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An inexpensive photoreactor using LED light sources and a fibre-optic CCD spectrophotometer as a detector was built by designing a special cell holder for standard 1.000 cm cuvettes. The use of this device was demonstrated by studying the aqueous photochemical reaction of 2,5-dichloro-1,4-benzoquinone. The developed method combines the highly quantitative data collection of CCD spectrophotometers with the possibility of illuminating the sample independently of the detecting light beam, which is a substantial improvement of the method using diode array spectrophotometers as photoreactors. [ABSTRACT FROM AUTHOR]

Abstract: The sensitivity of the normal picrate method for determination of total cyanide in cassava was increased tenfold using a small 1cm2 picrate paper, eluted using 0.5mL instead of 5mL of water as in the normal method. The absorbance was measured in a 2mm cuvette in the spectrophotometer. The sensitive method was calibrated against the normal picrate method. The total cyanide content in mg HCN equivalents/kg sample = ppm, is calculated from the absorbance (A) by the equation ppm = A×45.7 which is applicable from 0.1 to 50ppm. A new method to determine acetone cyanohydrin was developed based on irreversible denaturation of linamarase in 0.1M HCl at 30°C for 1h. Five gari samples from Mozambique gave a mean total cyanide content of 12ppm (range 6–15ppm) and mean acetone cyanohydrin content of 11ppm (range 5–14ppm). Acetone cyanohydrin liberates cyanide quantitatively in the human intestine. [Copyright &y& Elsevier]

A method is proposed for measuring the fluorescence quantum yield (QY) using a commercial spectrophotometer with a 150 mm integrating sphere (IS) detector. The IS detector is equipped with an internal cuvette holder so that absorbance measurements can be performed with the cuvette inside the IS. In addition, the spectrophotometer has a cuvette holder outside the IS for performing conventional absorbance measurements. It is shown that the fluorescence quantum yield can be obtained from a combination of absorbance measurements of the buffer and the analyte solution inside and outside the IS detector. Due to the simultaneous detection of incident and fluorescent photons, the absorbance measurements inside the IS need to be adjusted for the wavelength dependence of the photomultiplier detector and the wavelength dependence of the IS magnification factor. An estimate of the fluorescence emission spectrum is needed for proper application of the wavelength-dependent adjustments. Results are presented for fluorescein, quinine sulfate, myoglobin, rhodamine B and erythrosin B. The QY of fluorescein in 0.1 mol/L NaOH was determined as 0.90±0.02 where the uncertainty is equal to the standard deviation of three independent measurements. The method provides a convenient and rapid estimate of the fluorescence quantum yield. Refinements of the measurement model and the characteristics of the IS detector can in principle yield an accurate value of the absolute fluorescence quantum yield. [ABSTRACT FROM AUTHOR]

Background - On-line monitoring systems of spent dialysate, used to estimate dialysis dose, have been developed with different instrumentation during the last two decades. The routine use of an on-line monitoring system has been suggested to provide an adequate dialysis dose to the haemodialysis (HD) patient. The aim of this study was to show that monitoring the spent dialysate using UV-absorbance might bring new information about the clearance process. Methods - 108 HD treatments distributed among 16 clinical stable patients were monitored on-line using ultra violet (UV) absorbance. For the measurement of UV-absorbance a spectrophotometer was connected to the fluid outlet of the dialysis machine with all spent dialysate passing through a flow cuvette. The UV-absorbance curves were examined in combination with the recorded observations of events that occurred during the studied treatments. Results - The study demonstrates that UV-absorbance visualizes different kinds of events such as hypotension, conductivity alarms and restricted flow in artery needle blood pump stops that often occur during dialysis treatment. Conclusion - An on-line UV-monitoring system with a high sampling rate makes it possible to identify variations in dialysis clearance of different origin and gives feedback after performing interventions during a dialysis session. [ABSTRACT FROM AUTHOR]

This article presents information on a simple, inexpensive water-jacketed cuvette for the spectronic 20. Due to the instrument's reliability and low cost, the Spectronic 20 has become the standard in spectrophotometers for the undergraduate laboratory curriculum since it was first introduced nearly 50 years ago. It is well known that absorption of light by a sample placed in a spectrophotometer can raise the temperature of the solution in the cuvette and that an increase in temperature can alter equilibrium constants and reaction rate constants; the jacketed cuvette would provide a simple means to thermostat a sample for more accurate measurements.