Magnitude. Orders

Ephedrine is the pharmacologically active enantiomers of ephe-drine. The enantiopurity tests for (-)-ephedrine can be performed using a peroctylated y-cyclodextrin based plastic membrane electrode [26], Bis (l-butylpentyl)adipate (BBPAP) was used as plasticizer and 10 3 mol/L NH4C1 as inner solution. The slope of the electrode is 60 mV/decade of concentration, and the potentiometric enantioselectivity coefficient is less than 10 4 The limit of detection is of 10 7 mol/L magnitude order. 

EPMEs based on carbon paste impregnated with a-, />- and y-cyclo-dextrins are proposed for the assay of L-proline [31]. Response characteristics showed that the proposed electrodes could be reliably used in the assay of L-proline, with the best enantioselectivity and time-stability exhibited by a-cyclodextrin based EPME. The EPMEs based on the proposed unsubstituted cyclodextrins showed lower detection limits (10 10 magnitude order) than the one previously studied, based on /J-cyclodextrin derivative [30]. The widest linear concentration range is recorded for the y-cyclodextrin based EPME (10 8-10-3mol/L). The recovery tests performed for the assay of L-proline in the presence of d-proline (recoveries higher than 99.65%) proved that the proposed... 

S-ramipril can be determined as raw material and from its pharmaceutical formulations, using the EPME based on impregnation of 2-hydroxy-3-trimethylammoniopropyl-//-cyclodextrin (as chloride salt) solution in a carbon paste, in the 1.8 x 10 5-2.3 x 10 1 mol/L (pH between 2.5 and 6.0) concentration range with an average recovery of 99.94% (RSD = 0.030%) and 98.98% (RSD — 0.67%), respectively [33]. The detection limit is of 10-5 mol/L magnitude order. The slope is near-Ne-rnstian 52.00 mV/decade of concentration. Enantioselectivity was proved over D-proline, when a 10 4 magnitude order was obtained for potentiometric selectivity coefficient. 

Three EPMEs based on macrocyclic glycopeptide antibiotics— vancomycin and teicoplanin (modified or not with acetonitrile)—were proposed for the determination of l- and D-enantiomers of methotrexate (Mtx) [48]. The linear concentration ranges for the proposed enantioselective membrane electrodes were between 10 6 and 10-3 mol/L for l- and D-Mtx. The slopes of the electrodes were 58.00 mV/pL-Mtx for vancomycin-based electrode, 57.60 mV/pD-Mtx for teicoplanin-based electrode and 55.40 mV/pD-Mtx for teicoplanin modified with acetonitrile-based electrode. The detection limits of the proposed electrodes were of 10 8 mol/L magnitude order. All proposed electrodes proved to be successful for the determination of the enantiopurity of Mtx as raw material and of its pharmaceutical formulations (tablets and injections). 

Novel EPMEs based on carbon paste impregnated with (1,2-methanofullerene C60)-61-carboxylic acid (I), diethyl (1,2-methanofullerene C60)-61-61-dicarboxylate (II) and tert-butyl (1,2-methanofullerene C60)-61-carboxylic acid (III) were designed for the assay of S-clenbuterol raw material and in serum samples [52], All EPMEs showed near-Nemstian responses (56.8, 57.0 and 57.1mV/decade of concentration) for S-Clen, with correlation coefficients for the equations of calibration of 0.9996 (I), 0.9998 (II) and 0.9998 (III), respectively, and low detection limits (of lO-10 and 10 11mol/L magnitude order). R-Clen, on the other hand, showed non-Nemstian response. All electrodes displayed good stability and reproducibility over 1-month test period, when used every day for measurements (RSD <0.1%). 

This configuration based on the use of two surfaces, magnetic beads for immunoassay and screen-printed electrodes for electrochemical detection, allows to obtain a faster and a more sensitive detection of the immunoreaction than using a unique surface (screen-printed electrode) in this case it is possible to perform the electrochemical measurement in faster times (less then 30 min) and improve the sensitivity (around two magnitude orders). For this reason, this approach is advised in the development of an electrochemical immunosensor specific to any analyte. 

Miniaturization and utilization of biocompatible materials for construction have allowed the electrochemical sensors to be successfully used for in vivo measurements. Usually, they are arranged as sensor detection systems in an array.316 Because spectrometric methods cannot be reliably applied for in vivo measurements, their uncertainty cannot be compared with that obtained by in vivo measurements using electrochemical sensors. The main problems for in vivo measurements are the sterilization of sensors, dimension of sensors (usually cannot exceed a nanometer magnitude order), and their geometric configuration. The calibration of sensors for in vivo measurements is also a problem because high-quality standards are necessary. 

The limit of detection of an analytical method must be directly correlated with the concentration of the analytes in the sample.329 Generally, the magnitude order for the limit of detection for different types of methods (e.g., anodic stripping voltammetry, potentiometry, atomic absorption spectrometry, UV/Vis, etc.) is known. Also, the approximate concentration range of the analyte in samples is known. For validation of the method for the analysis of an analyte from a specific sample, the limit of detection must be lower than the concentration of the analyte in the sample. 

Supercritical fluid extraction (SFE) has certain advantages due to the properties, interimate between liquid and gas. Particularly, the viscosity of a supercritical phase is in the gas magnitude order while solubility properties (repartition coefficients, K) correspond to the liquid phase. E.g. at 160 bar and 60°C carbon dioxide has the density 0.7 g/mL and the polarity close to toluene, and is called therefore dense gas . 

From the previous sections it follows that when designing the interface, starting on the desired performance of the heterogeneous material at the macroscopical scale, of 12 magnitude orders, may be the dimensional gap required to obtain the optimum material (9). 

For secondary redox reaction comparatively large rate constants (magnitude order 10" to 10 " (L mol yr ) are reported. This confirms that these reactions are fast compared to primary redox reactions and can be assumed to be in local equilibrium. Non-redox precipitation/dissolution reaction result from literature data as slow kinetic reactions with rate constants ranging from 10 to 10 " [1 moF yr ]. 

An experimental study by Wu et al. (1998) on the competitive adsorption resulted in the magnitude order of metal ions (Ag", Ni, Zn, Cu, Cd, Pb , Cr ) adsorbed onto oxide and silicate minerals in near-neutral solution with low ionic strength in mol/nm as follows ... 

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