Volume 73, Issue 10

Miniaturization and chip technology play an important role for analytical chemistry instrumentation in the future. A brief theory of the relevant microfluidics with reasons for miniaturization is given.

Metabolome analysis is a systematic chemical analysis of metabolites, which may be used to investigate the metabolic activity in the cell. Capillary electrophoresis (CE) is one of the most promising techniques for the metabolome analysis, because it gives high-resolution separations in a reasonable time and requires a minimum amount of samples. General characteristics of CE are discussed from the viewpoint of metabolome analysis. Micellar electrokinetic chromatography (MEKC), a separation mode of CE, enables the separation of neutral analytes by using micelles as pseudostationary phases. MEKC is also powerful for the separation of ionic analytes to improve selectivity. To solve relatively poor concentration sensitivity with UV absorbance detection, on-line sample preconcentration techniques were developed resulting in up to few thousand-fold increases in sensitivity. Laser-induced fluorescence detection is another solution to increase concentration sensitivity, but most analytes are not natively fluorescent. Therefore, several derivatization reactions were performed to selectively detect a class of analytes with high sensitivity. Some preliminary results are shown with formic acid extracts of Bacillus subtilis.

Electrochemical labeling of double-stranded (ds) DNA is achieved by redox-active DNA intercalators. Threading intercalators derived from naphthalenediimide appended with ferrocene reporter group in the side arms are particularly useful for this purpose. This allows a sensitive electrochemical detection of DNA hybridization on an array, providing a great potential for low-cost, high-throughput, and quick DNA screening technique in post-genome study.

Plasma-source mass spectrometry, usually in the form of inductively coupled plasma mass spectrometry (ICP-MS), has matured into a widely accepted method for ultra-trace multielemental analysis. However, the method exhibits shortcomings. For example, it does not provide adequate precision for isotope ratio measurements if many isotopes are to be determined. Moreover, isobaric overlaps (spectral interferences) can be very troublesome in some situations. Similarly, matrix interferences can adversely affect many determinations. Yet, it is in the area of high-speed transient measurements that ICP-MS perhaps suffers its greatest weakness. When sampling devices such as flow injection, laser ablation, electrothermal vaporization, or chromatography are employed, the user must choose between broad elemental or isotopic coverage and signal-to-noise ratio (S/N). In turn, compromised S/N means lower precision or poorer detection limits. Here, new instrumentation aimed at overcoming these limitations will be described. One system, based on a time-of-flight mass spectrometer, provides excellent detection limits, resolving power better than commercial quadrupole mass filters, precision of at least 0.02% rsd in a ratioing mode, and extraordinarily high speed for use with transient sampling devices. The second instrument is based on a sector-field mass spectrometer but, unlike other such units, is equipped with a focal-plane array detector. So equipped, the system can detect a broad mass range at once.

Over the last decade, infrared-visible sum-frequency generation has been developed into a powerful vibrational spectroscopic technique, especially for surface studies. We give here a brief review of the technique and a few recent applications of the technique to liquid and polymer surfaces. We also describe how the technique has found unique applications in our studies of surface melting of ice, ferroelectric ice films, and molecular chirality in chiral liquids. Doubly resonant sum-frequency generation as surface-specific two-dimensional spectroscopy is discussed.

In recent years, luminescence imaging has been widely employed in neurochemical analysis. It has a number of advantages for the study of neuronal and other biological cells: (1) a particular molecular species or cellular constituent can be selectively visualized in the presence of a large excess of other species in a heterogeneous environment; (2) low concentration detection limits can be achieved because of the inherent sensitivity associated with fluorescence and chemiluminescence; (3) low excitation intensities can be used so that long-term observation can be realized while the viability of the specimen is preserved; and (4) excellent spatial resolution can be obtained with the light microscope so subcellular compartments can be identified. With good sensitivity, temporal and spatial resolution, the flux of ions and molecules and the distribution and dynamics of intracellular species can be measured in real time with specific luminescence probes, substrates, or with native fluorescence. A noninvasive detection scheme based on glutamate dehydrogenase (GDH) enzymatic assay combined with microscopy was developed to measure the glutamate release in cultured cells from the central nervous system (CNS). The enzyme reaction is very specific and sensitive. The detection limit with CCD imaging is down to mM levels of glutamate with reasonable response time. We also found that chemiluminescence associated with the ATP-dependent reaction between luciferase and luciferin can be used to image ATP at levels down to 10 nM in the millisecond time scale. Similar imaging experiments should be feasible in a broad spectrum of biological systems.

Among the recent topics of photothermal (PT) applications of lasers, we focus on ultrafast (<=1.0 ns) photothermal/photoacoustic (PT/PA) phenomena occurring at interfaces, which play important roles in nanoscale materials science and technology. Here, we describe our recently developed novel PT techniques called transient reflecting grating (TRG) spectrometries. These techniques have been applied to the studies of solid surfaces, film substrates, and solid/liquid interfaces.

The main calorimetric principles used in isothermal microcalorimetry are briefly discussed. Different chemical calibration and test reactions are discussed, with a focus on reactions suitable for ambient conditions: reactions initiated by mixing of liquids (including titration microcalorimetry), dissolution of solid compounds and of slightly soluble gases, a photochemical process, and thermal power signals released over an extended period of time. Guidelines on the use of standardized chemical test and calibration reactions in isothermal microcalorimetry are presented. A standardized terminology in reporting characteristics of isothermal microcalorimeters is proposed.

Available experimental data on stability constants of proton and metal complexes for 10 phosphonic acids [methylphosphonic acid, 1-hydroxyethane-1,1-diylbisphosphonic acid, dichloromethylenebisphosphonic acid, amino-methanephosphonic acid, N -(phosphonomethyl)glycine, imino- N , N -bis(methylenephosphonic acid), N -methylamino- N , N -bis(methylenephosphonic acid), nitrilotris(methylenephosphonic acid), 1,2-diaminoethane- N , N , N´ , N´ -tetrakis-(methylenephosphonic acid), and diethylenetriamine- N , N , N´ , N´´ , N´´ -pentakis-(methylenephosphonic acid)], published in 1950­1997, have been critically evaluated. For the latter phosphonate, all the data are rejected, as well as protonation constants [HL]/[H][L] for three other ligands. Higher-quality data are selected and presented as "Recommended" and "Provisional".