Use of a fluorosurfactant in micellar electrokinetic capillary chromatography

Beads prepared from a thermosensitive polymer, hydroxypropylcellulose, exhibit temperature-dependent porosity. At temperatures below 40°C the beads are swollen having large pores, while at temperatures above 45°C the beads are in a shrunken state having smaller pores. In the presence of 1 M NaCl the transition temperature decreased to about 30°C. In a swollen state the size of pore is large enough to accommodate lysozyme (mol. mass 14 400) and -chymotrypsin (mol. mass 21 600) but not bovine serum albumin (mol. mass 67 000). When the beads are shrunken, all the proteins are eluted from the column packed with hydroxypropylcellulose beads in the volume close to the void volume of the column.     

Heritability of Stroop and flanker performance in 12-year old children

Background  

There is great interest in appropriate phenotypes that serve as indicator of genetically transmitted frontal (dys)function, such as ADHD. Here we investigate the ability to deal with response conflict, and we ask to what extent performance variation on response interference tasks is caused by genetic variation. We tested a large sample of 12-year old monozygotic and dizygotic twins on two well-known and closely related response interference tasks; the color Stroop task and the Eriksen flanker task. Using structural equation modelling we assessed the heritability of several performance indices derived from those tasks.     

The contribution of high frequencies to human brain activity underlying horizontal localization of natural spatial sounds

Background  

In the field of auditory neuroscience, much research has focused on the neural processes underlying human sound localization. A recent magnetoencephalography (MEG) study investigated localization-related brain activity by measuring the N1m event-related response originating in the auditory cortex. It was found that the dynamic range of the right-hemispheric N1m response, defined as the mean difference in response magnitude between contralateral and ipsilateral stimulation, reflects cortical activity related to the discrimination of horizontal sound direction. Interestingly, the results also suggested that the presence of realistic spectral information within horizontally located spatial sounds resulted in a larger right-hemispheric N1m dynamic range. Spectral cues being predominant at high frequencies, the present study further investigated the issue by removing frequencies from the spatial stimuli with low-pass filtering. This resulted in a stepwise elimination of direction-specific spectral information. Interaural time and level differences were kept constant. The original, unfiltered stimuli were broadband noise signals presented from five frontal horizontal directions and binaurally recorded for eight human subjects with miniature microphones placed in each subject's ear canals. Stimuli were presented to the subjects during MEG registration and in a behavioral listening experiment.     

Isotachophoresis of allergenic extracts

One aspect of the isotachophoretic determination of protein patterns in biological samples of interest is the characterization of allergens. This group of (glyco) proteins, causing allergic reactions, is used both for diagnosis and in the treatment of allergy. The aim of this investigation was to obtain a maximum amount of information, within one run, on the (glyco)protein composition of a number of allergenic extracts (e.g., from pollen or house dust mites). Commercially available extracts were dialysed prior to analysis to remove disturbing buffer constituents. A high-pH system was chosen in order to obtain a maximum amount of information from the samples (1-2 microliter). The leading electrolyte was 0.01 M C1-, buffered with Tris (pH 8.2), containing 0.2% w/v hydroxyethylcellulose, and the terminating electrolyte was beta-alanine, buffered to pH 10 with Ba(OH)2. The total analysis time was 15-20 min using a PTFE capillary (0.2 mm I.D.). The pre-separation current was 30 microA and the current during detection was 15 microA. UV absorption was measured at 280 nm. For optimal discrimination of the compounds of interest, an ampholyte mixture was used for spacing. The analytical procedure yielded highly reproducible UV patterns. Significant differences between various allergenic extracts were observed. It was concluded that isotachophoresis is a powerful method for the physico-chemical characterization of individual allergenic extracts, e.g., with respect to manufacturing and quality control.     

Determination of heavy metals by isotachophoresis

The suitability of isotachophoresis for the analysis of metals in, e.g., environmental samples was studied. In a cationic operational system the heavy metals Fe, Cu, Ni, Cd, Co, Zn, Pb and Mn were simultaneously determined. The separation was achieved through complex formation with one of the counter ions, hydroxyisobutyric acid. The other counter ion was acetic acid, the leading ion was 0.02 M potassium or sodium (pH 4.1) and the terminator was H+. The analysis time was 15 min at 60 microA in a 0.2 mm I.D. capillary. Aqueous samples containing ppm and ppb amounts were enriched on a cation exchanger with an extremely low affinity for sodium (Chelex 100). Good recovery, linearity, precision and accuracy were obtained even down to the ppb range. Although the sensitivity of the method is not greater than that of some of the more established methods for the individual metals, a great advantage of isotachophoresis is the simultaneous determination of the metals, with equal response factors. An example is given of the determination of metals, including aluminium, in serum.