Filters, in-line

A common cause of unusually high pressure is a plugged in-line filter. In-line filters are found at the very beginning of the flow line in the mobile phase reservoir, immediately before and/or after the injector, and just ahead of the column. With time, they can become plugged due to particles that are filtered out (particles can appear in the mobile phase and sample even if they were filtered ahead of time), and thus the pressure required to sustain a given flow rate can become quite high. The solution to this problem is to backflush the filters with solvent or clean them with a nitric acid solution in an ultrasonic bath. 

Another option would be to place several filters in line. Generally the term filter refers to a component that removes larger particulates and moisture compared to filters that are called coalescers. Filters generally won t catch the fine aerosols that the coalescer will trap. 

This method was developed by Stefan Huber (Karlsruhe, Germany) and consists of three size exclusion chromatography columns which divide the organic carbon into several fractions as a function of size, but also hydrophobic and ionogenic characteristics. A sample of up to 3 mL is injected into the instrument and filtered in-line with a 0.45 )um filter. The deposit on the filter is backwashed after 5 minutes and directly analysed with the TOC analyser to determine the particulate organic carbon content (POC). 

Above and beyond these problems are the troubles created s the fact that, in bacteria-laden water, bacteria have found their way into every nook and cranny in the HPLC system. The components with the largest surface areas (inlet reservoir filters in-line and column ifits) serve as active multiplication sites for more bacteria. Results of this type of bacterial growth are seen chromatographically as spurious, irreproducible peaks. Correction of the problem is time-consuming. Each stainless steel component needs to be cleaned with a solution of dilute nitric acid followed by water and methanol rinses. (Make sure that each component in the HPLC system is compatible with nitric acid. Components that are not should be cleaned according to the manufacturer s instructions or replaced.)... 

Samples are collected by use of a personal sampling pump that can be calibrated within 5% of the recommended fiow rate with the sampling filter in line. 

Figure 1 Deposition by impaction A schematic drawing of the respiratory tract, which can be seen as three filters in line, to protect the fragile alveoli from particles. The first two filters, mouth and throat and tracheobronchial airways, work by impaction (i.e., particles tend to continue forward and deposit when the gas flow changes direction). Impaction is the most important deposition mechanism for medical aerosols in the upper airways and in larger bronchus, and correlates well with the impaction parameter AD F. In the last filter, the bronchioles, impaction is insignificant owing to the large total cross-sectional area, leading to low velocities.

For the case of a double-D coil we multiply each matrix element with an element shifted by a constant distance of the same line. This is done in x- and y-direction. The distance between the two elements is the correlation length X for filtering in x-direction and a second correlation length for the movement in y-direction. Thus one gets two new matrices Ax and Ax for the filtering from the left to the right (positiv x-direction) and vice versa (negativ x-direction). 

Ions of different m/z values pass sequentially in time through the quadrupole mass filter to reach an in-line, single-point ion collector. 

Depth filters are usually preferred for the most common type of microfiltration system, illustrated schematically in Figure 28. In this process design, called "dead-end" or "in-line" filtration, the entire fluid flow is forced through the membrane under pressure. As particulates accumulate on the membrane surface or in its interior, the pressure required to maintain the required flow increases until, at some point, the membrane must be replaced. The useful life of the membrane is proportional to the particulate loading of the feed solution. In-line microfiltration of solutions as a final polishing step prior to use is a typical apphcation (66,67). 

Hydrofluoric acid [7664-39-3] M 20.0, b 112.2"(aq azeotrope, 38.2% HF), d 1.15 (47-53% HF), pK 3.21. Freed from lead (Pb ca 0.002ppm) by co-precipitation with Srp2, by addition of lOmL of 10% SrCl2 soln per kilogram of the cone acid. After the ppte has settled, the supernatant is decanted through a filter in a hard-rubber or paraffin lined-glass vessel [Rosenqvist Am J Sci 240 358 1942. Pure aqueous HF solutions (up to 25M) can be prepared by isothermal distn in polyethylene, polypropylene or platinum apparatus [Kwestroo and Visser Analyst 90 297 7965]. HIGHLY TOXIC. 

Incorporates flow and pressure regulators, an in-line filter, and an internal heat exchanger. 

When a sampling train requires an unusual combination of sampling media (e.g., glass fiber filter proceeding impinger), the same media/devices should be in line during calibration. 

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