Continuous titrators

Oscarson J L, Izatt R M, Hill J O and Brown P R 1994 Continuous titration calorimetry Solution Calorimetry, Experimental Thermodynamicsyo IV, ed K N Marsh and PAG O Hare (Oxford Blackwell)... 

Titrate liberated iodine with thiosulfate Ee/1 = 55.847 Ee203/2 = 79.845 I2 + 2 820 = 2 D + 8401 [titrate solution (pH ° 7.0) with thiosulfate until color is pale yellow. Add K1 and starch and continue titration to disappearance of blue color. I2/2 =... 

Add 3-4 ml CPC solution (-0.005 N in distilled water). After each addition of CPC turn the graduated cylinder upside down 10 times. Too vigorous shaking leads to the formation of a stable emulsion. Add as rapidly as possible more CPC until the red chloroform layer settles out rapidly and clearly. Continue titrating slowly until the two layers have the same color. 

The activity of PE was measured [25] from the increase of carboxylic groups during the pectin deesterification (5 g/L) in phosphate-citrate buffer 50 mM, pH 4.7. Continuous titration of the reaction mixture with NaOH 0.01 M was employed for product determination. 

P.C. Thijssen, N.J.M.L. Janssen, G. Kateman and H.C. Smit, Kalman filter applied to setpoint control in continuous titrations. Anal. Chim. Acta, 177 (1985) 57-69. 

This wording may be considered as duplication, because one can hardly think of continuous titration without automation however, the intention is simply to stress its character as an alternative to automated discontinuous titrations. The principle of continuous titration can be illustrated best by Fig. 5.151 it applies to a steady stream of sample (C). Now, let us assume at first that the analyte concentration is on specification, i.e., it agrees with the analyte concentration of the standard (B). If, when one mixes the titrant (A) with the sample stream (C), the mass flow (equiv./s) of titrant precisely matches the mass flow of analyte, then the resulting mixture is on set-point. However, when the analyte concentration fluctuates, the fluctuations are registered by the sensor it is clear that the continuous measurement by mixing A and C is only occasionally interrupted by alternatively mixing A and B in order to check the titrant for its constancy. 

In fact continuous titration belongs to this class, but has already been treated above on the basis of the use of the sensor merely as an end-point indicator of the titration reaction. For the remaining non-separational flow techniques, such a multiplicity of concomitant developments has occured since 1960 that in a survey we must confine ourselves to a more or less personal view based substantially on the information obtained from some important reviews and more specific papers presented at a few recent conferences78 82, or from leaflets offered by commercial instrument manufacturers. The developments are summarized in Table 5.1. 

In an early work by Mertz and Pettitt, an open system was devised, in which an extended variable, representing the extent of protonation, was used to couple the system to a chemical potential reservoir [67], This method was demonstrated in the simulation of the acid-base reaction of acetic acid with water [67], Recently, PHMD methods based on continuous protonation states have been developed, in which a set of continuous titration coordinates, A, bound between 0 and 1, is propagated simultaneously with the conformational degrees of freedom in explicit or continuum solvent MD simulations. In the acidostat method developed by Borjesson and Hiinenberger for explicit solvent simulations [13], A. is relaxed towards the equilibrium value via a first-order coupling scheme in analogy to Berendsen s thermostat [10]. However, the theoretical basis for the equilibrium condition used in the derivation seems unclear [3], A test using the pKa calculation for several small amines did not yield HH titration behavior [13],... 

Lee S, Salsbury FR Jr, Brooks CL III (2004) Constant-pH molecular dynamics using continuous titration coordinates. Proteins 56 738-752. 

To determine the activity of pectinesterases having pH optima near 7.0, various modifications of continuous titration are now used (autotitrators with recording pH-meters, constant temperature vessels provided with magnetic stirring, and flushing with ni-... 

