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In the analysis of odorants in tequila in Figure 24-21, tequila was diluted with water and extracted four times with dichloromethane(CH2Cl2) , b.p. 40∘CThe400mLof(CH2Cl2)was evaporated down to1mLand1μ³¢of the extract was injected on-column onto a poly(ethylene glycol) open tubular column (30m×0.53mm,filmthickness=1μ³¾), film thickness ) initially at and then ramped to 230∘C

(a) Why was the diluted tequila extracted four times with dichloromethane instead of once with a larger volume?

(b) Why was on-column injection used?

(c) Why was a poly(ethylene glycol) column chosen for this application?

(d) What was the phase ratio of the column?

(e) Why was a wide-bore 0.53-mm-diameter column chosen for this application?

Short Answer

Expert verified

(a). As a result, diluted tequila is extracted four times with dichloromethane rather than once at a higher volume.

(b).On-column injection minimises the likelihood of heat degradation as well as the odour of a larger number of molecules.

(c). The use of poly (ethylene glycol) in the column is due to the fact that poly (ethylene glycol) is a polar column, which is ideal for polar analytes.

(d).The column's phase ratio βis 132.

(e).As a result, a wide-bore column with a diameter of0.53mm enables for bigger injections of compounds, the scent of the components can be recognised during elution.

Step by step solution

01

Definition of dichloromethane

  • Methylene chloride, often known as dichloromethane, is a colourless liquid with a slight pleasant odour that evaporates quickly and does not burn easily.
  • It's frequently used as a paint stripper and an industrial solvent.
02

Determine the diluted tequila extracted four times with dichloromethane instead of once with a larger volume

(a)

  • It must be explained why diluted tequila is extracted four times with dichloromethane rather than once with a larger volume.
  • To explain why diluted tequila is extracted four times with dichloromethane instead of once with a larger volume.
  • Small extractions repeated several times have been found to be more significant than a single extraction. As a result, diluted tequila is extracted four times with dichloromethane rather than once at a higher volume.
03

Determine the on-column injection

(b)

  • It is necessary to explain why on-column injection is used.
  • On-Column Injection: For thermally sensitive chemicals, on-column injection is the optimum method for quantitative analysis.
  • It's a low-resolution approach that won't work for columns smaller than a certain diameter0.2mm.
  • On-column injection can be used to handle both large and small amounts of dilute and concentrated solutions.
  • To describe how on-column injection is used.
  • On-column injection minimises the likelihood of heat degradation as well as the odour of a larger number of molecules.
04

Determine the poly(ethylene glycol) column chosen for this application 

(c)

  • It is necessary to explain why a poly (ethylene glycol) column was used.
  • To describe how to use a poly (ethylene glycol) column
  • The retention index of the compounds is determined by the total polarity phases as well as the selectivity of each column's polar interaction types.
  • The use of poly (ethylene glycol) in the column is due to the fact that poly (ethylene glycol) is a polar column, which is ideal for polar analytes.
05

Determine the phase ratio of the column

(d)

It is necessary to compute the phase ratio β

Phase ratio β

The dimensionless phase ratio is the volume of the mobile phase divided by the volume of the stationary phase. The phase ratio is determined as follows:

β=r2dr

Where,βphase ratio

r is the column's radius.

df=temporalthicknessofthestationaryphaseIncreaseinthicknessofstationaryphase,decreasesinβthatincreasestheretentiontimeandcapacityofsample.TofigureoutthephaseratioβGiven,Diameterofcolumn=0.53mmThickness=1μ³¾Thecolumn'sphaseratioiscomputedas,β=r2dtβ=0.265mm0.002mmβ=132Thecolumn'sphaseratioβis=132.

06

 Step 6: Determine the wide-bore 0.53-mm-diameter column chosen forthis application

(e)

  • The reason for the wide-bore column's0.53mm diameter must be explained.
  • To explain why a wide-bore column with a diameter of0.53mm was chosen.
  • Because a wide-bore column with a diameter of 0.53mmenables for bigger injections of compounds, the scent of the components can be recognised during elution.

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Most popular questions from this chapter

Where would an unknown with a retention index of 936 be eluted in Figure 23-7?

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?

(a) When a solution containing234mg of pentanol (FM 88.15) and237mg of 2,3 -dimethyl-2-butanol (FM 102.17) in10.0ml was separated, relative peak areas were pentanol: 2,3 -dimethyl-2-butanol = 0.913 : 1.00. Considering pentanol to be the internal standard, find the response factor for 2,3 -dimethyl-2-butanol.

(b) Use Equation 24-8 to find the areas for pentanol and 2,3 -dimethyl-2-butanol in Figure 24-8.

(c) The concentration of pentanol internal standard in the unknown solution was93.7mM . What was the concentration of 2,3 -dimethyl2-butanol?

Nitric oxide (NO) is a cell-signaling agent in physiologic processes including vasodilation, inhibition of clotting, and inflammation. A sensitive chromatography-mass spectrometry method was developed to measure two of its metabolites, nitrite(NO-2)and nitrat(NO3),in biological fluids. Internal standards,NO-152and15NO-3, were added to the fluid at concentrations of 80.0 and, respectively.Natural14NO-2and14NO-3plus the internal standards were then converted to volatile derivatives:

Because biological fluids are so complex, the derivatives were first isolated by high-performance liquid chromatography. For quantitative analysis, liquid chromatography peaks corresponding to the two products were injected into a gas chromatograph, ionized by negative ion chemical ionization (giving major peaks forNO-2andNO3-and the products measured by selected ion monitoring. Results are shown in the figure on the next page. If the internal standards undergo the same reactions and same separations at the same rate as theN14analytes, then the concentrations of analytes are simply[14NOx-]=[15NOx-](R-Rblank)

where R is the measured peak area ratio(m/z46/47fornitriteandm/z62/63fornitrite)for nitrite andfor nitrate) andRblankis the measured ratio of peak areas in a blank prepared from the same buffers and reagents with no added nitrite or nitrate. The ratios of peak areas areand. The ratios for the blank werem/z46/47=0.062andm/z62/63=0.058. Find the concentrations of nitrite and nitrate in the urine.


Describe how retention time of butanol on a poly (ethylene glycol) column will change with increasing temperature. Use the retention time for butanol in Figure 24-9b as the starting point.

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