Reproducibility and Stability

In an earlier paper (Snell et al., 1981a) we reported on the long-term dynamic stability of a-Si H FETs. Tests on one specimen have been continued during the last 2 years and Fig. 11 shows photographs of the 

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The characteristics of ITO described in the previous paragraph make it a useful material for use as the anode in an OLED. At the same time, they arc the cause of many difficulties which have been observed in the reproducibility and stability of OLED devices. We shall return to this topic in more detail later, but suffice it... 

The three main requirements for a satisfactory reference electrode, given by Ives and Janz [107], are reversibility (non-polarizability), reproducibility, and stability. Hydrogen electrodes have been chosen as the primary reference electrode due to their excellent reproducibility [54], The electrode is represented schematically as... 

The correct understanding of these words and their implications is of fundamental importance for the scientific and industrial community interested in sensor science development, since it allows the correct dissemination of both experimental and theoretic results, even if other important terms in the sensor field have not been discussed in this chapter, such as speed of response, reversibility, repeatability, reproducibility, and stability, to which some attention was paid during the presentation of this work at the ASI. 

The settling phase where the field is already very close to its final value (with residual differences below 100 kHz of H Larmor frequency), and later settles down to its final value whose required reproducibility and stability is of the order of 100 Hz. Since the linearly driven ramp is no... 

Electron impact (El) is probably the most widely used technique for ionization in MS. It is characterized by a high sensitivity, reproducibility and stability. The ionization is based on thermally produced electrons, which orthogonally cross the analyte stream and create mainly positive ions by extracting electrons from the analyte molecules (Fig. 7). 

FIGURE 22.10 Controlled-release of guaifenesin from a L-OF b OFTCAPTI tielivery system. (Modi ed from Li, S., etal.L-ORO SOFTCAP Robustness, Reproducibility, and Stability, published poster, Annual AAPS meeting, November 2001.)... 

The fundamental parameters for this validation include accuracy, precision, selectivity, sensitivity, reproducibility, and stability [58], Other parameters are limits of detection (LODs) and quantification (LOQs), linear dynamic range (LDR) [56], In the case of LC-MS/MS based procedures, appropriate steps should be taken to ensure the lack of matrix effects throughout the application of the method, as outlined by several authors [55, 60-64]. 

For the evaluation of any separation medium, three types of characterization are important in determining the overall usefulness of the material within column reproducibility, column-to-column reproducibility and stability. All of these factors have been tested for the etched chemically modified capillaries in order to determine the reproducibility of the etching and chemical modification processes as well as the ruggedness of the silanization/hydrosilation method for the attachment of various organic moieties to the roughened inner wall. 

Electrochemical measurements can be readily adapted for on-line monitoring. An electrochemical detector uses the electrochemical properties of target analytes for their determination in a flowing stream. An electrochemical flow system, based on an SWV operation at a carbon-fiber-based detector, for use in the on-line continuous monitoring of trace TNT in marine environments was developed [16]. Such flow detector offers selective measurements of sub-part-per-million concentrations of TNT in untreated natural water samples with a detection limit of 25ppb. It responds rapidly to sudden changes in the TNT concentration with no apparent carryover. About 600 runs can be made every hour with high reproducibility and stability (e.g., relative standard deviation (RSD) = 2.3%, n = 40). The system lends itself to full automation and to possible deployment onto various stationary mobile platforms (e.g., buoys and underwater vehicles). 

Comparing the values for cal[site)DsKs and KM/KS obtained from all the different experiments (Tables 2.5 and 2.6), we find that the agreement between the different experiments is good and confirms the validity of the proposed model and demonstrates the excellent reproducibility and stability of these films for NADH oxidation. 

Electrode-Preparation and Aging. Electrode preparation procedures are given by Keston (14) and by Ives and Janz (II). Electrodes were prepared from a paste containing 90% silver oxide and 10% silver bromate placed on a platinum spiral and heated in a furnace for 7 min at 650°C. Janz and Taniguchi (12) have reviewed the preparation, reproducibility, and stability of this electrode. Taylor and Smith (13) found the equilibrium potential to be stable within 0.02 mV. Electrodes... 

