Caution samples

Since these volumes are determined from external dimensions of the samples, they do not reflect actual changes in the cell wall volumes, and where this is claimed or assumed, the data needs to be treated with caution. Sample geometry is a crucial factor affecting the results obtained. In particular, the orientation of growth rings with respect to the sample... 

Caution. Samples of S4N4 are explosive under the influence of heat or mechanical stress. The dry recrystallized product should not be removed from the flask with a metal spatula. Use of Teflon spatula or glass rod is recommended. It is highly recommended that S4N4 not be prepared in amounts greater than 0.5 g at any given time. 

Note 4 Caution—Samples of high-aromatic content will probably dissolve polycarbonate Aims. 

Occurrence of Plasticizers in the Environment. The contamination of laboratory chemicals and equipment causes problems in the analysis of very low concentrations of phthalates in environmental samples. Strenuous efforts have been made to overcome these difficulties in recent studies but the results of many earHer investigations must be treated with caution. 

There are numerous solubility data in the literature the standard reference is by Seidell (loc. cit.). Valuable as they are, they nevertheless must be used with caution because the solubihty of compounds is often influenced by pH and/or the presence of other soluble impurities which usually tend to depress the solubihty of the major constituents. While exact values for any system are frequently best determined by actual composition measurements, the difficulty of reproducing these solubility diagrams should not be underestimated. To obtain data which are readily reproducible, elaborate pains must be taken to be sure the system sampled is at equihbrium, and often this means holding a sample at constant temperature for a period of from 1 to 100 h. While the published cui ves may not be exac t for actual solutions of interest, they generally will be indicative of the shape of the solubility cui ve and will show the presence of hydrates or double salts. 

Hjertberg et al. [72] have studied various PVC samples using Shimizu and Ohtsu s method [69]. They concluded that this method mainly gave a measure of the content of saturated 1,2-dichloroethyl chain end groups, the presence of which has been conclusively demonstrated [73]. With caution they contend there are 0-0.2 head-to-head structures per 1,000 monomer units. 

Outliers, observations that are very inconsistent with the main sample of data, i.e., apparently significantly different from the rest of the data. While there are statistical methods to test whether these values may be aberrant and thus should be removed, caution should be exercised in this practice as these data may also be the most interesting and indicative of a rare but important occurrence. 

Determination of calcium. Pipette two 25.0 mL portions of the mixed calcium and magnesium ion solution (not more than 0.01M with respect to either ion) into two separate 250 mL conical flasks and dilute each with about 25 mL of de-ionised water. To the first flask add 4 mL 8 M potassium hydroxide solution (a precipitate of magnesium hydroxide may be noted here), and allow to stand for 3-5 minutes with occasional swirling. Add about 30 mg each of potassium cyanide (Caution poison) and hydroxylammonium chloride and swirl the contents of the flask until the solids dissolve. Add about 50 mg of the HHSNNA indicator mixture and titrate with 0.01 M EDTA until the colour changes from red to blue. Run into the second flask from a burette a volume of EDTA solution equal to that required to reach the end point less 1 mL. Now add 4 mL of the potassium hydroxide solution, mix well and complete the titration as with the first sample record the exact volume of EDTA solution used. Perform a blank titration, replacing the sample with de-ionised water. 

Next is to make sample prototype tooling and sample prototype products for the test. Samples made by machining or other simplified model making techniques do not have the same properties as the product made by molding or extrusion or whatever process is to be used (Chapter 3, PROTOTYPES). A product made this way is a sample rather than a testable prototype. Simplified prototypes may reduce trial mold cost and produce adequate test data in some cases. Its main value is appearance and feel to determine whether the aesthetics are correct. Any testing has to be done with considerable reservation and caution. 

The constant matrix in Group III is conveniently defined as all the sample except the elements being determined, but a word of caution is necessary. If these elements are present at appreciable concentration, then absorption and enhancement effects to which they give rise must of course be considered for, as was pointed out in Section 7.3, these effects do not reside in the matrix alone. 

As a caution, however, one must carefully purify the sample since small amounts of low molecular weight impurities can contribute significantly to II, even though their mass percentage in the sample is small. 

Knox and Piper (13) assumed that the majority of the adsorption isotherms were, indeed, Langmuir in form and then postulated that all the peaks that were mass overloaded would be approximately triangular in shape. As a consequence, Knox and Piper proposed that mass overload could be treated in a similar manner to volume overload. Whether all solute/stationary phase isotherms are Langmuir in type is a moot point and the assumption should be taken with some caution. Knox and Piper then suggested that the best compromise was to utilize about half the maximum sample volume as defined by equation (15), which would then reduce the distance between the peaks by half. They then recommended that the concentration of the solute should be increased until dispersion due to mass overload just caused the two peaks to touch. 

Sample shelves also become overcrowded quickly, but it is often required to keep samples for extended periods of time. Older samples can be stacked into cardboard cartons, clearly identified by laboratory project references or quality control numbers, and stored at a convenient location away from the laboratory. Periodically they should be inspected and the out of date ones eliminated. One word of caution, however. Under current pollution control rules, laboratory samples may not be indiscriminatly disposed of as garbage. The laboratory operator should call in a waste disposal service when in doubt. 

Another reversal location method is to expose the TLC plate to iodine vapour in a closed chamber that contains some iodine crystals. Iodine is lipophilic and accumulates in hpophihc sample spots, showing a brown color on a pale yellow-brown background. The same result is obtained by spraying with an iodine solution (250 mg iodine dissolved in 100 ml of heptane). In nearly all cases, this iodine accumulation is totally reversible without altering the sample, because outside the closed chamber iodine evaporates quickly from the plate. Caution should be taken with this iodine treatment in the case of unsaturated compounds because iodine vapor can react with double bonds [16]. 

The use of a matrix blank is the simplest way to overcome a matrix effect, but the analyst must ensure that the matrix blank is uniform and does not change between sample sets. Acquiring a uniform blank matrix may be problematic if assays are conducted over an extended time period. Caution must be taken when an analysis, validated for one matrix or species, is used for a different tissue or species, because... 

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