Characterization of a high throughput approach for large scale retention measurement in liquid chromatography.

Many contemporary challenges in liquid chromatography-such as the need for "smarter" method development tools, and deeper understanding of chromatographic phenomena-could be addressed more efficiently and effectively with larger volumes of experimental retention data than are available. The paucity of publicly accessible, high-quality measurements needed for the development of retention models and simulation tools has largely been due to the high cost in time and resources associated with traditional retention measurement approaches. Recently we described an approach to improve the throughput of such measurements by using very short columns (typically 5 mm), while maintaining measurement accuracy. In this paper we present a perspective on the characteristics of a dataset containing about 13,000 retention measurements obtained using this approach, and describe a different sample introduction method that is better suited to this application than the approach we used in prior work. The dataset comprises results for 35 different small molecules, nine different stationary phases, and several mobile phase compositions for each analyte/phase combination. During the acquisition of these data, we have interspersed repeated measurements of a small number of compounds for quality control purposes. The data from these measurements not only enable detection of outliers but also assessment of the repeatability and reproducibility of retention measurements over time. For retention factors greater than 1, the mean relative standard deviation (RSD) of replicate (typically n=5) measurements is 0.4%, and the standard deviation of RSDs is 0.4%. Most differences between selectivity values measured six months apart for 15 non-ionogenic compounds were in the range of +/- 1%, indicating good reproducibility. A critically important observation from these analyses is that selectivity defined as retention of a given analyte relative to the retention of a reference compound (kx/kref) is a much more consistent measure of retention over a time span of months compared to the retention factor alone. While this work and dataset also highlight the importance of stationary phase stability over time for achieving reliable retention measurements, we are nevertheless optimistic that this approach will enable the compilation of large databases (>> 10,000 measurements) of retention values over long time periods (years), which can in turn be leveraged to address some of the most important contemporary challenges in liquid chromatography. All the data discussed in the manuscript are provided as Supplemental Information.

Quenching action of monofunctional sulfur mustard on chlorophyll fluorescence: towards an ultrasensitive biosensor.

An ultrasensitive fluorimetric biosensor for the detection of chemical warfare agent sulfur mustard (SM) was developed using its monofunctional analogue. SM is a vesicant and a potent chemical threat owing to its direct toxic effects on eyes, lungs, skin and DNA. This work investigates the quenching action of the analyte on chlorophyll fluorescence as elucidated by nuclear magnetic resonance, Fourier transform infrared spectroscopy and mass spectrometry studies suggesting the electrophilic attack of carbonium ion on nitrogens of the porphyrin moiety of chlorophyll. The properties of immobilisation matrix were optimised and scanning electron microscope observations confirmed improvement in pore size of sol-gels by addition of 32 % (v/v) glycerol, a feature enabling enhanced sensitivity towards the analyte. Chlorophyll embedded sol-gel was treated with increasing concentrations of monofunctional SM and the corresponding drop in maximum fluorescence intensity as measured by emission at 673 nm was observed, which varied linearly and had a detection limit of 7.68 × 10(-16) M. The biosensor was found to be 6 orders of magnitude more sensitive than the glass microfibre-based disc biosensor previously reported by us.

Abnormal corpus callosum myelination in pediatric bipolar patients.

BACKGROUND: Decreased signal intensity in the corpus callosum, reported in adult bipolar disorder patients, has been regarded as an indicator of abnormalities in myelination. Here we compared the callosal signal intensity of children and adolescents with bipolar disorder to that of matched healthy subjects, to investigate the hypothesis that callosal myelination is abnormal in pediatric bipolar patients. METHODS: Children and adolescents with DSM-IV bipolar disorder (n=16, mean age+/-S.D.=15.5+/-3.4 y) and matched healthy comparison subjects (n=21, mean age+/-S.D.=16.9+/-3.8 y) underwent a 1.5 T MRI brain scan. Corpus callosum signal intensity was measured using an Apple Power Mac G4 running NIH Image1.62 software. RESULTS: Bipolar children and adolescents had significantly lower corpus callosum signal intensity for all callosal sub-regions (genu, anterior body, posterior body, isthmus and splenium) compared to healthy subjects (ANCOVA, all p<0.05, age and gender as covariates). LIMITATIONS: Relatively small sample size. CONCLUSIONS: Abnormalities in corpus callosum, probably due to altered myelination during neurodevelopment, may play a role in the pathophysiology of bipolar disorder among children and adolescents.

Smaller cingulate volumes in unipolar depressed patients.

