APLIKACIJSKI ČLANKI APPLICATION ARTICLES Total Organic Carbon - TOC in Water Part I: Measurement and Instrumentation I. Sorii MIKROIKS d.o.o., Ljubljana, Slovenia 1.0 INTRODUCTION The content of organic substances is an excellent indication of water quality. Monitoring of TOC - Total Organic Carbon - proved to be a fast, sinnple and reliable method of water analysis. TOC monitoring systems are used in various industrial areas. The applications are process and waste water monitoring, high purity or cooling water analysis. Furthermore, TOC analysers can be applied to assess pollution levels in municipal waste water, drinking water, ground and surface water. Table 1. Typical applications and users of TOC Instru- mentation APPLICATIONS USERS Process water Chemical industry Waste water Foodstuff industry Cooling water Power plants Boiler feed water Semiconductor industry Reclaim water Electronics industry High purity water Semiconductor and Pharmaceutical industry Surface water Paper industry Ground water Textile industry Drinking water Mineral oil rafineries Airports Waterworks Sewage plants ........................ Research facilities Traditional water quality parameters were COD (Chemical Oxygen Demand) and BOD (Biochemical Oxygen Demand). For BOD measurement bacteria and nutrients are added to the water, and their consumption of oxygen is recorded, generally in mg/l of water. On the other hand, for COD measurement, concentrated sulfuric acid and chromium are used to establish the maximum possible oxygen consumption of the sample. In the river Rhine in 1992 at the German - Dutch border, the BOD was measured at an average of three mg/l and the COD was 10 mg/l, /1/. However, the laboratory measurements of these parameters are time consuming and not suitable for the quality control. On-line versions of COD and BOD monitors are available, but very expensive and not reliable. TOC can offer cost - effective, quick and reliable monitoring. The TOC values can be correlated with the COD and BOD values if necessary. Of course, the relationship depends on kind of water pollution. As a rule of thumb: COD = TOC x 3 and BOD = TOC x 1. In table 1 some applications and typical users of TOC instruments are shown. 2.0 CONVENTIONAL LABORATORY BASED METHODS FOR TOC ANALYSIS TOC analysis methods were originally developed in the early 1960s to understand better the contents and treatment of drinking and waste water, /2/. Consequently, these methods were developed to detect high values of TOC. As the market expanded and more commercial suppliers offered instruments, variation of the original designs intended for lower concentrations appeared. Analytical technologies utilized to measure TOC share the objective of completely oxidizing any organic molecules in a water sample to carbon dioxide (CO2), measuring the resultant CO2 level and then expressing this response as carbon concentration. Included in these techniques are combustion oxidization, flame ionization detection, wet oxidation using acid, persulfate and NDIR detection, calorimetric methods and aqueous conductivity methods. 2.1 Combustion Oxidation The original combustion oxidation method measures total carbon (TO). It requires sample injection by syringe into a high temperature furnace with a platinum or cobalt catalyst. This process theoretically oxidizes all of the carbon materials to CO2 which is directly propor- tional to the organics present in the sample. Then, the CO2 is swept into a non-dispersive infrared detector (NDIR) by a stream of dry nitrogen for final measurement, A variation of this method employs a stream splitter which directs equal parts of the sample to two furnaces at different temperatures to measure the total inorganic carbon (TIC) at 150°C, and TC at 950°C. The TOC can then be calculated as: TOC = TC - TIC 2.2 Flanne Ionization Detection Another early method for high TOC concentrations employs flame ionization detectors (FID) which reduce the CO2 content to methane (CH4). Sample oxidation requires the addition of sodium persulfate and a heated catalyst. Additional plumbing allows the volatile or pur-geable organics to be measured. These systems are quite complicated and require hydrogen for the FID operation in addition to the acids, oxidants and carrier gases. 