Hans Peter Henrik Grieneisen

Performance of an ultraviolet light‐emitting diode‐induced fluorescence detector in capillary electrophoresis

The performance of a fluorescence detector in capillary electrophoresis (CE) using a light‐emitting diode (LED) as excitation source is reported. An ultraviolet LED pulsed at a repetition rate of 500 Hz, combined with a time‐discrimination and averaging acquisition system, was used. Limits of detection of 3 and 18 fmoles (at a signal‐to‐noise ratio equal to 3) were achieved for fluorescamine‐derivatized bradykinin and lysine, respectively. This system exhibited a linear response for a concentration range between 54 and 417 νM for derivatized lysine, and between 1.81 and 23.58 νM for derivatized bradykinin. This detection system showed to be very convenient for routine analytical applications.

Direct modeling of external quantum efficiency of silicon trap detectors

It is shown the feasibility of direct fitting of external quantum efficiency for silicon trap detectors which are applied as radiometric transfer standards at several National Institutes of Metrology. The model considers the internal quantum efficiency and the reflectance of the detector, whose parameters are fitted in the measured data of external quantum efficiency. The advantage of the suggested approach is the possibility of pursuing interpolation of spectral responsivity without loss of physical meaning of the fitted parameters.

Development of a LED based standard for luminous flux

Incandescent lamps, simple artifacts with radiation spectrum very similar to a black-body emitter, are traditional standards in photometry. Nowadays leds are broadly used in lighting, with great variety of spectra, and it is convenient to use standards for photometry with spectral distribution similar to that of the measured artifact. Research and development of such standards occur in several National Metrology Institutes. In Brazil, Inmetro is working on a practical solution for providing a led based standard to be used for luminous flux measurements in the field of general lighting. This paper shows the measurements made for the developing of a prototype, that in sequence will be characterized in photometric quantities.

Modernization of Koesters interferometer and high accuracy calibration gauge blocks

The Optical Metrology Division (Diopt) of Inmetro is responsible for maintaining the national reference of the length unit according to International System of Units (SI) definitions. The length unit is realized by interferometric techniques and is disseminated to the dimensional community through calibrations of gauge blocks. Calibration of large gauge blocks from 100 mm to 1000 mm has been performed by Diopt with a Koesters interferometer with reference to spectral lines of a krypton discharge lamp. Replacement of this lamp by frequency stabilized lasers, traceable now to the time and frequency scale, is described and the first results are reported.