Login Registrieren

Warning: foreach() argument must be of type array|object, bool given in /var/www/html/web/app/themes/studypress-core-theme/template-parts/header/mobile-offcanvas.php on line 20

Chapter 25: Q37P (page 711)

A reversed-phase separation of a reaction mixture calls for isocratic elution with 48%methanol 52%water. If you want to change the procedure to use acetonitrile/water, what is a good starting percentage of acetonitrile to try?

Short Answer

Expert verified

Considering a vertical line (intersects each solvent line at the same elegant strength) at 48% methanol intersects the acetonitrile at 38%. Use acetonitrile/water instead of 48% methanol water 52%, the good starting percentage of acetonitrile must be 38%.

Step by step solution

01

Definition of isocratic elution

When the mobile phase has a constant concentration, isocratic elution is a term used in chromatography where the concentration of the mobile phase is constant throughout the chromatographic process.

02

Percentage of acetonitrile

Considering a vertical line (intersects each solvent line at the same elegant strength) at 48% methanol intersects the acetonitrile at 38%. Use acetonitrile/water instead of 48% methanol water 52%, the good starting percentage of acetonitrile must be 38%.

Unlock Step-by-Step Solutions & Ace Your Exams!

Full Textbook Solutions
Get detailed explanations and key concepts
Unlimited Al creation
Al flashcards, explanations, exams and more...
Ads-free access
To over 500 millions flashcards
Money-back guarantee
We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

(a) Make a graph showing retention times of peaks 6, 7, and 8 in Figure 25-12 as a function of %acetonitrile (%B). Predict the retention time of peak 8 at 45% B.

(b) Linear-solvent-strength model: In Figure 25-12, t_m = 2.7 min. Compute k for peaks 6, 7, and 8 as a function of %B. Make a graph of log k versus Φ, where Φ= %B/100. Find the equation of a straight line through a suitable linear range for peak 8. The slope is -S and the intercept is log k_w. From the line, predict t_r for peak 8 at 45% B and compare your answer with (a).

(c) Gradient elution: A linear eluent gradient from 40 to 80% acetonitrile over 30 min is performed on the column in Figure 25-12. Assuming a dwell volume of 0 mL, use your data from (b) to plot the retention factor of peaks 6 and 8 during the gradient. What are the general characteristics of the plot?

(d) Why are the peaks in a gradient separation sharp?

After poisonous melamine and cyanuric acid appeared in milk in China (Box $11 - 3$ ) in $2008$ , there was a flurry of activity to develop methods to measure these substances. An analytical method for milk is to treat 1volume of milk with 9 volumes of $H_{2} O_{2} {CH}_{3} CN (20 : 80 vol / vol)$ to precipitate proteins. The mixture is centrifuged for $5 \min$ to remove precipitate. The supernatant liquid is filtered through a $0.5 - μm$ filter and injected into a HILIC liquid chromatography column (TSK gel Amide-stationary phase) and products are measured by mass spectrometry with selected reaction monitoring (Section $22 - 5$ ). Melamine is measured in positive ion mode with the transition $m/z127→85$ . Cyanuric acid is measured in negative ion mode with the transition $m / 2128 \to 42$ .

(a) Write the formulas for the four ions and propose structures for all four ions.

(b) Even though milk is a complex substance, only one clean peak is observed for melamine and one for cyanuric acid spiked into milk. Explain why

(a) When you try separating an unknown mixture byreversed-phase chromatography with 48%acetonitrile 50%water,the peaks are too close together and are eluted in the range k = 2- 6Should you use a higher or lower concentration of acetonitrile in thenext run?

(b) When you try separating an unknown mixture by normal-phasechromatography with 50%hexane50% methyl t-butyl ether, thepeaks are too close together and are eluted in the range k = 2 - 6Should you use a higher or lower concentration of hexane in thenext run?

A known mixture of compounds A and B gave the following HPLC results:

A solution was prepared by mixing $12.49 m g$ of $B$ plus $10.00 mL$ of unknown containing just and diluting to $25.00 mL$ . Peak areas of $5.97$ and $6.38$ were observed for $A$ and $B$ , respectively. Find the concentration of $A (mg / mL)$ in the unknown.

(a)explain how to measure k and resolution.

(b)state three method for measuring $^{t_{m}}$ in reversed-phase chromatography.

(c)state three method for measuring $^{t_{m}}$ in hydrophilic interaction liquid chromatography.

(d)Estimate $^{t_{m}}$ for $^{15 \times 0.46}$ column containing $^{5 - μm}$ particles operating at a flow rate of $^{1.5 mL / \min}$ Estimate $^{t_{m}}$ if the particle size were $^{3.5 - μm}$ instead.

See all solutions

Recommended explanations on Chemistry Textbooks

Making Measurements

Read Explanation

Organic Chemistry

Read Explanation

The Earths Atmosphere

Read Explanation

Chemical Reactions

Read Explanation

Kinetics

Read Explanation

Physical Chemistry

Read Explanation

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free