Li et al. [77] reported the electrocatalytic oxidation of norepinephrine at a GCE modified with SWCNTs. The electrode showed a very good reproducibility and stability. A linear relationship was obtained between the oxidation peak current and norepinephrine concentration between 1.0 x 10 and 1.1 x 10" M and the detection limit was 6.0 x 10 M. The electrocatalytic activity of the SWCNTs-modified-GCE was also demonstrated with dopamine, epinephrine and ascorbic acid. 

Ascorbic acid (1) is most commonly used for testing the performance of electrodes in redox systems. Thus, a Ag-Ag ascorbate selective electrode was constructed with view to use it for vitamin C determination. Its reproducibility and stability was satisfactory and ascorbate ion concentration could be determined in neutral, alkaline and alcoholic media" . A voltametric study was carried out for the evaluation of graphite-epoxy composite (GEC) electrodes for use in the determination of ascorbic acid and hydroquinone. They were compared with mercury and CPE in similar operating conditions of pH and supporting electrolytes. Like all redox electrodes, also GEC electrodes deteriorate on exposure to air or after repeated usage, and the surface had to be renewed for activation. GEC electrodes were found to be adequate for redox system analyses"". The electrocatalytic oxidation of 1 is an amplification method for determination of specific miRNA strands using the An biosensor described in Table 1 . 

Further enhancement of the SERS can be achieved through precise control over the parameters at the metal particle size scale [10] Most SERS-active substrates were made from pure metallic nanostructures such as metal nanoparticles [33-35], metal particle arrays [5], roughened metal surfaces [36], or a combination with metal nanostructures and other nanomaterials [17, 18, 29, 37-39]. Recently, many strategies have shown the adsorbation of molecules on the surface of Ag and Au substrates for SERS applications [40]. SERS-active Ag nanostructures substrates are required to satisfy certain conditions with good reproducibility and stability [39]. For this reason, it is indispensable to develop and optimize the methods to prepare the SERS-active Ag substrates [41]. 

Such structural information could provide strong arguments concerning the chemical structures of the polymers and can be extremely important for bioimmobilization purposes. In addition, it offers valuable information about the distribution and geometry of the resulting layer. On the other hand, the stability of this film and the active surface area strongly affect the performance (especially reproducibility and stability) of the final biosensor device, particularly when electrochemical transduction schemes are employed. Such parameters can be determined using electrochemical procedures. 

Haugen P, Tung MA, Runikis JO. Steady shear flow properties, rheological reproducibility and stability of aqueous hydroxyethylcellulose dispersions. Can ] Pharm Sci 1978 13 4-7. 

Transfer 1 mL of blank sample to the cuvet and zero the machine at 595 ran. Repeat with duplicate blank sample to check reproducibility and stability of readings (see Note 16). 

The Knudsen diffusion gas separation layer can be modified by e.g. sol-gel, cvd, or crystallisation techniques to enhance the selectivity, but this decreases the permeation. Silica is the material mainly used for modification. However, data on reproducibility and stability are still scarce. The large scale use of high selective inorganic membranes and these membranes at high temperatures, up to at least 600°C, will probably last another 5-10 years. On a laboratory scale (maximum membrane surface area of about 50 cm ) these high selective membranes are now available, although stability can be a problem in certain atmospheres. 

Preparation As compared to single-crystal Ag surfaces, the preparation of pc-Ag electrode may seem to be a relatively simple task. However, a pc-Ag surface, which ensures reproducibility and stability, also requires a special procedure. Ardizzone et al. [2] have described a method for the preparation of highly controlled pc-Ag electrode surface (characterized by electrochemical techniques and scanning electron microscopy (SEM)). Such electrodes, oriented toward electrocatalytic properties, were successfully tested in halide adsorption experiments, using parallelly, single-crystal and conventional pc-Ag rods as references. 

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