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Quantitative Raman in liquids The Raman One is a fast (//4) single-stage dispersive Raman imaging spectrograph with a thermoelectrically cooled 16-bit 2D CCD array detector. It operates in the near-IR region of the spectrum and allows quantitative determinations to be made in liquids. Inconsistencies in optical alignment have made it difficult to acquire quantitative information in liquid samples using conventional (nonFT) Raman instruments. This system uses a near-IR diode laser integrated into the sample compartment and a fiber-optic sampling probe to eliminate the need for precise optical alignment during spectral acquisition from samples. The fiber-optic probe acquires emitted light in bulk, in a wide cone with a base of 5-7 mm, so that small inhomogeneities in a liquid sample are compensated for and measurements are more reproducible. Applications include process monitoring with remote sampling for free acid determinations in strong
INSTRUMENTATION DNA analysis Techne PHC-3 thermal cycler has been upgraded to include a heated lid to eliminate the need for mineral oil overlays during DNA amplification and sequencing reactions. Three versions accommodate 40 0.5-mL microcentrifuge tubes or 40 or 96 0.25-mL microreaction tubes. Separate heated lids are also available with a kit for retrofitting them onto existing models. Man-Tech • 401
GC GC Cryo-Trap is a cryocooling and heating trap designed for cryofocusing semivolatile and volatile compounds at the head of gas chromatograph capillary col64 A
When current is applied, the sample molecules in each unit migrate into a trap made of exclusion membranes. Peptide fragments above 3-5 kDa or nucleic acids that are 14-150,000 base pairs long can be isolated in nanogram-to-milligram amounts. Schleicher & Schuell • 404
mixed acids. Because the unit operates in the near-IR region of the spectrum, spectra can also be acquired through ordinary glass vials, cuvettes, or bottles. The diode laser operates at 785 nm for reduced scattering and S/N, comparable in some cases to FT-Raman systems that operate at > 1000 nm. The spectrograph contains a Rayleigh rejection filter, and the entrance slit and three userselectable gratings are controlled through an RS-232 interface with the user's 386 or higher version PC. The system requires a 33-MHz math coprocessor with 8 MB RAM, a 150-MB hard drive, Windows 3.1 software, and a mouse. Chromex • 402
umns or megabore guard columns. It can be used for applications such as thermal desorption, headspace analysis, and multidimensional GC system development. Volatiles can be trapped outside the gas chromatograph oven at temperatures down to -70 °C using liquid C02. The unit is equipped with brackets for mounting directly onto the outside of a HewlettPackard 5890 Series gas chromatograph. Scientific Instrument Services • 403 Electrophoresis Elutrap electroseparation system isolates and concentrates nucleic acids or proteins from gel slices or dilute solutions. The gel slice or sample is placed in a detachable unit that fits into one of the channels of an electrophoresis chamber.
Analytical Chemistry, Vol. 66, No. 1, January 1, 1994
HPLC Preparative process HPLC system Model LC 300.10001 contains a 300-mm-i.d. column with dynamic axial compression. The column is mounted upside down to permit full automation of unpacking and repacking operations and minimal contact with organic solvents. The maximum column bed length is 600 mm for a column volume of 38 L and an injection capacity of up to 500 g per injection (- 4 tons per year). The modular system can be adapted for user-specified pumping, detection, and automation systems as well as for the number of collection valves required, guard columns, and other features. Prochrom • 405
LITERATURE Mercury determination Technical note discusses the instrument detection limits of an automated mercury analyzer and describes the preparation and analysis of mercuric chloride standards for a five-point calibration curve. Detection limits of < 1 pptr can be achieved. Thermo Separation Products • 406 Chiral separations Brochure compares five classes of chiral stationary phases for HPLC of amino acid enantiomers. Topics include mechanisms of chiral recognition, indirect separation of chiral compounds, column selection, preparative-scale chiral columns, and the use of guard columns. An applications section presents sample chromatograms and technical data for 75 analytes, and a two-page cross-reference table for ana-
FESEM imaging at low voltage The S-4500 scanning electron microscope, which uses a cold field emission electron source, is designed for high-resolution imaging at low accelerating voltages. The image resolution of < 4.5 nm at 1 kV allows the microscope to be used for studies of beam-sensitive or nonconducting materials such as glasses, polymers, ceramics, electron beam resists, or thin films without the need to coat specimens. The microscope operates in the accelerating voltage range of 0.530 kV and magnifies objects in the range of 20-500,000 x. At 15 kV, resolution is < 1.5 nm. To enhance resolution at 1 kV, the microscope incorporates dual second-electron (SE) detectors. In addition to the standard SE detector placed in the specimen-scanning chamber, a second "upper" detector sits in the lens system. The ability to image at low voltage without coating specimens means that products such as semiconductors can be studied nondestructively and that coating artifacts can be eliminated. The objective aperture has four openings that can be selected and aligned outside the vacuum system. Scanning modes include normal, split/dual magnification, line, position set, spot, analysis area finder, selected area analysis, and oblique (y-modulation) scanning. Hitachi U 407
lytes, separation media, column types, and applications is included. 28 pp. Phenomenex • 408
water. The second note in the series describes the use of flow injection for rapid sample introduction in ICPMS. Perkin Elmer • 409
FIA with ICPMS "Flow Injection Atomic Spectrometry (FIAS) Application Reports" is a series of application notes describing the use of flow injection with ICPMS. The first note describes optimization and use of the technique. It demonstrates an application of FIA/ICPMS with hydride and cold vapor generation for the determination of heavy metals in drinking, river, and sea
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Real-time DNA sequencing of long strands Model 4000L automated DNA sequencer detects and identifies 800 or more bases in a single electrophoretic gel separation of a DNA digest An IR fluorophore dye is used for cycle-sequencing protocols or Sanger dideoxy protocols to prepare the samples, which are loaded onto the system's gel apparatus. The 4000L is an upgrade of Model 4000, which was offered for sale at the beginning of 1992. The 4000L accommodates 66-cmlong gels in addition to the 33-cm gels used with the Model 4000 for a typical single-base resolution accuracy of 99% at the 800th base using single-strand DNA During the run, a solid-state laser diode excites the dye at 785 nm. Individual bands are detected by a fluorescence microscope with a silicon avalanche photodiode filtered at 820 nm. The microscope, which is integrated with the laser and positioned at the bottom center of the gel, scans at 1.4-17.9 cm/s and can be focused automatically through the system's dedicated sequencing and control software. The first bands reach the bottom of the gel within 1 h, and a typical run lasts 20 h for a sample with 800
or more bases. Because the system records the bands as they run off the gel, the gel doesn't need to be stained, photographed, or handled for preservation. However, it cannot be used as a permanent record as conventional DNA gels can. The software displays a densitometric image of the gel as the bands run down to the bottom. It assigns band positions, makes base identifications, and flags ambiguous bands with an IUPAC code to enable rapid file searching. The assigned DNA sequence is displayed alongside the gel image. The software also allows automatic, semiautomatic, and manual base assignment as well as image manipulations such as scaling, colorization, background subtraction, and band normalization or "smile" correction. Data can be stored in TIFF files and a variety of other image formats, and sequences can be stored in ASCII files for exporting to publishing software. Li-Cor 1 4 1 0
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