Mixed interference method

In this method, an entire calibration curve is measured for the primary ion in a constant background of interfering ion. aj(BG) is the activity of the constant interfering ion in the background. afiDL) is the low detection limit (LDL) of the Nernstian response curve of the electrode as a function of the primary-ion activity. In the mixed interference method the selectivity is calculated from the following equation ... 

Pullin, M. J., and Cabaniss, S. E. (1995). Dissolved organic-matter fluorescence as a mixing tracer—Quantitation of interferences, method sensitivity, and preliminary data. Abstr. Papers Am. Chem. Soc. 210, 37-IEC Part 1. 

Selectivity coefficient — Kvf], is a measure of the contribution of an interfering ion B to the potential of an -> ion-selective electrode in a mixed solution containing the primary ion A and an interfering ion B. It is defined by the modified - Nikolskij-Eisenman equation. The smaller the value of JC °g, the better the selectivity of the electrode with respect to the primary ion A. Selectivity coefficients can be evaluated by measuring the response of an ion-selective electrode in mixed solutions of A and B (fixed interference method) or in separate solutions of A and B (separate solution method). 

Active ester formation by the mixed anhydride method is accompanied by the side reaction of esterification at the carbonate moiety of mixed anhydride 51 which generates mixed carbonate 52 (Scheme 12).This decreases the yields, but is more of a nuisance than an obstacle as the side products do not interfere with crystallization of the esters as the former are soluble in the crystallizing solvent. More mixed carbonate is formed from derivatives of the hindered amino acids and proline none is formed from a-unsubstituted acids. A-Hy-droxysuccinimide gives rise to much less byproduct than 4-nitrophenol other phenols generate intermediate amounts. Less byproduct is generated when the reagent is isopropyl chloroformate. The impurity can be readily removed from a solution of the ester by adsorption of the compounds on reverse-phase chromatography beads followed by separation by selective displacement. ... 

Ion-selective membrane electrodes have as a main characteristic their selectivity. They are constructed to be utilized to determine an analyte directly in the solution without any prior separation from the matrix. This is achieved assuming a high selectivity of the electrode vs. the possible interfering ions. The selectivity is characterized through the potentiometric selectivity coefficient. The values of the coefficients that can be taken into account for validation are those obtained through the mixed solutions method at a ratio between analyte and interferent of 1 10. The method is... 

Mixed Solution Method. There are various measurement methods using mixed solutions of the two ions. The. fixed interference method is commonly used. Consider, for example, the testing of a lithium ion-selective electrode in the presence of sodium ion. A lithium calibration curve is prepared in the presence of a fixed concentration of sodium, for example, 140 mM as found in blood. A plot such as that given in Figure 13.16 results. In the upper portion of the curve, the electrode responds in a Nemstian manner to the lithium ion. As the lithium concentration decreases, the electrode potential is increasingly affected by the constant background of sodium ions, and in the lower portion of the curve the electrode exhibits a mixed response to both the lithium and the sodium. When the lithium concentration is very small, the response is due solely to sodium (the baseline potential). 

Figure 2.1 also demonstrates a common method of obtaining the selectivity coefficient, whereby the emf response is measured for solutions containing a fixed amount of interferent with varying activities of the primary ion. A, for which the electrode is designed. This is known as the mixed solution method with fixed amount of interferent and calculated from... 

An alternative mixed-solution method for expressing selectivity involves varying the interferent activity, ab> 3t constant primary ion activity, a. This method is normally used for expressing the pH range over which ion-selective electrodes are useful. 

The selectivity coefficient, defines the ability of an ISE to distinguish a particular ion from others (5). According to lUPAC, can be evaluated in mixed in solutions of primary and interfering ion (Fixed Interference Method), or separate solutions (Separate Solution Method and Matched Potential Method). The smaller the value of the greater the electrode s preference for the principal ion. 

Potentiometrie selectivity coefficients were evaluated by a mixed solution method, with an interference ion concentration of 10 M, and calculated using the following relationship ... 

The other version of the mixed solution method is the d interference method. It is based on the... 

This procedure can be applied to most P2P mixes but is especially effective on the methods to follow. However, in super clean methods, such as the PdCl2 below, where lots of isosafrole is produced, the iso byproduct can interfere with crystal formation. Someone-Who-ls-Not-Strike once found that when an appreciable amount of isosafrole was formed to the detriment of MD-P2P, the oil screwed up the crystal matrix disallowing it to form. Confused, the chemist tried to rescue the uncrystallized oil from the aqueous solution by extracting out the oil to try other things. But when the solvent hit the solution, the P2P crystallized out. Go figure The... 

