Auto-samplers

The sample area should be able to incorporate an auto-sampler which can work with both flame and furnace atomisers. Improved analytical precision is obtained when an auto-sampler is used in conjunction with a furnace atomiser. 

Oligosaccharides were isolated preparatively by high-pH anion exchange chromatography carried out on a LC-system (Dionex Corporation, Sunnyvale CA) equipped with a CarboPac PA-1 column (9 x 250 mm), coupled to a Spectra System AS 3500 auto sampler. The detection was carried out using Pulsed Amperometric Detection (PAD-II). 

The concept of an integrated micro-fluidic-based system has now been developed (Zhang et al. 2006), with an example shown in Fig. 7. This particular system is based on conventional chromatographic instrumentation and employs a multi-valving system, located between two syringe pumps, shown in the foreground, to enable the introduction of multiple reagents from an auto-sampler to be loaded onto the micro-reactor. Because of the low diffussional distances obtained in this sys-... 

A second strategy relies on parallel experimentation. In this case, the same experimental step is performed over n samples in n separated vessels at the same time. Robotic equipment such as automated liquid-handlers, multi-well reactors and auto-samplers for the analysis are used to perform the repetitive tasks in parallel. This automated equipment often works in a serial fashion as, for example, a liquid handler with a single dispensing syringe filling the wells of a microtiter plate, one after another. However, the chemical formation of the catalyst or the catalytic reaction are run at the same time, assuming that their rate is slow compared to the time needed to add all the components. The whole process appears parallel for the human user whose intervention is reduced. 

As we have seen so far, libraries of hydrogenation catalysts are never composed of more than a few dozen members, up to 100 to 200 at the most. Consequently, modern analytical equipment such as gas chromatography (GC) or high-performance liquid chromatography (HPLC) equipped with an auto-sampler or even flow-through NMR systems are sufficient to handle the analysis of the entire library. Nevertheless, a few groups have initiated research towards the development of fast, sometimes parallel, analytical procedures. A few reviews have appeared on this subject [59]. Here, we will concentrate on the methods developed to analyze hydrogenation reactions, or methods that could likely be applied. 

The focus of this chapter has been on the synthesis of new catalysts by parallel and combinatorial methods. Another aspect important to the development of new catalysts by these methods is the screening of these large libraries. We will not attempt to cover this topic comprehensively but do feel it is necessary to summarize some of the approaches that have been taken. Methods for screening libraries can be divided into both serial and parallel methods. Generally, the serial methods are adaptations of standard methods that allow for rapid individual analysis of each member of a library. Serial approaches for the analysis of libraries can be as simple as use of an auto sampler on a GC or HPLC system or as advanced as laser-induced resonance-enhanced multiphoton ionization of reaction products above the head-space of a catalyst (16) or microprobe sampling MS (63). The determination of en-antioselectivity in catalysis is a particular problem. Reetz et al. (64) reported the use of pseudoenantiomers and MS in the screening of enantioselective catalysis while Finn and co-workers (65) used diastereoselective derivatization followed by MS to measure ee. 

For HPLC, the injector is a valve. In the charge position, a 50- jL syringe is used to fill the sample loop that holds a specific volume of sample solution. The valve is switched to the run position, and the eluent carries the sample out of the sample loop and into the column (auto samplers are also available for HPLC). A recording of the detector output is automatically started at the time of injection and produces a chromatogram of the separated components. 

In the purge-and-trap procedure, vials filled to the brim with the water samples are loaded into an auto-sampler, and then when the unit is operating, samples are drawn, one by one, into a tube where helium sparging occurs. Because the THMs are volatile, the helium sparging draws them out of the samples. The helium-THM gaseous mixture then flows through a trap in which the THMs are adsorbed and concentrated. This is followed by a desorption step in which the desorbed THMs are guided to the GC column. A Hall detector is used. 

Allison Trentman of the City of Lincoln, Nebraska, Water Treatment Plant Laboratory loads vials of water samples into the auto-sampler in preparation for analysis for trihalomethanes. The helium sparging tube is the vertical tube on the front of the unit on the left. 

Automated injectors are often used when large numbers of samples are to be run. Most designs involve the use of the loop injector coupled to a robotic needle that draws the samples from vials arranged in a carousel-type auto-sampler. Some designs even allow sample preparation schemes such as extraction and derivatization (chemical reactions) to occur prior to injection. 

John Howe, an analyst in the laboratory of MDS Pharma Services in Lincoln, Nebraska, checks an auto-sampler tray used with an HPLC instrument in the analysis of biological samples for drugs. A given run may include a large number of sample extracts to run alongside quality controls and standards, hence the need for an auto-sampler. 

The analyte solution is placed (injected) into the furnace with a micropipet or auto-sampler. Following this, a temperature program is initiated in which the furnace heats rapidly to 1) evaporate the solvent, 2) char the solid residue, and finally 3) atomize the analyte, creating the atomic vapor. 

All aldehydes used in the experiment were freshly distilled or washed with aqueous NaHC03 solution to minimize the amount of free acid. Chiral HPLC was performed using a chiral OJ-H column (0.46 cm x 25 cm, Daicel industries) with a water 717 auto sampler and a UV-vis detector (254 nm). The eluting solvent used was different ratios of hexane and 2-propanol. Chiral gas chromatography analysis was performed in a Shimadzu auto sampler with cyclodextrins columns as chiral stationary phase (fused-silica capillary column, 30 m X 0.25 mm x 0.25 gm thickness, /3-Dex-120 and /3-Dex-325 from Supelco, USA) using He as a carrier gas (detector temperature 230 °C and injection temperature 220 °C). 

Sample introduction can be accomplished in various ways. The simplest method is to use an injection valve. In more sophisticated LC, automatic sampling devices are incorporated where sample introduction is done with the help of auto-samplers and microprocessors. 

Analysis of the analytes was done by gas chromatography on a HP 5890 equipped with 7673 auto-sampler and DOS series chemstation (Hewlett Packard Co., Avondale, PA). A 25m HP-5 column with 200 um internal diameter and 0.33 um film thickness was used for all separations reported herein. The injection mode was purged splitless (1 uL injection) and the temperature ramp used for all separations was 60°C for 1 minute ramping then to 300°C at 20°C/minute. 

It is a good investment to have routines in building analysis sequences for quantitative analyses on analytical instruments equipped with auto-samplers. It is... 

Doyle et al [9] published an article describing two fully automated assays, one for zaprinost and the other for pantoprazole and its sulfone metabolite. Both assays were developed to support pharmacokinetics studies. Plasma or serum (20-200 pL) was placed directly into an auto-sampler, and all subsequent manipulations were performed mechanically [9],... 

It consists of a 25-mm-diameter Deldrin filter holder (Gelman product No. 1109) with one of the nylon hose nipples removed. The filter used is a 25-mm-diameter, 0.5-pm pore size Fluoropore membrane filter (Millipore catalogue No. FHLP 025 00). An auto sampler cup cap is used to seal the apparatus, both before and after use. In use, the filter holder is attached to an Edwards E2 M12 vacuum pump. 

Equipment Use a Hewlett-Packard 5890 Series II GC equipped with a flame-ionization detector (FID), a pressure-programmable on-column injector, an HP 7673 auto-sampler, and an HP Series II integrator, or equivalent. A Chrompack SIM-DIST CB fused-silica GC column (Chrompack Inc., Raritan, NJ) with a 5-m x 0.32-mm id and a 0.1- xm film thickness, or equivalent. A deactivated fused-silica precolumn (0.5-m x 0.53-mm id) coupled to the analytical column via a butt connector (Quadrex Corp., New Haven, CT), or equivalent. 

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