Environmental calibration

The U.S. Environmental Protection Agency publishes sets of Series Methods that describe procedures for detecting and estimating the quantity of environmentally hazardous substances. There are strict requirements for accuracy, reproducibility, and for calibration of mass spectrometers. 

A solvent free, fast and environmentally friendly near infrared-based methodology was developed for the determination and quality control of 11 pesticides in commercially available formulations. This methodology was based on the direct measurement of the diffuse reflectance spectra of solid samples inside glass vials and a multivariate calibration model to determine the active principle concentration in agrochemicals. The proposed PLS model was made using 11 known commercial and 22 doped samples (11 under and 11 over dosed) for calibration and 22 different formulations as the validation set. For Buprofezin, Chlorsulfuron, Cyromazine, Daminozide, Diuron and Iprodione determination, the information in the spectral range between 1618 and 2630 nm of the reflectance spectra was employed. On the other hand, for Bensulfuron, Fenoxycarb, Metalaxyl, Procymidone and Tricyclazole determination, the first order derivative spectra in the range between 1618 and 2630 nm was used. In both cases, a linear remove correction was applied. Mean accuracy errors between 0.5 and 3.1% were obtained for the validation set. 

U.S. Environmental Protection Agency, "Transfer Standards for Calibration of Air Monitoring Analyzers for Ozone," EPA-600/4-79-056. Office of Air Quality Planning and Standards, Research Triangle Park, NC, 1979. 

There are two categories of equipment which determine the selection of equipment general-purpose and special-to-type equipment. It should not be necessary to specify all the general-purpose equipment needed to perform basic measurements, which would be expected to be known by appropriately trained personnel. You should not need to tell an inspector or tester which micrometer, vernier caliper, voltmeter, or oscilloscope to use. These are the tools of the trade and they should select the tool which is capable of measuring the particular parameters with the accuracy and precision required. However, you will need to tell them which device to use if the measurement requires unusual equipment or the environmental conditions prevailing require that only equipment be selected that will operate in such an environment. In such cases the particular devices to be used should be specified in the test or inspection procedures. In order to demonstrate that you selected the appropriate device at some later date, you should consider recording the actual device used in the record of results. With mechanical devices this is not normally necessary because wear should be detected well in advance of there being a problem by periodic calibration. 

The serial numbers of the standards used to calibrate the device The environmental conditions prevailing at the time of calibration A statement of measurement uncertainty (accuracy and precision)... 

The standard requires the supplier to ensure that the environmental conditions are suitable for the calibration, inspections, measurements, and tests being carried out. 

If you cannot select suitable equipment for your current environment, you may need to control the environment in order to carry out the measurements. In such areas the environmental factors important to maintaining stable measurement should be monitored and the monitoring equipment calibrated. Chart recorders enable you to monitor conditions without having to be in constant attendance. The environment should be controlled in areas where calibration is carried out in order to provide stable conditions in which accurate and precise measurement can be taken. However, some modern equipment is so stable that environmental controls are unnecessary except in special circumstances. 

Unlike the other requirements, which only referred to inspection, test, and measuring equipment, this clause adds test facilities. Facilities include the equipment and the area or room in which it is kept or used. Test facilities are any room, area, or complex in which tests are carried out. Inspection, measuring, and test facilities include functional and environmental test laboratories, test and inspection chambers, calibration rooms. 

Don t calibrate test devices in the same environment as they will be used unless you compensate for the environmental effects on measurement accuracy. 

A convenient method of carrying out such a galvanic test in the laboratory has been described by Wesley in which the vertical circular-path machine is used. Each assembly includes two pairs of dissimilar metals—one pair coupled galvanically while the other pair is left uncoupled in order to determine the normal corrosion rates under the same environmental conditions. The type of motion provided (specimens moving in a vertical circular path) enables electrical connections to be made without mercury cup or commutator and the leads can be connected to a calibrated resistance for current measurements attached to the specimen carrier. 

Throughout this book the use of a number of standard analytical samples is recommended in order that practical experience may be gained on substances of known composition. In addition, standard reference materials of environmental samples for trace analysis are used for calibration standards, and pure organic compounds are employed as standard materials for elemental analysis. 

