Contamination from glassware

Initially, this method utilized 5-mL conical centrifuge tubes as the collection device for final elution of the extract from the Cig tubes. In practice, these tubes were found to be very difficult to clean and in few instances were the cause of cross-contamination when low-concentration samples were extracted following samples with very high concentrations. Since no commercial graduated tubes were available, disposable culture tubes are used as the receiver. These tubes are individually calibrated before use. A solvent blank sample may be processed through the method from extraction to quantification to determine if contamination from glassware occurs. 

Suspected contaminant from glassware cleaning procedures or analytical methods. 

The determination is especially susceptible to contamination from glassware. Extreme care must be exercised and all glassware must be rinsed with I I nitric acid before use. 

An interesting example of the contamination risks which may be caused by a laboratory vessel is that of boron. Determination of very low boron concentrations, involves a prior separation by distillation and subsequent analysis by spectrometry, with a suitable reagent such a curcumin or carminic acid. The use of laboratory vessels made of borosilicate glass (such as Duran or Pyrex) could lead to very large errors in the boron content found. Such errors are caused by sample contamination from the boron present in the glassware. 

Zhang, J.-Z., C. Fischer, and P.B. Ortner. 1999. Dissolution of silicate from glassware as a contaminant in silicate analysis of natural water samples. Water Research 33 2879-2883. 

Nondrug-related impurities can be extracted from various components employed in the sample preparation of a low-dose drug product. Classic sources of this type of contamination are glassware,20 filters, centrifugation tubes, HPLC vials and caps and transfer pipettes.20 Chemicals from the pH electrode can also be extracted into the sample diluent while adjusting the pH of the solution. In addition, impurities in reagents used in sample preparation1 can pose issues. 

In addition to these precautions the necks of all bottles and pipettes etc., should be flamed . This does not have the function of sterilising the glassware but of raising its temperature above the ambient and thus causing an upflow of air around the bottle or pipette. It prevents airborne contaminants from settling into flasks or onto pipettes. 

These metal analyses indicate a marked reduction of both titanium and iron in the dialytic extract relative to both the coal and the soxhlet extract. The question remaining is, how much of this metal is background It should be noted here that attainment of good trace element analyses in the low ppm range requires very careful experimental precautions and replicate analyses. This particular experiment is, by its nature, difficult to conduct in a scrupulous "trace element clean" manner. However, if it is assumed that contamination from any source (solvents, glassware, utensils, etc.) will usually add to the concentration of metal, we can use the metal content determined in the dialyzate as an upper limit for soluble metals content. The higher iron and titanium concentrations in the soxhlet extract indicate that these metals may be associated with material which is not truly soluble, such as microparticulate mineral matter. 

The normally moderate to high zinc contents in foodstuffs coupled with excellent AAS detectivity for this element, indicate FAAS to be the technique of choice for virtually all food analyses. Should in the odd instance, greater detectivity be required, resort can be made to chelation-extraction with APDC—MIBK as outlined in Section IV.B.ll(ii), or EAAS [227], The ubiquitous nature of zinc can lead to problems with contamination from reagents, glassware, plastic ware and other apparatus when low levels are determined. 

The major outside source of contamination to buffers is the ingress of ammonia from the atmosphere. Glassware may also be a source of contamination all glassware for use with amino acid analysis... 

At the high sensitivity of the electron capture detector, the laboratory is a prime source of contamination. All reagents and glassware should be checked for contamination. Heat treating the glassware to 300°C. overnight is a convenient way to avoid contamination from this source. 

Eluted material almost always includes unwanted extraneous matter co-extracted from the paper or thin-layer chromatogram. Thus it is advisable to use the eluent from a blank area as a reference solution. Contamination from plasticisers, solvents, and dirty glassware can also be a serious problem when a spectrum has to be obtained from a few micrograms of a compound. Even momentary contact of dry adsorbent with plastic tubing can remove appreciable quantities of plasticisers. Hence the following precautions should be taken ... 