Effect of substrate concentration. In the following experiments the cholinesterase activities were measured by a continuous titration method. The digest of acetylcholine and horse-serum cholinesterase (total vol. 10 ml.), containing bromothymol blue and 0-0002 m phosphate, was titrated with 0-01 n NaOH to maintain the pH at 7-4. The titrations, which were carried out at 20°, were linear over a period of 10-15 min. The velocity was expressed as ml. 0-01 n NaOH/5 min. under the conditions used, it was proportional to the enzyme concentration. When an inhibitor was added, this was equilibrated with the enzyme, etc., for 5 min. at 20° before adding the substrate contained in a volume of 1 ml. 

The principles of titration calorimetry will now be introduced using isoperibol continuous titration calorimetry as an example. These principles, with slight modifications, can be adapted to the incremental method and to techniques based on other types of calorimeters, such as heat flow isothermal titration calorimetry. This method, which has gained increasing importance, is covered in section 11.2. 

Figure 11.2 Typical temperature-time curve for an isoperibol continuous titration calorimetric experiment involving an exothermic process.

Figure 11.5 Typical curve for a continuous titration calorimetry study of an exothermic reaction, using the calorimeter of Figure 11.1 in the heat flow isothermal mode of measurement./ is the frequency of the constant energy pulses supplied to the heater C in Figure 11.1 b. Adapted from [196,197],...

If adequate therapeutic effect is not observed within 5 minutes, repeat loading dose and follow with maintenance infusion increased to 100 mcg/kg/min. Continue titration procedure, repeating loading infusion, increasing maintenance infusion by increments of 50 mcg/kg/min (for 4 minutes). As desired heart rate or a safety endpoint (eg, lowered blood pressure) is approached, omit loading infusion and titrate the maintenance dosage up or down to endpoint. Also, if desired, increase interval between titration steps from 5 to 10 minutes. 

A) Anon, IEC, NewEdn, 14, 305(1936)(Peroxide formation in ethers and a test for peroxides in ether) [Procedure a) Add 10ml ether (sample to test) to 150ml of 2N sulfuric acid soln, followed by 3 drops of 1% soln of Amm molybdate (a catalyst to favor the liberation of dine) and 15ml of 10% KI soln. Shake well aiiJ allow to stand for 15 mins b) Titrate the liberated iodine with 0.05N Na thiosulfate and shake well after each addn until near discoloration of soln c) Add a few cc of starch soln and continue titration until disappearance of blue color]... 

N potassium bromide-bromate so In and 5m of coned HO. Close the flask immediately with the stopper previously moistened with a drop of 10% KI soln, mix the contents by swirling and, after allowing to stand for 10+0.5 mins, add 25ml of 10% KI soln. Titrate the liberated iodine with Q.1N Na thiosulfate soln until near discoloration add 5ml of starch soln and continue titration until the blue color is completely discharged. Run concurrently a blank titration using the same reagents as above... 

For its standardization with TiClg soln, measure accurately 45 ml of the above prepd ferric ammonium sulfate into titration flask F of Fig 3j add 25 ml of 1555 hydrochloric acid and, while passing C02 thru rhe flask, titrate from buret C with 0.2N TiClg soln (already standardized by potassium dichromate) until near the end point. Then add 5 ml of 20% ammonium thiocyanate indicator and continue titrating until, the red color just disappears. 

Discard the filtrate and transfer the ppt quantitatively to an iodine reaction flask by successive washings with 3NHC1 and hot w. Cool, add iO mi of 10% KI solo and titrate with N/10 Na SjOj soln until near discoloration. Add 5 ml of 0.5% starch soln and continue titration to greenish coloration Following reactions take place ... 

Transfer a 50.0ml aliquor to a 250ml glass stoppered Erlen flask, add 4-5g CP KI crysts, shake to dissolve, and add 10ml dil sulfuric acid(l 3). After allowing to stand for 10 mins, titrate the liberated iodine with 0.1N Na thiosulfate soln, until the yel color nearly disappears, Then add 5ml starch indicator and continue titration until the blue color just disappears- Correct for any thiosulfate consumed by the blank. One ml of 0.1N Na thiosulfate soln is equivalent to 0.00490 g K2Cr207... 

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