Cations separation into Groups

VI.9 SEPARATION OF CATIONS INTO GROUPS ON THE SEMIMICRO SCALE Once a solution is produced, the systematic search for cations can be started. As the first step, cations should be separated into groups later separations within the individual groups must be carried out. When making these separations, the results of preliminary tests must always be kept in mind. If we know for sure that certain cations are present or absent, we can make appropriate simplifications in our separation procedures, which will result in considerable gain of time. 

Inspired by the separation ability of cyclic selectors such as cyclodextrins and crown ethers, Malouk s group studied the synthesis of chiral cyclophanes and their intercalation by cation exchange into a lamellar solid acid, a-zirconium phosphate aiming at the preparation of separation media based on solid inorganic-organic conjugates for simple single-plate batch enantioseparations [77-80]. 

In a laboratory environment, the method of qualitative analysis of cations is often required. The objective of qualitative analysis is to separate and identify the cations present in an unkonwn solution. Cations are first separated into five main groups depending on their solubilities ... 

In Section 16.15, we ll see that mixtures of metal cations, M2+, can be separated into two groups by selective precipitation of metal sulfides, MS. For example, Pb2+, Cu2+, and Hg2+, which form very insoluble sulfides, can be separated from Mn2+, Fe2+, Co2+, Ni2+, and Zn2+, which form more soluble sulfides. The separation is carried out in an acidic solution and makes use of the following solubility equilibrium ... 

The mono-strapped complex 98, which is prepared by the ethyl benzoate displacement method (Section II. C), has planar chirality owing to the presence of different 1,3-substituents on the r 6-arene and can be separated into its enantiomers by chiral HPLC. Each enantiomer reacts with AgOTf/H20 to give the corresponding di-strapped aqua cation in which a second chiral centre is present because there are now three different groups in the tripodal set. However, each... 

V.8 SEPARATION OF CATIONS INTO GROUPS Once the sample is dissolved, the separation of cations into groups can be attempted. This can be done according to the scheme outlined in Table V.12. 

Table V.12 Separation of cations into groups (Anions of organic acids, borates, fluorides, silicates, and phosphates being present). Add a few drops of dilute HC1 to the cold solution. If a ppt. forms, continue adding dilute HC1 until no further precipitation takes place. Filter. (1)...

Table V.12 Separation of cations into groups (contd.)...

V.10 SEPARATION OF GROUP II CATIONS INTO GROUPS IIA AND IIIB Having precipitated the sulphides of the Group II cations (cf. Section V.8, Table V. 12) the next task is to separate these into Groups IIA (Hg2+, Bi3+, Pb2+, Cu2+ and Cd2+) and IIB (As3+, As5+, Sb3+, Sb5+, Sn2+, Sn4+). There are two methods recommended for the purpose, one making use of (yellow) ammonium polysulphide, the other making use of potassium hydroxide. 

For the separation of Group II cations into Groups IIA and IIB two methods were suggested (cf. Section V.10, Tables V.14 and V.15). To separate and identify the Group IIB cations, one of the two recommended procedures must be followed, according to the method chosen in the previous step. If the ammonium polysulphide method (method a) has been followed in Section V.10, then method (a) has to be applied here. Method (b), on the other hand, has to be used if the potassium hydroxide method was followed to separate Groups IIA and IIB. 

These operations are all incorporated into Table V.12, describing the general separation scheme of cations into groups. 

When a suitable solvent has been found, prepare the solution for analysis using about 50 mg of the solid the volume of the final solution should be 1-1-5 ml. Use this solution for the separation of cations into groups according to Section VI.9. 

Separation of cations into groups can be carried out according to the instructions of Table VI. 11. Note, that this method is suitable only if anions of organic acids, borate, fluoride, silicate, and phosphate are absent. Modifications of the separation scheme in the presence of these anions are described in Section VI. 17. 

Table VI.ll Separation of cations into Groups on the semimicro scale (anions of organic adds, borate, fluoride, silicate, and phosphate being absent) Add 2 drops (1) of dilute HC1 to 1 ml of the clear solution in a 3 ml centrifuge tube (or a 4 ml test-tube). If a ppt. forms, stir and add a further 1-2 drops to ensure complete precipitation. Centrifuge (2) wash the ppt. with a few drops of cold water (3) and add washings to centrifugate.

VII.14 SEPARATION AND IDENTIFICATION OF GROUP II CATIONS IN THE PRESENCE OF MOLYBDENUM, GOLD, PLATINUM, PALLADIUM, SELENIUM, AND TELLURIUM The first step in this separation process is to separate cations into Groups IIA and IIB. 

For the separation of cations into Groups IIA and IIB the prescriptions of Table VII.2 should be followed. 

Table VII.2 Separation of Group II cations into Groups HA and IIB in the presence of...

Before describing the general scheme for the separation of the cations into groups, the student should take note of the following facts ... 

Table VII13 Separation of cations into groups (anions of organic acids, fluoride, and phosphate being absent) (contd.)...

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