Although it is not officially condoned, mobile-phase (MP) recycling has become a widespread practice that is not well documented in terms of its effects on sample quantification. MP was spiked with three different concentrations of two analytes, tartaric acid and sodium citrate, to simulate MP recycling. These MPs were used to analyze eight different concentrations of these analytes in standard solutions. When analyte concentration in the MP exceeds that in the sample, a vacancy (negative) peak is observed, and when its concentration in the MP is equal to that in the sample, no peak is observed for that analyte. The slopes of the linear regression lines for standards in MPs with different concentrations of analyte did not change, although the gamma-intercept values decrease with increasing concentration of analyte in the MP. These results show that the concentration of analytes in recycled MP can be determined by comparing the absolute value of the gamma-intercept of the linear regression line with the corresponding peak area from the linear regression line for clean (solute-free) MP, provided other chromatographic parameters do not change. Suggestions are made for determining when recycled MP should be discarded.

A set of parameters for pyrolysis characterization of linear low density polyethylene (LLDPE) were chosen to measure its combustion behaviour. Two kinds of parameters were selected, material and reaction. The material parameters were: effective values of the mass density (ρ); specific heat capacity (c); thermal conductivity (k); absorption coefficient (қ) and emissivity (ε). The reaction parameters were the exponential factor (Z), the energy of activation (Ε) and the reaction mechanism f(α). In addition simultaneous thermal analysis (STA) tests were carried out at heating rates of 2, 5 and 10 K/min in N 2 atmosphere to obtain the kinetic triplet and cone calorimeter tests at irradiance levels of 25, 40, 50 and 75 kW/m 2 to compare the simulated mass loss rate against real mass loss rate. Finally the cone calorimeter tests were used as input values to optimize the parameter set to perform real mass loss rate.

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