Storage of samples

Raw materials. Most luminous organisms can be stored at —70°C or below under aerobic conditions, or with dry ice, without a significant loss of luminescence activity for a period of several months or more, although a trial is always recommended. Even if a substance already extracted is unstable when stored with dry ice (like the luciferase of Cypridina and the luciferins of euphausiids and dinoflag-ellates), the same substance in the organisms before extraction can be safely stored at — 70° C or with dry ice. The material can also be stored with liquid nitrogen for added safety, but the quantity storable in a laboratory setup (e.g., Dewar flask) is limited. 

Oxygen-sensitive substances. Substances that are moderately sensitive to oxygen (such as crystalline coelenterazine and Cypridina luciferin) can be stored aerobically at below — 70°C in a desiccated container for many years. They can be permanently stored in an evacuated fuse-sealed glass container even at room temperature, in darkness (for the technique, see Method II below). 

Alternatively, moderately oxygen-sensitive substances can be stored under vacuum or in high purity argon gas, at a temperature 

For the storage of a substance dissolved in a volatile solvent, the solution must be placed directly in the flask, not within a vial. During the evacuation, gently sway the flask and adjust the evacuation speed to avoid sample loss due to a sudden boiling of the solution. Replace the inside space of the flask completely with the solvent vapor (typically methanol) by boiling the sample solution for a period of 1-2 minutes before closing the stopcock. In using this method, however, 

Storage under vacuum in a sealed tube (Method II). Substances that are extremely oxygen-sensitive, such as the fluorescent compound F of euphausiids and dinoflagellate luciferin, have to be stored in an evacuated sealed container at a low temperature. For long-term storage, they must be fuse-sealed in an evacuated glass vial using the method outlined below. 

When samples cannot be analyzed immediately, they must be stored. The composition of a sample may change during storage because of reactions with air, light, or interaction with the container material. The container used for collection and storage of the sample and the storage conditions must be chosen to minimize changes in the sample. 

Sample containers must be labeled accurately and in such a way that the label does not deteriorate on storage do not use water-soluble marking pen on samples to be put in a 

How many samples do we need to collect for a given analysis How large must the sample be to insure that it is representative These types of questions can be answered by statistics. We also need to have a basic knowledge of statistics to understand the limitations in the other steps in method development, so we will now briefly introduce the statistical concepts and calculations used by analytical chemists. 

In order to design the correct experiment to answer the analytical question being asked, statistics is needed to select the size of the sample required, the number of samples, and the number of measurements that must be performed to obtain the needed accuracy and precision in the results generated by the experiment. Statistics is also used to express the uncertainty in measured values, so that the users of the data understand the limitations associated with results. 

The number 50.1 has three significant figures (5, 0, 1). Since the measurement is no better than 0.1%, the last digit in 50.1 is uncertain by at least +1. The last significant 

Sample containers must be labeled accurately and in such a way that the label does not deteriorate on storage do not use water-soluble marking pen on samples to be put in a freezer, for example. The label should clearly identify the sample and any hazards associated with the sample. Many analytical laboratories have computer-based sample tracking systems that generate adhesive bar-coded labels for samples, exactly like the bar codes used on retail items in stores. These computer-based systems are called Laboratory Information Management Systems (LIMS) and catalog and track not only the samples but also the analytical data generated on the samples. 

After preparation, all pure products should be stored in suitable clearly and permanently labelled containers. The bulk samples of stable solids and liquids may be stored in screw-capped and ground glass stoppered bottles respectively. Hygroscopic samples, or those liable to decomposition by contact with atmospheric moisture, should either be stored in a desiccator or in a bottle which is sealed by painting over the closure with molten paraffin wax. Where there is a possibility of photochemical decomposition of chemicals it is general good practice to keep them out of direct sunlight and to store them in brown bottles. 

Small specimens of all products, including reaction intermediates isolated from reaction sequences, and particularly samples of fractions isolated as the result of lengthy chromatographic or other purification procedures, should invariably be retained for reference purposes. The commercially available straightsided specimen tubes with polyethylene plug seals, which are available in a range of sizes, are suitable in the case of solid samples. It is usually advantageous to label them with the name and a code reference to enable physical data (elemen- 

If the sample needs to be sealed in an atmosphere of nitrogen, the inlet of the protecting tube is connected to a low-pressure supply of the gas when the syringe or pipette has been withdrawn. When all the air has been displaced the tube may be slowly withdrawn and the ampoule sealed. Filled ampoules containing volatile samples should be thoroughly chilled in a suitable cooling bath 

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Cataloging and storage of samples may inundate the laboratory, resulting in storage and retrieval problems. Mislabeled and lost samples are frequent problems. The longer the special samples remain in the laboratory, the greater the likehhood that some will be lost or mislabeled. 

