Monitoring trace anion contamination in disk drive components

Ion chromatography was used to determine trace anionic contamination on the surface of hard disk drive components. These contaminants can have a detrimental effect on device reliability and yield. Disk drive components were soaked in deionized water and these extracts were analyzed for anions. The anions fluoride, acetate, formate, acrylate, methacrylate, chloride, nitrite, bromide, nitrate, benzoate, sulfate, oxalate, phthalate and phosphate were separated on a high-performance anion-exchange column and determined at concentrations less than 1 microg/l with suppressed conductivity detection. The extract solutions were analyzed either by injecting 1 ml or by preconcentrating 5 ml. We evaluated the performance of both methods.     

Pulsed 95 GHz high-field EPR heterodyne spectrometer with high spectral and time resolution

Various time resolved EPR methods are applied to different test samples to demonstrate the abilities of pulsed high-field EPR spectroscopy. Two-pulse-echo field swept EPR spectroscopy on a nitroxide radical shows the increased spectral resolution by separating different spin systems by their relaxation properties. Additionally N¹⁴ electron-spin-echo-envelope-modulation (ESEEM) is observed for these systems at fields as high as 3.5 T. Thus, the N¹⁴ hyperfine interaction couplings can be probed by ESEEM and pulsed ENDOR (electron-nuclear-double-resonance) experiments. The sensitivity of pulsed ENDOR experiments is compared with cw-ENDOR. The different linewidths and amplitudes of the two methods are discussed. Transient nutation experiments on light induced triplet states demonstrate the high sensitivity and time resolution of high-field pulsed EPR. The sensitivity and time resolution of our 95 GHz spectrometer are determined and compared with pulsed X-band EPR spectrometer performances.     

Cardiac glycosides: 3. synthesis of β-D-digitoxose analogues

Earlier studies have shown that the β-D-digitoxose (2,6-dideoxy-β-D-mannopyranose) directly attached to the cardiac glycoside steroid C3 has the greatest effect on biological activity. This report describes the synthesis of eight digitoxosides (2a-9a), with widely varying cyclic and acyclic C17β-side groups, and the corresponding C3',C4'-acetonides (2b-9b). NMR analysis of conformational strain introduced by the acetonide groups is supported by crystallographic analysis of the sugars' torsion angles.     

Determination of biogenic amines in alcoholic beverages by ion chromatography with suppressed conductivity detection and integrated pulsed amperometric detection

The determination of biogenic amines in alcoholic beverages is important to assess the potential risks associated with the consumption of high concentrations of these compounds. In addition, product storage conditions and the length of storage can cause the formation of biogenic amines that reduce product quality. We report a new method using cation-exchange chromatography with either suppressed conductivity, integrated pulsed amperometry, UV, or a combination of these detection techniques to determine biogenic amines in alcoholic beverages. The main objective was to provide a direct comparison between IPAD and suppressed conductivity detection for determining biogenic amines in alcoholic beverages. Suppressed conductivity is the simplest detection approach for determining putrescine, cadaverine, histamine, agmatine, phenylethylamine, spermidine, and spermine with good sensitivity (0.004-0.08 mg/l) and was used to evaluate the influence of storage time and conditions on the evolution of biogenic amines in alcoholic beverages. Integrated pulsed amperometric detection (IPAD) detects more biogenic amines than suppressed conductivity detection, enabling the detection of dopamine, tyramine, and serotonin. Tyramine was simultaneously determined by UV detection and IPAD to provide confirmation and ensure the accuracy of the analytical results. The linearity of biogenic amine responses was within 0.1-20 mg/l and peak area precisions were 0.24-4.97% for IPAD, suppressed conductivity-IPAD, and UV detection. The sensitivity for the 10 biogenic amines using the 3 detection techniques varied considerably from 0.004-1.1 mg/l and recoveries were within 85-122%.     

Negative and positive magnetoresistance manipulation in an electrodeposited nanometer Ni contact

We show that, in a nanometric size stable electrodeposited Ni contact, it is possible to modify the magnetoresistance by applying current pulses and external magnetic fields whereby the same current path is used for detection and modification. We can pass from positive to negative magnetoresistance with values as large as 25% at room temperature, all in the same contact. We propose that the effect may be due to switching and moving domain walls in the contact region under the combination of current effects and external fields.