Automated sample system

This means for improvement concerns the experimental procedures that are used to collect and analyze the calibration samples. In PAC, sample collection can involve either a highly automated sampling system, or a manual sampling process that requires manual sample extraction, preparation, and introduction. Even for an automated data collection system, errors due to fast process dynamics, analyzer sampling system dynamics, non-representative sample extraction, or sample instability can contribute large errors to the calibration data. For manual data collection, there are even more error sources to be considered, such as non-reproducibility of sample preparation and sample introduction to the analyzer. 

As the need for accurate data that can be statistically reduced develops, automated sampling systems are used. The elements of an automated system include the airflow-handling system, sensors, data transmission storage, display apparatus, and data processing facility. The overall system is no more valuable than the weakest link of this chain. 

Strachan, N.J.C. Nicholson, F.J. Ogden, I.D., An automated sampling system using ion mobility spectrometry for the rapid detection of bacteria, Anal. Chim. Acta 1995, 313, 63-67. 

Instrument qualification including control of sampling if an automated sample system is used (RSD is calculated for 5 replicate sampling), control of detector sensitivity (peak height is measured for the peaks obtained from the above experiment), a similar procedure can be followed if manual sample application is used. 

In the on-line way to operate, an automated sampling system is used to extract the sample and present it to an analytical instrument for measurement. This makes this way distinct from the first two. Further, it is possible to subdivide the on-line way into two categories intermittent methods that require injection of a portion of the sample stream into the instrument and continuous methods that permit the sample to flow continuously through the instrument. 

In on-line control, an automated sampling system attached to a reactor or by-pass system is used to extract the sample, if needed conditioned, and presented to an analytical instrument or probe for measurement. Sampling delays can be significant in on-line installations, because of the transit line and gear pumps. On the other hand, on-Une devices are isolated from the main stream by the use of a gear pump, and the temperature and pressure of the polymer sampling flow can thus be controlled. Their maintenance can therefore be done without a complete process shutdown. Many of the apparent disagreements between results from split side stream on-line analysers and results from the laboratory can be traced back to differences which occur because samples differ in acquisition time, location and stability. The main characteristics of on-line process analysis are summarised in Table 7.4. 

Headspace techniques are often the method of choice since there is virtually no sample preparation involved. One simply places the food sample in a closed vessel, allows the headspace to equilibrate and then samples the headspace with a gas-tight syringe or an automated sampling system. Problems with sample carry over in the syringe and reproducibility favor automated systems for headspace sampling. The primary limitation of headspace sampling is a lack of sensitivity. One may not isolate sufficient quantities of indicator compoxmds to permit accurate and precise quantification. However, the simplicity, reproducibility and speed of this method make it exceptionally desirable for quality control purposes. 

With the increasing demand to analyze more and more samples, manufacturers of autosamplers and sample introduction accessories are designing automated sampling systems to maximize sample throughput. This is being achieved in a variety of different ways by optimizing the sample delivery process to reduce the pre- and postmeasurement time. Some typical optimization procedures include the following ... 

Adamchuk VI, Morgan MT, Ess DR (1999) An automated sampling system for measming soil pH. Trans ASAE 42(4) 885-891... 

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