System carryover

Carryover. Small amounts of analyte may get carried over from the previous injection and contaminate the next sample to be injected [10]. The carryover will affect the accurate quantitation of the subsequent sample. The problem is more serious when a dilute sample is injected after a concentrated sample. To avoid cross-contamination from the preceding sample injection, all the parts in the injector that come into contact with the sample (the injection loop, the injection needle, and the needle seat) have to be cleaned effectively after the injection. The carryover can be evaluated by injecting a blank after a sample that contains a high concentration of analyte. The response of the analyte found in the blank sample expressed as a percentage of the response of the concentrated sample can be used to determine the level of carryover. Caffeine can be used for the system carryover test for assessing the performance of an injector and serves as a common standard for comparing the performance of different injectors. 

As a final note in this discussion of on-line methods, it is widely known that on-line methods are more prone to system carryover. The primary reason is that the valves used for CS present additional surfaces for contact with the analyte. In a paper recently published by Grant and co-workers, the issue of analyte carryover in TFC was addressed [79]. These authors incorporated a series of multiple-wash steps along with a switching valve made of polyarylethyl ketone (PAEK) to reduce carryover present in a generic method that provided a throughput of 1.5 min/sample. 

A Unal example of direct bioanalysis was recently published by Dethy et al. and involves the appUcation of infusion nanoelectrospray (nano-ESI) from a silicon chip [110]. In this example, supernatant obtained from protein precipitation was directly infused with an automated pipette-tip delivery system. Individual, conductive pipette tips that contain sample were sequentially introduced to the backplane of a silicon chip for analysis. The front plane of the chip that consisted of 100 individual nano-ESI nozzles, was positioned near the API orifice of a TQMS for direct serial analysis. Quantitation of verapamil and its metaboUte norverapamil occurred in human plasma over a range of 5-1000 ng/mL. It is possible to achieve analysis times of less than 1 minute per sample with this technology. An important advantage, demonstrated by this work, is the unique abiUty to avoid system carryover with this device [110]. 

Advantages of microfluidics for bioanalysis could potentially include lower costs for laboratory reagents and equipment and the avoidance of system carryover. Perhaps the biggest advantage will be in the introduction of novel formats for innovation that are not readily envisioned at the present time. For instance, the solution to improved ionization or parallel detection may lie in nanotechnology. As nanotechnology is reduced to practice, we may witness a dramatic shift in how future bioanalysis is conducted in drug discovery. 

The system carryover was tested by analyzing a blank sample with the same microchannel and tip before and after analyzing the highest concentration of... 

Polymeric microfluidic systems coupled to a microfabricated planar polymer tip can be used as a stable ion source for ESI-MS. A parylene tip at the end of the microchannel delivers fluid which easily produces a stable Taylor cone at the tip via an applied voltage. The described device appears to facilitate the formation of a stable spray current for the electrospray process and hence offers an attractive alternative to previously reported electrospray emitters. When this interface was employed for the quantification of methylphenidate in urine extracts via direct infusion MS analysis, this system demonstrated stable electrospray performance, good reproducibility, a wide linear dynamic range, a relatively low limit of quantification, good precision and accuracy, and negligible system carryover. We believe polymeric devices such as described in this report merit further investigation for chip-based sample analysis employing electrospray MS in the future. 

One disadvantage of fluidized heds is that attrition of the catalyst can cause the generation of catalyst flnes, which are then carried over from the hed and lost from the system. This carryover of catalyst flnes sometimes necessitates cooling the reactor effluent through direct-contact heat transfer hy mixing with a cold fluid, since the fines tend to foul conventional heat exchangers. 

Formation of Airborne Emissions. Airborne emissions are formed from combustion of waste fuels as a function of certain physical and chemical reactions and mechanisms. In grate-fired systems, particulate emissions result from particles being swept through the furnace and boiler in the gaseous combustion products, and from incomplete oxidation of the soHd particles, with consequent char carryover. If pile burning is used, eg, the mass bum units employed for unprocessed MSW, typically only 20—25% of the unbumed soHds and inerts exit the combustion system as flyash. If spreader-stoker technologies are employed, between 75 and 90% of the unbumed soHds and inerts may exit the combustion system in the form of flyash. 

Soluble iron or aluminum carryover ia the clarifier effiueat may result from inorganic coagulant use therefore, elimination of the inorganic coagulant can minimise the deposition of these metals ia filters, ion-exchange units, and cooling systems. 

Condensate Polishing. Ion exchange can be used to purify or poHsh returned condensate, removing corrosion products that could cause harmful deposits in boilers. Typically, the contaminants in the condensate system are particulate iron and copper. Low levels of other contaminants may enter the system through condenser and pump seal leaks or carryover of boiler water into the steam. Condensate poHshers filter out the particulates and remove soluble contaminants by ion exchange. 

TROUBLE EXCESSIVE CARBON ON VALVES PROBABLE CAUSE(S) 1. Excessive lube oil. 2. Improper lube oil (too light, high carbon residue). 3. Oil carryover from inlet system or previous stage. 4. Broken or leaking valves causing high temperature. 5. Excessive temperature due to high pressure ratio across cylinders. 

Hooding A condition that gives rise to a sharp decline in tray efficiency and a sharp increase in pressure drop. Flooding is commonly due to either an excessive carryover of liquid to the next tray, or to an inability of the system to convey the liquid flow to the tray below. 

The efficiency of power generation is significantly reduced by any deposits formed on the turbine blades by BW carryover and severe turbine damage may also result. Tiirbine efficiency also is reduced by demands for output that exceed the rated maximum and by extended operation beyond the maintenance period or design life. Additionally, errors in steam flow meters, thermometers, and pressure gauges, and so forth cause the control system to regulate the generation of electricity at some further reduced level. 

These factors severely enhance the risks of condensate system corrosion by carbonic acid (resulting from a breakdown of the alkalinity in the boiler water and carbon dioxide [C02] carryover into the steam) and BW carryover. In addition, boiler operation is more difficult because the possible COC is severely limited, there-... 

The effect of carryover and after-precipitation is that solids settle out and cause pre-boiler system fouling and result in reduced flow and equipment waterway blockages. Check valves are especially prone to blockage. 

The pickup, transport, and redeposition of corrosion debris and deposits can happen anywhere in steam distribution and condensate return systems and are not confined to any particular boiler plant size or pressure rating. For example, deposit pickup may occur in a superheater with redeposition taking place perhaps in a pressure reducing station, steam trap, or condensate line. The starting point for transport mechanisms is often a combination of BW carryover and condensate line corrosion. 

Where carryover occurs, much of the solids content is deposited in the first parts of the steam and condensate system, such as superheaters, but the balance can be transported all the way back to the pre-boiler system and from there to the boiler itself. Thus, a chain of cause and effect may once again develop in a manner similar to the progression of problems in other areas of the boiler system. 

When bubbles accumulate at the steam-water interface, dissolved solids pass into the post-boiler steam section, and this carryover contaminates the steam and causes fouling of the system. Where the foam-... 

Steam and condensate systems, corrosive gases in 284 carbon dioxide carryover 288... 

We shall see below that there is some evidence for energy carryover in this system. We therefore cannot decide from our data whether... 

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