岛津TOC in daily practice.pdf

As market leader in TOC analysis,Shimadzu connects tradition with ex-perience.This enables users to profitfrom personal support or by attendingseminars and user meetings organizedby Shimadzu.These application-orientedmeetings serve for the exchange of in-formation and experiences.In this particular field of applicationnotes,specific sets of subjects TOC indaily practice are listed that are notcovered by one of the special applica-tions.These are subjects that are relatedto the TOC parameter,independently ofthe matrix.The wealth of experience in TOC analy-sis naturally finds its way into the devel-opment of our TOC systems.Whetheronline analyzers or laboratory TOC sys-tems they all impress by their greatflexibility,high availability,extremerobustness and stability,simple andintuitive operation and advanced oper-ating and evaluation software.Manyadditional functions facilitate the userswork and provide more freedom for oth-er important tasks.This chapter also applies to the indi-vidual modules,kits or options of Shimadzus TOC analyzers.Useful func-tions are also described.Further details are available in the indi-vidual application notes(for instanceTOC determination methods,Totalnitrogen determination or Blank val-ues).In addition to the information onTOC in daily practice,there are alsoapplication notes on Pharmaceuticalindustry,Chemical Industry,TOC spe-cial applications,Environmental analy-sis and TOC process analysis.5.TOC in daily practiceThe EN 1484 standard“Guidelines for the determination of total organic carbon(TOC)and dissolved organic carbon(DOC)”defines various terms and parameters.Definitions according to EN 1484 TC:Total carbon the sum of organically bound and inorganically bound carbon present in water,including elemental carbon.TIC:Total inorganic carbon the sum of carbon present in water,consisting of elemental carbon,carbon monoxide,carbon dioxide(also carbonates and hydrogen carbonates),cyanide,cyanate,and thiocyanate.TOC instruments mainly detect CO2,originating from hydrogen carbonates and carbonates,just like TIC.TOC:Total Organic Carbon organically bound carbon present in water,bonded to dissolved or suspended matter.Cyanate,thiocyanate and elemental carbon are also determined.POC:Purgeable Organic Carbon the TOC content that is purgeable under the conditions of this method.NPOC:Non Purgeable Organic Carbon the TOC content that is not purgeable under the conditions of this method.The following graph shows how the parameters are linked:Determination methods The TOC can be determined according to three different methods:Difference method For the difference method,the parameters TC and IC are measured.The TOC is then determined by way of calculation.TC:The analysis of the total organic carbon is carried out via oxidation(thermal or wet-chemical)and subsequent determination of the resulting carbon dioxide using NDIR detection.TIC:Through acidification of the sample using a mineral acid at room temperature and subsequent NDIR detection of the expelled carbon dioxide the inorganic carbon is detected.TCTOCNPOCPOCICSum parameter Total Organic Carbon TOC Determination methods according to EN 1484 SCA-130-501 The TOC is calculated from the difference between TC and TIC:TOC=TC-TIC Limitations of the difference method The inorganic carbon content may not be too high in comparison to the TOC.Error propagation can result in a high level of uncertainty for the calculated TOC value.The EN 1484 standard recommends that the TOC value,when using the differential method,should be higher or equal to the TIC value(TOC TIC).Example:TC Value=100 mg/l(RSD=2%)2 mg/l (98 102 mg/l)IC Value=98 mg/l(RSD=2%)1,96 mg/l(96,04 99,96mg/l)TOC=2 mg/l 3,96mg/l (-1,96-5,96 mg/l)Due to error propagation,the total error is 3.96 mg/L.According to the difference method,the error of the total result is larger than the calculated TOC content!In the worst case,this can result in a negative TOC value.Addition method For the addition method,the parameters POC and NPOC are measured.The TOC is then calculated.POC:Degassing of the volatile compounds with subsequent catalytic combustion at 680C and determination of the resulting carbon dioxide using NDIR detection.NPOC:Measurement of the non-purgeable organic compounds,after POC analysis using catalytic combustion at 680C and subsequent determination of the resulting carbon dioxide using NDIR detection.The TOC is calculated via addition:TOC=POC+NPOC Direct method For the direct or NPOC method,it is assumed that the sample does not contain any significant amounts of volatile or purgeable organic compounds.According to this assumption,the TOC is directly determined as NPOC.NPOC:Acidification of the sample using a mineral acid(for instance HCL)to a pH 2,whereby carbonates and hydrogen carbonates are completely converted to carbon dioxide.The carbon dioxide is removed from the sample solution via a sparge gas.Direct NPOC measurement(similar to TC measurement)via oxidation