环境水中有机物综合指标检测方案

analytikjena analytikjena aApplication field/Industry branch： Chemistry/Polymer Industry Clinical Chemistry/Medicine/Sanitation/Health Care Electronics Semiconductor Technology Energy Environment/Water/Waste Geology/Mining Nutrition/Agriculture Metallurgy/Electroplating Refineries/Petrochemistrv Pharmacy ■Cosmetics Material Analysis Other Optimum digestion technology enables affordable TOC andTNb detection in seawater samples Authors： Bernd Bletzinger and Birgit Wittenburg， Analytik Jena AG， Konrad-Zuse-Str. 1， 07745Jena Introduction The detection of minute TOC and TN， content in salty matrices， such as seawater， poses a specialchallenge for many TOC analyzers with thermocatalytic digestion. Why? Due to the high saltcontent with simultaneously low analyte concentrations the sample can often not be dilutedmeaningfully. In addition the reactor of the TOC/TN， device is continually loaded with sodiumchloride and other salts with every sample injection. With increasing load on the catalyst themeasuring results display significantly reduced recovery rates and increased measured valuevariations. The salt accumulating in the system also rapidly leads to the catalyst and otherconsumables of the combustion tube becoming useless and having to be replaced after a shortperiod of time. That there are alternatives is demonstrated by the measurements of deep sea water samplesusing a device of the multi N/C series shown below. Experimental General The detection of TOC/DOC (Dissolved Organic Carbon) and TN/TDN (Total Dissolved Nitrogen)in deep sea water samples is the focus of global ecosystem monitoring. To this end samples fromdifferent seawater currents and layers are commonly analyzed. The DOC and TDN concentrationsare normally significantly below 1 mg/L. The purpose of the analyses performed was to demonstrate with a long measuring series usingdeep sea water that the analyzer can continually measure very small DOC and TN， concentrationsin a heavily salty matrix with stability and precision without requiring intervention in the digestionsystem/reactor or other system components. Material The analyses for detecting the DOC and TN parameters were performed in a reference materialfrom the university of Miami "Florida Strait at 700m" that was available HCl-stabilized in ampules of10 mL each. The reference material is identified with the following concentration details：cpoc=492-516 pg/L and CTN= 462 pg/L. The salt content is approx. 35 g/kg， with the maincomponent being sodium chloride and sodium sulfate forming the second largest share. In addition， aqueous calibration standard solutions of potassium hydrogen phthalate andpotassium nitrate/ammonium sulfate were used in various concentrations to calibrate the analyzer. Device All analyses were performed in the TOC/TN analyzer multi N/C 3100 (Analytik Jena AG). This isequipped with a chemiluminescence detector for TN detection. The measuring device wasoperated in its default configuration， i.e. without using special reactor consumables or additionalhalogen traps. For the automatic sample supply the autosampler APG 64 (Analytik Jena AG) wasused. Fig.1： multi N/C 3100 with APG 64 Method A method permitting the simultaneous detection of the NPOC and TN， parameters from a singlesample injection was chosen. The sample volume was set to 200 pl， the combustion temperaturewas 750 °C. A platinum catalyst supported the combustion. Procedure The reference material was first filled into suitable sample cups to allow for an automatic detectionof both parameters by the autosampler. Special attention was paid to avoiding contamination bythe environment of the only minimally loaded sample material as far as possible. After sealing thecups a complete sampler (64 positions) was filled. After starting the chosen NPOC/TN method thealready acidified samples were automatically purged to remove inorganic carbon content (TIC) anddissolved CO2. Each subsequent sample was purged in parallel with the analysis of the previoussample. This considerably saves time during the analysis process. The samples pretreatedautomatically in this manner were transferred to combustion via a flow injection system. Multipleinjections from a sample cup took place； after every 15 reference samples ultrapure water wasanalyzed to check the blank value of the system. Results and discussion The results of the individual reference samples were combined into blocks of five each and areshown in the overview (fig. 2). The calculated average concentration value and the standarddeviation across all samples were 508 ug/L±25 pg/L (corresponding to a relative standarddeviation of approx. 5%) for DOC and 457 pg/L± 17 pg/L (corresponding to a relative standarddeviation of approx.4%) for TN. The measuring results achieved match the concentrations of DOC (492-516 pg/L)) iandTN (462 pg/L) specified for the reference material excellently. From the stable recovery rates andlow measured value variations across a multitude of sample injections can be concluded that nomatrix effects on the system can be detected in spite of the high salt introduction. This means thatboth digestion and detection are stable in behavior from the first to the last sample. The ultrapure water analyzed after every 15 samples also demonstrated a constant concentrationlevel (DOC <30 ug/L， TN <20 pg/L). This in turn confirms the fact that the introduced salt load didnot affect the capability of the system in any way. After concluding the experimental series the combustion tube was removed and examined forsigns of wear. After flushing with ultrapure water and replacement of the catalyst cover the reactortube could be used for further analyses. Fig. 2： Deep sea water reference material measuring series - excellent stability The specialty- the digestion technology The high stability of the measured values over a long period of time in highly salty samples is inparticular due to the digestion technology used in the analyzer. A special reactor geometrycombined with an optimum temperatureguidanceprevents thepremature andexcessivecrystallization of salts on the catalyst and its cover. Dependent on the concentration and chemicalnature of the salts introduced these are transported to a colder part of the reactor. No negativeeffects on the analytical capability are to be expected there. The frequent change intervals of thecatalyst -typical for themocatalytic TOC analyzers when introducing heavy salt loads - are thusreduced to a minimum. The quantity of catalyst material used in the combustion tube is very low not least due to thespecial geometry. Reduced maintenance cycles and low material consumption help to lower therunning costs for TOC/TN analysis significantly. Other robust system components contribute to thestability of the overall system when analyzing extreme matrices， e.g.the highly sensitive andcorrosion-proof Focus Radiation NDIR detector or the VITAmethod for flow-independent signalevaluation. Summary The results of the analyses demonstrate that using an optimum digestion technology the preciseand longterm stable measurement of samples with high salt content is possible. Necessarymaintenance intervals can be extended extremely by using a convincing digestion technology. The expectations of TOC users who often have to measure salty samples include the following requirements for a TOC analyzer： Numerous sample injections without necessary maintenance intervention in the system Self-diagnosis of the TOC analysis system - When is an intervention required? Low material consumption when replacing the consumables in the combustion tube Easy change of the catalyst/reactor consumables and rapid run-in behavior for quickmeasuring readiness Low operating costs (due to minimum maintenance effort and minimal use of materials) With the analyzers of the multi N/Ce series every user has devices available meeting theserequirements. Printout and further use permitted with reference to the source. C 2012 Analytik Jena AG Publisher： Analytik Jena AG Konrad-Zuse-Str. 1 Phone +49 (0) 364177-70 07745 Jena Fax +49 (0)36 41 77-92 79 Optimum digestion technology enables affordable TOC and TN detection in seawater samples/Reference number： Lit SP_TOC_e|Ble， BW