In Chapter 7 we examined several methods for separating an analyte from potential interferents. For example, in a liquid-liquid extraction the analyte and interferent are initially present in a single liquid phase. A second, immiscible liquid phase is introduced, and the two phases are thoroughly mixed by shaking. During this process the analyte and interferents partition themselves between the two phases to different extents, affecting their separation. Despite the power of these separation techniques, there are some significant limitations. 

Ferrous Sulfdte Titration. For deterrnination of nitric acid in mixed acid or for nitrates that are free from interferences, ferrous sulfate titration, the nitrometer method, and Devarda s method give excellent results. The deterrnination of nitric acid and nitrates in mixed acid is based on the oxidation of ferrous sulfate [7720-78-7] by nitric acid and may be subject to interference by other materials that reduce nitric acid or oxidize ferrous sulfate. Small amounts of sodium chloride, potassium bromide, or potassium iodide may be tolerated without serious interference, as can nitrous acid up to 50% of the total amount of nitric acid present. Strong oxidizing agents, eg, chlorates, iodates, and bromates, interfere by oxidizing the standardized ferrous sulfate. 

Sastry et al. [41] used a new spectrophotometric method for the estimation of primaquine, using 3-methylbenzothiazolin-2-one hydrazone. An aqueous extract of the sample of powdered tablets (containing 50 pg/mL of primaquine phosphate was mixed with 1 mL each of aqueous 8.5 mM 3-methylbenzothiazolin-2-one hydrazone and 11.84 mM CelV (in 0.72 M sulfuric acid), the mixture was diluted to 10 mL, and the absorbance was measured at 510 nm versus a reagent blank. Beer s law was obeyed for 0.7-12 pg/mL of the drug and for 50 pg, the coefficient of variation was 0.52%i (n = 8). Other antimalarials and pharmaceutical adjuvants did not interfere. 

El-Kommos and Emara [47] determined primaquine and other secondary aromatic amines pharmaceuticals by a spectrophotometric method using 4-dimethyl amino cinnamaldehyde. The reaction of the reagent with primaquine and with the other amines was investigated. Powdered tablets were extracted with methanolic 0.1 M perchloric acid. The extract was mixed 1 1 with methanolic 0.2% of 4-dimethyl amino cinnamaldehyde and the mixture was diluted with methanol before measurement of the absorbance at 670 nm for primaquine phosphate. Beer s law was obeyed for 2-20 pg/mL of primaquine. The pink and green color formed with primaquine was stable for at least 24 h. Recoveries were good. Amodiaquine did not interfere with the determination of primaquine. 

Howard [27] determined dissolved aluminium in seawater by the micelle-enhanced fluorescence of its lumogallion complex. Several surfactants (to enhance fluorescence and minimise interferences), used for the determination of aluminium at very low concentrations (below 0.5 pg/1) in seawaters, were compared. The surfactants tested in preliminary studies were anionic (sodium lauryl sulfate), non-ionic (Triton X-100, Nonidet P42, NOPCO, and Tergital XD), and cationic (cetyltrimethylammonium bromide). Based on the degree of fluorescence enhancement and ease of use, Triton X-100 was selected for further study. Sample solutions (25 ml) in polyethylene bottles were mixed with acetate buffer (pH 4.7, 2 ml) lumogallion solution (0.02%, 0.3 ml) and 1,10-phenanthroline (1.0 ml to mask interferences from iron). Samples were heated to 80 °C for 1.5 h, cooled, and shaken with neat surfactant (0.15 ml) before fluorescence measurements were made. This procedure had a detection limit at the 0.02 pg/1 level. The method was independent of salinity and could therefore be used for both freshwater and seawater samples. 

Lee [524] described a method for the determination of nanogram or sub-nan ogram amounts of nickel in seawater. Dissolved nickel is reduced by sodium borohydride to its elemental form, which combines with carbon monoxide to form nickel carbonyl. The nickel carbonyl is stripped from solution by a helium-carbon monoxide mixed gas stream, collected in a liquid nitrogen trap, and atomised in a quartz tube burner of an atomic absorption spectrophotometer. The sensitivity of the method is 0.05 ng of nickel. The precision for 3 ng nickel is about 4%. No interference by other elements is encountered in this technique. 

In this section, we present the first experimental evidence of the destructive interference (DI) and the constructive interference (Cl) in a mixed gas of He and Ne, which prove the validity of the method. The observed interference modulation is, as discussed in Sect. 4.2, attributed to the difference between the phases of the intrinsically chirped harmonic pulses from He and Ne, which leads to the novel method for broadband measurement of the harmonic phases and for observing the underlying attosecond electron dynamics. 

---