Electrodes picrate

Et)4NPi I (Et)4NPi Cq I Cw I calomel electrode picrate electrode... 

The rate of reaction is monitored using a picrate ion-selective electrode. 

Procedure. Prepare a set of external standards containing 0.5 g/L to 3.0 g/L creatinine (in 5 mM H2SO4) using a stock solution of 10.00 g/L creatinine in 5 mM H2SO4. In addition, prepare a solution of 1.00 x 10 M sodium picrate. Pipet 25.00 mL of 0.20 M NaOH, adjusted to an ionic strength of 1.00 M using Na2S04, into a thermostated reaction cell at 25 °C. Add 0.500 mL of the 1.00 x 10 M picrate solution to the reaction cell. Suspend a picrate ion-selective electrode in the solution, and monitor the potential until it stabilizes. When the potential is stable, add 2.00 mL of a... 

The potential of the ion-selective electrode actually responds to the activity of picrate in solution. By adjusting the NaOH solution to a high ionic strength, we maintain a constant ionic strength in all standards and samples. Because the relationship between activity and concentration is a function of ionic strength (see Chapter 6), the use of a constant ionic strength allows us to treat the potential as though it were a function of the concentration of picrate. 

T. P. Kinetic Studies with Ion-Selective Electrodes Determination of Greatinine in Urine with a Picrate Ion-Selective Electrode, /. Chem. Educ. 1983, 60, 74-76. 

This experiment includes instructions for preparing a picrate ion-selective electrode. The application of the electrode in determining the concentration of creatinine in urine (which is further described in Method 13.1) also is outlined. 

It was reported that neutral ionophore naphtho-15-crown-5 (N15C5, see Fig. 1) gives an excellent selective response to ion over Na+ ion when it is doped into an ion-selective electrode [2,3]. This result is very interesting considering the hole size of the crown. Ishibashi and coworkers studied the mechanisms of that selectivity using the technique of solvent extraction into 1,2-dichloroethane (DCE) where picrate anion was used as a counterion [4]. Their result is also interesting because Na+ is extracted as a... 

Procedures 3 and 4 are for acids of the HA type, but can be applied with minor modifications to acids of the BH+ type, for which homoconjugation is often negligible. From these studies, we find an appropriate pH buffer that is to be used to calibrate the glass electrode in routine pH measurements. Mixtures (1 1) of picric acid/tetraalkylammonium picrate and diphenylguanidine/diphenylguanidinium perchlorate are examples of the candidates for such a pH buffer. 

Creatinine, the degradation product of creatine, is determined in serum with the picrate electrode, which uses the Jaffe method to potentiometrically monitor creatinine picrate. A prior separation step is required to remove interfering sub-... 

The bridge solvent Sb may be either S or S" or any other solvent which supports the intention to reduce the voltage contribution of the liquid junctions between the electrode compartments. Tetraethylammonium picrate (TEA PIC) was chosen because the ions are bulky and preferential solvation may be neglected. The mobilities of TEA" and PIC" are very similar in a variety of solvents The electromotive force of cell (B) is given, following Scatchard ... 

Izutsu et al. studied the compiexing of Na" in acetonitrile solution with various protic and aprotic solvents using an ion-sensitive glass electrode. Parker s assumption of negligible liquid junction potential with an tetraethylammonium picrate salt bridge was adopted and found to be valid, even when water was added. The formation constants increased in the order methanol < H2O < DMF < NJ -dimethylace-tamide DMSO < HMPA. 

The solvent 1,2-dichloroethane was washed twice with deionized water. Tetraalkylammonium bromide Q Br" was converted to picrate salt Q pic" by solvent extraction method. A portion of 1,2-dichloroethane saturated with water (40 ml, = 0.13 mol dm ) was titrated with 10" mol dm tetraalkylammonium picrate by a piston burette in a thermostated vessel (25.0 °C). Conductivity was measured by Toa-denpa Model CG-511C. The cell constant of the electrode was calibrated by KCl aqueous solution and obtained as 0.0920 cm. A portion of titrant was dried and dissolved in an alkaline aqueous solution. Then the concentration of picrate ion was determined by spectrophotometry. 

Apparatus.—The vessel used for bringing di-iropropyl ketone into equilibrium with an aqueous solution of the picrate is shown in Fig. 1.— Equilibrating vessel, shown in fig. 1 The vessel was rocked in a thermostat, position for withdrawal of solutions, during which time the side-eirms were closed by or insertion of electrodes. ground-glass stoppers and the opening A by a... 

The design of the electrode vessel was derived from Lewis, Brighton and Sebastian 8 a guard (shown in hg. 4) was introduced to impede the diffusion of bridge electrolyte into the bulk of the oil phase. The preparation of the materials for the picrate electrode has been described in previous sections. The aqueous electrode, made up in a similar vessel, may be represented diagrammatically as... 

To provide a check on the behaviour of the external electrodes, each set of measurements began and ended with a measurement of the e.m.f. of a standard reference cell. The solutions in the equilibrium vessel for this cell were identical with those in the picrate electrode, and the complete cell may be represented ... 

It was found that, provided that the same picrate electrode was always used, the e.m.f. of this cell was reproducible to within 1 mV. 

If the solution layer contains a large background concentration of ammonium salt (NH4" picrate is often used), the pH of the immersed glass electrode is proportional to only one variable, [NH3], which is in turn dependent on the amount of NH3 that diffuses across the gas-permeable membrane, as shown by Eq. (19) ... 

Figure 1. Comparison of the interface between an electronically conductive electrode and a solution reduction of Fe3+) (A) and the interface between two immiscible solutions of electrolytes (ITIES) during current flow in a closed electric circuit [transport of picrate (Pi ) from nonaqueous phase (n) to water (w)] (B). (Reproduced from reference 4. Copyright 1990 American Chemical...

In general, the observed trends were the same as those described for quinolyl podands. Podands are able to extract primary amines well, logK x (picrates chloroform) for octylamine being 6.1 and for benzylamine 4.6 (compare this value with 6.7 for DC18C6 and 5.7 for the TOTA macrocycle). This allowed us to develop extraction-photometric procedures for the determination of octylamine and amphetamine at jttM level [113, as well as to produce an ion-selective electrode for octylamine [110,111. These podands show high selectivity secondary amines and alkali metals are not extracted and do not interfere in analytical procedures. 

That the distribution potential of the water-immiscible solvent (in particular, nitrobenzene) system, in the presence of TEAPi distributed between two phases, is close to zero. It can be concluded from the above assumptions that the EMF of cell XII is equal to the value of the distribution potential (defined by Eqs. (14,18-20) of the salt MX. It is noteworthy that salt bridges containing TEAPi were often used, and as mentioned above, both in direct studies of the distribution systems or in measurements of the ion transfer energy, e.g. of Ag, between two miscible or immiscible solvents [116-119]. In some works a bridge with TEAPi in di-isopropyl ketone was most frequently used but unfortunately, different reference interfaces or electrodes, e.g. calomel and picrate electrodes, were employed [48,62]. 

Liquid membrane electrodes should only be dipped for short periods of time in solutions which contain hydrophobic compounds, such as proteins or oils, in order to avoid a poisoning of the membrane. Between measurements in such solutions the electrode should be washed with copious amounts of distilled water. Poisoning of the membrane (for example by picrate anion with the potassium electrode) exhibits itself through a sudden loss of Nernstian response to the measured ion. With PVC-stabilized membranes surface impurities can be removed by wiping with a moist paper towel. Poisoning of electrodes with membrane fQters requires replacement of the fQter. 

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