Detection integrated pulsed

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).

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...

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]. 

CO Dasenbrock, WR Lacourse. Assay for cephapirin and ampicillin in raw milk by high-performance liquid chromatography-integrated pulsed amperometric detection. Anal Chem 70 2415-2420,1998. 

Hanko, V.P., Rohrer, J.S.J. Determination of neomycin sulfate and impurities using high-performance anion-exchange chromatography with integrated pulsed amperometric detection. J. Pharm. Biomed. Anal. 43, 131-141 (2007)... 

After exposing the model catalysts to CO molecules by molecular beam pulses with typical widths of 40 ms (resulting in maximal effective pressures of 2 X 10 mbar) and at a constant isotropic O2 pressure of 5 x 10 mbar, the resulting product molecules (CO2) were detected within isothermal conditions by an absolutely calibrated quadrupole mass spectrometer. From the integral of the detected CO2 pulses, the absolute number of formed CO2 per cluster could be obtained. Dividing this number by the reaction time (40 ms) and the number of atoms in the clusters results in the TOFs of this reaction for various cluster sizes with an estimated accuracy of 10%. From these results, a reaction probability can then be defined by dividing the TOF by the total flux of CO (composed of the direct adsorption or adsorption through reverse spillover) on the cluster. With these two numbers, a catalytic process is defined and allows the cluster s catalytic properties to be compared to other model systems. 

The rotational speed of the rotor, or turbine, increases linearly with flow velocity within + 0.5% over a wide flow range from 10 1 to 20 1 [10]. The turbine speed is typically measured by detecting the pulse of each blade electrically, mechanically, or optically each pulse represents a certain volume of fluid. The flow rate of the fluid is determined by integrating the total number of pulses over a period of time. The accuracy of these meters is better than 1% over a wide range of flow rates [4]. Accuracy is compromised, however, with blade wear, bearing friction due to wear, and when a vapor enters the line for liquid flows [10]. 

Bressani, Brevetto, and Chiavassa have described an instrument using this feature [39]. The absorber is moved with a constant velocity Vq and the source with varying velocity k sin cot. The detected y pulses are not distributed statistically but are periodically bunched by the extra modulation. A lock-in amplifier can be made to respond to the bunching frequency and with a suitably long integration time will produce a voltage proportional to dr/dvo. 

De Borba, B.M. Rohrer, J.S. Determination of biogenic amines in alcohohc beverages by ion chromatography with suppressed conductivity detection and integrated pulsed amperometric detection. J. Chromatogr. A, 2007,1155,22-30. 

K. Susumu, Integrated pulsed amperometric detection of glufosinate, biala-phos and glyphosate at gold electrodes in anion-exchange chromatography, J. Chromatogr. A., 2001, 919, 313-320. 

Besides various detection mechanisms (e.g. stimulated emission or ionization), there exist moreover numerous possible detection schemes. For example, we may either directly detect the emitted polarization (oc PP, so-called homodyne detection), thus measuring the decay of the electronic coherence via the photon-echo effect, or we may employ a heterodyne detection scheme (oc EP ), thus monitoring the time evolution of the electronic populations In the ground and excited electronic states via resonance Raman and stimulated emission processes. Furthermore, one may use polarization-sensitive detection techniques (transient birefringence and dichroism spectroscopy ), employ frequency-integrated (see, e.g. Ref. 53) or dispersed (see, e.g. Ref. 54) detection of the emission, and use laser fields with definite phase relation. On top of that, there are modern coherent multi-pulse techniques, which combine several of the above mentioned options. For example, phase-locked heterodyne-detected four-pulse photon-echo experiments make it possible to monitor all three time evolutions inherent to the third-order polarization, namely, the electronic coherence decay induced by the pump field, the djmamics of the system occurring after the preparation by the pump, and the electronic coherence decay induced by the probe field. For a theoretical survey of the various spectroscopic detection schemes, see Ref. 10. 

The disadvantages listed above are either alleviated or greatly diminished by the use of Integrated Pulsed Electrochemical Detection (IPAD), which is also a form of PED. Figure 4.4 shows the IPAD waveform and Table 4.7 describes the times and potentials that are generally used for amino acid detection. Here, the electrode current is integrated electronically throughout a rapid cycUc or square wave... 

High sensitivities down to the femtomole range are also achieved in carbohydrate and amino acid analysis by using integrated pulsed amperometric detection. 

Anion-exchange chromatography with direct detection via integrated pulsed... 

A popular application for ELSD in the food and beverage industry is the analysis of carbohydrates in various matrices. In contrast to integrated pulsed amper-ometric detection of carbohydrates, which is highly specific and sensitive, ELSD is considered to be the prevailing detection technique if carbohydrates are present in larger concentrations. However, the main problem encountered in... 

Figure 8.126 Schematics of a chromatographic system for carbohydrate analysis with integrated pulsed amperometric and MS detection.

Figure 8.129 Separation of carbohydrates derived from a microalgae whole-cell lysate with integrated pulsed amperometric and MS detection. Separator column CarboPac MAI column dimensions 250 mm x4 mm l.d. column temperature 30°C eluent 0.5 mol/L...

Dionex Corporation (2007) Dionex Application Note No. 182 Determination of Biogenic Amines in Alcoholic Beverages by Ion Chromatography with Suppressed Conductivity and Integrated Pulsed Amperometric Detections. Dionex... 

---