Total Sulfur (TS) stands for the sum parameter of all organic and inorganic sulfur compounds. Trace levels (0.02 – 10.000 mg/kg or ppm by weight) of Total Sulfur are measured with an elemental combustion analyzer according to UV-Fluorescence detection technique or Microcoulometric detection technique. These measurements are carried out mainly in the Oil & Gas Industry.
Petroleum products like gasoline, diesel and fuel oil, may include many organic sulfur compounds. These can be classified as acidic and non-acidic. Acidic sulfur compounds are the thiols (mercaptans). Thiophene, sulfides, and disulfides are examples of non-acidic sulfur. These organic sulfur compounds are products of the degradation of sulfur containing biological components, present during the natural formation of the crude oil. Hydrogen sulfide is the main inorganic compound found in crude oil. Most sulfur compounds can be removed from petroleum streams through hydrotreatment processes, where hydrogen sulfide is produced and the corresponding hydrocarbon released. Hydrogen sulfide is then absorbed in a suitable absorbent and recovered as sulfur.
The sulfur is being removed from petroleum distillates to reduce sulfur dioxide (SO2) emissions when fossil fuels are combusted and in order to protect catalysts in the refining process against poisoning. Elemental combustion analyzers are being used to monitor the amount of sulfur present in crude, intermediates and final products.
Environmental regulations like the TIER III and EURO VI wield a maximum of 10 mg/kg of Total Sulfur or ppm by weight in diesel oils. The maximum amount of 10 ppm is also included in the Chinese norms GB 19147-2013 for Diesel fuels and GB 17930-2013 for Gasoline, deriving from the CHINA 5 environmental program. The maximum allowable amount of sulfur present in fuels demonstrates a downward trend on global scale. This raises the importance of accurately measuring the total amount of sulfur in petro (chemical) products at trace level.
When a Sulfur containing sample is combusted at 1000 ℃, Sulfur dioxide (SO2) is formed:
R-S + O2 –> SO2 + H2O + CO2
The amount of Total Sulfur is measured by pulsed UV-Fluorescence detection technique. Applying this detection technique together with combustion of a given sample proceeds as followed:
Sulfur dioxide (SO2) is formed during oxidation and transferred to the reaction chamber. Here it is excited by a pulsed UV source and as the excited state is unstable, the excited SO2 instantly decays to its ground state energy level. During this process, UV light is emitted. As this light has a different wavelength than the orginial UV source, the Photomultiplier tube is able to detect this emission.
The amount of light emitted reflechts the total amount of SO2 present in the combusted sample flow, which in turn correspond the amount of Total Sulfur in the sample.
The equations for this reaction are:
SO2 + hv1 –> SO2*
SO*2 –> SO2 + hv2
High amounts of Nitrogen present in the sample could interfere with the amount of Total Sulfur given by a Elemental Combustion Analyzer, especially when measuring at trace level. TE Instruments developed a solution to prevent this from happening. For additional information regarding this solution, please contact our Sales Team: firstname.lastname@example.org
Total Organic Halogens (TOX), often referred to as Total Organic Halides, is the sum parameter of Total Organic Fluor (F), Chlorine (Cl), Iodine (I) and Bromine (Br). Total Organic Halogens are measured by adding the amount of Purgeable Organic Halogens (POX) to the amount of Adsorbable Organic Halogens (AOX) measured in a water sample. An elemental combustion analyzer is able to measure the POX and AOX content in (waste)water samples according to Oxidative Combustion Microcoulometry.
International method to measure the amount of Total Organic Halogens (TOX) in water samples: EPA 9020
Total Organic Halogens
Total Organic Carbon (TOC) is one of the most important environmental screening parameters for organic matter in all kind of water samples, including drinking water, ground water, surface water and waste water. Organic carbon deriving from substances like PCB’s, Acetic Acid, Xylene or Propanol could form compounds which are harmful to the environment and may deplete the amount of oxygen in water. The amount of TOC present in a water sample can be determined in two ways:
TC – IC = TOC
Total Carbon (TC) stands for the sum of all carbon present in a sample. A TC measurement is executed by introducing a sample into a heated furnace (680 °C) where all carbon is converted towards CO2. The detected amount of CO2 represents the amount TC in a sample.
There are four types of inorganic carbon (IC):
The different types are related to each other by the following pH-driven chemical equilibria:
CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3– ⇌ 2H+ + CO32-
For an IC analysis, a sample is transferred into the IC vessel. A fixed amount of acid is added to the sample in the IC vessel. The acid will drive the above mentioned equilibria towards CO2. The detected CO2 represents the amount of IC in the sample.
