Here is a list of my publications. It's not much, I was busy building things :-).
Abstract:In this paper, the design and performance characteristics of a pulsed tunable dye laser system for the simultaneous generation of two UV wavelengths are presented. The system is composed of an oscillator and an amplifier stage, pumped by the second harmonic of a commercial Nd:YAG laser. Dual-wavelength operation is achieved with one additional tuning mirror introduced to the prism expanded grazing incidence oscillator. The two obtained wavelengths are independently tunable, their separation is only limited bye the gain profile of the dye. Both wavelengths are frequency doubled by Second Harmonic Generation (SHG) in two KDP or BBO crystals. Performance characteristics such as bandwidths, efficiency, tuning range and wavelength separation are reported. As application two such systems are used for the simultaneous detection of the four elements cadmium, nickel, manganese and lead by Laser-Excited Atomic Fluorescence Spectrometry in a graphite furnace (ETA-LEAFS).
Abstract:A spectrometer for time-resolved high-resolution spectroscopic measuremenst of line splittings in inverse Zeeman corrected atomic absorption spectrometry is presented. The system consists of a continuum source, a longitudinal Zeeman-THGA module, a high-resolution double echelle monochromator, and a linear CCD array. Splitting patterns of atomic lines in a magnetic field have been determined and are compared with theory. The continuum source atomic absorption spectrometer can be used for the investigation of spectral interferences in Zeeman corrected AA Spectrometry. As an example, the background overcompensation at the cadmium 228.8 nm line in the presence of a Mg(NO3)2 + NH4H2PO4 mixture is examined.
Summary:Effective correction for non-specific spectral absorption, ie. absorption not
caused by analyte atoms, in Atomic Absorption Spectrometry (AAS) is necessary for the accuracy of
the concentrations determined using this method. Conventional methods are not generally capable of
providing sufficient information about the spectral surroundings of the wavelength used for analysis
and thereby of detecting interferences and effectively correcting for them. Continuum Source Atomic
Absorption Spectrometry (CSAAS), on the other hand, used in conjunction with high resolution
spectrometers and semi-conductor detectors, can provide high resolution spectral and temporal
information concerning the analyte absorption line and its spectral neighbourhood. Two high
resolution continuum source atomic absorption spectrometers, each consisting of a xenon short arc
lamp as continuum light source for the spectral range from 190 to about 900 nm, a transverse-heated
graphite tube furnace as atomizer, an echelle monochromator and a linear CCD detector for signal
input, are here presented. These systems, differing mainly in the degree of resolution of the
spectrometers, were used in various investigations described below.
In one of the continuum source spectrometers an Echelle monochromator with active wavelength
stabilizer and with a resolution (lambda/deltalambda) of about 110,000 was used. Parameters such as
characteristic mass (m0) and detection limits, which define the efficiency of the CSAAS
technique, were determined for various elements using this spectrometer. In addition the effect of
broad band and structured background in CSAAS was investigated. A new and effective method of
separating background from analyte absorption is presented.
The second spectrometer, equipped with an echelle monochromator having a dispersion of about
lambda/1,260,000 per pixel, was used to investigate fundamental problems in AAS. By measuring the
line width of absorption lines with this instrument the specifications of a spectrometer to be used
for routine analysis could be outlined.
With a Zeeman correction system integrated into the graphite tube furnace it was possible to study
atomic and molecular absorption behaviour in the magnetic field and thus to determine the causes of
the erroneous correction measurements which have been obtained using Zeeman AAS.
Abstract:A single element continuum source-atomic absorption spectrometer (CS-AAS) using a two-dimensional charge coupled array detector (2D-CCD) was assembled for use with graphite furnace atomization. The two-dimensional CCD was a split-frame transfer array, was thinned and back-illuminated for high quantum efficiency at approximately 200 nm, and was capable of an 80-Hz frame rate with a read noise of <15 electrons. The transfer of charges from the integrating arrays to the storage arrays took 0.65 ms, less than 4% of the frame period (16.42 ms). The transfer of charges to the storage array was perpendicular to the wavelength axis, eliminating source flicker noise, and was implemented without masking, producing vertical smearing. The smearing was manifested as a continuum background and was corrected using pixels between orders. The two-dimensional array, in conjunction with the high-resolution echelle spectrometer, allowed measurement of absorbance with respect to wavelength and height in the furnace. Computed absorbances were corrected for stray radiation and non-specific background absorption. Detection limits were equal to those for line source AAS, with the exception of As (193.7 nm) and Se (196.0 nm).
Abstract:The vertical spatial distribution of Sn in the graphite furnace was determined in the presence of 0.5% HCl (standards) and 10 µg of KCl, K2SO4, and NiSO4, with and without 5 µg of Pd, using a spectrometer capable of measuring spatially resolved absorbance. A normal gradient (decreasing concentration with increasing height in the furnace) was observed for Sn in HCl and KCl. This gradient was dramatically reversed in the presence of K2SO4(at all pyrolysis temperatures) and NiSO4 (at pyrolysis temperatures below 900 °C) and was accompanied by poor analytical recoveries. Accurate analytical recoveries and a normal gradient were obtained for NiSO4 when a pyrolysis temperature of 900 °C was used. Pd yielded normal gradients statistically different (steeper) than those obtained with Sn Standards in HCl. The gradient for Sn in the presence of Pd was not affected by 10 µg of KCl, K2SO4, and NiSO4. Accurate analytical recoveries were obtained for Sn in Pd in all the matrices tested in this study and at all pyrolysis temperatures. The change in the Sn gradient induced by KCl, K2SO4, and NiSO4 resulted in photometric errors that are problematic for conventional, line-source AAS. Selection of the height of the viewing region within the furnace can exacerbate or improve the analytical recoveries. The constant Sn gradient established by Pd removed photometric error as an error source in the determination of Sn.
Abstract:A continuum source atomic absorption spectrometry (CS-AAS) instrument consisting of a high-resolution echelle spectrometer and a two dimensional charge coupled device (2D-CCD) with a high frame rate was used to measure intensities as a function of height and time in the graphite furnace. The image of the furnace was reduced to a height less than that of the entrance slit to allow the full vertical profile of the furnace to be viewed. Spatially resolved absorbance, ASR, was computed as the average of the computed absorbances for each of the vertical elements, or pixels. Spatially integrated absorbance, ASI, was computed by summing the intensities for each of the vertical pixels and computing a single absorbance. ASR and ASI were computed for three viewing regions: the full image of the furnace (a 6 mm region), the image of the region above the platform (a 4 mm region) and a 2 mm region anywhere within the furnace, which corresponds to a sub-sample of the furnace image with a 2 mm slit height. Photometric errors induced by analyte non-homogeneity were greatest for platform atomization when the full furnace image was viewed and for either platform or wall atomization when a 2 mm sub-section of the furnace was viewed. These photometric errors had the potential for producing analytical errors only when a 2 mm sub-section was viewed. Analytical errors introduced by photometric errors for just four elements in a single standard reference material, Citrus Leaves, ranged from +5% to -15%. These results suggest that photometric error is problematic for conventional line source AAS.