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The observed behavior of benzyl alcohol \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{OH}\right)\) in capillary electrophoresis is given here. Draw a graph showing the number of plates versus the electric field and explain what happens as the field increases. $$ \begin{array}{cc} \text { Electric field }(\mathrm{V} / \mathrm{m}) & \text { Number of plates } \\\ \hline 6400 & 38000 \\ 12700 & 78000 \\ 19000 & 96000 \\ 25500 & 124000 \\ 31700 & 124000 \\ 38000 & 96000 \end{array} $$

Short Answer

Expert verified
As the electric field increases, the number of plates initially increases, reaches a maximum, and then decreases due to heating effects.

Step by step solution

01

Understanding the Data

The data shows the relationship between the electric field strength (in volts per meter) and the number of plates achieved in a capillary electrophoresis run of benzyl alcohol. Increasing the electric field typically increases the efficiency of separation, indicated by the number of plates, up to a certain point.
02

Plotting the Graph

Create a graph with the electric field on the x-axis and the number of plates on the y-axis. Mark each given data point: (6400, 38000), (12700, 78000), (19000, 96000), (25500, 124000), (31700, 124000), and (38000, 96000). Connect the points with a smooth curve.
03

Analyzing the Graph

Examine the plotted graph: as the electric field increases from 6400 V/m to 25500 V/m, the number of plates increases, indicating better separation. However, between 25500 V/m and 31700 V/m, the number of plates stays constant, and after 31700 V/m, it starts to decrease, showing that excessive electric field reduces separation efficiency.
04

Explaining the Trend

Initially, increasing the electric field enhances the separation efficiency because it accelerates the analytes through the capillary. However, after reaching an optimal field strength, further increases lead to excessive heat generation, causing band broadening and loss of resolution, resulting in fewer plates.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Electric Field
In the realm of capillary electrophoresis, the electric field plays a pivotal role in determining how fast and efficiently molecules are separated. The electric field, denoted in volts per meter (V/m), serves as the driving force that propels charged molecules through a capillary filled with a conductive medium.
This force influences how quickly the molecules, such as benzyl alcohol, move, and subsequently, how distinctly they are separated.
As the electric field strength increases, the charged molecules gain more energy and move swiftly towards their respective electrodes. Expressed simply:
  • Stronger fields increase velocity, minimizing time the analytes stay in the capillary.
  • They also contribute to rapid separations, which enlarges the number of plates.
However, with too much increase in the field, other issues can arise. Increases in temperature could potentially widen peaks, reducing separation efficiency. Knowing when to stop increasing is a fine art of balance between speed and resolution.
Separation Efficiency
Separation efficiency is a measure of how distinctly analytes separate during the electrophoresis process. It is often signified by a high number of theoretical plates, with more plates indicating better separation.
In a perfect setup, each analyte resolves into a sharp peak separated from others. However, various experimental conditions, like the electric field and heat generation, can influence this process. An optimal electric field encourages distinct peaks:
  • Maintains sharp and well-resolved peaks.
  • Reduces overlap among analytes.
Yet, pushing the field too high can counteract these benefits. The associated heat may cause diffusional band broadening — a negative factor for separation efficiency. Thus, understanding fuel efficiency in terms of controlling the electric field is key to maximizing separation efficiency.
Number of Plates
In chromatography and electrophoresis, the number of plates is a concept used to quantify the efficiency of separation in a column or capillary. The 'number of plates' doesn't refer to physical plates; rather, it's a theoretical concept representing optimal separation
  • Indicates how well the apparatus can resolve a set of analytes.
  • Higher number implies a better performance, showing greater distinctness between sample peaks.
In the context of benzyl alcohol's separation, the data show a trend: initially, as the electric field increases, so does the number of plates. The relation isn't infinite, however. Beyond a critical field, the number of plates begins to decline, suggesting deterioration in separation quality. This concept highlights a critical point where increased field strength reverses its benefits, which is crucial for optimizing electrophoresis outcomes.
Benzyl Alcohol
Benzyl alcohol, with the chemical formula \( ext{C}_6 ext{H}_5 ext{CH}_2 ext{OH}\), is an organic compound often analyzed using capillary electrophoresis. In this method, its behavior varies depending on the conditions within the capillary, notably the electric field strength. This alcohol acts as a neutral and non-charged species, but due to the electric field, its interaction within the capillary solution is crucial.
The analysis and separation efficiency of benzyl alcohol can be influenced significantly by:
  • Temperature control within the capillary.
  • The medium and its interaction with the alcohol's structure.
Capillary electrophoresis may show challenges with benzyl alcohol if parameters like field strength aren't optimized, potentially leading to inaccurate measurements. Thus, understanding its behavior is key to ensuring robust experimental results, where obtaining a higher number of plates is optimal for a fine separation output.

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Most popular questions from this chapter

Ferritin (molecular mass 450000 ), transferrin (molecular mass 80000 ), and ferric citrate were separated by molecular exclusion chromatography on Bio-Gel P-300. The column had a length of \(37 \mathrm{~cm}\) and a \(1.5-\mathrm{cm}\) diameter. Eluate fractions of \(0.65 \mathrm{~mL}\) were collected. The maximum of each peak came at the following fractions: ferritin, 22; transferrin, 32; and ferric citrate, 84. (That is, the ferritin peak came at an elution volume of \(22 \times 0.65=14.3 \mathrm{~mL}\).) Assuming that ferritin is eluted at the void volume and that ferric citrate is eluted at \(V_{\mathrm{m}}\), find \(K_{\mathrm{av}}\) for transferrin.

(a) A long thin molecule has a greater friction coefficient than a short fat molecule. Predict whether fumarate or maleate will have greater electrophoretic mobility. (b) Electrophoresis is run with the injection end positive and the detection end negative. At \(\mathrm{pH} 8.5\), both anions have a charge of \(-2\). The electroosmotic flow from the positive terminal to the negative terminal is greater than the electrophoretic flow, so these two anions have a net migration from the positive to the negative end of the capillary in electrophoresis. From your answer to part (a), predict the order of elution of these two species. (c) At \(\mathrm{pH} 4.0\), both anions have a charge close to \(-1\), and the electroosmotic flow is weak. Therefore, electrophoresis is run with the injection end negative and the detection end positive. The anions migrate from the negative end of the capillary to the positive end. Predict the order of elution.

In the separation of proteins by hydrophobic interaction chromatograpy, why does eluent strength increase with decreasing salt concentration in the aqueous eluent?

Fluorescent derivatives of amino acids separated by capillary zone electrophoresis had migration times with the following order: arginine (fastest) \(<\) phenylalanine \(<\) asparagine \(<\) serine \(<\) glycine (slowest). Explain why arginine has the shortest migration time.

To obtain the best separation of two weak acids in capillary electrophoresis, it makes sense to use the \(\mathrm{pH}\) at which their charge difference is greatest. Prepare a spreadsheet to examine the charges of malonic and phthalic acid as a function of \(\mathrm{pH}\). At what \(\mathrm{pH}\) is the difference greatest?

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