Shimadzu TOC Academy
The year 2022 marks the 50th anniversary since Shimadzu Corporation, the global market leader in TOC analyzers, first offered a total organic carbon analyzer. On this occasion, let's examine the basics of TOC and take a look at the history of Shimadzu TOC analyzers.
Introduction to TOC
Total organic carbon (TOC) refers to the total amount of carbon contained in organic matter in water. The TOC value is used as a representative water quality index that indicates how dirty water is. Due to the large number of possible organic substances, biochemical oxygen demand (BOD), chemical oxygen demand (COD), and potassium permanganate consumption tests were traditionally used as indices for collective measurements of all organic substances, regardless of type. These analytical methods measured total quantities by using microorganisms or oxidizing agents to decompose samples within a certain amount of time, but had issues with different types of organic substances decomposing at different rates.
Since TOC measurements are not prone to interference from coexisting substances in samples and can measure the total quantity of carbon in organic matter present in water more accurately, TOC measurements are now used in a wide range of fields, such as for evaluating the water quality of public drinking water or in pharmaceuticals, surveying or researching rivers or soil, and managing effluents from factories.
Types of TOC
The total amount of all carbon present in water is referred to as “total carbon” (TC), which can be classified into two major types, either total organic carbon (TOC) or inorganic carbon (IC). Total organic carbon can be further classified as either non-purgeable organic carbon (NPOC) or purgeable organic carbon (POC).
TOC Measurement Methods
Types of Measurements
The following two methods are used to determine the TOC present in water.
TC-IC Method:
TOC is determined as the difference between TC and IC measurement values. (TOC = TC - IC)
NPOC Method:
TOC is determined by measuring TC in samples pretreated to remove IC. (TOC = TC)
Measuring IC
TFor TOC measurement, IC refers to the total quantity of inorganic carbon contained inr (where CO2 indicates dissolved carbon dioxide, HCO3- bicarbonate ions, and CO32-carbonate ions). The quantities of dissolved carbon dioxide, bicarbonate ions, and carbonate ions in water are kept in an equilibrium that depends on the pH level of the water, according to the expression below.
If pH decreases, the equilibrium moves to the left in the expression above. At a pH of 3 or lower, almost all IC becomes dissolved carbon dioxide.
Based on that principle, IC is measured by adding acid to lower the sample pH below 3 and then measuring the CO2 extracted from the sample by bubbling in a CO2-free gas atmosphere.
Using TC-IC and NPOC Methods
Both the TC-IC method and the NPOC method are for measuring TOC, but which of the measurement methods to use is determined based on sample characteristics.
For samples with low IC concentration levels, such as public drinking water or purified water, the NPOC method is used because the TC-IC method is prone to measurement error that could result in lower measurement accuracy.
On the other hand, for samples with large amounts of volatile organic compounds or samples that are prone to foaming, for example, the TC-IC method is used because the NPOC method can result in loss of volatile organic compounds from samples during the bubbling in a CO2-free gas pretreatment step or the NPOC method can prevent accurate sample quantity measurements due to foaming.
TOC In Public Drinking Water
In which countries is it safe to drink tap water?
Can you drink tap water in North America? Mostly, yes. Like all regions, the tap water varies from city to city, North America has a higher quality of tap water safety than most other regions of the world. Notably, the vast majority of US cities and Canada have safe tap water. In Mexico, a highly-populated area like Mexico City and León have drinkable tap water. Outside of the major population centers, caution is advised.
But why are there so many countries with unsafe tap water?
The following are two possible reasons.
- Water sources are difficult to obtain in arid regions. Some regions are so dry that rivers and lakes dry up and make it difficult to secure sources for public water supply systems.
- Countries cannot build adequate infrastructure due to large land areas. Supplying water throughout a large country like the Russia or China is extremely costly.
Oxidation Methods for TOC Analyzers
Two methods are used to oxidize organic matter, either combustion oxidation or wet oxidation.
Combustion Oxidation Method
One of the main features of this method is its ability to efficiently oxidize organic carbon matter that is otherwise resistant to decomposition, such as carbon matter that contains insoluble or macromolecular organic substances.
The sample is injected into a high-temperature (650 to 1,200°C) combustion furnace to incinerate all organic carbon in the sample and measure it as fully oxidized carbon dioxide.
Because samples are combusted at a high temperature, the method enables complete oxidative dissociation of carbon even in persistent organic matter, or carbon in suspended substances or other water-insoluble particulate organic matter.
Due to the simplicity of using heat/combustion as the principle for oxidation, the method requires no reagents for pretreatment or posttreatment processes.
