EDTA as complexing agent

The inclusion of EDTA is occasionally not advantageous, as there are a number of reports of EDTA catalyzing the decomposition of drugs. Citric acid, tartaric acid, glycerin, and sorbitol can also be considered as complexing agents however, these are often ineffective. Interestingly, some Japanese formulators often resort to amino acids or tryptophan, because of a ban on EDTA in a particular country. 

Chrome Azurol S (CAS, formula 4.18) forms a coloured chelate complex with Be, and this has been used for the determination of Be [18-21], In acetate (or hexamine) buffer and in the presence of EDTA as masking agent, the Chrome Azurol S method is highly selective for beryllium. The absorbance of the complex depends on the pH, and on the concentrations of CAS, EDTA, and the acetate buffer. The absorbance increases with increasing CAS concentration, and decreases with increasing EDTA and acetate concentrations. A pH of 5 is the most suitable. Below this pH, the absorbance of CAS increases considerably, and above it the absorbance of the beryllium complex is decreased more by EDTA. 

Other methods for separating silver involve extraction of the diethyldithiocarbamate into chloroform [pH 4-11 (EDTA as masking agent)] [1]. The thiocyanate complex of silver can be extracted from 0.1-1 M solutions of H2SO4, HCl, or HCIO4 into TBP [2]. 

On the basis of the results of the first series of experiments, further runs were conducted on both sediments using EDTA as conditioning agent, with the purpose of forming soluble metal-chelant complexes and promoting heavy metal removal. 

Simple ligands are used as complexing agents, e.g., CN, OH, NH3, oxalate, halides, as well as stronger complexing agents, such as ethylenedi-aminetetraacetic acid (EDTA), citrate, tartrate, etc. 

Among the complexing agents that find use as titrating agents, ethylenediamine-A,A(A, A-tet-raacetic acid (acronym EDTA, and equation abbreviation, H4Y) is by far the more important, and it is used in the vast majority of complexometric titrations. The successive acid values of H4Y are pKi = 2.0, pisTj = 2.67, = 6.16, pTCt = 10.26 at 20°C and an ionic strength of 0.1. The fraction... 

We can account for the effect of an auxiliary complexing agent, such as NH3, in the same way we accounted for the effect of pH. Before adding EDTA, a mass balance on Cd + requires that the total concentration of Cd +, Ccd, be... 

Certain compounds, known as chelating agents (qv), react synergisticaHy with many antioxidants. It is beheved that these compounds improve the functional abiUties of antioxidants by complexing the metal ions that often initiate free-radical formation. Citric acid and ethylenediaminetetraacetic acid [60-00-4] (EDTA), C2QH2gN20g, are the most common chelating agents used (22). 

Ligno sulfonate—metal complexes are weaker complexes than those formed from amine-based complexing agents such as ethylenediaminetetracetic acid (EDTA). They are compatible with most pesticides /herbicides, but thek use in phosphate fertilisers is not recommended. 

After firing, the powder is washed in water typically with a small amount of complexing agent such as ethylenediarninetetraacetic acid (EDTA), sodium EDTA, or a weak acid such as citric acid to remove the excess chloride, volatile antimony oxychlorides which have recondensed on the phosphor during cooling, and manganese compounds which are not incorporated in the halophosphate lattice. The powder is then ready for suspension. 

Calcium is essential to several steps in the enzyme cascade of the blood clotting process, such as the conversion of prothrombin to thrombin (23). Clotting can be inhibited in stored blood suppHes by addition of complexing agents such as EDTA or citrate which reduce the levels of the free ion, Ca(Il). 

The main idea of research is application of accessible, simple and express methods that don t need expensive reagent techniques for analysis of phanuaceutical products based on bischofite. The determination of metal ions such as Mg, Zn, Cu, Fe by complex-formation titrations using a widely applicable chelating agent, EDTA, have been studied as a function of pH, complexing agents and indicators. The analysis consists of four parts ... 

Knabe has introduced mercuric acetate plus ethylenediaminetetraacetic acid (EDTA) as an oxidizing agent for tertiary amines (74). The solvent employed is 1 % aqueous acetic acid. In this system, the complexed mercuric ion is reduced to elemental mercury. Knabe s studies have centered on the... 

The reaction at any point in the column becomes progressively displaced to the right as fresh complexing agent arrives and the reaction products are removed. The solution of Ln(edta-H) and (NH4)3(edta-H) then reaches the development column where Cu is displaced and Ln redeposited in a compact band at the top of the column ... 

In equation (q) only the fully ionised form of EDTA, i.e. the ion Y4 , has been taken into account, but at low pH values the species HY3, H2Y2, H3 Y and even undissociated H4Y may well be present in other words, only a part of the EDTA uncombined with metal may be present as Y4. Further, in equation (q) the metal ion M"+ is assumed to be uncomplexed, i.e. in aqueous solution it is simply present as the hydrated ion. If, however, the solution also contains substances other than EDTA which can complex with the metal ion, then the whole of this ion uncombined with EDTA may no longer be present as the simple hydrated ion. Thus, in practice, the stability of metal-EDTA complexes may be altered (a) by variation in pH and (b) by the presence of other complexing agents. The stability constant of the EDTA complex will then be different from the value recorded for a specified pH in pure aqueous solution the value recorded for the new conditions is termed the apparent or conditional stability constant. It is clearly necessary to examine the effect of these two factors in some detail. 

---