Pulse adsorption

Figure 2.23. IR spectra obtained after subsequent 10 (rmol pulse adsorption of NO on a thermally preactivated Cu ZSM-S sample recorded at (a) 303 K and (b) 423 K (after [75]).

This sequence of steps was derived from a series of pulsed adsorption experiments, in which CH4 was decomposed stoichiometrically to carbon and H2, whereas C02 was shown to react stoichiometrically with the surface carbon yielding CO. 

Van den Berg [510] carried out direct determinations of molybdenum in seawater by adsorption voltammetry. The method is based on complex formation of molybdenum (VI) with 8-hydroxyquinoline (oxine) on a hanging mercury drop electrode. The reduction current of adsorbed complexions was measured by differential pulse adsorption voltammetry. The effects of variation of pH and oxine concentration and of the adsorption potential were examined. The method was accurate up to 300 nmol/1. The detection limit was 0.1 nmol/1. 

Stripping voltammetry has also been applied to the quantitation of the drug in formulations. A sensitive and precise method using square-wave adsorptive stripping voltammetry has been developed for the determination of sulpha-quinoxaline in veterinary formulations [157]. The differential pulse adsorptive stripping voltammetric determination of midazolam in injectable formulations as a method for quality control has been demonstrated [158]. 

AG Fogg, AA Barros, JO Cabral. Differential-pulse adsorptive stripping voltametry of food and cosmetic synthetic colouring matters and their determination and partial identification in tablet coating and cosmetics. Analyst 111 831—835, 1986. 

The coupling of diazotized /i-aminoacetophenone (DPAAP) with imidazole forms the basis of the differential pulse adsorption stripping voltammetry (DPASV) method for detection of histidine and its metabolites. The absorption of azo-histidine was found to obey Frumkin absorption isotherm <1999TAL319>. 

Treatment and Characterization of Catalysts. A dynamic pulse adsorption apparatus (16) was used to carry out in situ pretreatments, reductions, degassing and hydrogen chemisorption measurements. 

Analytical Methods and Speclatlon Electrothermal atomic absorption spectrophotometry (ETAAS), differential pulse adsorption voltammetry (DPAV), isotope-dilution mass spectrometry (ID-MS), and inductively coupled plasma mass spectrometry (ICP-MS) furnish the requisite sensitivity for measurements of nickel concentrations in biological, technical and environmental samples (Aggarwal et al. 1989, Case et al. 2001, Stoeppler and Ostapczuk 1992, Templeton 1994, Todorovska et al. 2002, Vaughan and Templeton 1990, Welz and Sperling 1999). The detection limits for nickel determinations by ETAAS analysis with Zeeman background correction are approximately 0.45 jg for urine,... 

M solutions. Figure 25-36a illustrates the sensitivity of differential-pulse adsorptive stripping voltammetry when it is applied to the determination of calf-thymus DNA in a 0.. i mg/L solution, f igure 25-36b shows the dependence of the signal on deposition time. Many other examples of this lype can be found in ihe recent literature. 

Khayamian, T., Ensafi, A.A., Benvidi, A. Extending the dynamic range of copper determination in differential pulse adsorption cathodic stripping voltammetry using wavelet neural network. Talanta 69, 1176-1181 (2006)... 

A number of studies have strongly suggested an effect of H2O is the oxidation of cobalt clusters for cobalt alumina catalysts, including the use of gravimetric techniques, TPD, pulse adsorption, and XPS [10-12], For the 25%Co/Al203 catalyst, the reversible effect of H2O may be due to a surface reoxidation process. The increase in CO2 selectivity (Table 9) suggests inereased WGS activity, as discussed in previous cases, potentially caused by a... 

Fig.2. Effect of accumulation time (in min) on differential pulse adsorptive stripping voltammetric behaviour of rabbit anti-/ -HCG (conditions Eacc + 0.05 V scan rate 5mV/s drop time 1 s).