Squids (Cephalopoda), 176, 181, 199 Stauroteutbis, 182, 335 Sternoptyx, 328, 338 Stigmatogaster, 336 Stomias, 338 Storage of samples, 356 under argon gas, 358 under vacuum in a sealed tube, 358 Structure determination of luciferin, 377... 

Many of the coagulation factors measured by global coagulation tests have limited stability, and the time and temperature of storage of sample will affect their measurements. Concepts of analyte stability and half-life in plasma extend to markers measured by immunoassay. Markers of platelet activation are affected by artifactual activation in vitro upon collection of the blood specimen. This section will highlight some of the nonanalytical variables that, if uncontrolled, can lead to spurious results and thus affect the interpretation of laboratory data. 

If we were to choose the ideal method for the analysis of any component of seawater, it would naturally be an in situ method. Where such a method is possible, the problems of sampling and sample handling are eliminated and in many cases we can obtain continuous profiles rather than limited number of discrete samples. In the absence of an in situ method, the next most acceptable alternative is analysis on board ship. A real-time analysis not only permits us to choose our next sampling station on the basis of the results of the last station, it also avoids the problem of the storage of samples until the return to a shore laboratory. 

Scarponi et al. [93] used anodic stripping voltammetry to investigate the contamination of seawater by cadmium, lead, and copper during filtration and storage of samples collected near an industrial area. Filtration was carried... 

The first aim of this work was to study the influence of an unwashed membrane filter on the cadmium, lead, and copper concentrations of filtered seawater samples. It was also desirable to ascertain whether, after passage of a reasonable quantity of water, the filter itself could be assumed to be clean so that subsequent portions of filtrate would be uncontaminated. If this were the case, it should be possible to eliminate the cleaning procedure and its contamination risks. The second purpose of the work was to test the possibility of long-term storage of samples at their natural pH (about 8) at 4 °C, kept in low-density polyethylene containers which have been cleaned with acid and conditioned with seawater. 

Preservation and Storage of Samples for the Determination of Dissolved Organic Carbon... 

Storage of samples and data according to laboratory policy or until the customer accepts the results... 

Methods have been developed to characterise odours according to strength (1) and offensiveness (2) using experienced panellists. Measures of offensiveness are necessarily subjective and odour strength (threshold dilution) will depend upon the odour threshold value as well as the concentration. For routine assessment these methods incur the cost of panel time and the problems inherent in the transport and storage of samples. 

Preservation, transport and storage of samples Investigation methods for soils, soil material and other materials Selection and pretreatment of samples Extraction and elution techniques (Table 4)... 

Storage (of samples, reference items, raw data, final reports etc.)... 

Reactivity. Some substances may decompose or be altered in structure after collection, shipment, and storage of samples on some sorbents. Often decomposition can be minimized by selecting sorbents that are inert or will stabilize the substances of interest. An example is the collection of amines on acid-coated silica gel. The acid forms a salt and prevents the oxidation of the amine groups. 

The saturated VLCFA and branched-chain fatty acids are stable compounds they are not likely to be destroyed by oxidative processes. In this respect, storage of samples does not require more precautions than freezing. 

All of the above org azidodithiocarbonates were wh crystn compds which at RT undergo slow spontaneous decompn with ultimate quant formation of the corresponding thiocyanate or isothiocyanate, sulfur and nitrogen. The velocity of this decompn is sufficiently retarded at low temp to permit storage of samples at 0° for several days without deterioration... 

The restructuring allows a re-conversion of Al[5] and Al[61 into tetrahedral Al. This process proceeds also during storage of samples in humid air for longer periods of time already at room temperature. Under these conditions the surface is covered by a water film due to the hydrophilicity of the material. This state is somewhat similar to the complete hydration achieved by stirring in water or aqueous salt solutions. Only with aluminum-rich MCM-41 (Si/Al < 10), some of the aluminum (5%) remains in the octahedral state. 

Ordinary (i.e. atmospheric pressure) desiccators are available in the Dry-Seal or ground flange range and have limited use for storage of samples in a dry atmosphere. 

Especially when long-term storage of samples is required the monitoring of analyte degradation is of special interest (Volden et al., 2005). 

ISO (2006c) 16000-11. Indoor Air-Determination of the Emission of Volatile Organic Compounds from Building Products and Furnishing-Sampling, Storage of Samples and Preparation of Test Specimens,... 

CEN/ISO EN/ISO 16000-11 Indoor Air-Part 11 Procedure for sampling and storage of samples and preparation of test specimens Will supercede 13419-3... 

Storage of samples between tests is another potential source of error. In an ideal world, samples should be kept in the chamber or under the cell throughout an emission test. However, given that many standard methods and protocols require a 2- or 4-week evaluation and that each fully configured emissions test... 

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