Detector coupling

A typical procedure for Na assay is One gram proplnt samples sealed in polyethylene vials are irradiated for at least seven hrs in the thermal column. In order to minimize any thermal neutron flux gradient, the samples are rotated uniaxially at 60 rpm. Following irradiation, the samples are allowed to decay for approx 15 hrs to permit all short-lived radioisotopes to decay to insignificance. The 1.369 MeV 7-photopeak of each sample is then counted for 10 min with a 7.6cm x 7.6cm Na iodide scintillation detector coupled to a 400-channel pulse-height analyzer... 

Ultraviolet spectroscopy is not as useful in detecting the -NC function. Despite its limitation, coeluting isothiocyano compounds are UV active ( 250 nm, e 1200) [27c]. Thus, a UV monitor can be interfaced with an LH-20 or silica column to detect column fractions containing -NCS compounds. Final resolution of enriched mixtures of previously fractionated isonitrile-related compounds is achieved by examining the responses generated by UV and RI detectors coupled in liquid chromatography. 

Working solutions (1 litre) which were 10 7 mol/1 in one of the elements to be studied were prepared by appropriate addition of the radioactive stock solutions to pH-adjusted artificial seawater. After the pH had been checked, 100 ml portions were transferred to the bottles to be tested. The filled bottles were shaken continuously and gently in an upright position, at room temperature and in the dark. At certain time intervals, ranging from 1 min to 28 d, 0.1 ml aliquots were taken. These aliquots were counted in a 3 x 3 in Nal (TI) well-type scintillation detector, coupled to a single-channel analyser with a window setting corresponding to the rays to be measured. 

Cerium was included in a list of 14 elements determined by Lee et al. [627] in seawater using neutron activation analysis. The metals were first precon-centraed on a mixture of Chelex 100 and glass powder. The elements were desorbed from the column by 4 M nitric acid, and aqueous solution was irradiated for 3 days and subjected to y-ray spectrometry method with a Ge(Ii) detector coupled to a 4000-channel analyser. Cerium was found to be present to the extent of 16.7 xg/l in water taken from the Kwangyang Bay (South Korea). 

A 3.5 ml portion in a 4 ml polyethylene vial was irradiated for 5 min. Another portion, 3.0 ml in a 3.5 ml silica vial, was irradiated for 3 d. After the short irradiation, 3 ml of the irradiated solution were transferred into an activity-free vial and submitted to y-ray spectrometry with a Ge(Ii) detector coupled to a 4000-channel analyser. After the long irradiation, the sample was allowed to cool for 3 d, then the surface of the silica ampoule was cleaned with dilute nitric acid and the sealed ampoule was placed in the counter (the background activity of the ampoule was negligible). Gamma-ray energy and the areas under peaks were calculated by computer. To determine the half-fives of the nuclides produced, the counting was repeated at appropriate intervals. 

Tseng et al. [69] determined 60cobalt in seawater by successive extractions with tris(pyrrolidine dithiocarbamate) bismuth (III) and ammonium pyrrolidine dithiocarbamate and back-extraction with bismuth (III). Filtered seawater adjusted to pH 1.0-1.5 was extracted with chloroform and 0.01 M tris(pyrrolidine dithiocarbamate) bismuth (III) to remove certain metallic contaminants. The aqueous residue was adjusted to pH 4.5 and re-extracted with chloroform and 2% ammonium pyrrolidine thiocarbamate, to remove cobalt. Back-extraction with bismuth (III) solution removed further trace elements. The organic phase was dried under infrared and counted in a ger-manium/lithium detector coupled to a 4096 channel pulse height analyser. Indicated recovery was 96%, and the analysis time excluding counting was 50-min per sample. 

Because a CCD is a two-dimensional array of pixels, it is possible to create a double-beam instrument with a single detector. Coupled in an optical design with an imaging grating, the output of two fibers may be imaged simulfaneously and separately onto the CCD and both spectra readout by the electronics. 

Godden and Stockwell [11] have described a specific fluorescence detection system to provide fully supported analytical systems for routine analysis of mercury at low levels. The fluorescence approach provides a wide linear dynamic range and extremely low detection limits. P.S. Analytical s Merlin Plus System provides a fuUy automated system which will produce results at a rate of around 40 per hour. This is due to the optimization of the optical design of the detector, coupled to the inherent features of the fluorescence technique. 

The structures of the substituents with one, two and three layers, (denoted as Gl, G2 and G3, respectively), as well as the MIM structures, were confirmed using ESI-MS. The molecular weights of the MIMs were also determined using laser light scattering (MALLS detector coupled with SEC). 

After centrifugation, samples from each phase were analyzed for W-178 and Ta-178 using a Ge (Li) detector coupled to a Nuclear Data ND60 Y-spectrophotometer. Tantalum-178 was quantitated using its 93 keV gamma-ray. After correction for physical decay, the values are calculated as the ratio of the concentrations... 

The application of high-sensitivity ICP-MS detectors coupled to HPLC has enabled the detection of trace arsenic compounds present in marine animals. Thus, arsenocholine has been reported as a trace constituent (<0.1% of the total arsenic) in fish, molluscs, and crustaceans (37) and was found to be present in appreciable quantities (up to 15%) in some tissues of a marine turtle (110). Earlier reports (46,47) of appreciable concentrations of arsenocholine in some marine animals appear to have been in error (32). Phosphatidylarsenocholine 45 was identified as a trace constituent of lobster digestive gland following hydrolysis of the lipids and detection of GPAC in the hydrolysate by HPLC/ICP-MS analysis (70). It might result from the substitution of choline with arsenocholine in enzyme systems for the biogenesis of phosphatidylcholine (111). 

A collimated beam of 7-rays (Fig 3), provided by a shielded 3.5-curie source of Cobdlt-60, is transmitted thru the rocket motor walls and is transformed into an electrical feedback signal by a 7-ray detector coupled to a linear rate meter. 

The optical source is a diode laser and fiber-emitter and fiber-detector coupling is accomplished using standard optical fiber connectors. The detector is a PIN photodiode connected to a transimpedance preamplifier and the signal is amplified and filtered using a lock-in amplifier that also tunes the modulation frequency of the laser source. The analytical signal is collected and treated by a PC. 

Highly sensitive detectors, coupled with the facility to store each absorption signal digitally for each separate analysis time in a microcomputer, have enabled absorbance changes as small as 0.001 to be accurately measured. 

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