Sri Lankan Journal of Physics, Volume 4, March 2003.

Adaptation of a technique to estimate rainfall from satellite data in Bangladesh
Md. Nazrul Islam*, C.M. Mukammel Wahid
Department of Physics, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh

In order to estimate rainfall from satellite data GMS (Geo-stationary Meteorological Satellite) Precipitation Index (GPI) was calculated for northeastern part (Sylhet) of Bangladesh. GPI was calibrated with ground-based raingauge rainfall. As was found, GPI underestimated i.e., raingauge rainfall overestimated for a few stations. Then GPI was adapted as Adjusted GMS Precipitation Index (AGPI). Satisfactory results were found using AGPI in estimating rainfall from satellite data. As expected, the raingauge rainfall was found about 68% of AGPI.

Sri Lankan Journal of Physics, Volume 4, March 2003.

Application of mass spectrometry to characterize the components present in a curcumin Sample
R.V. Coorey^a,* , and P. Håkansson^b
aDepartment of Physics, University of Colombo, Colombo-03, Sri Lanka ^bDivision of Radiation Sciences, Department of Ion Physics, Uppsala University, Sweden

The identification of the components present in crude samples purely by mass spectrometric techniques has been a long-standing problem. Conventionally, components present in a crude sample are isolated and purified by chromatographic methods and then various spectrometric techniques (including mass spectrometric techniques) are adopted for their structure elucidation and physical characterization. This paper gives an example illustrating the characterization of the components present in a crude sample purely by mass spectrometric techniques.

A commercially obtained curcumin sample (Assay: 65-70%) was chosen for this purpose. The mass analysis of this sample using time-of-flight reflectron mass spectrometric techniques namely plasma desorption (PD), laser desorption (LD) and electrospray ionization (ESI) gave evidence for the presence of curcuminoids other than curcumin in the sample. The electrospray Fourier transform ionization cyclotron resonance mass spectrometry combined with tandem mass spectrometry (MS/MS) has been adopted successfully to confirm the presence of all curcuminoids in the curcumin sample.

*Corresponding Author, E-mail: ramal@phys.cmb.ac.lk

Sri Lankan Journal of Physics, Volume 4, March 2003.

Relativistic calculations of secondary ions produced in plasma desorption mass spectrometry
R.M. Yoosoofmiya *, K.A.I.L.W. Gamalath
Department of Physics, University of Colombo

In Time of Flight (TOF) mass spectrometry, the ratio; mass/charge of ions of the sample under investigation is determined by a relationship between time of flight and spectrometer parameters. Usually this relationship is derived using classical (Newtonian) mechanics. Since high energies are involved in the flight of the particles a relativistic treatment is considered. It is investigated whether the relativistic effects are significant or not, for the motion of secondary ions produced in the Plasma Desorption Mass Spectrometer. Treating the motion of these ions relativistically, a relationship between the Time of Flight (TOF) and mass/charge of the ion was derived. Using advanced mathematical software package Maple 6, the derived relationship was compared with classically obtained results. Then it was found that relativistic effects are not significant and they can be ignored for the linear Plasma Desorption Mass Spectrometer.

*Corresponding Author, E-mail: imali@phys.cmb.ac.lk

Sri Lankan Journal of Physics, Volume 4, March 2003.

Electric field penetration effects in time-of-flight measurements
U.K. Abeywarna^{a, *}, T.R. Ariyaratne^b
aDepartment of Physics, University of Kelaniya, Kelaniya, Sri Lanka ^bDepartment of Physics, University of Colombo, Colombo, Sri Lanka

The field imperfections in the mass spectrometers were studied by means of two Plasma desorption time-of-flight mass spectrometers. The experiment was performed by investigating the influence of the field leakage due to the post acceleration on the measured values of the initial axial energy of secondary ions, in the presence of the grounded grids, which are usually employed to separate the fields inside the mass spectrometers. It has been found that the changes of 0.4% in the effective lengths of the acceleration gap and the field free region respectively are possible due to the field penetration into those regions from the post acceleration gap of the mass spectrometer. The analyses also show clearly the significance of the influence of the field penetration of the post acceleration on the measured values of the initial axial energy. The initial axial energies of H⁺, H₂⁺, ⁶Li⁺, ⁷Li⁺, Na⁺ and Cs⁺ measured under the minimum field penetration condition were found to be 4.7 eV, 4.7 eV, 0.6 eV, 0.7 eV, 0.7 eV and 1.3 eV respectively, and they had been reduced to 4.4 eV, 4.4 eV, 0.3 eV, 0.4 eV, 0.4 eV and 1.0 eV once the values were corrected separately for field penetration. These results indicate that the field penetration through a grid is a secondary effect and it is hardly unavoidable in the mass spectrometers.

*Corresponding Author, E-mail: kanthi@kln.ac.lk

Institute of Physics, Sri Lanka