2.3 Wet Oxidation Using Acids, Persulfate, and NDIR Detection The persulfate/NDIR methods are common in laboratory units. An acid is added to the sample water to reduce the pH to 2-3. At this low pH the inorganic carbon is oxidized to CO2 and measured. All remaining carbonaceous compounds are assumed to be TOC. Persulfate is added, sometimes with heating and/or UV radiation, to expedite oxidation of the remaining organics to CO2. The CO2 which is directly proportional to the amount of TOC in the original sample, is then measured in an NDIR detector. 2.4 Calorimetric Methods After sample acidification and sparging of the released CO2 from inorganic carbon, persulfate is added in the presence of UV radiation to oxidize the organics in the sample water. The CO2 produced passes through a semipermeable membrane and then is dissolved into a dilute, buffered Phenolphthalein solution. The colour of this solution is sensitive to the pH changes caused by the process and is measured in a spectrophotometer at 530 nm. 2.5 Aqueous Conductivity Methods CO2, produced by the acid/persulfate oxidation with possible UV assistance, can be measured for conductivity changes after dissolution into ultra-pure water. The change in conductivity is a direct function of the TOC present in the water sample. In the addition to the reagents required, these methods must include an independent water system capable of producing theoretically pure water at 18.2 Mohmcm resistivity. 3.0 TOC IN ULTRAPURE WATER (UPW) High-purity water has a very low conductivity (high resistivity). The theoretical specific conductance of "pure" water at 25 °C is 0.055 |j.S/cm (specific resistivity of this water is 18.15 Mohm-cm). When the conductivity of high purity water is measured at temperatures other than 25 °C only temperature compensation algorithms within microprocessor controlled instruments are adequate to provide reasonable estimates of the true conductivity at 25 °C. TOC is present in high-purity water in very small amounts, TOC levels of less than 250 |i.g/l for PW (pharmaceutical Purified Water), 50 jig/l for WFI (pharmaceutical Water-for-lnjection) and 10 |j.g/l or below (semiconductor UPW) are the norm in well controlled HPW systems. For these high-purity water TOC levels, the ).ig/l units are usually expressed as parts per billion (ppb). Semiconductor manufacturers have been already for a long time monitoring TOC in the HPW and many correlations with electrical parameters already exist. However, in pharmaceutical water only in near future the measurement of TOC is intended to replace the current USP oxidizable substance limit test for the detection of organic compounds.. TOC test is non-se-lective, sensitive, rapid, quantitative and highly reproducible. System suitability rather than a specific method of TOC analysis will be used to validate this measurement. 3.1 A TOC Analysis Method Designed Specifically for On-Line Process Monitoring We have noted that recent trends favour the transition of laboratory analytical techniques to the on-line processes. Advantages include accurate trend information, continuous monitoring, early detection of potential upsets and, in many cases, reduced operational attendance resulting in lower costs. In 1984, Anatel Corporation developed an advanced and patented method for measuring TOC in high purity water, /3/. This new technology, in addition to providing enhanced performance, was engineered into instrumentation designed specifically for on-line process monitoring. The equipment is reliable, rugged beyond the conventional standards of laboratory instrumentation, and provides detection limits for TOC that have never before been approached. 3.2 Operating Principle of the Anatel TOC Technology As with most significant new technologies, its appeal lies in the elegant simplicity of the method, /4/. Anatel eliminates the need and inconvenience of reagents, gases, and heating devices to achieve full oxidation of organics in the sample water. ITie instrument's compact design permits monitoring of each critical water purification component for optimal performance throughout the system. In on-line operation, a side stream of water is directed through the instrument's analysis cell for a user selected period. During this Sample Time, the resistivity and the tennpera-ture of the water are measured and displayed