Process Chromatography - Part B Flashcards

Flashcards covering the key concepts from the Process Chromatography - Part B lecture notes, focusing on liquid chromatography components, detectors, sample systems, multi-stream switching, and safety.

What are two examples of solutions analyzed by HPLC?

Materials that decompose on heating and inorganic salts with boiling points over 1000°C.

What is the mobile phase in liquid chromatography?

A liquid at thousands of psi pressure.

What are the eight major components of a liquid chromatograph?

Solvent reservoir, high pressure pump, sample injection, guard column, main column, detector, oven, and programmer controller.

What is the purpose of the solvent in liquid chromatography?

To dissolve and carry a small volume of liquid sample through the stationary phase to the detector.

Why must the solvent be degassed and filtered?

To prevent interference with flow and detector response due to gas bubbles, and to prevent column plugging by solids.

What are high pressure pumps for HPLC commonly based on?

A reciprocating piston design.

What is the purpose of a pulse dampener?

To reduce pressure fluctuations in the flow by stretching and contracting its volume.

What is the purpose of a guard column?

To protect the main column from being plugged by solid contaminants or damaged by impurities.

Name four types of Stationary phases used in HPLC Columns

liquid, solid, size-exclusion, and ion exchange

What is liquid-liquid chromatography (LLC)?

Liquid columns are packed with solid grains chemically bonded to a liquid stationary phase. The liquid stationary phase absorbs the sample constituents which are then eluted by solvent flow (the mobile liquid phase).

What happens in normal phase LLC?

The stationary phase is more polar than the solvent.

What happens in reverse phase LLC?

The stationary phase is less polar than the solvent.

How do size exclusion columns work?

They separate polymer molecules according to their size, with smaller molecules having longer retention times due to penetration into pores.

What are two common applications for ion exchange columns?

Analyzing water samples from the environment (e.g., rivers, lakes) and in water treatment plants.

What is the difference between cation and anion exchange columns?

Cation exchange columns analyze positively charged ions (cations) using a negatively charged stationary phase, while anion exchange columns analyze negatively charged ions (anions) using a positively charged stationary phase.

What is the role of the mobile solvent in ion exchange columns?

To remove the ions from the charged stationary phase, often using water at a specific pH containing ions that are more strongly attracted to the ion exchange materials.

What is the function of a detector in liquid chromatography?

To produce an electronic signal which varies with concentration.

Why are the injection valve, columns, and detector placed in a controlled temperature enclosure (oven)?

To maintain a constant temperature and prevent fluctuations in volume injected, sample retention times, and detector signal.

What tasks does a programmer controller manage in a liquid chromatograph?

Controls the solvent pump and sample injection valve. Processes the detector signal to determine retention times and chromatogram peak areas. Determines the sample composition from retention time and peak area data.Provides output communication signals for the analytical results.

What are three advantages of LC detectors?

Low internal volume, high sensitivity, and Low detection limit.

What property of the sample is utilized by LC detectors?

A property different from that of the solvent so that a detectable change occurs when sample components pass through them.

Give four examples of LC detector types.

refractive index; optical absorbance of ultraviolet (UV), visible or infrared (IR) light; UV fluorescence and electrical conductivity.

How do Refractive Index (RI) Detectors work?

By measuring the bending of light rays at the boundary between two materials and comparing the refractive index of pure solvent to that of solvent mixed with sample compounds.

How do Optical Absorbance Detectors work?

By measuring how much light (UV, visible, or IR) compounds absorb, with sample concentration being proportional to absorbance.

How do Ultraviolet Fluorescence Detectors work?

By passing a beam of UV light through a flow cell; sample molecules that fluoresce absorb UV light and emit weaker visible light, which is then detected.

How do Electrical Conductivity Detectors work?

By measuring the change in electrical conductivity between two metal electrodes when charged ions (sample ions) pass between them.

What is the purpose of Chemical suppression in Electrical Conductivity Detectors?

Chemical suppression is a common method of reducing the mobile phase conductivity.

