Organic compounds blank determinations

Perform a blank determination (see General Provisions), and make any necessary correction. Each milliliter of 0. IN perchloric acid is equivalent to 9.109 mg of C5H12N204H20. Lead Determine as directed under Lead Limit Test, Appendix IIIB, using a Sample Solution prepared as directed for organic compounds, and 5 pig of lead (Pb) ion in the control. Loss on Drying Determine as directed under Loss on Drying, Appendix IIC, drying a sample at 50° for 4 h. 

FOLLOW-UP PROBLEM 15.4 Fill in the blank in each reaction. Hint Examine any inorganic compounds and the organic product to determine the organic reactant.)... 

One of the most important problems in the analysis of phthalates from water samples is the detection of these compounds in the samples used as blanks. Phthalates have been detected in purified water commonly used in laboratories, including water distilled in a glass distillation apparatus, MUli-Q water, and commercially available water specially for VOC (Volatile organic compounds) determination. Therefore, special caution should be taken with the experimental use of water in laboratories. Some authors have reported the levels of phthalate esters found in the purified water employed in its studies (see Table 28.4). The concentrations found are frequently... 

The commonly used organic insect toxicants do not interfere in the analysis of Compound 118 by this new procedure. Hexane solutions of chlordan, DDT, methoxychlor, hexachlorocyclohexane (BHC), and toxaphene treated according to the procedure for determining Compound 118 gave a pale yellow color similar to that of the blank. 

Better collection methods are needed for stack measurements. Virtual Impactors or other devices that avoid the bounce-off problems of cascade Impactors should be developed. Methods for collection of very large amounts of size-segregated particles suitable for detailed organic analyses are needed. Better low-blank filter and collection-surface materials that can withstand high stack temperatures are needed. Careful attention should be given to the determination of vapor-phase species of volatile elements and compounds. 

Certain substances, such as alkyl amines, produce fluorescence. Presence of such fluorescence compounds in the sample can produce positive interference. Base hydrolysis may result in the formation of such substances. Similarly, coeluting compounds that quench fluorescence may cause negative interference. Blanks should be run using organic-free reagent water without sodium hydroxide and o-phthalaldehyde to determine the presence of such interfering substances. 

The purpose of trip blanks is to assess the collected sample representativeness by determining whether contaminants have been introduced into the samples while they were handled in the field and in transit, i.e. in coolers with ice transported from the site to the analytical laboratory. A possible mechanism of such contamination is the ability of some volatile compounds, such as methylene chloride or chlorofluor-ocarbons (Freons), to penetrate the PTFE-lined septum and dissolve in water. Potential sources of this type of contamination are either ambient volatile contaminants or the VOCs that could be emanating from the samples themselves, causing sample cross-contamination. To eliminate ambient contamination, samples must not be exposed to atmospheres containing organic vapors. Cross-contamination is best controlled by such QA measures as sample segregation and proper packaging. 

This column blank is not to be confused with sample blanks such as those determined for the 5-gal. jugs. This latter blank correction is applied to (1) extractable organics and nonvolatile hydrocarbon contents measured by the method and (2) UV and GC data. No correction from the sample blank is applied to the compound type analysis by mass spectrometer. Very little net error can be attributed to this omission of a blank correction. 

Photo-oxidation instead of wet-chemical oxidation is often considered an attractive method because of the very low blanks. However, irradiation with UV light does not seem to ensure complete recovery of mercury from organically assodated and related species. Reduced signals have even been observed following extended irradiation times (Gerwinski et al., 19%) which might indicate the formation of compounds with decomposition products from which Hg cannot be liberated by reduction with Sn. Therefore, to determine true total mercury concentrations, UV irradiation must be followed by wet-chemical oxidation. For samples with DOC concentrations of > 25 mg/L, an initial preoxidation by UV-irradiation was found necessary to ensure total oxidation of DOC and accurate determination of Hgx by the bromine monochloride method (Olson et al, 1997). 

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