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Chapter 24: Q11P (page 663)

What is the purpose of derivatization in chromatography? Give an example.

Short Answer

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Non-volatile carboxylic acid is converted to volatile trimethylsilyl ester derivative in the process of derivatization.

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01

Meaning of purpose of derivatization in chromatography

Derivatization in gas chromatography is a sample preparation technique that is performed to analytes for Converting them into forms that are easy to detectAn example of derivatization is the conversion of non-volatile carboxylic acid into volatile trimethylsilyl ester derivative, as shown below.

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Most popular questions from this chapter

This problem reviews concepts from Chapter 23 using

Figure 24-15.

(a) Calculate the retention factor for peak 11 given tm 5 6.7 min.

(b) Calculate the number of theoretical plates (N in Equation 23-31)

and the plate height (H) for peak 11.

(c) Find the resolution (Equation 23-23) between peaks 16 and 17.

The graph shows van Deemter curves for n-nonane at . in the 3.0-m-long microfabricated column in Box 24-2 with a -thick stationary phase.

van Deemter curves. [Data from G. Lambertus, A. Elstro, K. Sensenig, J. Potkay, M. Agah, S. Scheuening, K. Wise, F. Dorman, and R. Sacks, "Design, Fabrication, and Evaluation of Microfabricated Columns for Gas Chromatography," Anal. Chem. 2004, 76, 2629.]

(a) Why would air be chosen as the carrier gas? What is the danger of using

air as carrier gas?

(b) Measure the optimum velocity and plate height for air and for carrier

gases.

(c) How many plates are there in the 3 -m-long column for each carrier gas at

optimum flow rate?

(d) How long does unretained gas take to travel through the column at

optimum velocity for each carrier gas?

(e) If stationary phase is sufficiently thin with respect to column diameter, which of the two mass transfer terms (23-40 or 23-41) becomes negligible?

Why?

(f) Why is the loss of column efficiency at high flow rates less severe for

than for air carrier gas?

The gasoline additive methyl t-butyl ether (MTBE) has been leaking into groundwater ever since its introduction in the. MTBE can be measured at parts per billion levels by solid-phase microextraction from groundwater to which 25 % (wt/vol) NaCl has been added (salting out, Problem 8-9). After microextraction, analytes are thermally desorbed from the fiber in the port of a gas chromatograph. The figure on the next page shows a reconstructed total ion chromatogram and selected ion monitoring of substances desorbed from the extraction fiber.

(a) What is the purpose of adding NaCl prior to extraction?

(b) What nominal mass is being observed in selected ion monitoring? Why are only three peaks observed?

(c) Here is a list of major ions above m/z50 in the mass spectra. The base (tallest) peak is marked by an asterisk. Given that MTBE and TAME have an intense peak at m/z,73 and there is no significant peak at m/z,73 for ETBE, suggest a structure for m/z,73. Suggest structures for all ions listed in the table.

Genotoxic compounds damage DNA and cause mutations or cancer.Regulatory guidelines limit genotoxic impurities in pharmaceuticals. Mesityl oxide (4-methyl- 3-penten-2-one) is an intermediate product in the synthesis of some drugs. Search the literature for a gas chromatography method for the determination of mesityl oxide in the pharmaceutical enalapril maleate and answer the following questions.

(a) Give the citation (authors, title, journal name, year, volume, pages) for a research paper describing this analysis.

(b) What is the instrumental method used?

(c) What type of column was used?

(d) What quantification method is used?

(e) What are the precision, limit of detection, limit of quantification, and linear range of the method?

(f) For how long could a standard solution be used?

3. (a) What are the advantages and disadvantages of using a narrower open tubular column?

(b) What are the advantages and disadvantages of using a longer open tubular column?

(c) What are the advantages and disadvantages of using a thicker film of stationary phase?

See all solutions

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