Sample application fully automated

In principle, on-line SPE-LC can be automated quite easily as well, for instance, by using Such programmable on-line SPE instrumentation as the Prospekt (Spark Holland) or the OSP-2 (Merck) which have the capability to switch to a fresh disposable pre-column for every sample. Several relevant applications in the biomedical field have been described in which these devices have been used. Eor example, a fully automated system comprising an autosampler, a Prospekt and an LC with a UV... 

A second fully automated device, the HPTLC applicator AS 30 (described earlier), can be employed in connection with a sampling device. Automated refilling of the syringe is performed by editing a volume factor, e.g., 10 for application of 10 times 100 pi. This device can be recommended if loss of sample is not relevant (e.g., owing to automatic rinsing operations that afford at least 70 pi dead volume for a minimal 20-cm tube connection). However, the fully automatic mode is not recommended for valuable samples. Sample volume still present in the Teflon tube between the sampler and AS 30 syringe will be wasted and lost because this operation cannot be circumvented by the user. 

Applications Multidimensional SEC techniques can profitably be applied to soluble polymer/additive systems, e.g. PPO, PS, PC - thus excluding polyolefins. A fully automated on-line sample cleanup system based on SEC-HRGC for the analysis of additives in polymers has been described, as illustrated for PS/(200-400ppm Tin-uvin 120/327/770, Irgafos 168, Cyasorb UV531) [982], In this process, the high-MW fractions are separated from the low molecular masses. SEC is often used as a sample cleanup for on-line analysis of additives in food extracts these analyses are usually carried out as on-line LVI-SEC-GC-FPD. 

Robotic systems in a small analytical laboratory have the greatest application in the intermediate sample manipulation steps. The removal of excess solvent with the Zymark evaporator [492], for example, can be closely controlled, fully automated, and operate in parallel (up to six samples per instrument). This technique has considerable advantages over rotary evaporation, which is prone to loose volatile organic compounds (e.g., chlorobenzenes) under vacuum and rapid vaporization. Automated repetitive manipulations are well served by a robotic system [492]. 

Online coupling SPE to either LC or GC is easily performed. In the simplest method, a precolumn is placed in the sample loop position of a six-port switching valve. After conditioning, sample application, and cleaning via a low-cost pump, the precolumn is coupled to an analytical column by switching the valve into the inject position. The solutes of interest are eluted directly from the piecolumn to the analytical column by an appropriate mobile phase. The sequence can be fully automated (Fig. 28). It is also a simple matter to enhance the gap between two solutes in elution from a precolumn (70). 

This applicator is a fully automated system which can be used to apply from 10 to 30 pL of up to 96 samples. 

After the operator has selected the desired method menu of the relevant samples and has started the instrument, all subsequent steps are fully automated. Since 1987 it is also possible to effect a direct identification of the sample so that there are no longer any problems in respect of a dialogue with a central EDP system. The samples are taken from the sample vessel by means of disposable single use pipette tips that are used for one sample only and exchanged via a computer-monitored pipetting unit. This method excludes the possibility of a carry-over between samples. In accordance with the preset conditions, the required slides are automatically moved to the sample dosage unit (see Fig. 23). Samples of 11 pi serum or plasma will be sufficient for kinetic measurements (enzymes), 10 pi of sample for all other tests. As soon as application of the sample has been completed, the slide is moved to the appropriate incubation chamber by means of the slide rotor (see Fig. 23). The chemical reactions take place in these chambers. This is followed by measurement either by reflectometer (end point or kinetic) or a potentiometric measurement unit. 

Mobile phase optimization using HPLC can easily be carried out using fully automated instruments, but this approach is extremely time-consuming. Conversely, modern thin-layer chromatographic techniques allow several mobile phases to be tested in parallel within a very short period of time. Furthermore, different methods are available to visualize the sample components, and the thin-layer chromatogram immediately provides information about the presence of products in the sample that remain at the point of application. 

Further advances have resulted from developments in instrumentation, particularly in the areas of scanning densitometry and automated sample application, which have now made fully instrumental quantitative TLC a reality far removed from the basic practice. TLC is now regarded as an indispensable tool in both quality control and research laboratories. The technique is easy to learn and is fast and versatile and in many instances may be preferred to the techniques of gas chromatography and high performance liquid chromatography. 

Several fully automated spray-on sample applicators are available. In one device, a motor driven syringe is used to suck up sample volumes of 0.1 to 50 p.1, which are then deposited as spots or bands on the layer [104]. The syringe feeds a stainless-steel capillary connected to a capillary atomizer. The applicator can be programmed to select samples from a rack of vials and deposit fixed volumes of the sample, at a controlled rate, to selected positions on the layer. The applicator automatically rinses itself between applications and can spot or band a whole plate with different samples and standards without operator intervention. A number of multi-sample applicators for the simultaneous transfer and deposition of several samples at the same time have been described [106-108]. 

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