Analytical chemistry assignment

Reference no: EM133048584

Analytical Chemistry Assignment

Question 1. What would be the best choice of pH adjustment acid for LC-MS (ESI) analysis of basic analyte with pKa is 3.1 if phosphate buffer is used and optimal eluent composition is 30/70 MeCN/water. Generally, trifluoracetic acid is used, but analyst selected HCl instead. Is it better and why, explain?

Question 2. While developing the separation method analyst got insufficient resolution of 0.7 for two critical components, overall analysis time was 20 min. His manager required resolution of 1.2. Analyst decided to increase efficiency by increasing the column length, but manager rejected this idea -why?. How much should analyst increase the length of the column to get resolution greater than 1.2 and how longer would be analysis time. What are the other drawbacks of this approach and what would be the possible way to solve analyst problem?

Question 3. Two peaks on chromatogram have retention factors k1 = 2.5 and k2 = 5.3. Column efficiency is 10000 theoretical plates, Void volume is 1 mL. Calculate the resolution between these compounds.

Question 4. On 10 cm (length) column two peaks have resolution 0.8 (not completely resolved). How long should be the column to get resolution greater than 2?

Question 5. Predict the order in which the four analytes elute from the GC column. Analytes and their boiling points:
A - CHCl₃ (61.2 ^oC);
B - CHClBr₂ (119^oC);
C - CHCl₂Br (90 ^oC);
D - CHBr₃ (149.1 ^oC).

Question 6. 100 mL of 0.2M aqueous solution of some organic compound was brought in contact with 5 mL of heptane at 20 oC (extraction). GC analysis of heptane phase after equilibration shows component concentration of 0.12 M. What is the partitioning coefficient of this component?

Question 7. Calculate the ionic strength of 0.10 M solution of Mg3(PO4)2 in formiate buffer (0.10 M formic acid and 0.40 M sodium formiate)

Question 8. Component retention in HPLC is 4 min. Peak height is 200 mA and peak area is 832 mA*sec. Calculate the efficiency for this system.

Question 9. A solution UV transmittance is 35% at 260nm in 1 cm cell pathlength. Calculate the transmittance if you dilute 25 mL of the solution to 75.0 mL and measure it in the cell with 5 cm pathlength?

Question 10. The pH of some buffer system (0.1 M acid and 0.1M sodium salt) at room temperature (25oC) is equal to 4. What pH will this buffer have if you dilute it with methanol to 50/50 aqueous/organic ratio? Explain.

Reference no: EM133048584

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