Glossary Of Common Laboratory Terms

Glossary of Common Laboratory TermsAccuracyA measure of how close a measured value is to the true value.Assessed by means of percent recovery of spikes and standards.AerobicAtmospheric or dissolved oxygen is available.AliquotA measured portion of a sample.AlkalinityThe capacity of the wastewater to neutralize acids. This isnormally due to the presence of carbonate, bicarbonate, and/orhydroxide.AmbientTemperatureThe temperature of the surrounding area.AnaerobicAtmospheric or dissolved oxygen is not available.AnalyteThe compound or property that is to be determined or analyzed.AnionA negatively charged ion. This will normally try to combine orattach to a cation. Examples of anions are nitrate, nitrite,sulfate, phosphate, chloride, acetate, cyanide, carbonate,bicarbonate, and hydroxide.AverageA way to represent a group of similar data points with a singlenumber. The average can be reported in three different ways;mean, median, and mode. Of these, the mean is what isgenerally meant or intended.BlankLaboratory grade water and other reagents are set up andtested as though it was another sample. This checks forbackground interference from reagents and allows forcorrection.BlindQA/QC samples that are the same as unknowns with theexception that the person testing the samples does not knowthese are standards. Blind samples tend not to receive specialtreatment from the laboratory personnel.BufferA solution or liquid mixture made up of an acid and itsconjugate base. The chemical makeup allows it to neutralizesmall quantities of acids or bases or without great changes in pHwhen acids or bases are added. Buffers are generally used tocalibrate pH meters.CalibrationThe process of preparing an instrument such that reliablePage 1of 8File:Main RY:Glossary of Common Laboratory Terms.docx

Glossary of Common Laboratory Termsoperation will be ensured. The systematic determination of howthe measurement system responds to the concentration of ananalyte.CationA positively charged dissolved particle which will normally tryto combine or attach to an anion. Examples of cations may beammonium, sodium, potassium, calcium, manganese, andmagnesium.Coefficient ofvariationThe measure of the ability to repeatedly obtain the same valuefor a single sample or method (i.e.; duplicate or replicateanalyses). This may also be called the precision. [Note: Accuracyis not the point here, but rather how many times the sameanswer is obtained when all factors of the analysis remainconstant — same sample, same volume, same method, etc.] Thisvalue is calculated the same as a Relative Standard Deviation.Composite SamplesA combination of grab samples collected at the same samplingpoint at different times. For most composite samples covering aspecific time period, the grab samples should be obtained atregular intervals and placed in a single container. These grabsamples can be collected automatically or manually. Thesampling interval can be based on time or flow.DesiccantA drying agent or substance capable of absorbing moisture.DesiccatorA sealed chamber in which samples can be dried in the presenceof a desiccant.Dissolved SolidsSolids that are in solution and cannot be filtered from thesolution as suspended solids can.Duplicate TestingTwo separate analyses are run on the same sample, using thesame sample volume and testing technique. Usually the averageresult is reported. Example: running two TSS on the planteffluent. These are used to check laboratory procedure andprecision. If more than two separate analyses are performed, itis referred to as replicate testing.ElectrodeA conductor through which a current of electricity enters orleaves. One or more may be contained in a probe. The term maybe used interchangeably with the term probe when talkingabout a piece of laboratory equipment.End PointWhere a titration is stopped. The point in a titration at whichPage 2of 8File:Main RY:Glossary of Common Laboratory Terms.docx

Glossary of Common Laboratory Termsthere is a sudden change in a physical property, such asindicator color, pH, conductivity or absorbance. The final valuewhen titrating a solution.Field DuplicateRefers to two different samples collected at the same time, samelocation, and with the same sampling procedure. Used to checkthe sampling techniques.FiltrateThe liquid that passes through a filter.Grab SampleA sample collected at a specific time and specific location, usedto determine the nature of the water for that specific time andlocation only.GravimetricAnalysisAn analytical method that relies on measuring the mass ofsolids, etc. in wastewater (and other liquids) by weighingprecipitates or residues to complete the analysis.IndicatorA chemical substance or compound having a physical propertythat changes abruptly, usually color, near the endpoint orequivalence point of a chemical reaction.Instrument BlankLaboratory pure water and other appropriate reagents are usedto zero instrumentation.Ion SelectiveElectrodeAlso known by the acronym ISE. These electrodes respond toions present in a sample. A potential develops across themembrane surface that is selectively dependent on theconcentration of one particular ion in solution. The magnitudeof the potential relates to the concentration of the ionconcentration. The higher the potential, the higher theconcentration.LiterDefined as exactly 1000 cm3.MeanA type of Average used by statisticians. A calculated valuebetween the largest and smallest values in a series which isusually determined be adding all values and dividing by thetotal number of values.MedianA type of Average used by statisticians. The value above andbelow which there is an equal number of data points. Themiddle number in a series after all values have been arranged orsorted from highest to lowest. There are equal numbers ofvalues above the median as below.Page 3of 8File:Main RY:Glossary of Common Laboratory Terms.docx

