Separation for the Azide Ion

Techniques are required for the concentration of small quantities of azide ion in solution or for separating the azide ion from interferences. There are several approaches  

Silver nitrate-carrier precipitations can be used advantageously to collect microgram to milligram quantities of azide ion by coprecipitation, using 10 mg chloride ion as a carrier in dilute acid solutions. Although no data have been reported using the technique, it cannot be excluded on a theoretical basis. 

Distillation ofhydrazoic acid from strong acid solutions is the most common method of separation [12, 17], For small quantities of azide ion in relatively large volumes of solvent, evaporation in alkaline media or carrier precipitation is necessary for the preliminary concentration of azide ions prior to distillation. The distillations are usually made from perchloric acid solutions. A 50-ml round-bottom flask, with a side-arm attached (so that a stream of inert gas passes through the solution) and an air condenser is preferable for distilling hydrazoic acid. The addition of a diluent carrier gas provides added safety. Absorbing solutions for the hydrazoic acid include known, excess quantities of ceric ion. standard base, or a known quantity of ferric perchlorate for colorimetric determination of small quantities of azide ion. The distillation separation is complex and lengthy, but the method is reliable and has universal applicability. 

A useful method for the separation ofhydrazoic acid is by a column extraction technique using a mixed-bed ion-exchange resin, a strongly acidic resin in the [H form], and a weakly basic resin in the (OH form). All cations and most anions are held on the column while hydrazoic acid runs through the column. Other cations and anions elute as water. Weak acids, e.g., boric, silicic, and carbonic will also run through the column. The technique has not been applied to the analysis of explosive azides however, it has been used for the analysis of alkali azides and for the preparation of standard solutions of hydrazoic acid [18]. 

Solvent extraction of the slightly ionized mercury (II) azide complex, HgNs, or neutral Hg(N3)2 in the pH range 4-6 has been investigated. With n-butanol the distribution coefficient is 10.6 at 25°C. The complex obeys Beer s law at 248 nm in both aqueous and butanol solution [23]. 

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