continuously. At the end of the Sample Time, the internal valve closes, "capturing" the water sample which is exposed to 185 nm UV radiation to begin oxidation. The optimally designed configuration of the UV lamp, quartz window, and reaction-enhancing titanium electrodes within the cell enssures efficient, complete, and reproducible oxidations. The photocatalytic reaction produces hydroxyl radicals (•OH) on the surface of the titanium electrodes. These •OH groups are strong oxidants and replace the per-sulfates that are needed in conventional instruments. This photocatalysis, along with a proprietary set of sophisticated software algorithms for monitoring the reaction, assures complete oxidation of the organics. CxHxOx-^ (H0H,UV-)-Ti02) CO2 + H2O The CO2 which is produced during the oxidation process disolves into the water and forms carbonic acid which dissociates into conductive ionic species: H2O + CO2 ^ H+ + HCO3" ^ 2H+ + C03= The change in conductivity due to the dissolution of CO2 into the water is directly proportional to the concentration of TOO originally present in the sample. Quartz plaie Therm'iStor temperaturo 0-100 "C Sample Vatvo Analysis Cell UV Lamp 85/254 nm optimized Outer electrode . Ti02 iiiPj inner electrode Water Water out in Ti02 Figure 1: Schematic of the A-1000 Analysis Cell M»0 H„0 TiOo H H H H > H O» O- O« 01 O Figure 2: Photocatalytic production of hydroxyl radicals C80 Cenlrolilef , i. I I .. I ■ '< IP m 1« ™J» S2CIP CoDlraftef.&öMaOf'Pnfltsr Ci3m|(en»sofs i \ ' h)! \ I- IM 13- :L: -:x J,; Pf'iiet — 1..............J - ■ ! iMt: 1 ! !£i n 1 i<- i .• lilV Si^x r.i,.") Figure 3: Schematic of the A-1000 network system with cable, connectors, connector block and multiple sensors 3.3 A-1000 Instrument Configuration The nninimum Anatel A-1000 TOC Analysis System combines a Controller and a Sensor unit. Multiple Controllers and Sensors may be linked together via a proprietary local area network (A-Net) to furnish a wide variety of potential system configurations. Possible applications include differential TOC measurements between two sensors. C80 CONTROLLER The C80 Controller serves as a control/display device for the A-1000 TOC measurement system. A 4-line by 16-character display presents information. Function and edit keys provide the ability to display and modify the various parameters which control the Sensor's operation. 810 SENSOR The S10 Sensor is the basic A-1000 analysis device. A 1 -line by 16-character display reports current TOC values in ppb. Operation parameters fo the SI 0 are established through a 080 Controller. S20 SENSOR The S20 combines the analytical and interface capabilities of the S10 Sensor with a C80 Controller. This union allows the control and reporting of the Sensor to be integrated into a single enclosure. The S20P Sensor's incorporation of an integral printer furnishes total instrument portability with point-of-use reporting capabilities. 5. SELF-CLEAN MODE In the Self-Clean Mode, the Sensor's solenoid valve is opened to allow water to flow through its measurement cell. The UV lamp is turned on to oxidize any organic contaminants,which are subsequenty flushed from the cell by the water flow. Conductivity and temperature are reported as described in the Purge Mode. 3.5 A-1000 Auto TOC Mode Analysis Times And States In the Auto TOC Mode, the A-1000's TOC analysis process is comprised of three stages: Sample Time, Oxidation State and Idle State-collectively referred to as the Cycle Time. Cycle Time (User selectable) Sample Time (User Selectable) T Oxidation State Idle State {if Present) • Cycle Time • User Selected Times (minutes) » Comprised of 3 States or Times • Sample Time • Oxidation State • Idle State • Analyzer Rate • Normal •Fast 3.4 A-1000 Operation Modes The Anatel A-1000 TOC Sensors operate in one of five modes: 1. AUTO TOC Auto TOC is the analysis mode for monitoring ultrapure water systems. The Sensor automatically performs successive measurements, reporting the TOO level, conductivity and temperature of the water stream at the end of each analysis cycle. 2. PURGE MODE The Purge Mode opens the Sensor's internal solenoid valve, allowing water to flow through and flush the measurement cell. Conductivity and temperature readings are continually updated and printed either at user-selected time intervals or based on a change precentage as dictated by the instrument's operational parameters. The Purge Mode is used to check the sample water flow rate through the Sensor. 