Pretreatment cleaning continued

During expeditions with the German research vessel Polarstern sea water was continuously pumped under clean conditions from the front of the ship bow at a depth of 10 m into a laboratory, where samples were collected into precleaned PE bottles. Subsequently, the samples were filtered using a 0.45 pm pore sized filter and then analyzed as soon as possible. For the analysis of VHOCs a 10 1 precleaned steel bucket was also used in some cases. Only ultra pure chemicals were used for the pretreatment of samples. 

There are several commercially available instruments using sorption systems for sample pretreatment. A representative example of those working in a continuous fashion is the Varian AASP (Advanced Automated Sample Processor) [10]. This uses cassettes of ten sorbent cartridges, each of which is packed with 40-50 mg of a particular bonded silica gel. It features three essential differences from typical manual systems, namely the use of lower sample and solvent volumes, the utilization of pressure rather than vacuum and the fact that the liquid emerging from the cartridge is completely eluted to the HPLC system, thereby increasing the sensitivity. Analytical Biochemistry Laboratories (ABC) markets a module (GPC 1002 A) for automated clean-up of residues in extracts by use of a gel-permeation column. 

After pretreating the aperture in the Teflon septum with 5 il of 20 mg/ml DOPC in decane and allowing it to dry, the back chamber was filled with degassed phosphate-buffered saline (PBS) and the device assembled. Care was taken not to trap air bubbles in the back chamber. The front chamber was then immediately filled with PBS. pip was monitored continuously until a stable value was reached. The bias potential was then adjusted to Vpip -50 mV ( i.e. the high photocurrent side of "Fpip) and a membrane painted over the aperture with a quick stroke of a camel s hair brush onto which 20 il of 20 mg/ml DOPC in decane had been pipetted. The thinning of the membrane to a bilayer could be followed either visually or electrically and was complete within an hour. After use the phospholipid bilayer membrane apparatus was taken apart and cleaned by soaking in IN NaOH and IN HCl, rinsed with water and methanol and air dried. 

The total incoming flow of feed can be treated with air under pressure, but it is more usual to introduce the air into a recycle stream of cleaned liquid and to allow the bubbles to develop in the flotation chamber at the point where the recycle stream enters. The feed stream is pretreated with chemicals, if necessary, prior to its introduction to the flotation chamber where it meets the bubble blanket. The fine particles in the supension are captured by the bubbles and are floated up to the surface where they form a thick scum which is removed by a continuous mechanical scraper. Some solids will settle fi om most feed streams and it is usual to provide for the withdrawal of accumulated silt fiom the base of the chamber. Figure 7.13 shows a conventional diflused air flotation system housed in a rectangular tank and Figure 7.14 a DAF unit which incorporates an inclined plate settler to capture by sedimentation those particles that escape flotation. 

The potential for membrane technologies to treat PW has been already assessed in various studies and field trails . One of these works demonstrated that, with proper pretreatment (hydrocyclone), a UF process can treat PW and generate a water stream with oil concentrations continuously below 2 ppm. In another study with PW from an oilfield in Montana (US), the combination of UF + RO, after some preliminary pretreatment, was able to reduce the TDS, Turbidity and Chemical Oxygen Demand (COD) by more than 99% and produce clean water to be reused for irrigation. 

Microemulsion-based cleaning formulations can provide outstanding performance, and solvent-continuous microemulsions with excellent oily soil cleaning and practical microemulsions employed in the preparation of fabric pretreaters were recently reported (104-106). 

Workstations and robotic systems are very expensive, so inexpensive alternatives such as flow configurations have been developed for automated sample preparation. The earliest flow systems for sample preparation were used for GC determination (with flame ionization detector [FID] or electron capture detector [EGD] detection) of organic compounds, which requires no special extraction or derivatization, in environmental matrices [30-34]. Automated GC-MS systems for the determination of volatiles in water or air [35-38] are the most commonly reported. Detailed descriptions of these systems can be found elsewhere in this book. Few continuous flow systems (CFSs) for the automated pretreatment of biological fluids in combination with GC-MS have been developed to date. The intrinsically discrete nature of the GC-MS sample introduction mechanism makes online coupling to continuous flow systems theoretically incompatible for reasons such as the different types of fluids used (liquid and gas) and the fact that the chromatographic column affords volumes of only 1 to 2 j,l of cleaned-up extract. Therefore, the organic extracts from CFSs have traditionally been collected in glass vials and aliquots for manual transfer to the GC-MS instrument (off-line approach) only in a few cases is an appropriate interface used to link the CFS to the GC-MS instrument (on-line approach). These are the topics dealt with below. 

Pretreatment of platinum in hot chromic acid was shown [83] to be equivalent to anodic activation. The electrode has a large reactivity after reduction of the oxygen layer that was formed at open circuit. In contrast to the pretreatment with hot chromic acid, the i — U curve of the first sweep after treatment of the platinum electrode in hot nitric acid does not have the shape characteristic for a clean surface. An intermediate product in the reduction of nitric acid seems to be strongly adsorbed on platinum. It takes several hours of continuous cycling between 0.05 V and 1.4 V at 30mV/sec before the i- U curve regains the regular shape. 

For relatively low solids content feeds, it is feasible to operate without continuous cross flow or surface shear, and this can reduce energy costs. Such applications include water treatment and pretreatment for RO desalination and reclamation. This mode of operation is called dead-end filtration or frontal filtration, and the key feature is that the deposition of retained species is allowed to grow. A t5q)ical cycle commences with a clean membrane (after backwash), and at constant flux the TMP rises according to Eq. (10.4). After a specified period (Q, or at a predetermined AP iax. the flux is stopped and the deposit is removed by backwashing and (usually) vigorous aeration. The contents of the membrane... 

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