The amount of TOC present in a sample can be detected by subtracting the detected amount of IC from the detected amount of TC.
TOC = NPOC (when POC is neglectable small)
When the Purgeable Organic Carbon (POC) content of a water sample is neglectable small, the amount of TOC can be measured directly. First, the sample is acidified and purged with oxygen for a set amount of time. All Inorganic Carbon (IC) converts into CO2 and evacuates to the ambient air. The Organic Carbon (TOC) content remains in the sample and is introduced into a heated furnace (680 °C), where all carbon is converted towards CO2. In this context, the amount of non-purgeable organic carbon (NPOC) stands for the amount of TOC present in the sample. The purgeable organic carbon (POC) components are purged out during the ‘sparging step’.
International test methods to measure the amount of Total Organic Carbon (TOC) according to Non Dispersive Infrared (NDIR) technique: ASTM D7573, EN 1484, EPA 415.1, EPA 9060, ISO 8245, USP 643, SM 5310B.
Total Organic Carbon
Total Nitrogen (TN) stands for the sum parameter of all organic and inorganic nitrogen compounds. Trace levels (0.02 – 10.000 mg/kg or ppm by weight) of Total Nitrogen are measured with an elemental combustion analyzer according to Chemiluminescence detection technique. These measurements are mainly carried out in:
• Oil & Gas industry (Refineries): Total Nitrogen in fuels (NO2) pollutes the environment, it’s corrosive to steel and poisons catalysts. Nitrogen compounds are more thermally stable compared to sulfur compounds and are often concentrated in heavier petroleum fractions and residues. Examples of Organic Nitrogen compounds that contribute to the Total Nitrogen number in petroleum products are Pyridines, Quinolines and Carbazoles. Hydrotreating of petroleum fractions is an established technique to remove nitrogen compounds.
• Fats and oils processing plants: The amount of Total Nitrogen is related to the quality of the intermediate or final products in the food industry. Fats and Oils are also used to produce Biodiesel, therefore the Total Nitrogen number needs to be below the maximum allowable amount for fuels.
• Plastic Manufacturing Facilities: Nitrogen containing additives present in a polyolefin sample are measured to monitor physical properties and quality control of polymers in general.
Total Chloride, Total Chlorine or Total Halogens, stand for the sum parameter of organic as well as inorganic Fluorine (F), Chlorine, (Cl), Bromine (Br) and Iodine (I). Trace levels of Total Chloride are measured with an elemental combustion analyzer according to Microcoulometric detection technique / Microcoulometry.
In the petrochemical industry, Total Chloride and Total Chlorine are used interchangeably.
In the environmental monitoring industry, the sum parameter is expressed as Total Halogens.
All these terms have the same defintion and are abbreviated as TX.
Applications where the amount of Total Chloride is examined:
• Organic Chlorides will form hydrochloric acid, this formation needs to be avoided to minimize corrosion in piping and equipment used during refining processes in the Oil & Gas industry.
• During the production process of High Purity Solvents like Iso-octane, Benzene, Hexane and Methanol, expensive catalyst material is used. The catalyst material is affected by Chloride which is present in High Purity Solvents.
• Skydrol is a fire resistant hydraulic aviation fluid used in airplanes of for example Boeing and Airbus. The amount of Total Chloride in Skydrol is measured because it is corrosive to the hydraulic system components. One of the common liquid contaminants are chlorinated cleaning solvents. Liquid contaminants can alter the fluid’s fire resistant properties, affect seal performance, cause gel formation and lead to acid development.
• PET Bottles are widely used all over the world. The base Polymer PET may contain contaminants like the toxic PVC. In a quality control test the total amount of Chloride provides an indication of the contamination level.
Total bound Nitrogen (TNb) stands for the sum parameter of all organic nitrogen (e.g. urea, nicotinic acid), and inorganic nitrogen (e.g. Ammonium, Nitrates) compounds present in a water sample. Industrial plants monitor the amount of organic substances in their wastewater to ensure that it has been treated adequately before discharge. Environmental protection agencies created stringent regulations to which the discharged wastewater must comply. Polluting substances of organic matter that may be present in these effluents are harmful to the environment. If an excess amount of nitrogen is present in water, it may lead to low levels of dissolved oxygen and negatively alter various plant life and organisms. To protect the environment, the Total bound Nitrogen (TNb) sum parameter is measured in environmental and industrial laboratories. These measurements are also used in monitoring waste water treatment processes.
