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Chapter 28: Q14P (page 790)

Barbital can be isolated from urine by solid-phase extraction with\({{\bf{C}}_{18}} - \)silica. The barbital is then eluted with\({\bf{1}}:{\bf{1}}\) vol/volacetone: chloroform. Explain how this procedure works.

Short Answer

Expert verified

Barbital has the higher affinity for water so it is retained by the column and barbital dissolve in acetone.

Step by step solution

01

Definition of Barbital.

  • Barbital (or barbitone) was the first commercially accessible barbiturate, marketed under the brand names Veronal for the pure acid and Medinal for the sodium version.
  • From 1903 to the mid-1950s, it was used as a hypnotic (sleeping aid).
  • Barbital's chemical names are diethylmalonyl urea or diethylbarbituric acid; as a result, the sodium salt (marketed as medinal in the United Kingdom) is also known as sodium diethylbarbiturate.
02

Determine the procedure.

  • Barbital is isolated from urine by solid- phase extraction with \({{\rm{C}}_{18}}\)-silica.
  • It is then eluted with \(1:1\) vol/vol acetone: chloroform. Here we will explain how would this procedure work.
  • Barbital has a higher affinity for the \({{\rm{C}}_{18}}\)-silica phase than for water so it is retained by the column - this happens due to nonpolar properties of barbital considering also that it is highly hydrophobic
  • The barbital would dissolve in acetone: chloroform which would elute it from the column

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Most popular questions from this chapter

To pre-concentrate cocaine and benzoylecgonine from river water described at the opening of thischapter, solid-phase extraction was carried out at2mL pH2using the mixed-mode cationexchange resin in Figure 28-19. After passing 500mLof river water through 鈥�60mgof resin, the retained analytes were eluted first with2mLof localid="1663594337127" CH3OHand then with localid="1663594104084" 2mLof2% ammonia solution inCH3OH. Explain the purpose of using pH2for retention and dilute ammonia for elution.

Many metals in seawater can be preconcentrated for analysis by coprecipitation with\({\rm{Ga}}{({\rm{OH}})_3}\). A \(200 - \mu {\rm{L}}\)HCl solution containing \(50\mu {\rm{g}}\)of \({\rm{G}}{{\rm{a}}^{3 + }}\)is added to \(10.00\;{\rm{mL}}\) of the seawater. When the \({\rm{pH}}\)is brought to \(9.1\)with\({\rm{NaOH}}\), a jellylike precipitate forms. After centrifugation to pack the precipitate, the water is removed and the gel is washed with water. Then the gel is dissolved in \(50\mu {\rm{L}}\) of \({\rm{HN}}{{\rm{O}}_3}\)and aspirated into an inductively coupled plasma for atomic emission analysis. The preconcentration factor is\(10\;{\rm{mL}}/50\mu {\rm{L}} = 200\). The figure shows elemental concentrations in filtered and unfiltered seawater as a function of depth near hydrothermal vents.

(a) What is the atomic ratio (Ga added): (Ni in seawater) for the sample with the highest concentration of\({\rm{Ni}}\)?

(b) The results given by gray lines were obtained with seawater samples that were not filtered prior to coprecipitation. Colored lines are from filtered samples. Results for Ni do not vary between the two procedures, but results for Fe vary. Explain what this means.

From their standard reduction potentials, which of the following metals would you expect to dissolve in \({\rm{HCl}}\)by the reaction\({\rm{M}} + n{{\rm{H}}^ + } \to {{\rm{M}}^{n + }} + \frac{n}{2}{{\rm{H}}_2}:{\rm{Zn}},{\rm{Fe}},{\rm{Co}},{\rm{Al}},{\rm{Hg}},{\rm{Cu}},{\rm{Pt}}\),\({\bf{Au}}\)?

(When the potential predicts that the element will not dissolve, it probably will not. If it is expected to dissolve, it may dissolve if some other process does not interfere. Predictions based on standard reduction potentials at \({\bf{2}}{{\bf{5}}^{^{\bf{o}}}}C\) are only tentative, because the potentials and activities in hot, concentrated solutions vary widely from those in the table of standard potentials.)

The county landfill in the diagram was monitored to verify that toxic compounds were not leaching into the local water supply. Wells drilled at 21 locations were monitored over a year and pollutants were observed only at sites\(8,11,12\), and 13 . Monitoring all 21 sites each month is very expensive. Suggest a strategy to use composite samples (Box 0-1) made from more than one well at a time to reduce the cost of routine monitoring. How will your scheme affect the minimum detectable level for pollutants at a particular site?

Why is it advantageous to use large particles \(\left( {{\bf{50}}{\rm{ }}\mu {\bf{m}}} \right)\) for solid phase extraction, but small particles \(\left( {{\bf{5}}{\rm{ }}\mu {\bf{m}}} \right)\) for chromatography?
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