What are the three objectives of Process Chromatograph Sample Systems?

Obtain a representative sample, deliver the sample quickly, and condition the sample for safe injection.

What failures in the sample system cause it to not deliver a representative sample to the analyzer?

a poor choice of sample point location, a bad sampling method and sample changes during transport to the analyzer.

What happens if solid particles or liquids contaminates chromatography gas samples?

Contamination with solid particles destroys chromatographic valves, and contamination with liquids damages the stationary phases in the chromatographic columns. Solids and liquids can also plug the small sample diameter tubing.

How are Chromatographs protected from particles larger than 2 microns?

Filters.

What is the difference between In-line and by-pass filters?

The entire sample passes through an in-line filter, where a portion of the sample passes through the filter element in a bypass filter.

What is the purpose of Knock-out pots and Coalescing separators?

Knock-out pots separate heavy droplets which fall out of the gas phase and Coalescing separators remove tiny droplets found in mists.

In a sample system with an SCU, what is the order of components?

Bypass Filter, Pressure Regulator, coalescing Filter, membrane separator, in-line filter

What is the advantage and disadvantage of using Multi-Stream Sample Switching techniques?

The advantage of this technique is that only a single chromatograph need be purchased rather than one per stream. However, a chromatograph failure results in the loss of data for multiple streams.

What are common techniques for Multistream sample switching?

Common techniques use remotely activated two- and three-way valves,electrically operated solenoid valves or air actuated shutoff valves.

What are two potential problems associated with multi-stream sample systems?

Cross-contamination among streams and increased lag time.

Explain block and bleed sample systems

Block refers to closing valves to prevent the unselected stream from contaminating the sample going to the analyzer and Bleed refers to venting and reducing the pressure of contaminating sample streams.

Explain the issues around 'Dead Legs' in Block and Bleed Sample systems

Dead legs trap sample that comes from streams 2 and 3 when they are selected and cannot be purged out quickly, so they slowly contaminate the sample flowing to the analyzer.

How is 'Back purging' used in Multi-Stream Sample systems?

By flowing back stream 1 and removing the contaminating streams from a dead leg.

What are some of the general hazards with process chromatographs?

Explosions, toxic gas exposure, electrical shock, and contact with hot surfaces.

Name four methods of electrical safety protection that can be used in hazardous areas

Intrinsic safety, purging, pressurization, and explosion-proof housings.

When starting up a chromatograph safely, what is the correct order of actions?

Turn on instrument air flow, purge the enclosures, establish carrier gas flow, then turn on electrical power.

What should take place before any electrical repairs are carried out?

Most plants require that electrical power sources be shut off, locked and tagged.

Name two types of gas chromatograph detectors that use hydrogen

Flame ionization (FID) and flame photometric (FPD).

What steps can be taken to increase Safety when using Hydrogen?

Install hydrogen gas detectors, check for hydrogen leaks periodically, and turn off the hydrogen gas supply when servicing the chromatograph or shutting down.

What can be done to handle solvents more safely?

Keep solvents in sealed containers and store flammable solvent containers in a chemical storage cabinet.

What safety rules should be known about the process area?

The hazards such as exposure to toxic or flammable materials, the location of safety equipment, the plant safety rules and permit requirements and procedures, break in procedures and the personal protective equipment that must be worn.

What Safety steps should take place if maintenance work requires breaking into a sample system line?

First isolate it by closing block valves and releasing the pressure in the line, and wear the same type of protective equipment that is required to make process line breaks.

List some features of a Sample system that has been designed with safety in mind.

All components are accessible for maintenance, obstacle-free escape routes are available, Lines are labeled, Personal are protected from contact with toxic or corrosive materials, Hot or extremely cold surfaces are insulated AND the system is designed to flush and depressurize dangerous materials

What safety steps can be taken when using gas cylinders?

Cylinders should be secured in an upright position. When transported to and from their storage areas, a cylinder cap must be in place to protect the shutoff valve and They should only be moved if they are restrained to a cylinder cart.