Concurrent Backflush

The popular multi-component methods with short sample preparation and extract clean-up such as QuEChERS require special care for the chromatographic 

An optimum solution would be the separation of the analytes during the injection process from the high boiling matrix material. The more volatile low molecular weight analytes, for example, pesticides, are able to travel quickly into the analytical column, while high boilers move slowly and can be kept in the insert liner and a pre-column. Analytes that reach the analytical column stop motion at the beginning of the column and get focused by the column film. At this point, the pre-column can be swept backwards during the complete analysis run. For maintenance purposes, the pre-column as a cheap consumable can be replaced easily like the injector insert liner (Munari, 2000). 

The flow restriction connects the carrier gas line of the injector with the BKF line to purge the T-piece. The flow of the restriction is usually factory set. 

The timing of switching the BKF valve is set such that all analytes pass the precolumn to the analytical column. This time is called the transfer time. 

Inject a standard with the optimized oven temperature program required for the complete elution of the analytes of interest. 

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In the last few years, a third type of microfiltration operating system called semi-dead-end filtration has emerged. In these systems, the membrane unit is operated as a dead-end filter until the pressure required to maintain a useful flow across the filter reaches its maximum level. At this point, the filter is operated in cross-flow mode, while concurrently backflushing with air or permeate solution. After a short period of backflushing in cross-flow mode to remove material deposited on the membrane, the system is switched back to dead-end operation. This procedure is particularly applicable in microfiltration units used as final bacterial and virus filters for municipal water treatment plants. The feed water has a very low loading of material to be removed, so in-line operation can be used for a prolonged time before backflushing and cross-flow to remove the deposited solids is needed. 

Special focus has been set to the widely used and popular sample preparation methods as there are the pressurized liquid extraction (RLE), the thermal extraction of materials and food (outgassing), and in detail on the QuEChERS pesticide sample preparation used for GC-MS and LC-MS. As a consequence of the higher matrix load of these extracts and the recommended GC injection techniques, concurrent backflush, preventive maintenance and inlet deactivation became current topics of discussion. Olfactometry solutions have been added for apphcations in flavour analysis. 

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