3. DIFFERENTIAL MODE The Differential Mode is a comparison of two Sensors' Auto TOC or Purge Mode readings. A primary and a reference Sensor report their respective and differential measurements at the end od each analysis cycle. 4. MANUAL MODE The Manual Mode allows the user to interrupt automatic operation and manually initiate an analysis cycle. Figure 4: A -1000 analysis cycie time iine 1. SAMPLE TIME During the user selectable Sample Time, the UV lamp is turned off and the Sensor's internal solenoid valve is opened to allow pressurized water from the process stream to purge the connecting tubing, valves and measurement cell. The Sample Time interval must be sufficient in duration to furnish a fresh and representative water sample for each measurement cycle. The required duration of the Sample Time depends on: • -the length and internal diameter of the sampling system's transfer tubing from the process pipe to the analyzer. • -the water flow rate. • -the difference between the ambient temperature and the temperature of the process water. Typically, a Sample Time of two minutes is adequate at a flow rate od 100 ml/minute. The flow of water should be observed from the Sensor's WATER OUT port during the Sample Time interval. 2. OXIDATION STATE During the first ten seconds of the Oxidation State, the conductivity and the temperature of the sample water are measured to establish reference values which are stored in the A-1 OOO's memory for use in calculating the TOC results. The internal solenoid valve is then closed to capture afresh, discrete, representative water sample in the measurement cell. The UV lamp is turned on and oxidation of any organics within the sample occurs. The Oxidation State interval varies depending on the type and concentration of the organic constituents in the water and is characterized by Profile Types P1, P2 and P3. The sample's final equivalent TOG content is calculated and based on the conductivity and temperature at the completion of the Oxidation State. The sample's TOC in ppb, initial conductivity (|iS/cm) or resistivity (Mohm-cm) corrected to 25 °C, and temperature (°C), are sent to the A-1000's display, analog and serial output ports. 3. IDLE STATE AND VALVE AT IDLE If the TOC analysis is completed before the set Cycle Time has elapsed, the Sensor goes into an Idle State in wich the UV lamp is turned off awaiting the start of the next analysis. During this Idle State, the internal solenoid valve is either "Open" or "Closed" as determined by the A-1000's Valve @ Idle setting. Open - the Sensor's measurement cell is continuously purged with sample water until the conclusion of the Cycle Time. Closed - the internal solenoid valve prevents water flow until the conclusion of the Cycle Time and initiation of the next Sample Time interval. The next analysis cycle begins immediately if the duration of the Cycle Time is less then the time required for complete sample analysis. 4. ANALYZER RATE The A-1000's Analyze Rate determines the speed at which oxidation of the water sample occurs. "Normal" is the standard analysis rate. "Fast" performs the analysis up to three times quicker. The Fast rate is recommended only for applications where rapid results are crucial since prolonged operation on this setting reduces the life of the Sensor's UV lamp. 3.6. Oxidize state profile types During the Oxidize State of the Auto TOC analysis cycle, the Sensor continuously monitors the changing conductivity and temperature of the water sample trapped in the measurement cell until oxidation of the organics is complete. The relationship between conductivity and time is called the oxidation curve. One of three oxidation curve Profile Types is reported by the A-1000: "P1," "P2" or "P3." 1. PROFILE TYPE 1 (P1) - Easy to Oxidize Organics In a P1 sample, conductivity is always increasing until oxidation is complete. This profile indicates that only simple low molecular weight organics are present in the sample water. 2. PROFILE TYPE 2(P2) - Moderately Difficult to Oxidize Organics The P2 sample occurs only at TOC levels below 25 ppb and is very similar to a PI profile in which the contribution of the organic "background" of the cell must be adjusted. 