Multiple sample detectors

Tan [71] devised a rapid simple sample preparation technique for analysing polyaromatic hydrocarbons in sediments. Polyaromatic hydrocarbons are removed from the sediment by ultrasonic extraction and isolated by solvent partition and silica gel column chromatography. The sulphur removal step is combined into the ultrasonic extraction procedure. Identification of polyaromatic hydrocarbon is carried by gas chromatography alone and in conjunction with mass spectrometry. Quantitative determination is achieved by addition of known amounts of standard compounds using flame ionization and multiple ion detectors. 

Acquisition times commonly vary from seconds to minutes, often with negligible time between acquisitions, even when measuring multiple locations simultaneously (multiplexing). The dedication of different areas on the charge coupled device (CCD) detector to each measurement point makes this possible. The detectors used for MIR and NIR instruments cannot be multiplexed in the same fashion and must measure multiple samples sequentially. 

Zarowin (68) has made use of a multiple-sampling technique in the measurement of decay times. This method uses a periodically pulsed- or chopped-excitation source and a continuously operating photomultiplier detector. The fluorescent signal is displayed on an oscilloscope. The response of the photomultiplier tube must be fast enough to resolve individual photoelectron pulses, and the time density of pulses is then proportional to the light intensity. 

An automated solvent controller is available in the latest ASE system. It allows up to four solvents to be mixed and delivered to the extraction cells. This can reduce the time for measuring and mixing solvents and decrease users exposure to toxic solvents. The solvent controller can be programmed to change solvents between sequential extractions of multiple samples. The same sample can also be reextracted using different solvents. The ASE system has many built-in safety features, which include vapor sensors, liquid-leak detectors, vial overfill monitors, electronic and mechanical overpressurization prevention systems, solvent flow monitors, and pneumatic source pressure monitors. 

Gas chromatography-low resolution mass spectrometry was used to determine if TCDD is in the samples (12). The GC column used was a 6 ft. x 2 mm i.d. glass 2.5% BMBT liquid crystal on 100/120 mesh Chromosorb WHP (Altech Assoc.) at 225°C. In Figure 3 is shown the output from a standard and typical human milk extract run on an LKB-9000 with a SI-150 (System Industries) data system equipped with a computer controlled multiple ion detector (Ledland, Inc.). The entire extract was... 

By tuning these instruments to a single IR wavelength, one compound can be monitored for continuously at multiple sample locations. This mode of operation is similar to the single-head IR detector described in Section 6.2.1.2. 

The analysis scheme implemented at the Cos Cob site used three sets of tools hand-held test kits, an on-site mobile laboratory equipped with gas chromatograph/ electron capture detector (GC/ECD) and X-ray fluorescence (XRF), and an off-site laboratory with rapid turnaround capabilities (<48 h for virtually all analyses). By implementing all of these tools at the same time, the project eliminated the need for multiple sampling events and allowed the team to perform additional real-time sampling, enabling the team to delineate the extent of potential hot spots quickly. 

Cemi used spectral transmission and extinction using UV, visible and near IR to measure slurry particle size distributions with undiluted continuous flow [347]. The method uses multiple linear detector array spectrometers. It also uses multiple sample cells of different optical depths optimized for a specific spectral range, multiple optical paths and multiple linear detector arrays. 

Since electrons cannot pass without energy losses due to collisions through a few cm of gas at atmospheric pressure it is necessary to evacuate the electron path from the sample to the detector a rule of thumb says that the product of pressure times path length should not exceed 1 cm torr. Multiplicative electron detectors like channeltrons require vacua of 10 " to 10" torr or better, dependent on the type, but the study of solid surfaces requires much lower pressures, say 10" torr, in order to give the experimenter sufficient time to obtain spectra of the pure surface before it becomes contaminated by the gases in the sample compartment. 

De Graeve et al. described two methods for the papaverine determination in blood samples for pharmacokinetic studies, one utilizing a packed column with 0V-1 1 % and interfaced with a LKB 9000 S mass spectrometer equipped with a multiple ion detector for mass fragmentography,... 

Over the past decade, there has been considerable development in imaging type detectors for the measurement of ultraviolet (UV) and visible light. These new detectors have attracted the interest of a number of analytical spectroscopists. For absorption spectroscopy, analytical chemists have traditionally used such instruments as the photometer, which uses a narrow-band light source (for example the 254 nm emission line from a low pressure Hg lamp or a continuous source with a filter), a sample cell and a photomultiplier tube (FMT) as the detector. While useful for many specific applications, the single-wavelength photometer cannot determine multiple sample components simultaneously or provide a general absorbance characterization of the system. When information at multiple wavelengths is desired,... 

A third, usually more expensive, system has multiple detectors to count multiple samples simultaneously. Configurations available commercially are modular with groups of four detectors arranged over a slide-out drawer. Modules can be added for 8,16, or even 64 detectors. This counting system is useful for low-level samples that require long counting time (i.e., 24-96 h). A high sample load can justify the cost. 

Modern TIMS instruments are equipped with multiple ion detectors (see Fig. 17.15). In the 1980s, Faraday cup arrays became commercially available, and these provided significant improvements in isotopic precision and sample utilization. In the 1990s, arrays of pulse counting ion detectors with very compact EM... 

FIGURE 6.21 Typical separation and sorting setups using three main detector systems (a) single detector/single sample (b) multiple detector/single sample and (c) multiple detector/multiple sample. (After Tomaszek, T. 1993. Automated Separation and Sort, Modern Plastics, 34-36 (November).)... 

TRFF has the advantage that a continuous elution signal is obtained and molar mass detectors can be easily added to obtain composition molar mass interdependence an autosampler can also be added for multiple sample analysis. CRYSTAF takes advantage of discontinuous sampling to analyze a set of samples simultaneously. 

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