Total bound Nitrogen
The sample inlet system – often reffered to as introduction module – is used to introduce the Liquid, Solid, Gas or LPG sample into the quartz combustion tube of an elemental combustion analyzer. There are two types of sample inlet systems:
The applicable international standard prescribes which sample inlet system can be used to measure the samples correctly.
Sample Inlet System
When a sample is introduced into the sample inlet system, it enters the quartz combustion tube. The quartz combustion tube is placed into the furnace of the analyzer. The combustion tube is fabricated out of quartz glass to be able to withstand extreme temperatures up to 1150 °C.
The quartz combustion tube is constructed in such a way that it allows direct injection of the sample into the heated oxidation zone of the furnace and/or to accommodate the entry of a quartz sample boat. The surface of the oxidation section of the combustion tube must be large enough to ensure a complete combustion of the sample. However, some elemental combustion analyzer manufacturers pack the quartz combustion tube with oxidation catalyst to achieve this.
The XPLORER Series do not make use of oxidation catalyst. The unique construction of the Collision Flow Tube allows a secondary oxygen flow to collide with the combustion gases, which creates a dynamic turbulence of the oxidizing gas stream and replaces some of the depleted oxygen. Resulting in more oxidation power for samples which are difficult to oxidize. If the samples require a boat inlet system, the collision flow tube features the necesarry cooling mechanism, which is simply known as the Collision Flow Tube with Boat Cooling.
Quartz Combustion Tube
Purgeable Organic Halogens (POX) is the sum parameter of Purchable Organic Fluor (F), Chlorine (Cl), Iodine (I) and Bromine (Br). These volatile organic elements can be forced out a water sample while purging at certain temperature. The purged components are directly led into an elemental combustion analyzer and detected according to microcoulometry detection technique.
International methods to measure the amount of POX content in water samples: DIN 38414, EPA 9021, NEN 6401
Purgeable Organic Halogens
What is Microcoulometry?
When a Chloride containing sample is combusted at 1000 ℃, Hydrogen Chloride is formed (HX):
R-X + O2 –> HX + CO2 + H2O
The combustion gas, carrying halide ions, is led into a sulfuric acid scrubber for rapid water and interference removal. The dried and clean gas is led into the temperature controlled titration cell, where the halide ions react with silver ions, present in the titration cell. The amount of charge (the integral of the regeneration current over the measuring time) used to regenerate the lost silver ions, is directly related to the Total Chloride (TX) content of the sample.
The equations for this reaction are:
HX + Ag+ –> H+ + AgX
Ag –> Ag+ + e
When a Sulfur containing sample is combusted at 1000 ℃, Sulfur dioxide is formed SO2:
R-S + O2 –> SO2 + CO2 + H2O
The combustion gas, carrying Sulfur dioxide (SO2), is led into a sulfuric acid scrubber for rapid water and interference removal. The dried and clean gas is led into the temperature controlled titration cell, where the Sulfur dioxide reacts with Tri-iodine, present in the titration cell. The amount of charge (the integral of the regeneration current over the measuring time) used to regenerate the lost Tri-iodine, is directly related to the Total Sulfur content of the sample.
The equations for this reaction are:
SO2 + I3– + H2O –> SO42- + 3 I– + 4 H3O+
2 I– –> I2 + 2 e
I2 + I– –> I3–
Extractable Organic Halogens (EOX) is the sum parameter of Extractable Organic Fluor (F), Chlorine (Cl), Iodine (I) and Bromine (Br). Extractable Organic Halogens are measured by adding a solvent to the water sample to extract the Organic Halogen content. After water removal, the extracted content is measured by an elemental combustion analyzer according to microcoulometry detection technique. Typical samples are soil, sludge and sediments.
DIN 38414, DIN 38409, NEN 6402
Extractable Organic Halogens
An elemental combustion analyzer is able to measure the amount of Total Nitrogen, Total Sulfur and Total Chloride through high temperature combustion (approximately 1000 ˚C) in an oxygen rich environment. In contrast to CHNSO analyzers that also carry the name ‘elemental combustion analyzer’, elements can be detected from trace level (µg/kg or ppb level) up to 10.000 ppm or mg/L (1%). By combusting the sample, NO2, SO2 and HCl are formed which can be detected by either Pulsed UV-Fluorescence, Chemiluminescence or Microcoulometry detection technique.
Elemental Combustion Analyzer
The direct injection system – often referred to as liquids module – must be capable of delivering the sample material into the inlet carrier gas stream (Ar or He) at controlled and repeatable rate. The carrier gas stream transfers the evaporated liquid sample into the oxidation zone where it is combusted in an oxygen rich atmosphere at approximately 1000+ ℃.
