Chapter 29, Problem 29.11QAP

Interpretation Introduction

(a)

Interpretation:

The reason behind the non-elution of highly polar or ionic compounds in SFC is to be stated.

Concept introduction:

The polar or ionic compounds are the compounds that contain the ions of opposite charges which are held together by the electrostatic forces of attraction.

Explanation of Solution

Given information:

The polar compounds and Supercritical fluid chromatography (SFC).

The highly polar or ionic compounds are not usually eluted in SFC because the modifiers which are miscible in the carbon dioxide are also moderate polar solvents.

Berger ET all conducted on experiment and showed that there are some polar compounds such as triflouroaceticacid (TFA) which when added to modifiers increase the polarity which as a result becomes the reason for their non-elution.

Interpretation Introduction

(b)

Interpretation:

The types of mobile-phase additives used to improve the elution of highly polar ionic compounds are to be determined.

Concept introduction:

The mobile phase additives are the compounds which when added to the highly polar or ionic compounds improves the elution of them.

Explanation of Solution

Given information:

The mobile phase additives and the highly polar or ionic compounds.

The mobile phase additives which are moderately polar solvents and are miscible with carbon dioxide lead to the elution of highly polar or ionic compounds in SFC.

Let us consider the example of the following compounds. These compounds aresodium sulfonates, Propranolol, Trifluoroacetic Acid (TFA) and alsopure Freon-23, or pure Freon-13, then with methanol-modified carbon dioxide containing a basic additive.

Interpretation Introduction

(c)

Interpretation:

The reason for the ion-pairing SFC not to be used generally is to be determined.

Concept introduction:

Ion pairing with the analytic is one of the possible retention mechanisms being considered.

Explanation of Solution

Given information:

Ion pairing SFC and the use of sodium sulfonates to elute secondary and quaternary ammonium salts.

In the ion-pair formation, the compounds such as Benzyltrimethylammonium chloride,Propranolol HCl, and cetylpyridium chloride get chosen for the role of the probe analytes. Sodium-1decanesulfonate, sodium 1-heptanesulfonate, and sodium 1-ethansulfonate were found to be the mobile phase additives. An Ethylpyridine column has shown some advantages over the elution of the given ammonium analyte and there was no requirement of the additive to elute these ionic compounds. The analytes were eluted from the DeltabondCyano phase within very few minutes successfully and these were retained without any additive or with the use of ammonium acetate as an additive.

Interpretation Introduction

(d)

Interpretation:

The reason for the addition of ammonium salts as mobile phase modifiers in SFC is to be determined.

Concept introduction:

Ammonium salts as mobile phase modifiers in SFCwere very strongly or irreversibly retained without additive (at the same percentage of methanol) were successfully eluted from a DeltabondCyano stationary phase.

Explanation of Solution

Given information:

The ammonium salts that were studied include ammonium acetate, tetramethylammonium acetate, tetrabutylammonium acetate, ammonium chloride and lithium acetate.

Pinkston et al. conducted the experiment and reported that the application of mass-spectrometry compatible with volatile ammonium salts as mobile phase additives in SFC.The various types of Ammonium sulfonate salts such as Ammonium formate, ammonium acetate, and ammonium carbonate were used to elute several cationic also known as quaternary ammonium salts and anionic which are also known as sulfonic acid salts) organic ions under SFC conditions. Now if on adding the ethanol to 1.1 mm of ammonium as mobile phase modifier, analytes,a three-descriptor model was developed in this study which showed difference in the retention value.

Interpretation Introduction

(e)

Interpretation:

The comparison of the compatibility of SFC with MS and HPLC and GC with MS.

Concept introduction:

All are types of chromatographic techniques.

Explanation of Solution

SFC is compatible with both HPLC and GC. High-performance liquid chromatography and gas chromatography more or less similar to each other. They have a normal phase chromatography.

The GC can never be used for nonvolatile compounds and LC will not be employed for those compounds with the functional groups that can’t be detected by electrochemical detectors used in LC.

Interpretation Introduction

(f)

Interpretation:

The effect observed when authors studied the effect of column outlet pressure on the elution of sodium 4-dodecycelbenzene sulfonate on three different stationary phases with five mobile phase additives and the explanation for the effect is to be explained.

Concept introduction:

Retention changes under pressure and this change arises from the change in the molar volume of the different substances.

Explanation of Solution

Given information:

The column outlet pressure on the elution of sodium 4-dodecycelbenzene sulfonate on three different stationary phases with five mobile phase additives.

There are three factors that act along with the effect of pressure on column outlet and these are temperature, volume and the pressure itself. The elution of sodium 4-dodecyclebenzene sulfonate, when subjected under high pressure, reduces the solvation layer of the alkyl-bonded phase of the C18 stationary phase. Since it is known that the proteins change conformation, exposing their hydrophobic regions.

Interpretation Introduction

(g)

Interpretation:

What elution mechanisms were considered by the authors.

Concept introduction:

The elution mechanisms were mainly used for extracting one material from another material by washing with a solvent.

Explanation of Solution

The following elution mechanisms were considered by the author-

• HPLC
• Ion exchange chromatography.
• Affinity chromatography
• Reversed HPLC
• Liquid chromatography.

Interpretation Introduction

(h)

Interpretation:

The mobile phase additive that gives the fastest elution of the sulfonate salts is to be determined along with the name of the one that provided the longest retention times.

Concept introduction:

Less polar molecules will get eluted fast than the high polar molecules when used with a weak polar solvent.

Explanation of Solution

Given information:

Sulfonate salts and their types with some retention mechanisms.

Sodium 1- decanesulfonate has the fastest elution time or sharpest peak on the basis of the comparison of three sulfonate additives and sodium ethanesulfonate has the latest elution/broadest peak. The cationic analyte in which the ion is paired with the decanesulfonate salt will elute from the column in the shortest period of time because the ion-pairs that are formed by sodium 1-decanesulfonate, in turn, will get combined with the propranolol cations will be more soluble in the mobile phase as the additive has the greatest non-polar character. The sodiumethanesulfonate has the least hydrophobicity as the additive propranolol ion eluted last.

Interpretation Introduction

(i)

Interpretation:

Whether a silica column gives the result similar to or different from a cyno- bonded phase column.

Concept introduction:

Cyno columns are usually prepared by bonding a cyanopropyl silane to the silica.

Explanation of Solution

Given information:

Two columns Silica column and Cyno-bonded phase column.

The rule is that like attracts like. Silica gel column and Cyno-bonded phase columns give the same result because they both exhibit similar kinds of properties. Silica gel is used in adsorption chromatography while Cyno bonded phase is used in reversed-phase chromatography.

The retention of the compounds on the Silica column changes as the amount of water absorbed changes. Since the Cyno is a bonded phase, it will be more tolerant of the trace amounts of water which are absorbed in the mobile phase.