Sample Collection and Conditioning

Figure 19.1 is a block diagram of a typical process analyzer system, consisting of a sample collection and conditioning system, sample manifold, sample inlet, ion source, mass analyzer, detector, and a data analysis and output system that interfaces with the process control system. The dashed line indicates the parts of the overall system that are considered to comprise the analyzer itself (i.e., what is normally included when one purchases a process MS). Figure 19.2 is a photograph of a commercial process MS that incorporates these components. Aspects of these various components are described below, with emphasis on how they are applied in a process mass spectrometer. 

Type of Container to Be Used. The specific type of contained used to collect blood or urine samples is sometimes indicated in a protocol, especially if a special anticoagulant or additive is required or if other specific conditions of sample collection and handling are required. It is generally not necessary to provide this information for commonly requested laboratory tests. 

Pre-entry criteria define the conditions and circumstances under which site characterization activities will be initiated and the manner in which these activities will proceed. At each stage of the process (i.e., approach to the site, on-site characterization activities, sample collection, and exiting the site), specific criteria may be defined for proceeding to the next stage. The pre-entry criteria may also specify the general makeup of the site characterization team under various circumstances. For example, under low-hazard conditions chemical facility teams may perform site characterization, while specially trained responders might be called upon to assist in the case of potentially hazardous conditions at the site. The criteria developed for a particular chemical facility should be consistent with the role that the facility has assumed in performing site characterization activities. 

System installation in a permanent location may require a sample conditioning system featuring some degree of automation, such as automatic cleaning (the system illustrated above features such a system) and outlier sample collection and the need to interface to an existing control system process computer. The latter may require that the system operates with a standardized communications protocol, such as Modbus, for the chemical industry. Certain specialized industries use different protocols, such as the semiconductor industry, which uses SECS and SEC-11 protocols. A standardized approach designated the Universal Fieldbus is another method/protocol for process analyzers which is being supported by certain hardware manufacturers. 

The aerosol samples collected by the SFU were analyzed both gravimetrlcally for total suspended particulate mass less than 15pm, and by particle induced x-ray emission (PIXE) for elemental content. The filters were weighed before and after sampling using a Cahn 25 electrobalance sensitive to Ipg. Typical precision of TSP determined by this analytical method is 0.5pg/m for samples collected under conditions of low aerosol concentrations ( ). After weighing, the filters were analyzed for elemental content (elements heavier than Na) using the UC Davis PIXE system. This analysis technique is described in Cahill al ( ). 

In air monitoring program accurate concentration determinations require careful attention to the sample collection and subsequent analysis of the collected sample. The analysis is the most critical step, especially if very low levels (ppb) of contaminants are being determined. However, in many cases, sampling may be the least accurate step since this job is performed in the field with portable equipment under conditions far less favorable than those that can be created and controlled in the lab ). ... 

It is possible to substitute the coefficient of variation for the standard deviation in the above equation. If the conditions of patient preparation, sample collection, and sample handling are standardized, preanalytical variation is minimized and the total variation is then determined by the combined influence of the analytical and intraindividual variations, thus ... 

A result indicating 85% donor cells and 15% recipient cells might be equally consistent with an engrafting marrow 3 weeks after transplantation or with relapse 6 months following transplantation. The date of the transplant in relation to sample collection, the conditioning regimen used before transplant, and evidence from peripheral smear or bone marrow aspirate examination may be helpful in interpreting results. Unusual history, if unknown, can cause considerable confusion. For example, some recipients may have received more than one stem ceil transplant or may have had a donor who is an identical twin. 

Defining the scope of the method Support for PK/PD/other studies Desired sensitivity Matrix of study samples Sample collection and storage conditions Assay format/technology platform... 

Subsurface physical, chemical and biological conditions are quite variable in space and time. These factors can be the source of considerable "natural" variability in ground-water chemistry at both clean and contaminated sites. Sampling and analytical errors or variability can be controlled if these activities are planned and documented as protocols which take into account the unique characteristics of individual sampling points and conditions. It is critical that a sound hydrogeologic basis exists for the steps in the sampling protocol which precede actual sample collection. 

The first category (Table 9.2), (1) Sample, collects the conditions of sample preparation. In the example here, kidney from a rat will be used following trans-cardiac perfusion. The tissue blocks will be infiltrated with 20% sucrose overnight, frozen in isopentane, and sectioned on a cryostat. For processing, the sections will be placed on a microscope slide. To calculate how much incubation and rinse solutions are needed, the size of the incubation chamber is listed. In the example, 250 p,l will just cover the tissue and can be used for each step. 

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