Maintaining Sample Integrity

Obtaining the aqueous solution to analyze is often a challenge in materials analysis. Thin films usually can be dissolved by acids without dissolving the underlying substrate, however sometimes this is difficult. A film can also be oxidized and the oxide dissolved. Temperatures involved in this procedure are sometimes quite elevated so care must be taken to maintain sample integrity. The chemistry of the sample must be kept in mind so that the limits of the analysis are known. 

A good sample custodian is one who has all the analytical laboratory skills outlined in Chapter 1 (see Section 1.5) and utilizes them in executing any analytical laboratory operation. A conscientious and careful laboratory technician will succeed in maintaining sample integrity. See Workplace Scene 2.2. 

The elimination of mannal sample handling with the inherent gain in safety and, to some extent, the elimination of operator error (and being able to maintain sample integrity). 

As far as chemical variables are concerned, especially in case of trace determinations, all the steps of sample collection, treatment in the field and storage must be carefully considered in order to maintain sample integrity before analysis. In this respect the selection of appropriate equipment and non-contaminant materials, as well as the application of efficient cleaning procedures, are of paramount importance. For the most critical applications clean chemistry laboratories (equipped with Class 100 laminar flow cabins) must be available in the field or on board. 

Freezing is considered to be an acceptable preservation method for wet sediments collected for the determination of inorganic constituents (Forstner, 2004). It has been shown that rapid deep-freezing can best maintain sample integrity, thus enabling reliable evaluation of contaminant concentrations. The lower the deepfreezing temperature the better a minimum temperature of —80°C was suggested. 

Devices are commercially available that maintain sample integrity and trace detection limits, while eliminating interfering sample matrices. Dionex offers an Auto Neutralization Module that neutralizes concentrated acid with electrically generated hydroxide ions [4],... 

Ouyang, Z., Federer, S., Porter, G., Kaufmann, C., and Jemal, M. (2008) Strategies to maintain sample integrity using a liquid filled automated liquid handling system with fixed pipetting tips. Journal of Laboratory Automation, 13, 24 32. 

To obtain TRIR spectra with sufficient sensitivity, we typically signal average several thousand laser shots at each IR frequency of interest. A flow cell, therefore, is necessary to prevent excessive sample decomposition, especially when photo-irreversible processes are monitored. A reservoir of solution (typically 10-20 mL) is continually circulated between two calcium or barium fluoride salt plates. To maintain sample integrity for non cyclic systems, one is usually forced in the dispersive TRIR experiment to acquire data in a series of short (e.g., 100-200 cm ) scans rather than in one complete scan. Thus, a substantial amount of sample may be required. Sample integrity is also of significant concern in the step-scan FTIR experiment because data must be collected at each mirror position. To address this concern, very large reservoirs of solution are required alternatively, a sample changing wheel [33] or very focused pump-probe beams in combination with sample translation [34] have been used with thin film samples. 

Requires stringent analytical protocols and safe handling procedures and facilities to maintain sample integrity and avoid contamination of facilities and exposure of personnel. 

Clinical procedures must assure that no unaccounted sources of C or carbon enter the defined sample, introducing a C in (Eq. 16.4) that is not easily understood in postclinical analysis. AMS sensitivity is specific for the particular isotope tracer, helping to focus procedures for maintaining sample integrity. AMS quantitation is not affected by the presence of other radioisotopes, such as tritium, when C is used as the isotopic tracer. Much of the early work developing AMS for biochemical studies was performed in laboratories that... 

Pre- and guard columns can be used for online sample cleanup in conjunction with LC, which helps maintain sample integrity while protecting expensive and fragile stationary phases. Samples may also be preconcentrated prior to elution onto separation column. 

Whole air sample, where a sample is taken and returned unchanged to the laboratory for analysis. This approach is very useful for maintaining sample integrity and where the analyte concentration is sufficiently high to avoid a sample preparation stage before analysis. 

Optional) Store tissues and sections wrapped in aluminum foil at -80°C. This maintains sample integrity for up to a few months. CAUTION Improper storage conditions can result in postmortem tissue degradation see Note 4.1.2). 

While the procedures covered by this practice will produce a representative sample of the flowing liquid into the sample receiver, specialized sample handling may be necessary to maintain sample integrity of more volatile materials at high temperatures or extended residence time in the receiver. Such handling requirements are not within the scope of this practice. Procedures for sampling these fluids are described in Practice D 1265, Test Method D 1145, and GPA 2166. 

Automatic Samplers—An automatic sampler includes not only the automatic sampling device that extracts the samples from the line, but also a suitable probe, connecting lines, auxiliary equipment, and a container in which the sample is collected. It must maintain sample integrity. Refer to API MPMS Chapter 8.2. Automatic samplers are classified as follows ... 

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