Compound A Compound B Compound C Rf Student 1 Rf Student 2 Rf Student 3 0.20 0.21 0.15 0.50 0.52 0.44 0.70 0.69 0.63

A2

A young researcher was evaluating a standard method for determining the methylmercury content in blue fin tuna using high performance liquid chromatography (HPLC). She determined the standard deviation (?)(s) for the method to be 0.440.44 ppb and assumed that ?s was a good approximation of ?σ . As a test, she used this method to evaluate the methylmercury content in a National Institutes of Standards and Technology (NIST) standard and determined the unknown amount to be within 0.210.21 ppb (?)(μ) of the known mean with 99% probability. How many replicate measurements of the NIST standard did the researcher perform?

6. The concentration of caffeine in an energy soft drink was determined by standard addition using HPLC. The following procedure was used: a standard caffeine solution was prepared by adding 0.09850g of caffeine to 25.0 cm3 of water.A series of solutions were prepared by adding known volumes of the standard solution to the soft drink before diluting to 100 cm3. The volume of standard and the caffeine peak area are shown in the table: Energy Drink (cm3) Added caffeine Std (cm3) Peak area       15 0 965   15 5 1352   15 10 1739   15 15 2126   15 20 2513       Determine the concentration of caffeine in the soft drink as mg cm-3.   A. 3.3 B. 2.3 C. 4.3 D. 7.3

In chromatography, it is desirable to increase the resolution. a) increase the plate height (H) b) decrease the plate height (H) c) decrease the number of plates (N) to

-3 A 0.3202 (±0.0001) g sample of a pure monoprotic acid required 20.04 (±0.02) cm° of 0.1005 (±0.0005) mol dm neutralisation. Find the molar mass of the acid in g mol together with its uncertainty also in g mol, with an appropriate number of digits. NaOH for -1 Select one: a. 1.59 x 102+ 0.2 g mol b. 1.60 x 10 + 0.03 g mol C. 1.590 x 102 + 0.03 g mol d. 1.590 x 10- + 0.2 g mol 1.60 x 10-+0.2 g mol е. Clear my choice

Which statement(s) are correct for gas chromatography? A) the components in a mixture can be identified from their retention time. B) the relative peak areas give the proportions of components in a mixture. C) Calibration curves are used to confirms the concentrations of components in a mixture.

In a particular trial, a student got a value for R of 0.083. Calculate the percent deviation of this result. Enter a number without the % sign. The percent deviation should be reported as a positive value.

4.Consider the peaks for pentafluorobenzene and benzene in the gas chromatogram shown here.  The elution time for unretained solute is 1.06 min.  The open tubular column is 30.0 m in length and 0.530 mm in diameter, with a layer of stationary phase 3.0 μm thick on the inner wall.  a) Measruing the width, w, at the baseline on the chromatogram, find the number of plates for these two compounds b) Use your answer to (a) to find the resolution between the two peaks c) Using the number of plates N=sqrtN1*N2 with the values from (a) calcuate what the resolution should be and compare your answer with the measured resolution in b

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