**3.2 Visible spectrophotometric methods based on formation of complex with metal**

The formation of colored complexes as a consequence of the interactions between metal ions and analytes (penam and cephem analogs) resulted from:


Direct complexation of β-lactam analogs and metal ions with formation of yellowish-brown chelate complex was possible due to the presence of suphur atoms in the β-lactam ring and the thiazole ring. Cephem analogs (cefpodoxime, ceftizoxime, ceftazidime, ceftiaxone and cefixime) gave with palladium(II) ions, absorbing complex, in the presence of sodium lauryl sulphate as surfactant, in the range 300–500 nm [42]. Β-lactam analogs containing the phenolic ring with free *ortho* position to the hydroxyl group (amoxicillin trihydrate, cefperazone sodium, cefadroxil monohydrate, cefprozil anhydrous) reacted with nitrous acid forming the nitroso derivatives. They were capable of tautometric interconversions to form colored complex in the presence of copper(II) ions (Fig. 12). The stoichiometric ratios (nitroso derivative to copper(II)) were determined by the Job's method 2:1 [43].

Fig. 12. Scheme of the reaction of nitrous acid, Cu(II) with phenolic β-lactam analogs [43].

The determination of cephalexin, cefixime, ceftriaxone, cefotaxime based on the Bent-French method, in which degradation products of β-lactam analogs with metal ions form the colored complexes, was developed. Hydroxamic acids formed by hydroxiaminolysis of cephem analogs (1:3), formed complexes with iron (II) ions (Fig. 13) [44].

Fig. 13. The scheme of hydroxamic acid-iron(III) [44].

120 Macro to Nano Spectroscopy

4-aminoantipyrine in the presence of potassium hexacyanoferrate(III) in alkaline

3-methyl-2-benzothiazolinone hydrozone hydrochloride in the presence of ceric

4-aminophenazone in the presence of potassium hexacyanoferrate (III) (λmax = 510 nm)

N

S

COOH

CH3

OH

R

O

+

Cl Cl

NCl

O

Cl Cl

N

R

OH

O

O

N H

OH

C6H5

N N CH3

<sup>N</sup> C6H5 <sup>H</sup> O

> N N CH3

C6H5

O

K3[Fe (CN)6 ]

N N CH3

+

O

OHH3C

O

**3.2 Visible spectrophotometric methods based on formation of complex with metal** 

a reaction between the degradation products of β-lactam analogs and metal ions.

The formation of colored complexes as a consequence of the interactions between metal ions

Direct complexation of β-lactam analogs and metal ions with formation of yellowish-brown chelate complex was possible due to the presence of suphur atoms in the β-lactam ring and the thiazole ring. Cephem analogs (cefpodoxime, ceftizoxime, ceftazidime, ceftiaxone and cefixime) gave with palladium(II) ions, absorbing complex, in the presence of sodium lauryl sulphate as surfactant, in the range 300–500 nm [42]. Β-lactam analogs containing the phenolic ring with free *ortho* position to the hydroxyl group (amoxicillin trihydrate,

*N*-bromosuccinimide or *N*-chlorosuccinimide in alkali medium (λmax = 395 nm) [40]

2,6-dichloroquinone-4-chlorimide (Gibb's reagent) (λmax = 620 nm) [39]

R R =

R

H2N

R N

R

H3C

sodium persulfate in alkaline medium (λmax = 350 nm) [41]

HO

medium (λmax = 505 nm [37]

N S

+

OH

R +

N S

+

CH3

CH3

N N

N NH

OH

R

Fig. 11. Schemes of some oxidation reactions of cefadoxil [39].

and analytes (penam and cephem analogs) resulted from: a direct reaction between β-lactam analogs and metal ions

ammonium sulphate (λmax = 410 nm) [38]
