SANCIONES UNILATERALES

A series of Investigations were carried out to explore the effect of increasing the gas pressure in the source during FAB, samples containing a range of matrlcies. During these experiments the source block was fitted with covers to reduce the source conductance, while additional buffer gases were introduced into the source using the standard Kratos Cl gas inlet system ( Fig. 2.3.1 ).

The effect of increasing the source pressure is best examined by considering its effects on various aspects of the resulting spectrum. For samples containing no matrix, various pressures of argon gas were introduced as a buffer gas into the source during bombardment. For low argon pressures no notable effects on the distribution of clusters in the resulting spectrum was observed, although the total ion current showed a slight decrease with extended bombardment times.

As the buffer gas pressure was increased, in a stepwise manner, the total ion current was found to increase slowly with increasing source pressure. This behaviour continued until a critical pressure was reached after which a rapid increase in total ion current was observed for small increments in pressure. At very high pressures evidence of a gradual decrease in total ion currents was observed, reflecting source saturation ( Fig. 2.3.3 >.

Similarly, the presence of increasing buffer gas pressures in the source is found to influence the relative intensities of the cluster

species observed In the resulting spectrum. At very low buffer gas pressures and In the absence of a matrix compound a slight Increase in the relative Intensity in the cluster spectrum is observed. However, as the pressure increases the relative intensity of the higher mass

clusters are observed to decrease rapidly. At higher buffer gas

pressures evidence of fine structure in the distribution of the spectral intensities is observed, with possible odd/even alternation and enhanced spectral intensities for x = 3 being observed in the uranyl cluster spectrum. For samples containing a matrix compound or co-solvent, at low buffer gas pressures an increase in the relative intensities of the adducts formed is observed. However as the buffer gas pressure

increases the number of observed adducts decrease, with no adducts being detected at high buffer gas pressures.

This suggests that the buffer gas may act so as to stablise the formation of the higher mass cluster at very low pressures, possibly by a third-body assisted association reaction,

K o - i - + M + X ---» I t , * + X

with the excess exothermic energy being removed by the buffer gas. However on further increasing the buffer gas pressure the increased number of collisions increase the possibility of clusters undergoing collision induced dissociations or collisions resulting in the production of charged species. This i6 displayed in the increased relative intensities of the lower mass clusters and the corresponding increase in total ion currents observed.

I

I

1

Fig 2.3.1 Diagramatic Representation of the Position of the Source Covers to reduce the Source Conductance, hence Allowing the Effect of Source Pressure on Cluster Formation to be Studied

Fig 2.3.2 a> Gas Inlet Plate, Materials Stainless steal, all Dimensions in mm

b) Source Block Cover, Material 'PEEK', all Dimensions in mm

c) Source Lens Plate, Material Stainless steal, all Dimensions in mm

Fig 2.3.3 Schematic Representation of the Change In Total ion current, I, with Increasing Duration of Bombardment, T, at a lumber of Buffer Gas Pressures

2.4.1 MATERIALS

All chemicalB used were of standard laboratory grade.

Uranyl nitrate hexahydrate Uranyl acetate dihydrate Uranium trioxide Thorium nitrate Lanthanum nitrate Cerium nitrate Praseodymium nitrate Samarium nitrate Europium nitrate Terbium nitrate Holmlum nitrate Fisons B. D. H B. D. H B.D. H B. D. H Aldrich Aldrich Aldrich Aldrich Aldrich Aldrich Lanthanum acetate B.D.H

Cerium acetate Strem

Praseodymium acetate Aldrich

Europium acetate Aldrich

Holmlum acetate Strem

Glycine L-Alanlne L-Valine L-Serine Fisons Aldrich Sigma Sigma f 1 0 1

L-Lysine Sigma L-Proline Sigma L-Glutamine Sigma L-Glutamic acid B. D. H. L-Tryptophan B. D. H. Cysteine Sigma Threone _Aldrich |3-Alanine Aldrich

a-Aminobutanoic acid Sigma

(3-Anrinobutanoic acid Sigma

K-Ajninobutanoic acid Sigma

Hexachloropropene Aldrich

Sulpholane B.D.H.

2.4.2 PREPARATIONS

a) THE PREPARATION OF THE AMINO ACID COMPLEXES OF DIOXOURANIUM(VI>

These were prepared by a standard method, in which uranyl nitrate hexahydrate was added to an aqueous solution of the ligand, in a 4 : 1 mole ratio (53). The resulting solution was then allowed to evaporate in a dark environment.

The resulting complexes for the amino acids took the form of bright yellow oils, apart from those corresponding to L-proline and L- tryptophane which formed yellow-brown oils (possibly due to their aromatic nature).

b> THE PREPARATION OF LANTHANIDE MALONATES

A standard method was used whereby a given mass of lanthanide nitrate was dissolved in a minimum volume of distilled water, to this malonolc acid was added ( in a 1 : 4 mole ratio respectively >. The resulting cloudy solution was evaporated and cooled until a white crystalline solid formed

c) THE PREPARATION OF URAHIUJt(IV>CHLORIDE, OCI* (53)

Uranium tetrachloride was prepared by the reaction of uranium trioxide with hexachloro-propene as a chlorinating agent, giving a final product of high purity and yield.

This was carried out by refluxing uranium trioxide (2. 5g> with 25 cm of hexachloropropene in a three-necked flask, under a nitrogen atmosphere, for six hours. The reaction mixture was heated slowly at first until the vigorous initial reaction had subsided, during which the temperature was kept below 373 K. The temperature was then allowed to increase slowly until a steady reflux occurred. At this point a red-brown solid, UCle , was observed at the base of the flask; this was then observed to yield green UC1.» as the reflux continued. The resulting solid was filtered under a nitrogen atmosphere, washed with dry CCl« and dried under high vacuum. The resulting UC1.« was then sealed in an evacuated tube, due to its hydroscopic nature.

The compounds and complexes formed by the above reactions were analysed using a combination of infra red and UV/visible spectroscopy.