Average molecular weight determination of polymers with polydispersities greater than 1.2 is an ongoing challenge in the field of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Mass discrimination effects observed in the analysis of these polymers have been attributed to sample preparation, desorption/ionization, and instrumental factors. In an effort to separate these factors, we studied poly(methyl methacrylate) (PMMA) standards using two different ion detection systems installed on the same time-of-flight mass analyzer. Equimass blends of narrow PMMA standards were used to simulate a polymer with a wide polydispersity. MALDI-MS analysis was also performed on a PMMA standard with a polydispersity of 1.7. All samples were analyzed by size exclusion chromatography for comparison. Although sample preparation and ionization/desorption factors were found to influence the spectral appearance of the MMA distributions, we demonstrate that, under similar sample preparation and instrument conditions, different ion detection systems produce different results for synthetic polymer blends. The differences in the detector responses for the blends and wide polydisperse standard arise from several factors related to the ion detection system: (1) detection mechanisms, (2) saturation effects, and (3) signal-to-noise limitations.

Densities, viscosities, and refractive indices of the ternary system acetone + ethanol + 2,2,4-trimethylpentane at T = 298.15 K and the binary systems acetone + ethanol, acetone + 2,2,4-trimethylpentane, and ethanol + 2,2,4-trimethylpentane were measured at T = (288.15, 298.15, and 308.15) K and atmospheric pressure over the whole composition range. Densities were determined using a vibrating-tube density meter. Viscosities were measured with an automatic Ubbelohde capillary viscometer. Refractive indices were measured using a digital Abbe-type refractometer. Excess molar volumes V E, deviations in the viscosity from the mole fraction average Δη, and deviations in the refractive index from the volume fraction average Δn D for the mixtures were derived from experimental data. The binary and ternary data of V E, Δη, and Δn D were correlated with liquid composition by using the Redlich−Kister and Cibulka equations.

Densities, viscosities, and refractive indices of the ternary system diisopropyl ether + ethanol + 2,2,4trimethylpentane at T ) 298.15 K and the binary systems diisopropyl ether + ethanol and diisopropyl ether + 2,2,4-trimethylpentane were measured at T ) (288.15, 298.15, and 308.15) K and atmospheric pressure over the whole composition range. Densities were determined using a vibrating-tube density meter. Viscosities were measured with an automatic Ubbelohde capillary viscometer, and refractive indices were measured using a digital Abbetype refractometer. Excess molar volumes (V E ), deviations in the viscosity from mole fraction average (∆η), and deviations in the refractive index from volume fraction average (∆n D ) for the mixtures were derived from experimental data. The binary and ternary data of V E , ∆η, and ∆n D were correlated with liquid composition by using the Redlich-Kister and the Cibulka equations.