BACKGROUND: The anterior cingulate cortex is a key structure in brain networks involved in mood regulation. Abnormalities in this brain region are possibly implicated in the pathophysiology of depression. This anatomical magnetic resonance imaging (MRI) study compared cingulate cortex volumes in unipolar depressed patients and age- and gender-matched healthy control subjects. METHODS: Thirty-one unmedicated DSM-IV unipolar patients (24 female, aged 39.2 +/- 11.9 years [mean +/- SD]) and 31 healthy control subjects (24 female, aged 36.7 +/- 10.7 years) were studied in a 1.5-T GE Signa magnet (General Electric Medical Systems, Milwaukee, Wisconsin). Cingulate volumes were compared by analysis of covariance with intracranial volume as the covariate. RESULTS: The unipolar patients had significantly smaller anterior and posterior cingulate volumes bilaterally compared with healthy control subjects. When patients were divided into currently depressed (n = 21) and remitted (n = 10) subgroups, currently depressed patients had significantly smaller anterior and posterior cingulate volumes bilaterally compared with healthy control subjects, whereas remitted patients had significantly smaller left anterior cingulate volumes compared with healthy individuals. CONCLUSIONS: Gray matter abnormalities in the cingulate cortex are implicated in the pathophysiology of unipolar depression. Smaller cingulate volumes in currently depressed patients support the hypothesis that cingulate cortex abnormalities are state dependent, whereas changes in left anterior cingulate might be trait related.

Sources of declarative memory impairment in bipolar disorder: mnemonic processes and clinical features.

BACKGROUND: There is mounting evidence that declarative memory processes are impaired in patients with bipolar disorder. However, predictors of the observed impairment are not well understood. This study seeks to: (i) better characterize the nature of declarative memory impairment in bipolar disorder, and (ii) determine the relationship between clinical variables and memory function in bipolar disorder. METHODS: 49 adult patients with bipolar disorder in varying mood states and 38 demographically matched healthy participants completed a comprehensive neurocognitive battery assessing general cognitive functioning, processing speed, and declarative memory. The California verbal learning test was used to characterize learning and memory functions. RESULTS: Although patients with bipolar disorder utilized a similar semantic clustering strategy to healthy controls, they recalled and recognized significantly fewer words than controls, suggesting impaired encoding of verbal information. In contrast, lack of rapid forgetting suggests relative absence of a storage deficit in bipolar patients. While severity of mood symptomatology and illness duration were not associated with task performance, gender and family history significantly affected memory function. CONCLUSIONS: Results suggest that declarative memory impairments in bipolar patients: (1) are consistent with deficits in learning, but do not appear to be related to different organizational strategies during learning, and (2) do not appear to be secondary to clinical state, but rather may be associated with the underlying pathophysiology of the illness.

Cingulate cortex anatomical abnormalities in children and adolescents with bipolar disorder.

OBJECTIVE: In vivo imaging studies have suggested anatomical and functional abnormalities in the anterior cingulate in adults with mood disorders. This anatomical magnetic resonance imaging study examined the cingulate cortex in children and adolescents with bipolar disorder and matched healthy comparison subjects. METHOD: Sixteen patients (mean age=15.5 years, SD=3.4) with DSM-IV bipolar disorder and 21 matched healthy comparison subjects (mean age=16.9 years, SD=3.8) were studied. Three-dimensional gradient echo imaging was performed (TR=25 msec, TE=5 msec, slice thickness=1.5 mm) in a 1.5-T GE Signa magnet. Cingulate volumes were compared by using analysis of covariance, with age and intracranial volume as covariates. RESULTS: The patients with bipolar disorder had significantly smaller mean volumes relative to the healthy subjects in the left anterior cingulate (mean=2.49 cm(3 [SD=0.28] versus 3.60 cm3 [SD=0.12], respectively), left posterior cingulate (2.53 cm3 [SD=0.32] versus 2.89 cm3 [SD=0.09]), and right posterior cingulate (2.19 cm3 [SD=0.13] versus 2.28 cm3 [SD=0.08]). No significant between-group difference was found for the right anterior cingulate (2.64 cm3 [SD=0.21] versus 2.71 cm3 [SD=0.10]). CONCLUSIONS: The findings indicate smaller cingulate volumes in children and adolescents with bipolar disorder, suggesting that such abnormalities may be present early in the illness course.

Attention deficits in bipolar disorder: a comparison based on the Continuous Performance Test.

Although attentional deficits measured by Continuous Performance Tests (CPTs) have been observed in patients with bipolar disorder, their relationship with clinical state is not well understood. The identical pairs Continuous Performance Test (CPT-IP) shows particular promise as a measure sensitive to trait abnormalities in attentional function. In this study, the CPT-IP was administered to 27 patients with bipolar disorder (22 type I, 5 type II) and 25 demographically matched healthy comparison subjects, in order to assess the presence and nature of attentional deficits as a function of mood symptoms. Results showed significantly impaired CPT performance in bipolar patients compared with healthy subjects. Patients made fewer hits (p < 0.01), were slower to respond (p < 0.007), and had poorer discrimination (p < 0.05) and bias (p < 0.006) than comparison subjects. Severity of mania and depression was not correlated with any of the CPT measures. Our findings suggest that attentional dysfunction may be a trait deficit associated with bipolar illness. However, within-subjects longitudinal studies examining fluctuations in performance over time are needed.