Procedures should be established to periodically monitor all operations that may have an environmental impact, and similar scheduled periodic checks should be made to ensure that procedures and operations are still in line with regulatory and other requirements. If equipment is involved in the monitoring process then procedures should also be in place to ensure correct calibration. Procedures are also needed to record any preventative or corrective actions identified and to ensure that they are completed to schedule. The whole EMS should be audited periodically to check that it is consistent with the planned policy and has been properly implemented. The details of audits should be discussed and reviewed by management at the highest level with a view to continuous improvement through the modification of both policy and procedures. 

The results of environmental monitoring exercises will be influenced by a variety of variables including the objectives of the study, the sampling regime, the technical methods adopted, the calibre of staff involved, etc. Detailed advice about sampling protocols (e.g. where and when to sample, the volume and number of samples to collect, the use of replicates, controls, statistical interpretation of data, etc.) and of individual analytical techniques are beyond the scope of this book. Some basic considerations include the following, with examples of application for employee exposure and incident investigation. 

Currently available CRMs Calibrants are available for TBT (very evident, as TBT is an anthropogenic contaminant) and for a number of other organic tin compounds. There is also an interesting choice of environmental CRMs (sediment and mussel tissue) certified for TBT content. 

A limited number of pure substances are available from NIST, primarily clini-cally-relevant compounds such as cholesterol, urea, uric acid, creatinine, glucose, cortisol, tripalmitin, and bilirubin (NIST SRM website). These compounds are certified for purity (greater than 99 %) and are used as primary calibrants in definitive methods for these clinical analytes (see below). Several additional pure substances are available for specific applications such as microchemistry, i.e. elemental composition (acetanilide, anisic acid, cystine nicotinic acid, o-bromobenzoic acid, p-fluoro-benzoic acid, m-chlorobenzoic acid), polarimetric standards (sucrose and dextrose), acidimetric standard (benzoic acid and boric acid). Only three pure substance NIST RMs are available for environmental contaminants, namely the chlorinated pesticides, lindane, 4,4 -DDT, and 4,4 -DDE. 

With solid sampling-electrothermal vaporization-inductively coupled atomic emission spectrometry (SS-ETV-ICP-AES), Cu in two environmental CRMs was determined using a third CRM with similar matrix as calibrant. Comparison with a reference solution showed good agreement (Verrept et al. 1993). 

To satisfy government agencies, instruments need to be adequately tested, calibrated, and/or standardized according to documented procedures. Current GLP standards state that equipment used in the generation, measurement, or assessment of data and equipment used for facility environmental control must be of appropriate design and capacity to function according to the protocol and shall be suitably located for operation, inspection, cleaning, and maintenance. 

One of the limitations of the portable field survey instruments in the measurement of americium is that their quantitative accuracy depends on how well the lateral and vertical distribution of americium in the soil compares with the calibration parameters used. These methods can provide a rapid assessment of americium levels on or below surfaces in a particular environment however, laboratory-based analyses of samples procured from these environmental surfaces must be performed in order to ensure accurate quantification of americium (and other radionuclides). This is due, in part, to the strong self absorption of the 59.5 keV gamma-ray by environmental media, such as soil. Consequently, the uncertainty in the depth distribution of americium and the density of the environmental media may contribute to a >30% error in the field survey measurements. Currently, refinements in calibration strategies are being developed to improve both the precision and accuracy (10%) of gamma-ray spectroscopy measurements of americium within contaminated soils (Fong and Alvarez 1997). 

Verification is the complement of calibration model predictions are compared to field observations that were not used in calibration or fidelity testing. This is usually the second half of split-sample testing procedures, where the universe of data is divided (either in space or time), with a portion of the data used for calibration/fidelity check and the remainder used for verification. In essence, verification is an independent test of how well the model (with its calibrated parameters) is representing the important processes occurring in the natural system. Although field and environmental conditions are often different during the verification step, parameters determined during calibration are not adjusted for verification. 

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