ASV anodic stripping voltammetry ATP adenosine triphosphate AuE gold electrode CV cyclic voltammetry DPV dififerential pulse voltammetry DPASV differential pulse adsorptive stripping voltammetry GCE assy carbon electrode MFE, mercury film electrode NPGE nanoporous gold electrode SPE screen-printed electrode. 

Zarei, K., Teymori, E., and Kor, K. (2014). Very sensitive differential pulse adsorptive stripping voltammetric determination of 4-nitrophenol at poly (diphenylamine)/multi-walled carbon nanotube-)8-q clodextrin-modified glassy carbon electrode, Int J. Environ. Anal Chem., 94, pp. 1407-1421. 

Pulse adsorption and differential heats of adsorption - Flow Injection Adsorption Thermodynamics (FIAT)... 

Figure 8. Pulse adsorptions following sequential injections of 20 pi of 0.01 molar aqueous solution of K2PtCl6 (0.2 pmol) into water percolating throught 25.8 mg of graphitised carbon black mixed with PTFE powder. Flow rate of water - 3 mlh, temperature - 20°C.

Simultaneous determination of the heats and the amounts of adsorption is essential in the pulse adsorption experiments to establish what proportion of the injected solute is irreversibly adsorbed. In most cases the capacity of solid surfaces for irreversible adsorption is limited to a part of the total surface as determined by the BET method. The other part of the surface may continue to selectively adsorb the injected solutes, but the adsorptions become irreversible after saturation of the surface sites absorbing irreversibly. The injections of solutes which are reversibly adsorbed produce heat effects composed of overlapping positive and negative portions prohibiting eui accurate determination of the heats of adsorption, in which case the saturation technique of section 2.2 may be required. 

A recently obtained example of pulse adsorption of NH.i on ZMS-5 zeolite, activated at 200°C for 8 hours, from a He carrier at atmospheric pressure is shown in Figure 17. The pulses of ammonia were irreversibly adsorbed producing constant heats of adsorption ranging from 110 kJmol to 130 kJmol. These values are in the lower range of the heats of adsorption obtained by A. Auroux et al on a different ZMS-5 zeolite, activated at 500°C [31]. Similar work with the flow adsorption microcalorimeter at higher pressures is likely to reveal new aspects of NH3 interactions with a variety of adsorbents and catalysts which will probably be more closely related to their uses in industrial practice. 

Another important property of the basal planes is their affinity for polycyclic aromatics. This was found by pulse adsorption of dilute solutions of anthracene and pyrene in cyclohexane which produced very high molar heats of adsorption at low surface coverages. Later work by the author indicated that in spite of the strong initial adsorption, the polycyclic compounds do not form closely packed layers on the basal planes but are localised on certain more active parts of the graphene surface without the formation of plateaux in their adsorption isotherms [40]. 

The behaviour of specific strongly adsorbed compounds which do not react after adsorption but render the surface resistant to the action of corrosive agents, such as acetic acid, is exemplified by the interaction of benzotriazole with copper surfaces [47]. Pulse adsorption of acetic acid on a pure copper powder produced a strong irreversible adsorption which was substantially reduced after saturation of the metal powder with a dilute benzotriazole solution. A return to high reactivity with acetic acid was obtained after the desorption of benzotriazole. 

Similar determinations can be carried out by using the pulse adsorption FIAT methodology described in section 2.5. 

Billova S, Kizek R, Palecek E (2002) Differential pulse adsorptive stripping voltammetry of osmium-modified peptides. Biogeosciences 56 63-66... 

Reddy TM, Reddy SJ (2004) Differential pulse adsorptive stripping voltammetric determination of nifedipine and nimodipine in pharmaceutical formulations, urine, and serum samples by using a clay-modified carbon-paste electrode. Anal Lett 37 2079-2098... 

Sreedhar M, Reddy LM, Sirisha KR, Reddy SRJ (2(X)3) Differential pulse adsorptive stripping voltammetric determination of dinoseb and dinoterb at a modified electrode. Anal Sci 19 511-516... 

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