3. PROFILE TYPE 3 (P3) - Difficult to Oxidize Organics A P3 sample contains organic compounds which form significant amounts of intermediate organic acids which have a higher conductivity than the equivalent CO2 that is finally formed. This produces an initial high level of conductivity which then decreases as the oxidation process proceeds to completion. A change in Profile Type is an important information and usually indicates that something has happened within the water system. An abrupt change usually indicates a change in the organic content of the water. For example, a change from a PI to a P3 Profile Type would result from the introduction of more complex organic compounds. 3.7 Alarms The user may set an alarm limit for the TOC level that is detected by the Sensor. Any TOC limit excursions are indicated on the C80 Controller by the flashing of the entire LCD display as well as the affected Sensor's channel LED. When enabled, an audible beeper also sounds and, if connected, a hardcopy printout of the Profile Type 1 (PI) - Easy to Oxidize Organics Conductivity (uS/cm) Time (minutes) Profile Type 2 {P2) Conductivity (uS/cm) Time (minutes) Profile Type 3 (P3) - Difficult to Oxidize Organics Conductivity (uS/cm) Time (minutes) Figure 5: Oxidize state profile types excursion is generated automatically. The Sensor's digital OUTPUT #1 port may be used to transmit the alarm to a compatible device. Alarms are acknowledged by pressing the (alarm) key on the C80 controller. 3.8 Errors The C80 Controller is also used to display any Sensor malfunctions, reported as numeric Error Codes, indicating an electromechanical or analytical failure. The Sensor's channel LED and the Controller's display flash to alert the user of the problem and the error is acknowledged by pressing the (alarm) Key. Each Sensor maintains an error log of as many as 30 separate entries consisting of the Error Code number, the total number of occurrences of that error, and a time stamp of the initial occurrence. 3.9 Analyzer outputs The A-1000 Sensor communicates to external devices through an RS-232C interface, 4-20 mA analog signals and digital output ports. 1, SERIAL OUTPUTS An RS-232C port is provided to drive a printer or other serial communications device. 2, ANALOG OUTPUTS Two types of ports are provided for signals to analog devices. The primary port provides a 4-20 mA signal which represents TOC. The secondary port is through the Sensor's DIAGNOSTIC port to allow the use of External DAC (Digital-to-Analog Conversion) modules to trasmit 4-20 mA signals representing temperature and resistivity values. The minimum and maximum levels corresponding to the 4 and 20 mA signals may be defined by the user for TOC, temperature and resistivity. The user also may select one of three default output states for the analog signals should a fatal error be encountered by the Sensor. 3, DIGITAL OUTPUTS The Alarm Status and the state of the internal solenoid valve are available on the Sensor's two digital output ports. 3.10 ANATEL - 1000 system specifications SPECIFICATIONS AI 000 TOC Operating range 0,05 - 9999 ppb 1 Repeatability better than ±0,05 ppb < 5 ppb better than ± 1 % > 5 ppb Accuracy ± 1 % 1 Display Resolution Minimum input water resistivity Input water temperature Temperature measurement Input water pressure Operating temperature RESISTIVITY Operating range Temperature compensation Readout resolution Precision INPUT/OUTPUT CONFIGURATION Calibration: Validation: Dimensions: MODEL 0,00- 19,99 ppb 20,00- 199,9 ppb 200 + ppb 5 Mohmcm for all water 1 Mohmcm for neutral waters 0,2 Mohmcm for water with CO2 as conductive species 0 -100 °C YES 15-100 PSIG max 5 - 40 °C 0,01 - 18,2 Mohmcm 0,05- lOOnS/cm to 25°C over entire 0 - 100°C temperature range or temperature uncompensated resistivity 3 significant figures as resistivity 4 significant figures as conductivity ±3% water IN/OUT AG plug Network RS-485 : 8 S10 sensors can be connected to C80 Printer RS-232G Data RS-232C to computer!! Digital output (2) and input (2) Against reference instrument According to USP 23 IQ/OQ Guidelines and SOP available H325mmxW172mmx D112mm Weight 5,4 kg C80 Controller S10 Sensor S20: Controller -t- Sensor (portable) S20P: Controller + Sensor + Printer (portable) 4.0 The Anatel Model A-2000 for Wide Range TO C Analysis The A-2000 is designed specifically to address higher range TOG analysis of feedwaters to high purity systems, clean-in-place applications in the pharmaceutical industry, reclaim and reuse water in semiconductor manufacturing, drinking water, power generation systems, chemical processing, and effluent streams. The A-2000 TOG Analyzer offers four user-selectable analysis modes: • TC - Total Garbon » TIG - Total Inorganic Garbon • TOG Direct and • TOG Indirect TOG measurements are made directly by sparging to remove any TIG present or indirectly by analyzing for both TG and TIG. The difference between these two measurements is the TOG value. 4.1 A-2000 Components A-2000 system measures TOG by oxidizing the organic carbon to GO2 with persulfate in the presence of ultraviolet light. The GO2 produced is measured directly by a nondispersive infrared detector (NDIR). This method measures both the purgeable and non purgeable organic carbon that are present. The main A-2000 components are: High Efficiency Photoreactor The high efficiency photoreactor consists of a hollow quartz tube, more than 1 meter length, wrapped into a helix just 2" long, encircling a 254 nm UV lamp.The tube, measuring just 3 mm in outside diameter and 2 mm in internal diameter ensures that the sample is always strongly exposed to penetrating UV energy for maximize oxidation performance. The long, small diameter quartz tube ensures fast, complete, UV promoted persulfate oxidation in just minutes. ! />'5 iS) I'.(Of , ill >1 If r^i ' >! Liquid/gas separator The membrane in the liquid/gas separator chamber is actually round, silicone tubing, more than half a meter long, wrapped into a compact spiral measuring less than 2 inches in length. The water/reagent mixture permits only CO2 to pass through the silicone wall as it flows through the tubing. This design maximizes the membrane surface area exposed to the sample mixture, so that the diffusion of CO2 across the membrane is fast, efficient, and complete. NDIR Detector The NDIR detector consists of a single chamber (optical path) with an infrared light source at one end, and a filtered photodetector at the other end. The chamber is first filled with N2 carrier gas to establish a baseline reading. Then the chamber is emptied, and filled with N2 carrier gas mixed with the CO2 sample. CO2 in the optical path absorbs an amount of infra-red energy, at a specific wavelength, proportional to the amount of CO2 present. Because the energy is absorbed, it never reaches the filtered photodetector, which outputs a signal proportional to the amount of CO2 gas in the chamber. In this way, TOC Is measured very accurately and precisely as the concentration of CO2 produced by the sample oxidation. Sample/Sparge Chamber The sample/sparge chamber is actually a cylinder about 3" long and 1" in diameter, constructed of electro-polished stainless steel. The cylinder contains the acidified sample while N2 carrier gas bubbles through it. This bubbling action, known as " sparging ", agitates the liquid sample, and frees the inorganic carbon (e.g. H2CO3, COs"^, HCO3") from solution so it can escape into the atmosphere leaving a TIC free sample. The sample/sparge chamber is only used during the TOC fast operating mode. Multi-Port Switching Valve The electronically actuated multi-port switcing valve is expected to provide reliable performance with continuous use for many years. The computer rotates the 8-port valve to control the flow of sample, acid, persulfate and calibration solution to the syringe pump, drain and other A-2000 components. Use ofamuiti port switching valve in combination with a syringe pump for mixing is part of the A-2000 sequential injection analysis (SIA) design. Syringe pump All initial mixing of liquid sample components takes place in the rugged digitally controlled syringe pump. Acid, persulfate and sample are precisely mixed according to modified, proven, sequential-injection-analysis (SIA) principles in this sturdy, long-lasting, computer controlled, glass syringe pump. Reagents All reagents used for operating the A-2000 wide range TOC analyzer can be easily purchased from any chemical supply house or can be ordered directly from Anatel for maximum convenience. 