Integrated pulse amperometry

It is used in IC systems when the amperometric process confers selectivity to the determination of the analytes. The operative modes employed in the amperometric techniques for detection in flow systems include those at (1) constant potential, where the current is measured in continuous mode, (2) at pulsed potential with sampling of the current at dehned periods of time (pulsed amperometry, PAD), or (3) at pulsed potential with integration of the current at defined periods of time (integrated pulsed amperometry, IPAD). Amperometric techniques are successfully employed for the determination of carbohydrates, catecholamines, phenols, cyanide, iodide, amines, etc., even if, for optimal detection, it is often required to change the mobile-phase conditions. This is the case of the detection of biogenic amines separated by cation-exchange in acidic eluent and detected by IPAD at the Au electrode after the post-column addition of a pH modiher (NaOH) [262]. 

NaOH flow rate 0.2 mL/min detection integrated pulsed amperometry on a Au working electrode and MS (positive ion scan mode m/z 120-600, cone voltage SO V) sample microalgae whole-cell lysate. 

Figure 10.315 Anaiysis of lipoic acid. Separator column CarboPac PA1 eluent 0.1 mol/L NaOH + 0.5 mol/L NaOAc flow rate 1 mL/min detection integrated pulsed amperometry on a gold working electrode injection volume 50 pL peak 40mg/L lipoic add (1).

Integrated pulsed amperometry has also been applied for the simultaneous analysis of homocysteine and methionine in plasma [590]. Homocysteine has been established as an independent risk factor for cardiovascular disease [591]. 

Figure 10.338 Separation of homocysteine and other physiological amino acids. Separator column OmnIPac PCX-500 column dimensions 250 mm x2 mm i.d. column temperature 30 °C eluent 0.15mol/L NaCIOV MeCN (95 5 v/v) + 19.7 mmol/L HCIO4 flow rate 0.25 mL/mln detection integrated pulsed amperometry on a gold working...

We wish only to remind readers that there are three main methods of electrochemical re-vealment conductivity, direct current (d.c.) amperometry, and integrated amperometry (pulsed amperometry is a form of integrated amperometry). In revealment by conductivity, the analytes, in ionic form, move under the effect of an electric field created inside the cell. The conductivity of the solution is proportional to the mobility of the ions in solution. Since the mobile phase is itself an electrolytical solution, in order to increase the signal/noise ratio and the response of the detector, it is very useful to have access to an ion suppressor before the revealment cell. By means of ionic exchange membranes, the suppressor replaces the counterions respectively with H+ or OH , allowing only an aqueous solution of the analytes under analysis to flow into the detector. 

LaCourse and Owens [26] showed the superiority of integrated amperometry over conventional pulsed amperometric detection in their work on organic sulfur compounds under reversed-phase conditions. Pulsed amperometry allows direct detection of thio-redox systems (-SH/-S-S-), provided they carry a pair of free electrons at the sulfur atom. As an illustration, the chromatogram in Figure 8.18 displays the separation of lipoic acid, which carries a disulfide bridge as a structural element... 

HPAEC analyses were carried out to determine the oligomeric products released from various pectic substrates after depolymerization by the PL isoenzymes. Action pattern analyses for the concerted action of PL isoenzymes utilized 68% esterified pectin as substrate. One-ml reaction mixtures in a buffer system as detailed in section 2.2. comprising 0.5% (w/v) substrate and 5 U of enzyme were incubated for 30 s to 18 h, and then thermoinactivated. Samples of 750 pi were applied to a Carbopac PA-1 (Dionex) column before the carbohydrates were eluted over a period of 70 min using a gradient of 0.2 M KOH, 0.05 M K-acetate to 0.2 M KOH, 0.7 M K-acetate. Detection employed a Pulsed Electrochemical Detector (PED, Dionex) in the integrated amperometry mode according to the manufacturer s recommendations. 

Figure 8.17 Example of a pulse sequence in integrated amperometry of amines on a gold working electrode.

Figure 8.19 (a and b) Multiqfclic pulse sequences for integrated amperometry of sulfur-containing antibiotics. 

Figure 8.20 Separation of ampicillin utilizing integrated amperometry with a multiq clic pulse sequence in comparison with UV detection. Separator Vydac C8 (208TP5451) column dimensions 150 mm x4mm i.d. column...

Figure 8.23 Pulse sequence for integrated amperometry of ethanolamines and their separation on a nanobead-agglomerated cation exchanger. Separator lonPac CS10 eluent ...

Figure 8.25 Pulse sequence for integrated amperometry of amino acids. The detector signal is the charge (measured in Coulomb) that results from the integration of the current yield from the oxidation of the amino group between 0.11 and 0.56 s.

The possibility of detecting sulfur-containing antibiotics such as ampicillin and lincomycin via integrated amperometry utilizing a multicyclic pulse sequence was described in Section 8.1.2.2. Dasenbrock and LaCourse [359] developed this method to determine cephapirin and ampicillin in raw milk. At... 

Fig. 7-20. Separation of lincomycin utilizing integrated amperometry with a multicyclic pulse sequence in comparison to UV detection. -Separtor column 150 mm X 4 mm i.d. Vydac C8 (208TP5451) column temperature 30°C eluant 0.1 mol/L NaOAc - acetonitrile (91 9 v/v), pH 3.75 flow rate 1 mL/min peaks (1) - (3), (5) unknown impurities, (4)...

Fig. 7-23. Pulse sequence for integrated amperometry of primary alkylamines and their separation on a weak acid cation exchanger. - Separator column lonPac CS14 eluant 2.5 mmol/L H2SO4 +...

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