Amperometry integrated

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. 

Clarke, A. R, Jandlik, P., Rocklin, R. D., Liu, Y., and Avdalovic, N., An integrated amperometry waveform for the direct, sensitive detection of amino acids and amino sugars following anion-exchange chromatography, Anal. Chem., 71, 2774,1999. 

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. 

Figure 3.262 Separation of amino acids on AminoPac PAID. Eluent NaOH/NaOAc gradient see Table 3.32 flow rate 0.25 ml7min detection integrated amperometry on a gold working electrode analytes lOOpmol each of arginine (1), ornithine (2), lysine (3), glutamine...

Figure 3.265 Optimized separation of amino acids and carbohydrates on an AminoPac PA10. Eluent NaOH/NaOAc gradient graphically depicted flow rate 0.25 mUmin detection integrated amperometry on a gold working electrode peaks (1) arginine, (2) fucose, (3) galactosamine, (4) glucosamine, (5)...

Figure 3.266 Direct injection of a carbohy-drate/amino acid mixture (trace 1) and a chromatogram obtained with in-line sample preparation of the same mixture (trace 2). Separator column AminoPac PA10 eluent NaOH/NaOAc gradient flow rate 0.25 mL/min detection integrated amperometry on a gold working electrode peaks 125 pmol of each amino acid -i-10 pmol/L of each carbohydrate. Note In the chromatogram of trace 1, the...

Figure 3.271 Analysis of a collagen hydrolysate and an amino acid/amino sugar standard with anion-exchange chromatography and integrated amperometry. Chromatographic...

Table 3.36 Comparison of integrated amperometry and postcolumn derivatization with ninhy-drin as detection methods for determining amino acids in a collagen hydrolysate.

Amino acid Integrated amperometry Ninhydrin method... 

The advantage of integrated amperometry lies in the coulometric compensation of the charges resulting from the formation and subsequent reduction of the metal oxide. Thus, baseline drifts and baseline disturbances caused by small variations in the mobile-phase composition are eliminated. Moreover, the whole system is less sensitive to variations in pH, which influences the potentials for... 

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

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... 

Although a slightiy higher sensitivity is achieved with UV detection at 254 nm, integrated amperometry k five times more sensitive than UV detection at optimized wavelength. 

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 8.22 Ion-exchange reactions inside a CERS as preparation for integrated amperometry of amines.

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 4 Puise sequence for integrated amperometry of primary aikyiamines and their separation on a weak acid cation exchanger. Separator coiumn lonPac CS14 eiuent 2.5mmoi/L HjSO +100 moi/L NajSOVMeCN (5% (v/v) to 40% (v/v) after 8 min) flow rate ...

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... 

Figure 10.237 Analysis of cephapirin and ampicillin in a milk extract utilizing integrated amperometry. Separator column Luna C-8 (Phenomenex, USA) column dimensions ...

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