Analyte-free water blanks

To imitate water samples, trip blanks are prepared in volatile organic analysis (VOA) vials with septum caps lined with polytetrafluoroethylene (PTFE). The vials are filled without headspace with analyte-free water. For soil sampled according to the requirements of EPA Method 5035, field blanks may be vials with PTFE-lined septum caps, containing aliquots of methanol or analyte-free water. 

Trip blanks prepared in vials and containing aliquots of methanol or analyte-free water accompany soil samples collected in a similar manner for low concentration VOC analysis according to EPA Method 5035. In this case, field samples and trip blanks have the same contamination pathway when exposed to airborne contaminants and the same VOC transport mechanism. These trip blanks provide important information, which may enable us to recognize the artifacts of improper sample handling, storage, or shipping. 

Equipment blank is a sample of water collected from the surface of a decontaminated sampling tool to verify the effectiveness of a cleaning procedure. Equipment blanks are sometimes called rinsate blanks. They are collected as samples of the final rinse water from non-disposable sampling tools after they have been cleaned between samples. The field crew pours analyte-free water over the tool s surface that has come in contact with the sampled medium. The water is diverted directly into sample containers and analyzed for the project contaminants of concern. 

If analyte-free water is not available, the field crew may use tap or bottled water for the final rinsing. A sample of source water, called the source blank may be also analyzed for the project contaminants of concern. 

Ambient (field blanks) are sample containers with PTFE-lined septum caps filled with analyte-free water in the field to establish whether contamination could have been introduced into water samples from ambient air during sampling. The laboratory provides a bottle of analyte-free water, and the field crew pours this water from the bottle into a sample container in a manner that simulates the transfer of a sample from a sampling tool into a container. Ambient blanks are analyzed for the contaminants of concern that may be airborne at the site in order to assess the sampling point representativeness. 

Decontamination procedure consists of washing the equipment with a detergent solution and rinsing it with tap water and with analyte-free water. The water from the final rinse is collected into sample containers and as the equipment blank is analyzed for the contaminants of concern. 

To collect equipment blank, place a clean funnel into the sample container. Spray the cleaned surface with analyte-free water from the squeeze bottle and direct the water from the cleaned surface into the funnel. Alternatively, pour the water from the cleaned surface directly into the sample container. (This step requires substantial manual dexterity and may need two persons.)... 

Storage blanks (40 mL vials with analyte-free water) are placed in cold storage with samples for VOC analysis. Regular analysis of storage blanks enables laboratories to detect whether sample cross-contamination may have taken place in cold storage. 

The primary source of data interpretation error in elemental analysis is laboratory contamination affecting the method blank and the samples. Method blank is a volume of analyte-free water prepared and analyzed in the same manner as the samples. Method blank is also called analytical blank or preparation blank. 

If VOCs are not among the contaminants of concern, bottled drinking water or commercially available deionized water often serves as an equitable substitute for analyte-free reagent water. (Certain VOCs are present in drinking water as the artifacts of water disinfection process.) If VOCs are among the project contaminants of concern, commercially available distilled water may be used for a final rinse. When bottled water is not available, and water of unknown quality is used for equipment blank collection, a source blank of such water is analyzed. The only situation when a source blank may be needed is when the sampled medium is water and low contaminant concentrations of organic compounds and metals are a matter of concern. 

Every test series must be accompanied by a blank test in which deionized, copper-free water instead of the sample is subjected to the entire analytical procedure described above. 

Extraction of Ca with Azo-azoxy BN. Add sufficient 5M NaOH to the sample solution to make the NaOH concentration 0.5-1 M. Shake the solution for 1 min with the solution of Azo-azoxy BN. Strip calcium from the extract with a small volume of 1M hydrochloric acid. Determination of Ca. The sample solution should contain not more than 30 pg of Ca, and be free from ammonium salts and Analytical Group I-III metals (to mask small amounts of these metals, add 10 mg each of KCN and Na2S. Neutralize the sample solution (to pH 7-8) with NaOH or HCl, and add 20 mg of Na2S04. Add 12 ml of the GBHA solution and 1 ml of 1 M NaOH, and dilute the solution with water to the mark in a 25-ml standard flask. After 10 min, measure the absorbance of the solution at 516 nm against a blank solution. 

Blank samples are used to make sure that glassware, equipment, and instrumentation are free of the analyte of interest and potential interferences. It does no good to analyze drinking water for trace amounts of acetone when laboratory glassware and procedures contribute 10 ppb per sample. Blanks provide information about the accuracy of the technique used and can help detect systematic errors such as a contaminated reagent or contaminated glassware. 

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