0.3 Molar phosphoric acid (H3PO4) is used to lower the sample pH and allow CO2 and other dissolved purgeabies to migrate Sampie/Spafge Chamber {pH<2) Samp!B NDIR :Det8Ctof AC. ^ D.in SarapfÄ/Sparg« Chamb«f (pM<2) Umpk HOm Oet«c»r (Lamp OFF) Calibration Syfing« Separator Figure 8: Operating schematic for measurement of TIC Carrier Cäs Sampie/Sf>arg« Chamber (pH<2) Sample -MOfR Datector Calibration Syrinqe _ . AC,4 Psmiffote st^n^^ f^p Oram out of solution. 1.6 Molar sodium peroxidisulfate (Na2S208) Is used, in conjunction with 254 nm UV energy, to oxidize the sample to CO2 suitable for measurement by the NDIR detector. Anatel also provides 500 ppb sucrose (C6H12O6) solution designed for pharmaceutical calibration of the instrument. Sucrose NF is the proposed calibration compound recently recommended to the United Stets Pharmacopeia (USP) for performing calibrations oh TOC analyzers. Carrier Gas A-2000 carrier gas must be at least 99.98% pure nitrogen (N2), pressurized to 4 bar, and capable of flowing at 250 ml/min. The carrier gas is used to sweep CO2 and inorganic carbon (e.g. H2CO3, COa'^, HCO3") to the NDIR cell for measurement. Additionally, carrier gas alone is used as a background measurement of NDIR performance. 4.2 Simplified A~2000 Operating Schematics 4.2.1 Total Carbon -TC The A-2000 measures TC by oxidizing all of the oxi-dizable materials in the raw sample water, and measuring the amount of CO2 prodiced by the oxidation. 1. Acid and sodium peroxidisulfate are added to the sample in the syringe pump. The persulfate oxidizes the sample while the acid allows CO2 gas to escape from the acidified sample by lowering the sample pH. 2. The entire sample is transported directly to the high efficiency photoreactor, without sparging, and the sample molecules are oxidized to CO2 and byproducts according to the following equation: CxOxHx + NazSaOs hv — CO2 + H2O + Na2S04 + H2SO4 254 nm UV energy accelerates and promotes the persulfate oxidation. 3. The resulting CO2 is separeted from the byproducts by diffusion through a selectively permeable membrane in the liquid/gas separator. 4. The CO2 is transported to the NDIR detector within the N2 carrier gas stream. The NDIR detector outputs a signal proportional to the concentration of CO2 in the carrier gas stream. 4.2.2 Total Inorganic Carbon - TIC To measure TIC, the A-2000 must separate the inorganic carbon (e.g. H2CO3, COg"^, HCO3") from the sample solution, so that it can be measured. 1. The sample is adjusted to pH<2 by adding phosphoric acid in the syringe pump which allows the TIC to dissociate as CO2. 2. The CO2 is separated from the byproducts by diffusion through a selectively permeable membrane in the liquid/gas separator. The lamp stays off throughout the analysis to prevent any oxidation by the UV energy alone. 3. The CO2 is transported to the NDIR detector within the N2 carrier gas stream. The NDIR detector outputs a signal proportional to the concentration of CO2 in the carrier gas stream. Nüt! Oetccte Step 1 = TIC measurement {Lamp OFF) ESSSi Step 2 » TC measurement {Lamp ON) Step I and Steo 2 4.2.3 Total Organic Carbon - TOC Fast To measure TOC directly the A-2000 must first transport the sample to the sample/sparge chamber where the TIC (e.g. H2CO3, COs"^, HCO3") is removed from the TOC by sparging. 1. The sample is adjusted to pH<2 by adding phosphoric acid in the syringe pump. 2. The sparging process allows purified nitrogen gas to bubble through the sample mixture in the sample/sparge chamber. This bubbling action frees the inorganic carbon from solution so it can escape into atmosphere, leaving a TIC free sample. 3. The remaining TOC, still in liquid phase, is combined with sodium peroxidisulfate in the syringe pump and transported from the sample/sparge chamber to the high efficiency photoreactor where the molecules are oxidized to CO2 gas by the addition of sodium persul-fate and 254 nm UV energy: CxOxHx + NaaSaOs hv ^ CO2 + H2O + Na2S04 + H2SO4 3. The CO2 is separeted from the byproducts by diffusion through a selectively permeable membrane in the liquid/gas separator. 4. The CO2 is transported to the NDIR detector within the N2 carrier gas stream. The NDIR detector outputs a signal proportional to the concentration of CO2 in the carrier gas stream. 