Sequestering agents

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/7#+                                ' [...]... determine calcium and magnesium by titration They do not contribute to detergency nor do they exhibit a threshold effect EDTA EDTA: Good sequestering agent for calcium and magnesium at alkaline pH but no sequestering agents on Fe3+ at alkaline pH Not stable with oxidising agents Low solubility in acidic medium Some ligands can bond to a metal atom using more than two pairs of electrons An example is ethylenediamminetetraacetate... more strongly held is the metal ion in the complex Therefore Ligand that give high log K values with a particular metal are very effective sequestering agents Table 9 lists some formation constants for several chelating agents The data shows the specificity of some agents, i.e gluconic acid which is particularly effective for iron Also the data shows that EDTA is effective across the board Formation... chelation values of polyacrylates have no demetallising effect on metal containing dyestuffs They are completely non foaming They are very suitable as dyebath conditioners, soaping agents and washing aids Being non surface active agents they are easily rinsable and thus reduce the quantity of water required for removing their traces from the substrates, unlike all surfactants The typical chelation values... selecting a sequestering agent for the process : 1 Stability Constant: As chelation is a reversible reaction, the equilibrium is dependent on the process pH and the concentration of the metal ions and chelating agent, which react together to form a chelate The stability of the metal complex is expressed in terms of its stability constant If we represent chelation of metal ion, Mm+ with sequestering. .. stability constant is Ks = MA (m-n) (Mm+) (An-) A high value of Ks indicates high sequestering effect For example, in the case of aminopolycarboxylates, the stability constant for same metal iron increases in the order NTA, EDTA, DTPA In the case of metal ions, the stability constant increases in the order Factors to selecting a sequestering agent From the above information it can be deduced that the NTA-Mg2+... concentration for the given process, when premetallised dyes are to be used Factors to selecting a sequestering agent 4 Other Features: Stability of chelate to prolonged process periods, dispersing properties, crystal-growth inhibition, effect on equipment, etc are also to be considered when selecting a commercial sequestering agent ... close to the chelation values offered by amino polycarboxylates or the phosphonates This problem has been overcome by development of sugar acrylates Sugar Acrylates 5.Sugar Acrylates Sugar acrylates have sequestering values as high as amino polycarboxylates or the phosphonates They are biodegradable, effective components in cellulosic fabric pretreatment during desizing, scouring, bleaching and mercerising... from the complex For example, Fe3+ displaces Ca2+ from a Ca2+ chelating agent complex Of course, the chelating agent should be capable of chelating Fe3+ under given conditions Factors to selecting a sequestering agent 2 The pH of the Process: The pH of the system will influence the formation of the chelation complex For example, NTA, EDTA cannot chelate Fe3+ under alkaline conditions, whereas DTPA... Sodium -13%) EDTA - Ferric Ammonium Salt of EDTA (Ethylene Diamine Tetra Acetic Acid) 2 Nitrilotriacetic Acid (NTA) D Hydroxycarboxylic Acids Advantages and Disadvantages: Hydroxy acids are effective for sequestering iron They are not effective for calcium or magnesium FORMATION OF COMPLEXES FORMATION OF COMPLEXES Most polyvalent ions can form complexes with certain ions or molecules This type of complex