Glossary of Common Laboratory TermsMeniscusThe curved surface of a liquid.Method BlankA sample of laboratory pure water analyzed following the samestep-by-step procedure used on the samples, including allreagents and solvents. The method blank will show anyinterference caused by a step in the procedure or by chemicals.The result of the method blank should be zero or nearly zero. Ifit is not, the magnitude of the interference must be consideredwhen calculating the concentration of the samples.At least one method blank should be run a each time theanalysis is performed.ModeA type of Average used by statisticians. The value that occursmost frequently in a group of values.MSDSMaterial Safety Data Sheet — A document that providesinformation about a given chemical product. It includes thename, composition (chemicals in the product), hazards, first aidmeasures, fire fighting measures, information regarding theproper steps to take with spills, handling and storage, personalprotection to be used, physical and chemical properties, andinformation about stability & reactivity, toxicology, disposal,transporting, and regulatory requirements.NephelometryA technique in which the intensity of light scattered by asuspension is measured to determine the concentration ofsuspended particles.NPDESNational Pollutant Discharge Elimination System. A provisionof the Clean Water Act that prohibits discharge of pollutantsinto waters within the United States unless the state or EPA hasissued a special permit.Percent RecoveryA means for expressing the accuracy of a test. Percent recoveryexpresses what proportion of a known quantity can bemeasured by a given analytical technique.PrecisionThe measure of the ability to repeatedly obtain the same valuefor a single sample or method (i.e. duplicate or replicatePage 4of 8File:Main RY:Glossary of Common Laboratory Terms.docx

Glossary of Common Laboratory Termsanalyses). This may also be called the coefficient of variation.[Note: Precision is a measure of reproducibility. Precision is notsynonymous with accuracy.]ProbeAn instrument or device used to get information about anenvironment. The use of a probe in a wastewater treatmentlaboratory generally has electrodes arranged in a given mannerwithin the probe to allow attachment to a meter or otherreading device to obtain desired information.QualityReliably and repeatedly attaining a standard of excellence.Quality AssuranceA program monitoring and controlling laboratory proceduresand results, to insure the reliability of results. The paperworkinvolved in monitoring the program, such as control charts andgraphs.Quality ControlUse of scientific methods to maintain the most accurate datapossible. Procedures performed to check against a standard,such as blanks, duplicates, and spikes.RangeThe difference between the highest and lowest values of a set.ReagentsReagents come in a variety of different qualities. For the workthat is done in environmental testing, the use of chemicalsmeeting American Chemical Society (A.C.S.) requirements isrecommended.Reagent BlankUsed to determine the background or "blank" of all thereagents used in a given method. A complete reagent blank,made up of all reagents used for a specific method is sometimesused to zero instruments for spectrophotometric analysis.Measures the response to of the analytical method to impuritiesin the reagents and other components other than the analyte.Relative StandardDeviation (%RSD)A measure of the reproducibility of an analysis. This isdetermined by dividing the standard deviation (of a samplerather than the population) by the mean for the same set andthen multiplying by 100%. An example of the calculation isshown below.Page 5of 8File:Main RY:Glossary of Common Laboratory Terms.docx

Glossary of Common Laboratory TermsReplicatesMore that two separate analyses are run on the same sampleusing the same sample volume and testing technique. Usuallythe average result is reported. Example: running more than twoTSS on the plant effluent. These are used to check laboratoryprocedure and precision.Spiked SampleA precise volume of a sample to which a precise volume ofstandard reference material is added. The spiked sampleconcentration equals the original sample plus the addedstandard. Spikes should be run 1 in every 20 samples. Theconcentration of the standard added should be approximatelyequal to the original sample value.Split SamplesTwo or more parts of a homogeneous sample divided foranalysis by different labs or by different analysts. Split samplesare used as a QC check of the analytical procedures.StandardStandards are samples for which the analyst knows the truevalue before running the test. Standards can be made in-houseor purchased from laboratory supply companies. Standards areoften used to calibrate instruments and to evaluate the accuracyof an analysis.Standard DeviationA measurement of the extent to which individual values in asample set differ from each other (or how closely they areclustered about the mean value). This manual will use alowercase s to indicate the standard deviation for a finite set ofdata. Some calculators have a dedicated function key for thestandard deviation of a sample labeled σn-1.StandardizationThe process by which the concentration of a reagent isdetermined by reaction with a known quantity of a secondreagent.Tare or Tare WeightThe weight of the vessel or filter before the item of interest isadded. The tare weight subtracted from the gross weight of theitem of interest and accompanying vessel gives the net weight ofthe item of interest. Many balances can be tared. That is, withthe empty vessel in place, the balance can be set to read zerograms.Page 6of 8File:Main RY:Glossary of Common Laboratory Terms.docx