Chapter 4 - Fundamentals of LC in LC-MS - part 2

Question 1

Difunctional binding to the silica surface can prevent

Answer 1

the hydrolysis of the siloxane bond.

Question 2

Tri-functional bonding to the silica surface is

Answer 2

sterically impossible.

Question 3

If bulky isobutyl groups are attached to the silicon atom of the bonded phase,

Answer 3

the stationary phase is protected from attack by H3O+ and is stable for long periods at low pH and high temps.

Question 4

Working at high pH

Answer 4

Polymeric and multi-dentate ligands
Hybrid silica
Polymeric and non-silica base material

Question 5

Most reproducible pumping system

Answer 5

Binary pumps.

Question 6

Pulsing from a single piston pump can lead to

Answer 6

undesirable disturbances in the chromatogram baseline.

Question 7

Dual-piston pump advantages

Answer 7

Virtually pulse free flow

Stable baseline and reproducible retention times

Question 8

Dual-piston pump disadvantage

Answer 8

Higher number of moving parts (higher running costs)

Question 9

Binary pumps use

Answer 9

two reciprocating pump units.

Question 10

High pressure mixing system in binary pump

Answer 10

The mobile phase and constituents are mixed on the high pressure side of the system after compression by the pump.

Question 11

Binary pump advantages

Answer 11

Reproducible gradient profile

Lowest gradient dwell volume

Question 12

Binary pump disadvantage

Answer 12

More complex and more expensive.

Question 13

A quaternary pump uses

Answer 13

one reciprocating pump and a solenoid controlled portioning valve located in line between the solvent degasser and the pump head.

Question 14

Quaternary pump advantages

Answer 14

Lower purchase price and maintenance costs.
4 different solvents for gradient elution.
4 channels can establish automatic flushing.

Question 15

Quaternary pump disadvantages

Answer 15

Not as good as binary pump at extremes of flow or gradient composition.
Low pressure solvent mixing is less accurate and reproducible.
Solvent is more prone to out-gassing.

Question 16

Gradient dwell volume is

Answer 16

the total volume in a gradient system between the point where the gradient is formed and the inlet of the column.

Question 17

Typical dwell volumes range from

Answer 17

1 mL to 5 mL (can be from 0.5 to 13)

Question 18

Dwell volume can be converted into dwell time by using

Answer 18

eluent flow rate.

Question 19

The injection valve works by

Answer 19

controlling the flow of liquid through components that allow the sample loop to be isolated or included in the mobile phase flow.

Question 20

The rotor seal is

Answer 20

etched with flow paths that allow mobile phase to flow into and out of the injection head.

Question 21

In complete loop filling, the loop should be overfilled ___ times.

Answer 21

3

Question 22

Partial loop filling should be no greater than ____% of injector loop capacity.

Answer 22

50

Question 23

With a partial loop filing injection volume of 20 microliters, reproducibility is poor between

Answer 23

10-40 microliters.

Question 24

Autosampler essential parts.

Answer 24

Standard size vials
Samples vials in trays that permit serial injection
Injection needle
Injection switch valve