Insights into the Retention Mechanisms on Perfluorohexylpropylsiloxane-Bonded (Fluophase-RP) and Octadecylsiloxane-Bonded (Betasil C18) Stationary Phases Based on the Same Silica Substrate in RP-LC

Physicochemical and biochemical properties for the dialkyl phthalates

Abraham descriptors for 40 phthalate esters have been calculated from a variety of experimental data, including water-solvent partition coefficients, high performance liquid chromatographic and gas chromatographic retention times. These descriptors can then be used to calculate a large number of physicochemical and biochemical properties of the esters; values are given for dinonyl phthalate as an example. Once the Abraham descriptors have been obtained for a given phthalate ester, no more than simple arithmetic is needed to calculate values of a huge range of properties. The 'three solubility method' yields data that are consistent for a particular physicochemical property, but not necessarily correct data. Previous literature values for air-water partition coefficients for the higher phthalates are likely to be incorrect by several orders of magnitude.

Liquid chromatography/tandem mass spectrometry with fluorous derivatization method for selective analysis of sialyl oligosaccharides

RATIONALE

A separation-oriented derivatization method using a specific fluorous affinity between perfluoroalkyl-containing compounds was applied to selective liquid chromatography/tandem mass spectrometric (LC/MS/MS) analysis of sialyl oligosaccharides. The perfluoroalkyl-labeled sialyl oligosaccharides could be selectively retained on an LC column with the perfluoroalkyl-modified stationary phase and effectively distinguished from non-derivatized species.

METHODS

Sialyl oligosaccharides (3'-sialyllactose, 6'-sialyllactose, sialyllacto-N-tetraose a, sialyllacto-N-tetraose b, sialyllacto-N-tetraose c, and disialyllacto-N-tetraose) were derivatized with 4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoroundecylamine via amidation in the presence of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (condensation reagent). The obtained derivatives were directly injected onto the fluorous LC column without any pretreatments and then detected by positive electrospray ionization MS/MS.

RESULTS

The method enabled accurate determination of the sialyl oligosaccharides in biological samples such as human urine and human milk, because there was no interference with matrix-induced effects during LC/MS/MS analysis. The limits of detection of the examined sialyl oligosaccharides, defined as signal-to-noise (S/N) = 3, were in the range 0.033-0.13 nM. Accuracy in the range 95.6-108% was achieved, and the precision (relative standard deviation) was within 9.4%.

CONCLUSIONS

This method enabled highly selective and sensitive analysis of sialyl oligosaccharides, enabling accurate measurement of even their trace amounts in biological matrices. The proposed method may prove to be a powerful tool for the analysis of various sialyl oligosaccharides.

The Effect of Column and Eluent Fluorination on the Retention and Separation of non-Fluorinated Amino Acids and Proteins by HPLC

The effect of column and eluent fluorination on the retention and separation of non-fluorinated amino acids and proteins in HPLC is investigated. A side-by-side comparison of fluorocarbon column and eluents (F-column and F-eluents) with their hydrocarbon counterparts (H-column and H-eluents) in the separation of a group of 33 analytes, including 30 amino acids and 3 proteins, is conducted. The H-column and the F-column contain the n-C(8)H(17) group and n-C(8)F(17) group, respectively, in their stationary phases. The H-eluents include ethanol (EtOH) and isopropanol (ISP) while the F-eluents include trifluoroethanol (TFE) and hexafluorosopropanol (HFIP). The 2 columns and 4 eluents generated 8 (column, eluent) pairs that produce 264 retention time data points for the 33 analytes. A statistical analysis of the retention time data reveals that although the H-column is better than the F-column in analyte separation and H-eluents are better than F-eluents in analyte retention, the more critical factor is the proper pairing of column with eluent. Among the conditions explored in this project, optimal retention and separation is achieved when the fluorocarbon column is paired with ethanol, even though TFE is the most polar one among the 4 eluents. This result shows fluorocarbon columns have much potential in chromatographic analysis and separation of non-fluorinated amino acids and proteins.

Experimental determination of LSER parameters for a set of 76 diverse pesticides and pharmaceuticals

Linear solvation energy relationships (LSERs) have more recently been proposed as the method of choice to describe and/or predict the partitioning behavior of neutral organic compounds over a large range of environmental matrices and for a broad variety of compounds in a consistent manner. However, when dealing with more complex, polar compounds with multiple functional groups, it has also been noted that there is a severe lack of substance descriptors quantifying the different intermolecular interactions that these compounds may undergo. In this study, we used a system of eight reversed phase, normal phase, and hydrophilic interaction HPLC systems to determine the substance descriptors for H-bond donor (A) and acceptor (B) interactions and for polarizability and dipolarity (S) for a set of 76 complex compounds containing multiple functional groups, comprising mainly pesticides and some pharmaceuticals. The obtained substance descriptors for most compounds are unique in that values of A, S, and B are high and lie at the very upper end of the numerical range of currently known substance descriptors. The substance descriptors have been cross-compared against literature values of the octanol-water (Kow) and air-water (Kaw) partition coefficients and against a set of heptan-methanol partition coefficients (Khm) experimentally determined with a consistent methodology herein. The comparison confirmed plausibility of the substance descriptors of all except six tested compounds. The newly determined substance descriptors promise to be highly valuable in chemicalfate modeling, allowing, in conjunction with available phase descriptors, for a better representation of partitioning of polar compounds in those models. The results also reveal a systematic deviation of the log Kow values predicted with our substance descriptors from the literature values. The deviation points toward a possible problem when existing LSER equations are applied to polar, multifunctional compounds with high values of A, S, and B. Hence, the substance descriptors determined herein should also be helpful in revisiting the validity of existing LSERs for complex, polar compounds.