Studies In The Gas Chromatography Of Amionia With Special Reference To Packings Containing Solutions Of: Silver Salts In Some.Organic Solvents

Abstract

It has been found that the gas chromatography of ammonia

on certain fixed phases containing salts yields chromatograms

consisting of a peak followed by a plateau or a succession of

'plateaux of progressively decreasing height. Such chromatograms

have been interpreted in terms of aromine formation in the column,, ~

and methods have been theoretically elaborated.for using

measurements on the chromatograms to find the dissociation pressures

of the ammines and the ratios of amnonia taken up to silver in the

fixed phase. These methods require the calibration of the ~etector,

so that arrnnonia partial pressures can be found from chromatogram

heights,, and this has been done by a chromatographic ~method. In

I

most cases,, the ratio of ammonia to silver. in the fixed phase does

not yield conclusive information on azmnine composition,, because there

is usually evidence that the salt is present in different forms or

is only partially converted to ammine.

Most attention has been devoted.to packings containing

silver salts 4issolved in organic liquids. Solutions of silver

nitrate in benzyl cyanide and benzonitrile, and of silver perchlorate

in benzyl cyanide,, benzonitrile,, fenchone and tetralin

have been found to yield chromatograms with plateaux, and a study

of these has shown that both the anion and the solvent influence

ammine formation. All these solutions react with amnonia to

form a white precipitate and therefore act a.s heterogeneous

fixed phases. New packings absorb some ammonia,, but this is

slowly removed by a current of carrier gas; the absorption is

ascribed to the formation of lower ammines having dissociation

pressures too low to be registered by the detector. The

apparent compositions of the lower amrnines have beeri determined by

measuring the initial absorption, and th~ir dissociation pressures

have been found for some packings by measuring the rate of removal

of ammonia by a current of carrier gas. Complicated ageing

processes take place in columns containing silver nitrate and

silver perchlorate in benzyl cyanide.

A survey of all the dissociation pressures deternrl.ned

shows that these fal;I. into three groups, at roughly 10- 4 , 10- 2

-1 and 10 atm~ The highest and lowest groups are shown by all

the systems studied, but the middle group only by solutions in

benzyl cyanide. A more detailed comparison of pressures in the

highest group shows that silver nitrate in a given solvent forms an

amm:ine with a dissociation pressure higher than that of the a.nunine

f?rmed by silver perchlorate in the sane solvent. .Al though the

stoichiometric data obtained are very rough, there is some indication

that ammines of similar composition a.re formed in

different solutions.

In contrast to the solutions enumerated above, silver

nitrate and silver perchlorate in m-toluidine form no precipitate

with ~ do not absorb ammonia initially and do not give

plateau chromatograms. On these solutidns, amnonia has a final

retention volume that is independent of sample size.

Experiments with silver perchlorate in mixtures of

fenchone and benzyl cyanide, silver nitrate in mixtures of

benzonitrile and m-toluidine, and silver nitrate and silver

perchlorate together in benzonitrile have shown that these threecomponent

systems produce ohromatograms having some plateaux. in

common with the chromatograms of the corresponding two-component

systems, but also showing plateaux not occurring in the latter.

A few tensimetric experiments have been performed with.

ammonia and solutions of silve::r; nitrate in benzonitrile1 and have

produced results in rough agreement with the gas-chromatographic

results.

Plateau chromatograms have also been obtained with granular

lead bromide and lead chloride; it appears that ammine formation

is confined to the surface of these salts.

Some packings containing salts have been found to give

ammonia chromatograms showing two peaks~ of which the first

increases in size with increasing humidity of the carrier gas,

and is ascribed to moisture taken up by the packing from the

ca.ITier and later displaced by the ammonia sample.