A new issue of this journal has just been published. To see abstracts of the papers it contains (with links through to the full papers) click here:
Selected papers from the latest issue:
Effect of Methanol Quality on the Ionisation of Herbicides, Insecticides and Fungicides Using Gradient Elution Liquid Chromatography
04 November 2011, 21:01:35
Publication year: 2011
Source: Journal of Chromatography A, Available online 4 November 2011
Michael J. Gray, Sohail Jahani Gary K.-C. Low
This paper explores the changes in the electrospray signal response of 39 structurally different compounds caused by the quality of the methanol, when used as a component in a gradient elution mobile phase.When three batches of LC-MS grade methanol from one manufacturer were evaluated, the largest variation in the electrospray signal responses of the 39 compounds examined was 18%. However, significant enhancement of the electrospray signals of up to 106% were observed among different brands of LC-MS grade methanol from different manufacturers. The effect of methanol quality on signal response was found to be compound dependent.This study also demonstrated that the senescence of the methanol was important. By using an expired batch of LC-MS grade methanol, electrospray signals were suppressed by as much as 95% for all compounds measured using positive mode electrospray. Conversely, the negative mode electrospray signals of compounds such as 4-octyl benzoic acid showed an enhancement of up to 96% when using the same batch of methanol.Linuron was used as a model compound to examine the change in the electrospray response, during gradient elution, when the proportion of an expired batch of methanol was varied. An infusion experiment showed that the linuron signal intensity decreased as the proportion of expired methanol increased in the mobile phase, which was in direct contrast to the increase in linuron signal observed with a non-expired batch of methanol. A series of isocratic experiments also showed that the linuron signal decreased as the proportion of expired methanol increased in the mobile phase.The ion ratios of several of the compounds studied changed significantly when using the expired batch of LC-MS methanol. The change in the ion ratios accentuates the difficulty of identifying compounds from in-source spectral libraries.A protocol is recommended for assessing the quality of methanol for LC-MS applications.
Source: Journal of Chromatography A, Available online 4 November 2011
Michael J. Gray, Sohail Jahani Gary K.-C. Low
This paper explores the changes in the electrospray signal response of 39 structurally different compounds caused by the quality of the methanol, when used as a component in a gradient elution mobile phase.When three batches of LC-MS grade methanol from one manufacturer were evaluated, the largest variation in the electrospray signal responses of the 39 compounds examined was 18%. However, significant enhancement of the electrospray signals of up to 106% were observed among different brands of LC-MS grade methanol from different manufacturers. The effect of methanol quality on signal response was found to be compound dependent.This study also demonstrated that the senescence of the methanol was important. By using an expired batch of LC-MS grade methanol, electrospray signals were suppressed by as much as 95% for all compounds measured using positive mode electrospray. Conversely, the negative mode electrospray signals of compounds such as 4-octyl benzoic acid showed an enhancement of up to 96% when using the same batch of methanol.Linuron was used as a model compound to examine the change in the electrospray response, during gradient elution, when the proportion of an expired batch of methanol was varied. An infusion experiment showed that the linuron signal intensity decreased as the proportion of expired methanol increased in the mobile phase, which was in direct contrast to the increase in linuron signal observed with a non-expired batch of methanol. A series of isocratic experiments also showed that the linuron signal decreased as the proportion of expired methanol increased in the mobile phase.The ion ratios of several of the compounds studied changed significantly when using the expired batch of LC-MS methanol. The change in the ion ratios accentuates the difficulty of identifying compounds from in-source spectral libraries.A protocol is recommended for assessing the quality of methanol for LC-MS applications.
Highlights
► Differences in LC-MS methanol quality change the electrospray signal response. ► Changes in electrospray response occur among different LC-MS methanol brands. ► Linuron signal decreases during gradient elution as expired methanol increases. ► Solvent quality affects the ion ratios of several compounds. ► A solvent testing regime required for all in-coming batches of LC-MS solvents.Selective Displacement Chromatography in Multimodal Cation Exchange Systems
04 November 2011, 21:01:35
Publication year: 2011
Source: Journal of Chromatography A, Available online 4 November 2011
Rahul D. Sheth, Christopher J. Morrison, Steven M. Cramer
A library of displacer analogues with varying degrees of electrostatic, hydrophobic and hydrogen bonding moieties was evaluated for their ability to enhance the selectivity of multimodal (MM) chromatography under high loading conditions. The library was screened for displacement of model proteins using a robotic liquid handling system and selective batch separations were achieved for proteins that were inseparable with linear gradient chromatography. Trends in protein displacement were identified and displacers with higher hydrophobicity and net charge exhibited improved protein displacements. Proteins that interacted with the resins primarily via electrostatic interactions were more readily displaced than those that possessed a significant hydrophobic contribution to their binding. In addition, multimodal displacers were found to be more selective than single mode electrostatic displacers. Column chromatography studies were also carried out and baseline separations were achieved for model protein pairs using selective displacement. Finally, operation of these columns in the desorption mode resulted in baseline separation of model proteins which were not separable by selective displacement chromatography. This study indicates that the inherent selectivity of MM resins can be augmented by the selectivity of the displacer under non-linear competitive binding conditions, creating new opportunities for protein separations not possible using traditional gradient operations.
Source: Journal of Chromatography A, Available online 4 November 2011
Rahul D. Sheth, Christopher J. Morrison, Steven M. Cramer
A library of displacer analogues with varying degrees of electrostatic, hydrophobic and hydrogen bonding moieties was evaluated for their ability to enhance the selectivity of multimodal (MM) chromatography under high loading conditions. The library was screened for displacement of model proteins using a robotic liquid handling system and selective batch separations were achieved for proteins that were inseparable with linear gradient chromatography. Trends in protein displacement were identified and displacers with higher hydrophobicity and net charge exhibited improved protein displacements. Proteins that interacted with the resins primarily via electrostatic interactions were more readily displaced than those that possessed a significant hydrophobic contribution to their binding. In addition, multimodal displacers were found to be more selective than single mode electrostatic displacers. Column chromatography studies were also carried out and baseline separations were achieved for model protein pairs using selective displacement. Finally, operation of these columns in the desorption mode resulted in baseline separation of model proteins which were not separable by selective displacement chromatography. This study indicates that the inherent selectivity of MM resins can be augmented by the selectivity of the displacer under non-linear competitive binding conditions, creating new opportunities for protein separations not possible using traditional gradient operations.
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