CDTA

Fluoride. A fluoride concentration of ca 1 mg/L is helpful in preventing dental caries. Eluoride is deterrnined potentiometrically with an ion-selective electrode. A buffer solution of high total ionic strength is added to the solution to eliminate variations in sample ionic strength and to maintain the sample at pH 5—8, the optimum range for measurement. (Cyclohexylenedinitrilo)tetraacetic acid (CDTA) is usually added to the buffer solution to complex aluminum and thereby prevent its interference. If fluoroborate ion is present, the sample should be distilled from a concentrated sulfuric acid solution to hydrolyze the fluoroborate to free fluoride prior to the electrode measurement (26,27). 

Cyclohexane-l,2-diaminetetraacetic acid (H2O CDTA) []329]-6]-7] M 364.4, pK 1.34, pK2 3.20, PK3 5.75 (6.12), PK4 9.26 (12.35). Dissolved in aq NaOH as its disodium salt, then pptd by adding HCl. The free acid was filtered off and boiled with distd water to remove traces of HCI [Bond and Jones Trans Faraday Soc 55 1310 7959]. Recrystd from water and dried under vacuum. 

LCo(H20)6] ion, and bidentate /V-donor ligands such as cn, bipy and phen form octahedral cationic complexes [Co(L-L)3] , which are much more stable to oxidation than is the hexaammine [Co(NH3)6l . Acac yields the orange [Co(acac)2(H20)2] which has the tram octahedral structure and can be dehydrated to [Co(acac)2l which attains octahedral coordination by forming the tetrameric species shown in Fig. 26.3. This is comparable with the trimeric [Ni(acac>2]3 (p. 1157), like which it shows evidence of weak ferromagnetic interactions at very low temperatures. fCo(edta)(H20)] is ostensibly analogous to the 7-coordinate Mn and complexes with the same stoichiometry, but in fact the cobalt is only 6-coordinate, 1 of the oxygen atoms of the cdta being too far away from the cobalt (272 compared to 223 pm for the other edta donor atoms) to be considered as coordinated. 

Calcichrome. This indicator, cyclotris-7-( l-azo-8-hydroxynaphthalene-3,6-disulphonic acid), is very selective for calcium. It is in fact not very suitable as an indicator for EDTA titrations because the colour change is not particularly sharp, but if EDTA is replaced by CDTA (see Section 2.26), then the indicator gives good results for calcium in the presence of large amounts of barium and small amounts of strontium.13... 

D. Attainment of the end point. In many EDTA titrations the colour change in the neighbourhood of the end point may be slow. In such cases, cautious addition of the titrant coupled with continuous stirring of the solution is advisable the use of a magnetic stirrer is recommended. Frequently, a sharper end point may be achieved if the solution is warmed to about 40 °C. Titrations with CDTA (see Section 2.26) are always slower in the region of the end point than the corresponding EDTA titrations. 

DETERMINATION OF CALCIUM IN THE PRESENCE OF BARIUM USING CDTA AS TITRANT... 

There is an appreciable difference between the stability constants of the CDTA complexes of barium (log K = 7.99) and calcium (log K = 12.50), with the result that calcium may be titrated with CDTA in the presence of barium the stability constants of the EDTA complexes of these two metals are too close together to permit independent titration of calcium in the present of barium. 

Procedure. Prepare the CDTA solution (0.02M) by dissolving 6.880 g of the solid reagent in 50 mL of sodium hydroxide solution (1M) and making up to 1 L with de-ionised water the solution may be standardised against a standard calcium solution prepared from 2.00 g of calcium carbonate (see Section 10.61). The indicator is prepared by dissolving 0.5 g of the solid in 100 mL of water. 

Pipette 25 mL of the solution to be analysed into a 250 mL conical flask and dilute to 100 mL with de-ionised water the original solution should be about 0.02M with respect to calcium and may contain barium to a concentration of up to 0.2M. Add 10 mL sodium hydroxide solution (1M) and check that the pH of the solution lies between 11 and 12 then add three drops of the indicator solution. Titrate with the standard CDTA solution until the pink colour changes to blue. 