Wet Oxidation Method
With this method, an oxidizing agent is added to samples to chemically decompose carbon in organic matter for measurement as carbon dioxide. Though heat (up to 100°C) or ultraviolet irradiation can be applied to promote the oxidation reaction, the ability of the chemical reaction to oxidatively decompose matter is weaker than combustive oxidation, which tends to result in lower carbon recovery rates from suspended or other particulate organic matter, or persistent substances.
Therefore, due to its superior oxidative reaction, the combustion oxidation method is commonly used to measure TOC levels in environmental water, factory effluent, and other such samples, where water samples often contain large amounts of insoluble organic carbon.
Water Purification
In Shimadzu's home, Japan, river and lake water is purified at water treatment plants to ensure it is safe for drinking.
Four main methods are used to treat the water–(1) rapid filtration, (2) slow filtration, (3) membrane filtration, and (4) only disinfection.
(1) Rapid filtration
This method cleans water by flocculating and precipitating small suspended particles, bacteria, and other substances using chemicals, and then filtering the supernatant through a sand layer in a filtration pond. This method is especially suitable for treating water from rivers, lakes, and other sources with relatively high turbidity levels and is the most commonly used method.
(2) Slow filtration
This method cleans water by passing it slowly through a sand layer in a filtration pond, where microorganisms propagated on the surface of the sand layer (biofiltration membrane) remediate the water. It is referred to as “slow filtration” because the flowrate through the filtration pond is slower than with rapid filtration. It is best suited to treating water sources with relatively good water quality and minimal variations in water quality.
(3) Membrane filtration
This method removes suspended particles, microorganisms, and other substances from water by filtering them through a microfiltration or ultrafiltration membrane. Microfiltration and ultrafiltration membranes have different pore sizes or numbers of layers.
(4) Disinfection
This method uses chlorine to only disinfect water obtained from groundwater water sources with good water quality.
Thus, safe tap water is supplied by using a water treatment method appropriate for the water quality of the given river, lake, groundwater, or other water source.
Water Quality Inspections for Public Drinking Water
Public drinking water is supplied by using a water treatment based on the water quality of the given river, lake, groundwater, or other water source. However, the water quality of public drinking water can vary due to changes in the water quality or usage rate of the river or lake.
Therefore, it is important to regularly inspect the safety of treated water. In Japan, the Water Supply Act specifies water quality standards by law.
Japan’s Water Supply Act
In essence, the purpose of the Water Supply Act is to improve the lives of Japan’s citizens by creating public water supply systems throughout Japan that can cheaply deliver large quantities of clean water. However, what does “clean water” really mean?
To address that question, the Water Supply Act specifies water quality standards. Those water quality standards specify 51 types of inspection criteria, with water system contractors regularly inspecting public water systems to make sure public water supplies satisfy those criteria. That means only safe drinking water that passes those strict inspection standards is delivered to homes.
Inspecting Water Quality
Water from rivers or lakes is treated and supplied from the faucets in their homes as public drinking water according to the process illustrated above.
The fact that the 51 types of inspection criteria specified by the Water Supply Act are checked immediately prior to delivery to their homes indicates their importance.
Supplying Water that is Both Safe and Good-Tasting
Furthermore, in Japan, due to the increasing consumption of bottled mineral water, increasingly widespread use of residential water purification systems, and other factors, there is growing interest in water that is not only safe but also good-tasting.
Given such circumstances, to supply safe and good-tasting water, some prefectures have specified water quality goals for the taste of water that are separate from the inspection standards for the 51 criteria specified by the Water Supply Act.
| Inspection Parameter | Description |
|---|---|
| Evaporation Residues | The residues that remain after water is evaporated mainly consist of minerals. Water that contains large amounts of such minerals can taste bitter or astringent, whereas water that contains moderate amounts tend to have a smooth rich taste. |
| Hardness | Hardness indicates the calcium or magnesium content, which are the main mineral components in water. An appropriate level of hardness components is a requirement for good-tasting water. Water with low hardness is referred to as “soft” water and has no distinctive flavor. In contrast, water with high hardness is referred to as “hard” water and has a more persistent flavor, which some people prefer but some do not like. |
| Free Carbon Dioxide | In water, free carbon dioxide refers to dissolved carbon dioxide gas that gives water a crisp sensation, but too much can be overstimulating and reduces smoothness. |
| Potassium Permanganate Consumption | This is an index for organic matter in water. Higher concentrations can result in a bitter taste. |
| Odor Intensity | This indicates the intensity level of odors in water (regardless of the odor type). Moldy odors, algae odors, or other unpleasant odors from water can make water taste bad. |
| Residual Chlorine | This refers to residues of chlorine used to disinfect public drinking water. For public health reasons, public drinking water is required to contain at least 0.1 gm/L of residual chlorine, but if the residual chlorine concentration is too high, it can cause a chlorine bleach odor. |
| Water Temperature | Cold water physiologically tastes better. In addition, chlorine and other odors are less noticeable in cold water, which makes the water taste better. |
Source: Good-Tasting Water Research Committee, “Good-Tasting Water,” Journal of Japan Water Works Association, Vol. 54, No. 5 (1985)
The water treatment and water quality inspection practices described above have resulted in Japan being one of the few countries in the world with tap water that is safe to drink. However, achieving that requires sophisticated technology and high costs. For countries with a small land area, like Japan, it can be relatively easy to build the infrastructure, but for countries with large land areas, infrastructure can require massive amounts of time and expense. Many developing countries have regions without access to public water supply systems.
