Blank problems

The blank problem becomes more severe when volatile organic compounds are sampled in the presence of reactive gases. Pellizzari et al. (1984) and Zielinska et al. (1986) showed the influence of different reactive inorganic gases on the decomposition of Tenax GC and showed possibilities to protect the adsorbent with mild reduction agents. Clausen and Wolkoff (1997) tried to use the amount of degradation products formed on Tenax as an indicator for the presence of reactive species in indoor air. Helmig (1997) reviews techniques to reduce the adverse effect of ozone on sampled VOCs. 

The low Pb levels, associated to the high level of particulate matter in the original estuarine water sample rendered the determination of this element too difficult for allowing certification. The laboratories stressed that contamination and blank problems hampered a good agreement to be obtained which outlines that the state of the art is rather poor for such matrix. A new mean was calculated and is given as indicative value in the certification report [21. ... 

Although the method is applicable to the analysis of DEHP in surface water and allows achievement of a sufficiently low LoQ to conduct compliance checking in principle, many laboratories have serious blank problems and are hence, not able to meet the LoQ performance criterion (LoQ < 30 % EQS). 

A screening method for the analysis of 16 PAHs, 6 PCBs and 6 phthalate esters have been recently developed using a multisimplex strategy to optimize experimental parameters affecting PDMS SPME. Due to blank problems, detection limits for some phthalates were quite high, especially for DEHP (3.15 /rg/1). 

The blank problem becomes more severe when volatile organic compounds are sampled in the presence of reactive gases. Pellizzari et al. (1984) and Zielinska et al. 

For each of the following, fill in the blank with the correct response. All of these fill-in-the-blank problems pertain to material covered in the sections on alkanes, alkenes and alkynes,... 

In order to reach the interference-free limits of detection calculated by means of Eq. (1) and illustrated in Fig. 3 [6], it is necessary to eliminate other activities present in the sample using a radiochemical separation. This requires that the irradiated sample be decomposed, usually by the addition of nitric, perchloric, or sulfuric acids this does not create any blank problems but may easily result in losses of an ultratrace element to be determined. In order to control and minimize such losses a suitable amount of carrier of the element should always be added to the sample... 

Nb and Ta) are present. If boron trifluoride is separated by distillation, it cannot be excluded that according to the total acidity and the fluorine concentration in the distillate, methylenebluefluoride, which absorbs at exactly the same wavelength as the BF complex compound, can be formed. Thus, important interferences and blank problems can appear. What is true for methyleneblue complexes is also true for nil blue ones, which are claimed to give, according to further experiments of these authors, less interference problems. Meier (20) however asserts having realized and solved these problems for his methyleneblue method, partially by its calibration. 

As the carbon content of aluminium is generally low, combustion methods as such are only of limited use, as they suffer from blank problems and lack of sensitivity (1 /tg/g). In round robins organized by BCR on the analysis of carbon in primary ingot aluminium (Table V-8) only photon (or helium-3) activation analysis in combination with combustion and deuteron activation analysis in combination with Kjeldahl led to significant, and probably also accurate results. 

Thomas, S., Morawska, L., Bofinger, N., and Selby, M. (1997). Investigation of the source of blank problems in the measurement of lead in sub-micrometre airborne particulates by inductively coupled plasma mass spectrometry.J. Anal. At. Spectrom. 12(5), 553. 

The virtually unlimited lifetime of the KR makes it a reliable and stable preconcentration system. Comparative studies have demonstrated that with KR the preconcentration efficiencies are higher than for serpentine 8-shaped reactors (SR) (i.e. from 4 to 36 and from 3 to 12, for the KR and SR, respectively). Nonetheless, this method has limitations, including blank problems and errors induced as a result of different complexation efficiencies for analytes present in different chemical forms (e.g. oxidation states). ... 

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