s) Well-Supplied Drinking Water (?¯±?x¯±s) FAAS 57.57±0.68 ppm 64.77±0.70 ppm EDTA titration 58.32±0.96 ppm 65.62±0.97 ppm Method Comparison: For each drinking water sample (city and well), compare the Ca2+ content measured by FAAS and EDTA titration. Calculate the ? value for each sample. Do the methods produce statistically different results at the 95% confidence level when measuring the Ca2+content of the city-supplied drinking water? Do the…
3. A student administered ibuprofen to a lab mice orally. She would like to find out the amount of ibuprofen in blood plasma at a specific time using HPLC. The chromatographic peak areas after 2 hours, 4 hours, and 8 hours are 38.34, 20.5, and 14.95 respectively. What is the concentration of ibuprofen in the plasma at each aforementioned time? Below is the corresponding peak area of the 5 ibuprofen standards. Standard Concentration (mg/mL) Peak area 5.02 0.5 1.0 10.05 2.0 17.15 3.0 19.79 6.0 39.72
1. Methanol and ethanol are separated in a capillary GC column with retention times of 370 and 385 s, respectively, and half widths (W₁/2) of 9.42 and 10.0 s. An unretained butane peak occurs at 10.0 s. Calculate the separation factor and the resolution.