Even in Japan, if rivers, lakes, and other sources for public water systems become more polluted, the current water treatment infrastructure may not be adequate for ensuring safe and good-tasting water. Therefore, it is important to value safe and good-tasting water as something precious, rather than taking it for granted.
TOC Analysis for Public Drinking Water Management
One of the public drinking water inspection parameters is total organic carbon (TOC). The following describes the role of TOC in managing public drinking water.
What is “TOC”?
TOC is short for total organic carbon and is an index of organic matter used in a wide variety of fields.
In the field of public water supply systems, potassium permanganate consumption was previously used as an index of organic matter. However, potassium permanganate consumption measurements had the following drawbacks.
- Values can vary depending on the type of organic matter in water
- Measurement results can vary depending on the person performing the measurement
- Measurement accuracy is not consistent even for measurements performed by the same person
For these reasons, TOC measurement attracted interest as an instrumental analysis method that enables oxidation of nearly 100 % of organic matter and that does not vary between individuals. Therefore, TOC was introduced as a new water quality standard in 2005.
TOC is not only easy to measure easily and accurately with instrumental analysis, but also can be measured quickly in only a few minutes.
Purpose of Measuring TOC
Confirming the safety of public drinking water
Reactions between organic matter and disinfectants used for water treatment are said to generate substances that are harmful to humans. Therefore, measuring TOC in public drinking water provides an important index for confirming the safety of public drinking water.
The TOC level is also said to affect the taste of public drinking water, so it can be used as an index for how good public drinking water tastes.
Water Treatment Management
A variety of processes are used to eliminate microorganisms and organic matter from water at water treatment plants.
Measuring the TOC level at each process step can be used to confirm that each process is functioning properly. (pH and turbidity values are also measured in addition to TOC.) In addition to confirming water treatment functions, measuring TOC can also help optimize water treatment. Adjusting the amount of chemicals used based on the TOC values measured at each process step can also help reduce water treatment costs.
History of Shimadzu TOC Analyzers:
A History of Cutting-Edge Innovation
2022 marks the 50th anniversary since Shimadzu first released a TOC analyzer. Today, Shimadzu TOC analyzers are used in a wide variety of fields ranging from laboratory quality control applications for public water supply management, drinking water management, purified water management in the pharmaceutical and other industries, environmental water measurement, and wastewater management, to online measurement applications for water quality or pollutant management of factory effluents into rivers, oceans, etc.
Shimadzu development of TOC analyzers began after Shimadzu established a technical partnership with Hartmann & Braun of West Germany in 1965 and the National Industrial Research Institute of Nagoya asked Shimadzu to develop a TOC analyzer in 1967.
In 1972, Shimadzu developed and released its first TOC analyzer products: the TOC-100 automatic water quality monitoring system for continuous monitoring of water quality and pollutants in public waters based on the Water Pollution Prevention Act and the TOC-10 total organic carbon analyzer for laboratory use.
In 1983, Shimadzu developed the TOC-500, which was the world’s first TOC analyzer with 680 °C combustion catalytic oxidation capability. That significantly extended the life of combustion tubes and catalysts and improved ease of maintenance.
In 1989, the TOC-5000 featured a mechanism for automatically injecting samples and expanded the measurement range from the ppm level to the ppb level. That resulted in broader applicability of TOC measurements, including for purified water, and established Shimadzu as the global leader in TOC analyzers.
The TOC-V series released in 2000 featured additional functionality for measuring solid samples, purgeable organic carbon (POC), and total nitrogen (TN), which further expanded the applicability of TOC analyzers. Today, the TOC-L series released in 2011 continues to serve at the forefront of TOC analysis.
Initially, TOC analyzers were mainly used for ensuring the water quality of environmental waters, industrial effluents, and so on, but later, as TOC performance improved, the scope of applications expanded.
Now they are also used for quality control of purified and ultrapure water, for ensuring compliance with public drinking water quality standards, for controlling/evaluating pharmaceutical manufacturing processes, and for researching carbon-neutrality. Thus they serve a vital role in a variety of fields important for people and the Earth.
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Source: Shimadzu Corporation