Chemical monitoring sampling techniques

Laboratoiy procedures may need to be evaluated against the sampling techniques and materials involved in the toll. There may be new laboratoiy chemicals and hazards to be considered. This work may have been identified in the evaluation of special analytical techniques required for the process. A good practice is to ensure that the lab technicians have the necessaiy guidance and types of equipment on hand to monitor the process and waste streams accurately and safely. 

Most HPLC instruments monitor sample elution via ultraviolet (UV) light absorption, so the technique is most useful for molecules that absorb UV. Pure amino acids generally do not absorb UV therefore, they normally must be chemically derivatized (structurally altered) before HPLC analysis is possible. The need to derivatize increases the complexity of the methods. Examples of derivatizing agents include o-phthaldehyde, dansyl chloride, and phenylisothiocyanate. Peptides, proteins, amino acids cleaved from polypeptide chains, nucleotides, and nucleic acid fragments all absorb UV, so derivatization is not required for these molecules. 

There are several future trends for the development of passive sampling techniques. The first is the development of devices that can be used to monitor emerging environmental pollutants. Recently, attention has shifted from hydrophobic persistent organic pollutants to compounds with a medium-to-high polarity, for example, polar pesticides, pharmaceuticals, and personal care products.82 147148 Novel materials will need to be tested as selective receiving phases (e.g., ionic liquids, molecularly imprinted polymers, and immunoadsorbents), together with membrane materials that permit the selective diffusion of these chemicals. The sample extraction and preconcentration methods used for these devices will need to be compatible with LC-MS analytical techniques. 

Buser and co-workers have used different GC/MS techniques in the investigation of PCDTs in fly ash samples and in aquatic organisms [12, 31]. GC/MS and MS/MS were used for detection and to differentiate PCDTs from PCDDs. Various ionization [electron ionization (El) and negative-ion chemical ionization (NCI)] techniques and MS/MS experiments monitoring different daughter ions on a hybrid instrument were used to distinguish PCDTs from PCDDs [31]. 

Alvarez, D.A., Huckins, J.N., Petty, J.D. et al., 2007. Tool for monitoring hydrophilic contaminants in water Polar Organic Chemical Integrative Sampler (POCIS). In Greenwood, R., Mills, G.A. and Vrana, B. (eds), Passive Sampling Techniques in Environmental Monitoring. Comprehensive Analytical Chemistry Series, Barcelo, D (series ed.), Elsevier, Amsterdam, 171-97. 

For chemical monitoring, a list of priority substances has been established that includes metals such as cadmium, lead, and nickel. As far as metals are concerned, voltammetric techniques and more precisely electrochemical stripping analysis has long been recognized as a powerful technique in environmental samples. In particular, anodic stripping voltammetry (ASV) coupled with screen-printed electrodes (SPEs) is a great simplification in the design and operation of on site heavy metal determination in water, for reasons of cost, simplicity, speed, sensitivity, portability and simultaneous multi-analyte capabilities. The wide applications in the field for heavy metal detection were extensively reviewed (Honeychurch and Hart, 2003 Palchetti et al., 2005). 

There is a big drive for miniaturisation because of the many advantages it offers, such as shorter analysis times, better control, high throughput, reduction in chemicals and sample required, lower cost and remote monitoring applications. Some devices can be made so small that they can be integrated into larger instruments or incorporated into on-line or in-line systems or arrays. They can be transported easily and entirely new techniques and concepts are becoming available to analysts as the spatial dimensions are rednced. 

Diffusivities of various elements ate determined experimentally. Dopant profiles can be determined. The junction depth can be measured by chemically staining an angle-lapped sample with an HE/HNO mixture. The -type region of the junction stains darker than the n-ty e region. The sheet resistivity can also be measured using a four-point probe measurement. These two techniques ate used for process monitoring. 

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