Matrix ionic strength

SPE offers many advantages over liquid-liquid extraction and permits removal of interferents and analyte concentration at the same time. The extraction conditions are mainly affected by pH, matrix ionic strength of the elution solvent, flow rate, and physicochemical characteristic of the sorbent bed. 

Another approach to matrix matching, which does not rely on knowing the exact composition of the sample s matrix, is to add a high concentration of inert electrolyte to all samples and standards. If the concentration of added electrolyte is sufficient, any difference between the sample s matrix and that of the standards becomes trivial, and the activity coefficient remains essentially constant. The solution of inert electrolyte added to the sample and standards is called a total ionic strength adjustment buffer (TISAB). 

In the development of a SE-HPLC method the variables that may be manipulated and optimized are the column (matrix type, particle and pore size, and physical dimension), buffer system (type and ionic strength), pH, and solubility additives (e.g., organic solvents, detergents). Once a column and mobile phase system have been selected the system parameters of protein load (amount of material and volume) and flow rate should also be optimized. A beneficial approach to the development of a SE-HPLC method is to optimize the multiple variables by the use of statistical experimental design. Also, information about the physical and chemical properties such as pH or ionic strength, solubility, and especially conditions that promote aggregation can be applied to the development of a SE-HPLC assay. Typical problems encountered during the development of a SE-HPLC assay are protein insolubility and column stationary phase... 

The type of data produced in a f.a.b. experiment is affected by the pH and ionic strength of the matrix. The former may be controlled either by the addition of acids or bases, although, in practice, it is usually preferable to keep the matrix acidic. The ionic strength is partly dictated by the purity of the sample (many biological compounds are still contaminated with salts, even after extensive purification) and partly by exogenous additives. Three additives are especially useful for carbohydrate work. They are as follows. 

These three reactions require stopped-flow technique for kinetic study. All have a reaction order of two i.e. one in each reactant) with At2 independent of and ionic strength but pH-dependent, indicating both Mn " " and MnOH to be reactive. A matrix of second order-rate-coefficients (l.mole . sec ) at 25+1 °C is given below... 

Values of the calibration curves for the various column sets are given in Table IV. The corves themselves are shown in Figure 5. The slope of the calibration curves decrease with increasing ionic strength. This is the result of reduced electrostatic repulsion between particles and substrate which permits greater penetration of the porous matrix. 

Sample matrix effect Dilute matrix if possible, check pH of matrix, increase the ionic strength of the buffer, re-evaluate matrix... 

The concept of SPME was first introduced by Belardi and Pawliszyn in 1989. A fiber (usually fused silica) which has been coated on the outside with a suitable polymer sorbent (e.g., polydimethylsiloxane) is dipped into the headspace above the sample or directly into the liquid sample. The pesticides are partitioned from the sample into the sorbent and an equilibrium between the gas or liquid and the sorbent is established. The analytes are thermally desorbed in a GC injector or liquid desorbed in a liquid chromatography (LC) injector. The autosampler has to be specially modified for SPME but otherwise the technique is simple to use, rapid, inexpensive and solvent free. Optimization of the procedure will involve the correct choice of phase, extraction time, ionic strength of the extraction step, temperature and the time and temperature of the desorption step. According to the chemical characteristics of the pesticides determined, the extraction efficiency is often influenced by the sample matrix and pH. 

A common criticism of CE is the poor consistency of migration times for peaks compared with HPLC or GC. The effects of matrix components and small differences in ionic strength and pH can have significant effects in the separation. The use of a... 

Quantitative analysis using FAB is not straightforward, as with all ionisation techniques that use a direct insertion probe. While the goal of the exercise is to determine the bulk concentration of the analyte in the FAB matrix, FAB is instead measuring the concentration of the analyte in the surface of the matrix. The analyte surface concentration is not only a function of bulk analyte concentration, but is also affected by such factors as temperature, pressure, ionic strength, pH, FAB matrix, and sample matrix. With FAB and FTB/LSIMS the sample signal often dies away when the matrix, rather than the sample, is consumed therefore, one cannot be sure that the ion signal obtained represents the entire sample. External standard FAB quantitation methods are of questionable accuracy, and even simple internal standard methods can be trusted only where the analyte is found in a well-controlled sample matrix or is separated from its sample matrix prior to FAB analysis. Therefore, labelled internal standards and isotope dilution methods have become the norm for FAB quantitation. 

Protein separation by hydrophobic interaction chromatography is dependent upon interactions between the protein itself, the gel matrix and the surrounding aqueous solvent. Increasing the ionic strength of a solution by the addition of a neutral salt (e.g. ammonium sulfate or sodium chloride) increases the hydrophobicity of protein molecules. This may be explained (somewhat simplistically) on the basis that the hydration of salt ions in solution results in an ordered shell of water molecules forming around each ion. This attracts water molecules away from protein molecules, which in turn helps to unmask hydrophobic domains on the surface of the protein. 

Additional examples may be found in Table 1.20, based on work of Queiraz and Lancas.167 The effects of fiber chemistry, ionic strength, matrix pH, extraction time, organic additives, temperature, agitation, and derivatization along with the influence of plasma proteins on SPME were reported.167 Extraction time, pH, salt concentration in sample, and temperature data are presented in Figure 1.46. 

Respond to p02 calibration is the same for both gases and liquids Immune to sample matrix, and changes in pH, salinity and ionic strength of environment... 

Various pH sensors have been built with a fluorescent pH indicator (fluorescein, eosin Y, pyranine, 4-methylumbelliferone, SNARF, carboxy-SNAFL) immobilized at the tip of an optical fiber. The response of a pH sensor corresponds to the titration curve of the indicator, which has a sigmoidal shape with an inflection point for pH = pK , but it should be emphasized that the effective pKa value can be strongly influenced by the physical and chemical properties of the matrix in which the indicator is entrapped (or of the surface on which it is immobilized) without forgetting the dependence on temperature and ionic strength. In solution, the dynamic range is restricted to approximately two pH units, whereas it can be significantly extended (up to four units) when the indicator is immobilized in a microhetero-geneous microenvironment (e.g. a sol-gel matrix). 

Matrix effects in the analysis of nutrients in seawater are caused by differences in background electrolyte composition and concentration (salinity) between the standard solutions and samples. This effect causes several methodological difficulties. First, the effect of ionic strength on the kinetics of colorimetric reactions results in color intensity changes with matrix composition and electrolyte concentration. In practice, analytical sensitivity depends upon the actual sample matrix. This effect is most serious in silicate analysis using the molybdenum blue method. Second, matrix differences can also cause refractive index interference in automated continuous flow analysis, the most popular technique for routine nutrient measurement. To deal with these matrix effects, seawater of... 

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