Blank field

Spike Recoveries One of the most important quality assessment tools is the recovery of a known addition, or spike, of analyte to a method blank, field blank, or sample. To determine a spike recovery, the blank or sample is split into two portions, and a known amount of a standard solution of the analyte is added to one portion. The concentration of the analyte is determined for both the spiked, F, and unspiked portions, I, and the percent recovery, %R, is calculated as... 

Spike recoveries on method blanks and field blanks are used to evaluate the general performance of an analytical procedure. The concentration of analyte added to the blank should be between 5 and 50 times the method s detection limit. Systematic errors occurring during sampling and transport will result in an unacceptable recovery for the field blank, but not for the method blank. Systematic errors occurring in the laboratory, however, will affect the recoveries for both the field and method blanks. 

A good example of a prescriptive approach to quality assessment is the protocol outlined in Figure 15.2, published by the Environmental Protection Agency (EPA) for laboratories involved in monitoring studies of water and wastewater. Independent samples A and B are collected simultaneously at the sample site. Sample A is split into two equal-volume samples, and labeled Ai and A2. Sample B is also split into two equal-volume samples, one of which, Bsf, is spiked with a known amount of analyte. A field blank. Dp, also is spiked with the same amount of analyte. All five samples (Ai, A2, B, Bsf, and Dp) are preserved if necessary and transported to the laboratory for analysis. 

The first sample to be analyzed is the field blank. If its spike recovery is unacceptable, indicating that a systematic error is present, then a laboratory method blank. Dp, is prepared and analyzed. If the spike recovery for the method blank is also unsatisfactory, then the systematic error originated in the laboratory. An acceptable spike recovery for the method blank, however, indicates that the systematic error occurred in the field or during transport to the laboratory. Systematic errors in the laboratory can be corrected, and the analysis continued. Any systematic errors occurring in the field, however, cast uncertainty on the quality of the samples, making it necessary to collect new samples. 

If the field blank is satisfactory, then sample B is analyzed. If the result for B is above the method s detection limit, or if it is within the range of 0.1 to 10 times the amount of analyte spiked into Bsf, then a spike recovery for Bsf is determined. An... 

Field blanks Sample media that are exposed to the same conditions as the media use for the actual sampling but are not connected to a sampling pump. See also Laboratory blanks. 

Laboratory blanks Sample media that is not sampled on, but is analyzed by the laboratory to detect contamination or other problems associated with preparation and analysis of the samples. See also Field blanks. 

Field spikes with laboratory standards as well as spraying solutions were taken at a wide range of concentrations to determine the stability of the samples during both sampling and storage and possible contamination during the sampling procedure. Field blanks were also taken. 

Chromatographic procedures applied to the identification of proteinaceous paint binders tend to be rather detailed consisting of multiple analytical steps ranging from solvent extractions, chromatography clean up, hydrolysis, derivatisation reactions, and measurement to data analysis. Knowledge of the error introduced at each step is necessary to minimise cumulative uncertainty. Reliable results are consequently obtained when laboratory and field blanks are carefully characterised. Additionally, due to the small amounts of analyte and the high sensitivity of the analysis, the instrument itself must be routinely calibrated with amino acid standards along with measurements of certified reference proteins. All of these factors must be taken into account because many times there is only one chance to take the measurement. 

Calibrations made using certified amino acid sources are of the utmost importance. The evaluation of the content of amino acids in laboratory and field blanks implies a quantitative... 

Before beginning the analysis of FMs at low concentrations, the laboratory should analyze several laboratory blank samples to assess the degree to which the laboratory is contaminated. With every set of samples analyzed, the laboratory should also analyze a laboratory and field blank sample. Laboratory workers should be advised to be aware of their personal use of fragrance-enhanced consumer products and the potential for laboratory contamination. 

As suggested earlier, field-blank SPMDs are taken to the field in sealed metal cans and one or more cans are opened to the atmosphere at each site (note that field-blank SPMDs are typically left inside the open cans) during both deployment and retrieval of SPMDs from aquatic systems. The time periods that field-blank SPMDs are exposed to site air should be the same as that required to deploy and retrieve SPMDs. Afterwards, the cans with the field-blank SPMDs are resealed and shipped to the analytical laboratory along with the deployed SPMDs. Non-spiked (i.e., no PRCs) field-blank SPMDs and PRC-containing field-blank SPMDs are processed and analyzed exactly as are deployed SPMDs. However,... 

Also, Petty et al. (2002) performed an in depth analysis of the OCP fraction of SPMD extracts by gas chromatography-mass spectrometry (GC-MS) resulting in the tentative identification of about 400 airborne organic chemicals, which were not present in SPMD field blanks. The OCP fraction represents only one of several enriched fractions from SPMD samples. Table 8.1 summarizes the various classes of compounds tentatively identified in SPMDs exposed to indoor air. 

