Problems glassware

Contaminated solvents and glassware are a very well known problem in analysis involving extraction. The major problem in the use of solvents is contamination with plasticisers, especially DEHP. After sample extraction usually enrichment of the analytes is required prior to the analysis. 

The electrolyte volume of the STM cells is usually very small (ofthe order of a 100 pi in the above-described case) and evaporation of the solution can create problems in long-term experiments. Miniature reference electrodes, mostly saturated calomel electrodes (SCE), have been described in the literature [25], although they are hardly used anymore in our laboratory for practical reasons Cleaning the glassware in caroic acid becomes cumbersome. For most studies, a simple Pt wire, immersed directly into solution, is a convenient, low-noise quasireference electrode. The Pt wire is readily cleaned by holding it into a Bunsen flame, and it provides a fairly constant reference potential of fcj>i — + 0.55 0.05 V versus SCE for 0.1 M sulfuric or perchloric acid solutions (+ 0.67 0.05 V for 0.1 M nitric acid), which has to be checked from time to time and for different solutions. 

One of the main problems to be solved in the analysis of cationic surfactants is the strong adsorption of the surfactant to glassware, tubing and apparatus. To avoid losses, the solvent system used should contain a substantial percentage of organic solvent. Additionally, mobile phases containing more than 20-25% methanol will help to inhibit micelle formation [46]. 

Contamination is a major problem in lipid analysis and the use of plastic containers and stoppers, rubber bungs or tubing, and any grease on stopcocks, etc., must be avoided. All solvents used should be of the purest grade and be peroxide-free and all glassware should be scrupulously clean. 

Precautions should be taken when selecting various vessels of differing materials for the extraction of these steroids from their matrices. For example, the compatibility of some solvents with plastic extraction tubes may present some problems. If glass vessels are to be selected, it is recommended that all glassware is silanized prior to use since several steroids bind to glass surfaces. 

There is usually no problem of access to basic laboratory instruments and associated glassware, however, the only means of handling large numbers of tests is to apply some form of automation. An added advantage is that it improves the analytical precision and reproducibility. The most suitable technique has been based on the segmented continuous-flow principle invented by Skeggs (1957), and which was first marketed as the Technicon AutoAnalyzer. The system consists of a number of modules powered from a stabilized 110 V supply, and a typical layout is shown in Fig. 1.1. 

Adsorption is also a problem at trace levels. Few solutions below a concentration of 10 pg cm- can be considered to be stable for any length of time. Various preservatives to guard against adsorption of metals on to glassware have been reported in the literature. Common precautionary steps are to keep the acid concentration high and to use plastic laboratory ware. 

Typically, a positive -intercept indicates the existence of interference with the response or the saturation of responses at high concentrations. A negative -intercept indicates the possibility of method sensitivity problem (i.e., a low response cannot be detected) or analytes get retained in the glassware or HPLC system (i.e., a compatibility issue between sample solvent and mobile phase). 

It was agreed to set the LOQ at twice the blank level. This may render occasional problems for the C26 0 fatty acid as the LOQ of 0.336 pmol/1 is close to the lower end of the physiological concentration range. Glassware should be ultra-pure to reduce the blank values as much as possible. 

The accurate calibration of volumetric glassware must also take buoyancy into account. For example, in the previous problem, if the observed weight of water is that needed to fill a 100 ml volumetric flask exactly to the mark, we could easily calculate the true volume of the volumetric flask just as we did on p 86 ... 

It is essential that glassware not be contaminated with trace metals or other pro-oxidants. If this is a problem, consider disposing of the glass sample tubes after a single use. 

The tunicate gonads that were harvested for protein extraction never saw my colleague s laboratory and were worked up here in acid-cleaned glassware. The implication is that two laboratories on separate continents would have acquired the same contaminant, once as mRNA and once as a protein Micro-sequencing is a legitimate and well-established method and quite powerful in the hands of an expert. Contamination can be a problem, but it is not an insurmountable one, and fear beyond reason must not be allowed to paralyze progress. 

Determination of Correction for Sample Loss Due to Adsorption. Adsorption of the PGS to glassware can be a cause of significant losses of samples. The problem is particularly pronounced for relatively pure samples of PGS. The adsorption process described by the Langmuir isotherm indicates that, at very low concentrations, most material is adsorbed to the glassware. 

Although simple and relatively inexpensive spinning brush attachments can be used for general glassware washing, each piece of glassware must be individually handled. This tends to maintain the breakage problem. 

Laboratory glassware containing reaction mixtures of unknown nature (and sometimes of unknown origin) can pose difficult disposal problems. Such materials occur frequently in research laboratories, particularly in those that have a high rate of personnel turnover. Simple laboratory tests may provide enough information for safe disposal. The waste management system should provide a procedure designed to prevent the occurrence of such orphan wastes. 

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