4.2.4 Total Organic Carbon Determined Indirectly-TOCI The removal of TIC when measuring TOC directly, can also result in the loss of low molecular weight TOC, or "purgeable organic carbon" (POC). When POC composes a significant portion of TOC, such as in the drinking water industry, it may be advantageous to measure TOC indirectly as the difference: TOCi = TC -TIC. By mesuring TOC indirectly, POC is included and measured as TOC. TOCi is determined by separately measuring TC and TIC and calculating the mathematical difference. Determination of TIC (UV lamp off): 1. An aliquot of the sample is adjusted to pH<2 by adding phosphoric acid which allows the TIC to dissociate from the sample as CO2. 2. The sparging process allows purified nitrogen gas to bubble through the sample mixture in the sample/sparge chamber. This bubbling action frees the inorganic carbon from solution so it can escape into atmosphere, leaving a TIC free sample. 3. The CO2 is separeted from the byproducts by diffusion through a selectively permeable membrane in the liquid/gas separator. 4. The CO2 is transported to the NDIR detector within the N2 carrier gas stream. The NDIR detector outputs a signal proportional to the concentration of CO2 in the carrier gas stream. Determination of TC (UV lamp on): 1, Acid and sodium peroxidisulfate are added to a second aliquot of the sample in the syringe pump. 2. The second aliquote is transported directly to the high efficiency photoreactor without sparging, and the sample molecules are oxidized to CO2 gas and byproducts according to the following equation: CxOxHx + NazSzOa hv -> CO2 + H2O + Na2S04 -f- H2SO4 254 nm UV energy serves as a catalyst and promotes the persulfate oxidation. 3. The CO2 is separeted from the byproducts by diffusion through a selectively permeable membrane in the liquid/gas separator. 4. The CO2 is transported to the NDIR detector within the N2 carrier gas stream. The NDIR detector outputs a signal proportional to the concentration of CO2 in the carrier gas stream. 4.3 A-2000 performance specifications Measured parameter: TC, TIC TOC fast and TOC = TC - TIC Measuring range: TOC: 3 to 5000 ppb, 0.0 to 100.0 ppm, 0 to 2000 ppm TIC: 3 to 5000 ppb, 0.0 to 100.0 ppm, 0 to 2000 ppm Precision: TC/TOC/TIC ±2% in each range Analysis time: TIC: 1.5 min, TC: 3 min, TOC: 4 min Sample introduction: On-line Manual sipper tube Vial autosampler Communications: Output devices: Calibration: Validation: Gas requirements: Reagents: Dimensions: Optional autosampler: Network as many as 8 instruments Serial communication Four independent 0(4)-20 mA outputs Two user selectable alarm levels Relay outputs for alerts and alarms Full 8" backlit color LCD Convenient hard/soft key interaction Trend charts On-line help Built-in internal printer Built-in floppy drive Optional external graphics printer User selectable automatic or manual calibration Calibration from manual or autosampler vials Calibration from internal standard source Up to five calibration curves stored Automatic calibration reports Built in validation functions User selectable acceptance criteria Automatic validation reports Nitrogen, 99.98% purity and better, 4 bar, 250 ml/min Premeasured (or user prepared) 0.3M phosphoric acid and 1.6M sodium peroxidisulfate Easy reagent replacement Calibration standard - sucrose NH Reagent lifetime: 3 weeks H457mm x W635mm x D254mm Weight 32 kg 90 to 240 VAC ± 10%, 50/60Hz, 650VA H457mm X W286mm x D267mm Weight 10 kg 27 vials (40 ml EPA type) 90/120 VAC, 220/240VAC, 50/60Hz, 200VAmax 5.0 LITERATURE /1/ K.G. Malle, "Cleaning Up the River Rhine", Scientific American, January 1996 /2/ What You Should Know Before Buying ATotal Organic Carbon (IOC) Analyzer For A High-Purity Water System, ANATEL Corp. 1995 /3/ F. Blades, C. Frith, "New Analytical Technique for On-Line Detection of Trace Organics in Ultrapure Water", Seventh International Symposium of Contamination Control, Paris (18. September 1984) /4/ M. Retzik, P. Melanson, "The Design, Performance, And Validation Of An On-Stream Total Organic Carbon Analysis System For (Monitoring Ultra Pure Water", International Conference, Instrument Society of America (September 1993) For more information on ANATEL TOC measurement systems, please, call: Mr. Iztok Šorli MIKROIKS d. o. o. Dunajska 5, 1000 LJubljana, Slovenia tel. +386 (0)61 312 898 fax. +386 (0)61 319 170