A syringe drive mechanism or liquid auto sampler controls the sample dispense speed of the microliter syringe, typically set at 1 μL/s. A constant introduction rate ensures a controlled sample combustion which prevents the formation of soot. The needle tip of the syringe should be introduced fully into the hottest part of the inlet area of the furnace.
• Liquid Hydrocarbons
• Aromatic Hydrocarbons
• Gas & LPG
Direct Injection System
What is Combustion Ion Chromatography?
Combustion Ion Chromatography combines a combustion system with the analytical separation precision of an Ion Chromatograph in a fully automated configuration. Combustion Ion Chromatography (C-IC) enables the analysis of corrosive Halogens (Fluor, Chlorine, Bromine, and Iodine) and Sulfur compounds (e.g. Sulfate, Sulfite, Thiosulfate) in a wide range of sample matrices like polymers, organic solvents, and fuels. Corrosive halogens and sulfur compounds need to be monitored because they are corrosive, poison catalysts, damage industrial equipment and are harmful to the environment.
The analysis of speciated halides and sulfur in complex matrices like petrochemicals and solids is difficult and requires extensive sample preparation with conventional offline methods. Other detection techniques such as Oxidative Microcoulometry and UV-Fluorescence analyze Total Halogens (Total Chloride) and Total Sulfur as sum parameters. Combustion IC enables the determination of individual halides and sulfur by a single analysis while eliminating the complex and time-consuming sample preparation steps of conventional offline digestion/combustion methods, such as Schöniger Flask, Oxygen Bomb, Wickbold-Apparatus, and Microwave-induced combustion. Combustion Ion Chromatography not only reduces the cost of analysis but also significantly improves user-convenience and level of automation.
The principle of analysis consists of four steps:
1. A liquid, viscous, solid, gas or LPG sample of known weight or volume is introduced into the combustion unit at a controlled rate. Sample introduction is done either by boat inlet system or direct injection system, depending on the sample type and required detection level. Fully automated sample introduction can be achieved by means of an autosampler that suits the specific sample matrix.
2. Every sample matrix is completely oxidized by pyrohydrolytic combustion in an oxygen-rich environment at high temperature. Pyrohydrolytic combustion prevents loss of Fluorine in the quartz combustion tube. Halogens present in the sample are converted to H-X, X2, and Sulfur, to SOx.
3. After combustion, the output gas stream containing the analytes is transferred to a single- or multiple position absorber unit and trapped in the absorber medium. The absorber unit handles the rinsing and dosing of required reagents, including hydrogen peroxide (H2O2). In this process, the H-X, X2, and SOx are converted to F–, Cl–, Br–, I– and SO42-. The halide and sulfate anions will be separated on the IC column. The absorption tube(s) typically have a capacity of 10 or 20 mL.
4. After sample preparation, an aliquot of the absorber solution containing the analytes is injected into an Ion Chromatograph (IC) by means of a sample injection valve. The halide and sulfate anions are separated on the separator column of the IC. The conductivity of the eluent is reduced with an anion suppression device prior to the ion chromatograph’s thermal conductivity detector, where the anions of interest are analyzed. The IC detects the amount of speciated halogens (Fluor, Chlorine, Bromine and Iodine) and Sulfur compounds by calibrating the system. The combined system of pyrohydrolytic combustion followed by IC detection is referred to as Combustion Ion Chromatography (CIC).
• LPG & Gas
• Organic Solvents & Chemicals
• Plastics & Polymers
• Environmental Monitoring
• Electronic Components (e.g. RoHS, WEEE compliance)
• Coloring agents
• Polishing agents
Combustion Ion Chromatography
Adsorption of Organic Halogens onto activated carbon is part of the procedure for analyzing Adsorbable Organic Halogens or Total Organic Halogens. This can be done according the batch method or column method.
The column method is suitable for (waste)water samples which contain few particles. In any other case the batch method is needed. Multiple samples can be filtrated simultaneously through quartz glass columns, executed by a fully-automatic filtration system. After filtration, the Inorganic Halogens are removed by a Nitrate wash solution. Once the Inorganic Halogens have been removed, the activated carbon can be emptied in a quartz sample cup or introduced directly into an auto sampler. The activated carbon is transferred to the high temperature furnace and combusted.
When a Nitrogen containing sample is combusted at 1000 ℃, Nitrogen Oxide (NO) is formed:
R-N + O2 –> NO + H2O + CO2
After conditioning of the combusted sample, the amount of Nitrogen is detected by Chemiluminescence detection technique.
