Automatic sampling devices

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. 

With commercially available automatic sampling devices, large numbers of samples can be routinely analyzed by LC without operator intervention. Such equipment is popular for the analysis of routine samples (e.g., quality control of drugs), particularly when coupled with automatic data-handling systems. Automatic injectors are indispensable in unattended searching (e.g., overnight) for chromatographic parameters such as solvent selectivity, flow rate, and temperature optimization. 

The chromatographic process begins by injecting the solute onto the top of the column. The solvent need not be the mobile phase, but frequently it is appropriately chosen to avoid detector interference, column/analyte interference, loss in efficiency, or all of these. Sample introduction can be accomplished in various ways. The simplest method is to use an injection valve. In more sophisticated LC systems, automatic sampling devices are incorporated where sample introduction is done with tire help of autosamplers and microprocessors. It is always best to remove particles from the sample by filtering, or centrifuging since continuous injections of particulate material will eventually cause blockage of injection devices or columns. 

HPLC and Isolation of Mutagenic Fractions. Analytical and semipreparative reverse-phase HPLC separations were performed by using a water-to-acetonitrile linear gradient (J2). Separations were carried out on a Hewlett Packard Model 10084 B equipped with an automatic sampling device, a solvent programmer, a variable absorbance detector, and an automatically steered fraction collector. The instrument was fitted with a 3.9-mm X 30-cm prepacked analytical column of 10-/zm silica particles bonded with octadecylsilane (Bondapack-Cis) for analytical scale. For semipreparative scale separations, the HPLC was fitted with a 7.8-mm X 30-cm prepacked column packed with 10-/xm silica particles bonded with octadecylsilane. Samples for HPLC were injected at volumes of 20 /xL (flow rate 1 mL/min) and 80 /zL (flow rate 4 mL/min), and the absorption was measured at 254 nm. Fractions... 

Two questions, where to monitor or sample and how to obtain representative samples are both important. Surface water samples often are collected by automatic sampling devices controlled by a variety of sensors. The simplest method of collecting water is the grab technique, whereby a container is lowered into the water, rinsed, filled, and capped. Specialized samplers frequently are used to obtain water at greater depths. 

Figure 13.11 Schematic of an hydride reactor used for particular elements. This automatic sampling device houses a mixing tube where the hydride of the metal (or non-metal) is formed during reaction with sodium horohydride. An argon flow extracts the metal hydride formed (gas separator) carrying it to a silica glass tube heated to between 800 and 1000 °C in the flame.

As a basic rule, flow-proportional sampling is recommended flow-proportional composite samples can be produced from the individual samples taken, where necessary, with automatic sampling devices. In the case of time-proportional sampling, no account is taken of the quantity of water. 

Nevertheless, this must be regarded as a better solution than a single or multiple random sample. Production of time-proportional composite samples is also possible, using automatic sampling devices where applicable. The composite samples can be taken with or without settleable substances. If the water contains many settleable substances, it is more favourable to remove these substances before producing the composite samples and to investigate them separately in the laboratory. After removing the settleable substances, the water from the composite samples should be used for laboratory tests. If secondary turbid substances have formed in the water, these should be included in analyses. 

Composite samples are obtained by combining portions of multiple grab samples or by using specially designed automatic sampling devices. This type of sample can reduce sample number and the samples are more representative of heterogeneous matrices. However, the composite samples may lose the analyte relationships in individual samples and increase the potential for analytical interferences. 

Note 2—Automatic sampling devices or other sampling means, such as indium encapsulation, can be used provided the system can be operated at a temperature sufficienUy hi to completely vaporize hydrocarbons with atmoqiberic boiling points of S38 C (1000 F), and the sampling system is connected to the chromatographic column avoiding any cold temperature zones. 

Automatic Samplers—An automatic sampler includes not only the automatic sampling device that extracts the samples from the line, but also a suitable probe, connecting lines, auxiliary equipment, and a container in which the sample is collected. It must maintain sample integrity. Refer to API MPMS Chapter 8.2. Automatic samplers are classified as follows ... 

Modern applications of thin layer chromatography (TLC) should inevitably benefit from the best-standardized and best-performing materials and equipment. It means that the separations ought to be carried out on the commercially precoated chromatographic plates, the analyte samples ought to be spotted on to the adsorbent layer with the aid of an automatic sampling device, and the detection ought to be performed by means of densitometry. All these demands are particularly important in view of the fact that the TLC results tend to be less repeatable than in the... 

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