Plasma disadvantages

Poly(ethylene glycol) (PEG) molecules attached to adenosine deaminase (ADA) have been used in patients exhibiting symptoms of the severe combined immunodeficiency syndrome (SCID) caused by ADA deficiency. The modified enzyme has a plasma half-life of weeks as compared to the unmodified enzyme (minutes) (248). PEG-L-asparaginase has induced remissions in patients with non-Hodgkin s lymphoma (248). However, one disadvantage of PEG-enzyme treatment is its expense, ie, a year s treatment costs about 60,000 (248). 

Another disadvantage is that fragile substrates used in VLSI, such as some III-V and II-VI semiconductors materials, can be damaged by the ion bombardment from the plasma, particularly if the ion energy exceeds 20 eV. In addition, the plasma reacts strongly with the surface of the coating as it is deposited. This means that the deposition rate and often the film properties depend on the uniformity of the plasma. Areas of the substrate fully exposed will be more affected than the more sheltered ones. Finally, the equipment is generally more complicated and more expensive. 

Few authors have coupled HPLC to MIP-AES [680-682], despite the need for a nonmetal element-specific HPLC detector. Advantages of HPLC-He MIP-MS include improved detection for the halogens. The primary disadvantage is the inability of the plasma to tolerate aerosol introduction. 

List the advantages and disadvantages of dc-arc spectrometry and inductively coupled plasma spectrometry, when used to determine trace metals in solid samples. Indicate the main reasons for preferring ICP spectrometry, in most cases. 

Sample pooling is also used in a process called cassette assay in which samples are pooled from multiple (typically 5 or 6) dosing experiments.24-83 87-88 Hsieh et al.89 showed that one could pool the plasma from six NCEs into one sample per time point to reduce sample assay time. Kuo et al.88 used a similar sample pooling approach for NCEs dosed into rats. The advantage is that cassette assay requires fewer samples. Two disadvantages are the need to dilute samples and the difficult set-up. 

On the basis of the preceding discussion, it should be obvious that ultratrace elemental analysis can be performed without any major problems by atomic spectroscopy. A major disadvantage with elemental analysis is that it does not provide information on element speciation. Speciation has major significance since it can define whether the element can become bioavailable. For example, complexed iron will be metabolized more readily than unbound iron and the measure of total iron in the sample will not discriminate between the available and nonavailable forms. There are many other similar examples and analytical procedures that must be developed which will enable elemental speciation to be performed. Liquid chromatographic procedures (either ion-exchange, ion-pair, liquid-solid, or liquid-liquid chromatography) are the best methods to speciate samples since they can separate solutes on the basis of a number of parameters. Chromatographic separation can be used as part of the sample preparation step and the column effluent can be monitored with atomic spectroscopy. This mode of operation combines the excellent separation characteristics with the element selectivity of atomic spectroscopy. AAS with a flame as the atom reservoir or AES with an inductively coupled plasma have been used successfully to speciate various ultratrace elements. 

Compared to the carbamoylmethyl esters discussed in Sect. 8.2.3, glycolic acid esters appear somewhat disadvantageous because of the possibility of a parasitic reaction. The fact that the chemical hydrolysis of glycolic acid esters is faster while their enzymatic hydrolysis in human plasma is slower may not necessarily be detrimental. 

A disadvantage with conventional plasma treatment techniques is the requirement for treatments to take place in a vacuum, adding to the equipment costs. However, if a dielectric material is placed between the electrodes of the plasma equipment, then treatment can be performed at atmospheric pressure. This method is known as a dielctric barrier discharge treatment and has been the subject of some recently reported studies. 

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