Certain metals have a profound influence on the activity of the enzyme. Copper in concentrations as low as those resulting from contamination of glassware and reagents will catalyze nonenzymatic oxidation of p-phenyl-enediamine. For this reason it was recommended that 10 M EDTA (ethylenediaminetetraacetic acid) be incorporated in the reaction mixture (B28). However, higher concentrations of EDTA inhibit the enzyme, and it has been suggested that EDTA may form a complex with copper in ceruloplasmin and thereby inactivate the enzyme (H20, K3). The addition of EDTA to the reaction mixture therefore may not be desirable. We found that by simply avoiding copper contamination, by the use of precautions necessary in copper determinations, the nonenzymatic oxidation of p-phenylenediamine slows to an imperceptibly low rate, and in this situation there is of course no need to add EDTA. 

Pre-concentration is concerned with the reduction of a larger sample into a smaller sample size. It is most commonly carried out by using solvent evaporation procedures after an extraction technique (see, for example, Chapters 7 and 8). The most common approaches for solvent evaporation are rotary evaporation, Kudema-Danish evaporative concentration, the automated evaporative concentration system (EVACS) or gas blow-down . In all cases, the evaporation method is slow, with a high risk of contamination from the solvent, glassware and blow-down gas. 

Phthalates are common environmental contaminants that frequently contaminate laboratory glassware, sampling equipment, and solvents used to extract di- -butyl phthalate from various media for analysis (Staples et al. 1997). As a result, it is difficult to make accurate measurements at low levels (<10 ppb). Care must be taken to preclude environmental and other samples from contamination with di-n-butyl phthalate. 

One problem which is particularly critical when small quantities of ammo acids are measured is the risk of contamination with extraneous amino acids (aspartate, glutamate, serine, glycine, and alanine) from the glassware, solutions, and so forth (Lee and Drescher, 1978) Obvious precautions necessary to follow include the use of disposable gloves, freshly distilled water, and highly pure chemicals. Ammo acids in the blanks are further reduced if the glassware and plastic collection tubes are prerinsed several times with diluted phosphoric acid and distilled water. In order to avoid contamination from the injection loop, syringe, and elution buffer, the reaction mixture may be acidified after a set time (Jones et al., 1981). 

For all procedures after hybridization, we use separate glassware and graded ethanol solutions from those used prior to hybridization, because RNase A is used during the washing procedures and could contaminate aU glassware and... 

Keep contaminated material (glassware, mortars, vessels etc.) separated from clean equipment. 

There are modifications of the above procedure which do not require the complete separation of phosphorus from silica, but depend on the preferential reduction of silicomolybdic acid to molybdenum blue in the presence of phosphomolybdic acid. In general, it is emphasized that dependable results rely on careful avoidance of contamination of the sample with silica from glassware, elimination of interference by phosphorus, and maximum sensitivity in making the colorimetric measurement (409-411). Baumann described a preferred technique for analysis of silica in blood and other biological materials (see Chapter 1, Ref. 320). 

Care must be exercised in the use of glassware with standards so as to avoid contamination from comparatively high concentrations of organotin compounds. Sodium hydroxide solutions appeared to work best as a cleaning agent for glassware. 

Another facet of sample preparation for GTI methods is the potential for contamination. Given that most GTI methods are detecting analytes with concentrations of ng/mL or pg on column sensitivity, it only takes a few micrograms of the GTI to contaminate a sample and potentially provide a false positive failure of a batch. The probability of contamination increases especially in laboratories that test a particular process intermediate (also a GTI) at standard concentrations for an impurity/degradant method. Trying to analyze for trace levels of the process intermediate with a GTI method can be readily complicated from glassware contamination, contamination of a spatula, balance, or LC vials. It can also be problematic if the same LC or GC is used to test both the impurity/degradant method and trace GTI method. Extra care must be taken to prevent cross contamination. 

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