to CO2.Subsequent NDIR detection.The TOC corresponds to the NPOC:TOC=NPOC SCA-130-501 According to EN 1484,which contains the instructions for TOC determination,the POC(purgeable organic carbon)is the TOC content that can be expelled under the conditions of this method.This information is very unspecific and should be described here in more detail.The instruments in the TOC-L series can be extended with an option to include measurement of the POC parameter.The core feature of this option is the LiOH trap,which is placed in the flow line of the analyzer.For POC determination,the sample is aspirated using the TOC-L injection syringe,acidified with HCL and subsequently purged using carrier gas.In this step,CO2 originating from carbonates and hydrogen carbonates as well as all volatile organic compounds(POC)are purged from the solution.The LiOH trap binds the CO2 from the gas mixture(originating from the TIC).The volatile compounds pass the trap and reach the catalyst.Here,the volatile organic compounds are converted to CO2 and detected via NDIR detector.Fig.The addition method(NPOC+POC)During the course of the addition method,the remainder is used for NPOC determination.However,in the drinking water application or ultrapure water application,the POC content is completely negligible.Here,TOC=NPOC The POC can,nevertheless,play an important role in wastewaters,particularly in industrial effluents.CalibrationParticular attention should be paid to calibration of the POC.Standards that are prepared with volatile,purgeable organic substances are inherently very unstable.This is why IC standard solutions(prepared from carbonates and/or hydrogen carbonates)are used for POC calibration.Sampling of the IC solutions for POC determination is carried out using the TOC-L injection syringe.The IC solution is acidified in the syringe.The inorganic substances of the standard solution are converted to CO2 and transferred to the NDIR detector using a carrier gas.TOCNPOCPOCSum parameter Total Organic Carbon Determination of the purgeable organic carbon(POC)SCA-130-502 Fig.POC-Calibration with IC-standard System testing In POC analysis,it is of great importance that the LiOH trap functions perfectly.A test should,therefore,be carried out to confirm the efficiency of the CO2 trap.This test should be carried out each working day:An IC control solution(TIC=1000 mg/L)is prepared and analyzed as a POC sample.For efficient functioning of the LiOH trap,the POC measuring result must be 100%NPOC=0mg/l Recommended Analyzer/Configuration TOC-LCXX ASI-L POC-Option SCA-130-502 Although nitrogen compounds are essential for nature and the environment,high nitrogen depositions can lead to problems.Nitrogen compounds enter the environment primarily through agricultural processes.Nitrogen-containing fertilizers constitute the largest proportion.But nitrogen compounds can also enter the environment via chemical industrial processes.Excessively high concentrations of nitrogen compounds in the environment can cause eutrophication of water bodies.Eutrophication is the process of uninhibited growth of algae and other organisms due to an excess supply of nutrients.This overgrowth results in a lack of oxygen in the water,which can lead to fish mortality and to the formation of aquatic dead zones.Bound nitrogen occurs in nearly all waters,mostly in the form of ammonia,nitrate,nitrite or organic compounds.Total nitrogen TNb The variety of possible nitrogen compounds necessitated the definition of a sum parameter that represents the total nitrogen compounds.For this purpose,the so-called TNb(total bound nitrogen)was defined and standardized.The TNb is the total nitrogen content of a sample in the form of ammonium,nitrite,nitrate,as well as organic compounds.The TNb does not include dissolved or gaseous nitrogen(N2).A differentiation between inorganic and organic nitrogen compounds is,by definition,not possible.Determination according EN 12260EN 12260 describes the determination of nitrogen in the form of free ammonia,ammonium,nitrite,nitrate and organic compounds that can be converted under the described oxidative conditions.Sum parameter Total Organic Carbon TNb total bound nitrogen SCA-130-503 The conversion of the nitrogen containing compounds takes place via combustion in an oxygen atmosphere higher than 700 C to nitrogen oxide,which reacts with ozone to activated nitrogen dioxide(NO2*).In the subsequent reaction to NO2,light quanta are emitted(chemiluminescence)that are measured by the detector.Simultaneous TN determination using the TNM-L Based on the similar oxidation process,the TNb determination can be carried out simultaneously with the TOC measurement.For this application,the TNM-L option is installed on the top of the main TOC-L system.Fig.TOC-L CSH with TNM-L Modul The benefit is that no additional laboratory space is required.For the simultaneous determination,the sample is injected onto the catalyst at 720 C.All carbon atoms present in the sample are