Cyclic evolution of phytoplankton forced by changes in tropical seasonality.

Although the role of Earth's orbital variations in driving global climate cycles has long been recognized, their effect on evolution is hitherto unknown. The fossil remains of coccolithophores, a key calcifying phytoplankton group, enable a detailed assessment of the effect of cyclic orbital-scale climate changes on evolution because of their abundance in marine sediments and the preservation of their morphological adaptation to the changing environment1,2. Evolutionary genetic analyses have linked broad changes in Pleistocene fossil coccolith morphology to species radiation events3. Here, using high-resolution coccolith data, we show that during the last 2.8 million years the morphological evolution of coccolithophores was forced by Earth's orbital eccentricity with rhythms of around 100,000 years and 405,000 years-a distinct spectral signature to that of coeval global climate cycles4. Simulations with an Earth System Model5 coupled with an ocean biogeochemical model6 show a strong eccentricity modulation of the seasonal cycle, which we suggest directly affects the diversity of ecological niches that occur over the annual cycle in the tropical ocean. Reduced seasonality in surface ocean conditions favours species with mid-size coccoliths, increasing coccolith carbonate export and burial; whereas enhanced seasonality favours a larger range of coccolith sizes and reduced carbonate export. We posit that eccentricity pacing of phytoplankton evolution contributed to the strong 405,000-year cyclicity that is seen in global carbon cycle records.

Comparison between liquid chromatography-UV detection and liquid chromatography-mass spectrometry for the characterization of impurities and/or degradants present in trimethoprim tablets.

The characterization of impurities and/or degradants present in pharmaceutical compounds is an important part of the drug development process. Although LC-UV is commonly employed for impurities and degradant compound determination, LC-MS techniques are proposed in this work to be a viable modem alternative for the characterization of these compounds. LC-UV and LC-MS were compared for the detection of impurities present in different brands of trimethoprim tablets by using an in-line LC-UV-MS system with atmospheric pressure chemical ionization source (APCI) coupled with a reversed-phase gradient HPLC system. It was shown that, although chemical noise was higher when using full-scan LC-MS compared to LC-UV, low level impurities were better detected by mass spectrometry (MS) when modern software algorithms are employed. These included the "Contour" chromatogram algorithm and/or the "component detection algorithm" (CODA). In addition, MS allowed for the simultaneous determination of the molecular masses and some structural information of the impurities and/or degradants. The results also showed a large difference in the purity of trimethoprim among different manufacturers. LC-MS and tandem MS techniques were employed to acquire fragmentation patterns for trimethoprim and its degradants to gain insight into their structures.

High-throughput selected reaction monitoring liquid chromatography-mass spectrometry determination of methylphenidate and its major metabolite, ritalinic acid, in rat plasma employing monolithic columns.

This work presents a high-throughput selected reaction monitoring (SRM) LC-MS method for the determination of methylphenidate (MPH), a central nervous stimulant, and its de-esterified metabolite, ritalinic acid (RA) in rat plasma samples. A separation of these two compounds was achieved in 15 s by employing a 3.5-ml/min flow-rate, a porous monolithic column and a TurboIonSpray source compatible with relatively high flow-rates. In addition, a relatively fast autosampler and a new data acquisition system resulted in a time lag of less than 17 s between consecutive injections. Overall, 768 protein-precipitated rat plasma samples (eight 96-well plates) containing both MPH and RA were analyzed within 3 h and 45 min. The partial method validation described in this report included an assessment of linearity, intra and inter-assay precision and accuracy, and method robustness. Deuterated internal standards for the target compounds, d(3)-MPH and d(5)-RA, were employed. The calibration curves ranged from 0.1 to 50 ng/ml for MPH and from 0.5 to 50 ng/ml for RA. The limit of quantification (LOQ) for MPH and RA was 0.1 and 0.5 ng/ml, respectively. For both analytes, the intra- and inter-assay precision (relative standard deviation, % C.V.) and accuracy (relative error) did not exceed 15% for the quality control samples (QCs) QC1, QC2 or QC3 (0.3, 1.5 and 40 ng/ml for MPH and 0.15, 15 and 40 ng/ml for RA) for either analyte and did not exceed 20% at the lower limit of quantitation (LOQ) level. No carry-over from the autosampler was detected. The retention times remained constant throughout the experiment. Baseline resolution of MPH and RA was consistently observed throughout the plates analyzed. The described method demonstrates the feasibility for employing monolithic HPLC columns to effect rapid bioanalytical SRM LC-MS analysis of representative biological samples.

Optical measurements to determine the thickness of calcite crystals and the mass of thin carbonate particles such as coccoliths.

We describe a procedure for measuring the thickness and mass of calcite particles that works for most calcite particles <4.5-µm thick. The calcite particles are observed in cross-polarized light, which enables the light transmitted through the calcite particles to be correlated with their thickness. Three polarizing planes are used to minimize the darkening of crystals at some orientations (black cross). This allows direct measurement of the thickness without recourse to a transfer function. This procedure has been used recently to determine the degree of calcification of coccoliths, which provides an indicator of ocean acidification. It takes only a few minutes per sample, and it is an improvement over the former protocol, which did not allow measurement of the thickness and mass of particles thicker than 1.5 µm.