A number of toxicologically active 2,3,7,8-substituted PCDDs and PCDFs, planar PCBs and PCDD, PCDF, and PCDT homologs were measured in fish, SPMDs, and sediments. Only two target compounds exceeded the detection limits of 0.2-1 pg g in SPMD field blanks (see definition in Chapter 5). These exceptions were octachlorodibenzo-p-dioxin (OCDD) and octachlorodibenzofuran (OCDF) which were present in SPMDs at about 5 pg g However, negative... 

For a high level of confidence you will need to have both fleld and "method blanks. Field blanks are blanks from a similar source that do not contain the analytes of Interest. Control sites (uncontaminated sites) are used to obtain field blanks and If field blanks are not available, every effort should be made to obtain blank samples that best simulate a sample that does not contain the analyte (such as a simulated or synthetic field blank). Your method blanks will consist of all solvents, resins, etc. that you will use for extracting, concentrating and cleaning up the samples prior to analysis. You may want about half of these unspIked and the remainder spiked with known levels of your analyte standards. Similarly you may want to spike about half of your field blanks with known levels of your analyte standards so that any matrix effects will be Identified during the analysis. This plan would provide you with ... 

A QC assessment was done for all samples. De-ionized water field blanks were collected on seven different days to evaluate process contamination. Site duplicates were taken at eight sites to evaluate repeatability and site variation. Instrumental precision was constrained by analysis of laboratory duplicate solutions, and is typically less than 5%. Finally, standard reference material (SRM) water standards were analyzed with sample batches, to assess instrumental accuracy. 

Quality Assurance/Quality Control. QA/QC measures included field blanks, solvent blanks, method blanks, matrix spikes, and surrogates. Percent recovery was determined using three surrogate compounds (nitrobenzene-d5, 2-fluorobiphenyl, d-terphenyl-diQ and matrix spikes (naphthalene, pyrene, benzo[ghi]perylene) the recoveries ranged from 80 to 102%. Separate calibration models were built for each of the 16 PAHs using internal standards (naphthalene-dg, phenanthrene-dio, perylene-di2). Validation was performed using a contaminated river sediment (SRM 1944) obtained from NIST (Gaithersburg, MD) accuracy was <20% for each of the 16 analytes. 

The fine particle airstream from the cyclone was sampled by two total filters in parallel. A Millipore Fluoropore 47 mm diameter Teflon filter with a 1 pm pore size was used for the first seven samples. Subsequent samples were obtained with a 0.4 pm pore size 47 mm Nuclepore polycarbonate filter because particle absorption measurements and elemental analysis by particle induced X-ray emission (PIXE) were easier and more accurate using the Nuclepore filters. In parallel with the Nuclepore filter, a TWOMASS tape sampler collected aerosol using a Pallflex Tissuequartz tape. The aerosol deposit area was 9.62 cm on the Nuclepore and Millipore filters and 0.317 cm on the Tissuequartz tape. The flow rate was 16-20 1pm through the Nuclepore and Millipore filters and 10 1pm through the Tissuequartz tape. Each Millipore or Nuclepore filter was placed in a labeled plastic container immediately after collected, sealed with Parafilm, enclosed in a ziplock bag, and placed in a refrigerator in the trailer. The tape in the TWOMASS sampler was advanced between samples. The tape sample was removed about once every 8-10 weeks and stored similarly to the Nuclepore filters. The TWOMASS was cleaned at that time. All samples were stored in an ice chest during the return trip to Caltech. Field blanks were handled identically to the samples. Of approximately 100 filter samples collected in 1979, 61 were selected for analysis. The 61 were chosen to span the variation in bjp and to obtain representative seasonal and diurnal samples. Sample times varied from 6 to 72 hours, with an average of 20.1 hours. 

The aerosol mass on each Nuclepore filter sample was determined gravimetrically. Field blanks were obtained at Zilnez Mesa by drawing 50 X. of filtered air through preweighed Nuclepore... 

NATIONAL SEMICONDUCTC LF411 CN IC Field blank, j VOLTAGE-FEEDBACK Ol... 

All the results have been corrected for blank contribution. The XAD-2 cartridge blanks for the evaluation stage and the field cartridge blanks were essentially free of all of the compounds analyzed. However, the field samples, as well as the field blanks, had significant amounts... 

A field blank is similar to a method blank, but it has been exposed to the site of sampling. For example, to analyze particulates in air, a certain volume of air could be sucked through a filter, which is then dissolved and analyzed. A field blank would be a filter carried to the collection site in the same package with the collection filters. The filter for the blank would be taken out of its package in the field and placed in the same kind of sealed container used for collection filters. The difference between the blank and the collection filters is that air was not sucked through the blank filter. Volatile organic compounds encountered during transportation or in the field are conceivable contaminants of a field blank. 

What is the purpose of a blank Distinguish method blank, reagent blank, and field blank. 

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