converted to CO2 and,in parallel,the nitrogen atoms to NO.The gas mixture is then transported by the carrier gas stream through the NDIR detector,where the carbon dioxide content is measured.Subsequently,the gas mixture enters the chemiluminescence detector,connected in series,where the nitrogen content is determined(See Figure below).Fig.Simultaneous TOC/TN-Determination It should be noted that an optimal injection volume must be selected for both parameters.Recommended Analyzer/Configuration TOC-L CXX with TNM-L ASI-L SCA-130-503 Samples with high-salt loads generally are a problem for TOC analysis.The problem is less the conversion of organic compounds to CO2 than the effects of the salt on the catalyst.This leads to higher maintenance needs,as the salt can crystallize in the combustion system.In many applications for the instruments in the TOC-L and the TOC-4110/4200 series,the kit for salt-containing samples is an important component.It consists of a combustion tube of a special geometry and a unique mixture of catalyst beads.Sample preparation In this application,sample acidification is carried out with sulfuric acid which is used to modify the sample matrix.While NaCl has a melting point of 801 C,the melting point of Na2SO4 is higher(888 C).The potassium salts of sulfuric acid also have a significantly higher melting point than those of hydrochloric acid.This has a positive effect on the lifetime of the combustion tube.Compound Melting point NaCl 801C KCl 773C Na2SO4 888C MgCl2 708C CaCl2 782C K2SO4 1.069C Tab.Melting point of different salts Results indicate that the stability of the catalyst is increased,and that up to 12 times the number of samples can be measured before the catalyst must be exchanged and the instrument needs servicing.Fig.Catalyst filling Sum parameter Total Organic Carbon Kit for high-salt samples SCA-130-504 Endurance test To determine the performance of this option,a brine solution was measured in a long-term test.For this purpose,a 28%NaCl solution(matrix adapted with a 15%sulfuric acid solution and spiked to a 5 ppm TOC solution using a KPH solution)was injected 220 times.Initially,a blank value and a control standard with 10 ppm TOC were measured.The control standards were tested after 110 and 220 injections,respectively.The injection volume was 50 L.The following figure shows the excellent reproducibilities and the stability of the measurement.Fig.Results of endurance test Related application The high-salt kit is used for many different applications in order to keep the maintenance need for difficult matrices as low as possible.Examples:104 TOC-Determination in seawater 304 TOC-Determination in brine solution 306 TOC-Determination in soda solution 308 TOC-Determination in sodium nitrate 603 TOC-Determination in chemical industry Recommended Analyzer/Configuration TOC-L CXX ASI-L Kit for high-salt samples B-Type Scrubber(At very high halogen concentrations in the matrix,the B-type scrubber is recommended.This scrubber protects the detector cell of the NDIR detector.)High SaltConbutiuontubeHigh SaltConbutiuontube 28%NaCl in 5mg/LKHPInj:50uL Acid:15%28%NaCl in 5mg/LKHPInj:50uL Acid:15%0246810050100150200250InjectionsConcentrationmg/L01020304050AreaConcentratoinAreaSCA-130-504 The instruments of the TOC-L series are designed to successively analyze many different types of samples of different concentrations.For the autosampler,sample trays for different sample numbers and sample volumes are available.To eliminate cross-contamination between analyses of the different samples,the number of rinsing steps can be defined in the software.There is usually enough sample volume available to rinse the tubing and the injection system of the TOC-L several times.Depending on the measuring method,injection volume,measurement range and rinsing steps,10 20 mL of the sample is needed.Small sample volumes It can also occur,however,that only a few mL of sample are available.This is usually the case when there is only little sample available,the sampling process is complex or the sample is very valuable.For such cases,the kit for small sample volumes is available.The 5 mL syringe body can be exchanged for a 500 L syringe in a rapid conversion step.Moreover,the injection slider has to be exchanged too.Specification With this option,automatic dilution,acidification and sparging is not possible and the specifications are,therefore,changed as follows:Measurement range:TC,IC:to 2,000 mg/L TN:to 200 mg/L Injection volume:150l maximal Diameter:0.2 mm NPOC-Measurement:In ASI-L with external Sparge kit ASI-L:9ml Rack Example 5 mL sample is sufficient for NPOC determination using an ASI-L,9mL vials (3 injections with 150 L injection volumes)Sum parameter Total Organic Carbon Kit for small sample volumes SCA-130-505 The manual injection kit enables the analysis of water samples and gases.The sample for TC determination is directly injected into the combustion chamber using a L syringe.This is interesting for applicatio