Total Ionic Strength Adjustment Buffer (TISAB). Dissolve 57 mL acetic acid, 58 g sodium chloride and 4g cyclohexane diaminotetra-acetic acid (CDTA) in 500 mL of de-ionised water contained in a large beaker. Stand the beaker inside a water bath fitted with a constant-level device, and place a rubber tube connected to the cold water tap inside the bath. Allow water to flow slowly into the bath and discharge through the constant level this will ensure that in the... 

Calcium, D. of - continued in limestone or dolomite, (fl) 813 in presence of barium, (ti) 333 with CDTA, (ti) 333 with lead by EDTA, (ti) 333 with magnesium by EDTA, 328 by EGTA, (ti) 331 by flame emission, (aa) 804 Calcium oxalate, thermal analysis 498 Calcon 318 Calculators 133 Calibration of apparatus, 87 of burettes, 88 of graduated flasks, 88 of pipettes, 88 of weights, 74... 

Sb(SiMe3)3, 3, 259 SbCiotI12N208 [Sb(cdta)], 2, 783 SbC10H24N SbBut2(NMeI), 3, 260 SbC12Hl0F SbPh2F, 3, 258 SbC12Hl2Cl3N... 

The most conspicuous concentrations of calciiun in the cell-walls of the flax hypocotyl were in the epidermal and subepidermal layers, especially at the tricellular junctions (figure 13 D), where these were filled with pectic polymers [67], Open tricellular jimctions with intercellular spaces had smaller areas of calcium accumulation where the walls of each pair of cells diverged. These sites were occupied by relatively linear pectic polymers with a low degree of esterification, which could be visualised with gold-kbeUed endopolygalacturonase [68] and were extractable by chelation of calcium with CDTA. Similar pectic polymers are located in the corresponding sites in other plant tissue, as established by susceptibility to polygalacturonase... 

The CDTA- and NajCOj-soluble pectins were also used as test materials. Extracts were dialyzed against water and freeze-dried. They were then tested directly or after digestion with purified tomato PGl (treatment at 37 in sodium acetate, pH 4.5). 

How might these oligomers be produced in the fruit The easiest answer is that limited PG action on cell wall pectins generates them, and we have tested this point in vitro. CDTA- and Na2C03-soluble pectins and PGA (included as a positive control) were incubated with purified tomato PGl. Surprisingly, only the carbonate-soluble material and PGA were digested (based on HPLC analysis of reaction mixtures and generation of... 

Fig. 5. Effect of PGl digestion on the ethylene synthesis-inducing activity of CDTA-soluble tomato pectin (a), Na2C03-soluble tomato pectin (b) and polygalacturonic acid (c). Controls were treated with solutions of heat-inactivated PGl. Treatment doses were 10 /tg of uronic acid equivalents. The line legends shown in panel a apply to all panels. Bars indicate SEs for the means of measurements of sets of 8 discs/teatment. fr wt, Fresh weight.

To study the cell wall alterations diiring processing in detail, total pectic fractions were separated by extraction of AIR from fresh, blanched and sterilized beans with acetate buffer, CDTA and NajCOj. Analysis showed that sterilization caused a lai e increase in the amount of buffer soluble pectins (Figure 1). 

Stir with 1000ml 50mM CDTA at pH 6.5 for 6h at 20-22X. Filter on G3 glass filter, wash residue with water, centrifuge filtrate at SOOOrpm for 20min, dialyse, concentrate. Reextract the residue under the same conditions and freeze-dry the combined filtrates CDTA-Fraction... 

Figure 6. High-Performance Size-Exclusion Chromatography of solubilized pectin from the juice. Control is CDTA extracted pectin from parenchyma.

When the chelators are actually known, as in the case of industrial materials injected into the environment, it is possible to derive much more information from the analyses. Thus high pressure liquid chromatography has been used to separate the copper chelates of EDTA, NTA, EGTA, and CDTA with the final measurement of copper being made by atomic absorption [422,423]. 

---