The formed NO is led into a reaction chamber. Electronically generated Ozone is added which reacts with the Nitric Oxide which forms Nitrogen Dioxide in an excited state (NO2*). The excited NO2 emits light as it reverts to a lower level energy state. The emitted light is detected by a Photomultiplier Tube (PMT).
The amount of detected emitted light, corresponds with the amount of NO. This in turn represents the amount of Total Nitrogen present in the sample. Surplus of Ozone is converted to oxygen by a catalyst.
The equations for this reaction are:
NO + O3 –> NO2*
NO2* –> NO2 + hv
Total Organic Carbon is often used as a screening parameter for organic matter in all kinds of water samples, including ground water, surface water and waste water. These samples sometimes contain substantial amounts of insoluble particles such as sediments, which must be included in the TOC analysis. The international standards EN 1484 (Annex A) and ISO 8245 (Annex B) provide a test method to verify the homogenization and recovery of incompletely dissolved sample components (particulate matter max. 100 μm) in TOC samples, also known as the ‘cellulose test’.
The suspension is prepared by placing 225 mg of cellulose (C6H10O5) with particles sizes ranging from 20 µm up to 100 µm in 1 liter of water with a concentration of 100 mg/L carbon. The samples should be continuously stirred during analysis. This is often done through magnetic stirrers in the auto sampler of a TOC analyzer to ensure the sample is homogeneous before analysis. The mean value from a triple measurement should be between 90 mg/L and 100 mg/L, the repeatability variation coefficient should be below 10% (RSD).
The boat inlet system – often referred to as boat module – is used for the controlled introduction of liquid and solid samples into the heated furnace of the analyzer. Liquid samples are injected on quartz wool and solid samples are directly placed into the quartz boat. This can be done manually or by using an auto sampler.
The analyzer can position the sample carrying mechanism (quartz boat) at a retracted position, removed from the furnace, to enable sample introduction. Often there is a cooling mechanism available at the retracted position for the following purposes:
1. Cooling down of the quartz boat after sample analysis.
2. Preventing ‘pre-evaporation’ of samples with lower boiling point components.
A boat driver mechanism controls the movement of the quartz boat into and out of the furnace at a controlled and repeatable rate. After sample introduction, the quartz boat is transferred from the retracted position to the hottest area of the dual zone furnace. This area is typically heated at 1000+ ℃ to ensure a complete combustion of the sample. The rate at which the quartz boat moves into the combustion tube is saved in the customizable boat program and depends on characteristics of the sample. The combustion tube as well as the sample boat are made out of quartz glass which can withstand extreme high temperatures.
Almost every type of sample from solids to liquids can be introduced by the Boat Inlet System.
Boat Inlet System
Adsorption of Organic Halogens onto activated carbon is part of the procedure for analyzing Adsorbable Organic Halogens and Total Organic Halogens. This can be done according to the batch method or column method.
The batch method is suitable for all AOX sample types like (waste)water, pulp, paper, sludge, sediment, soil and salt water samples. Especially sludge and water samples containing lots of particles should be pre-treated according to the batch method. The sample is filtrated under pressure through a quartz glass frit or column containing activated carbon. After filtration, the Inorganic Halogens are removed by a Nitrate wash solution. Once the Inorganic Halogens have been removed, the activated carbon together with the quartz frit or column is introduced either manually or by an auto sampler into the high temperature furnace and combusted.
Adsorbable Organic Halogens (AOX) is the sum parameter of Adsorbable Organic, Chlorine (Cl), Iodine (I) and Bromine (Br). These organic elements are able to adsorb onto activated carbon. An elemental combustion analyzer is able to measure the Adsorbable Organic Halogens content in (waste)water, pulp, paper, soil, sludge, sediment and salt water samples according to microcoulometry detection technique. The entire procedure for the analysis of Adsorbable Organic Halogen consists out of the following steps:
1. Adsorption on activated carbon
2. Rinsing off the Inorganic Chlorides
3. Pyrolysis of the Organic Halogens
4. Detection by a microcoulometric cell
Adsorbable Organic Halogens
Activated carbon has a large internal surface making it ideal for adsorption purposes. During the sample preparation of AOX/TOX samples, activated carbon is used to adsorb the Halogen content present in a water sample.
After adsorption, the activated carbon is placed in a quartz-glass frit or directly introduced into a sample boat, and combusted at 1000 ˚C. The Xplorer measures the amount of AOX/TOX present in the sample based upon microcoulometry detection technique.
Sample preparation units for adsorbing the Organic Halogen content in water samples:
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