How to establish quality control in a laboratory

1What is Internal Quality Control (IQC)?

IQC is one of a number of concerted measures that analytical chemists can take to ensure that the data produced in the laboratory are fit for their intended purpose. In practice, fitness for purpose is determined by a comparison of the accuracy achieved in a laboratory at a given time with a required level of accuracy. Internal quality control therefore comprises the routine practical procedures that enable the analytical chemist to accept a result or group of results as fit for purpose, or reject the results and repeat the analysis. As such, IQC is an important determinant of the quality of analytical data, and is recognized as such by accreditation agencies.

2 What is Control Material or QC sample?

Internal quality control is undertaken by the inclusion of particular reference materials into the analytical sequence, are called "control materials” or “QC samples”.

As the control materials are treated in exactly the same way as the test materials, they are regarded as surrogates that can be used to characterize the performance of the analytical system, both at a specific time and over longer intervals.

Ideally both the control materials and those used to create the calibration should be traceable to appropriate certified reference materials or a recognized empirical reference method. When this is not possible, control materials should be traceable at least to a material of guaranteed purity or other well characterized material. However, the two paths of traceability must not become coincident at too late a stage in the analytical process. For instance, if control materials and calibration standards were prepared from a single stock solution of analyte, IQC would not detect any inaccuracy stemming from the incorrect preparation of the stock solution.

3 Quality assurance:

All those planned and systematic actions necessary to provide adequate confidence that a product or service will satisfy given requirements for quality. IQC is a part of quality assurance.

4 Accuracy: 

Closeness of the agreement between the result of a measurement and a true value of the measured.

5Precision:

 Closeness of agreement between independent test results obtained under prescribed conditions.

6 Traceability:

 Property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties

7Uncertainty of measurement:

Parameter, associated with the result of a measurement, which characterizes the dispersion of the values that could reasonably be attributed to the measured.

Establishing Control Values for QC samples.

Obtain minimum ten values for QC samples, by analyzing every day with average of minimum 2 duplicates.

Calculate Upper Warning Limit (UWL) and Lower Warning Limits (LWL).Normally UWL= (Standard deviation x 2) + Average of QC samples values. LWL= Average of QC samples values- (Standard deviation x 2)

Calculate Upper Control Limit (UCL) and Lower Control Limits (LCL).Normally UCL= (Standard deviation x 3) + Average of QC samples values. LCL= Average of QC samples values- (Standard deviation x 3).

1.       Monitor Quality of analysis through QC Chart.

Plot QC values in Excel sheet and make a chart, mark UWL, LWL, UCL, and LCL.

Now every day QC analysis with samples can monitored through QC chart.Example of QC chart given below.

COMPARISION OF ICP-OES

Features	Horiba Jobin Yvon Ultima 2	Varian-710ES	Perkin Elmer Optima5000DV
Optical grating and wavelength range	110 x 110 mm,120-800 nm	Not specified (It covers most of the elements)	Not specified (It covers most of the elements)
Solid State Detector	Yes	Yes	Yes
Solid State RF power supply	Yes	Not mentioned	Yes
Percentage and trace measurement same time	Yes	No	Yes(Radial and Axial)
Interference due to complex matrix	No	Reduce by software application	Reduce by software application
Radial & Axial view	Single radial	Different model for radial	Yes
Sheath Gas	Yes	Yes	Yes
Single exhaust for plasma and RF	Yes	Not mentioned	Not mentioned
Warm up time	15 min	10 min	Not mentioned exact time
Simultaneous analysis of hydride and non-hydride elements	Yes	No	No
High solid sample dilution	No dilution up to 30%	Yes, Dilution need	Yes, Dilution need

Identification of Wastewater Organisms

Facultative Bacteria

Most of the bacteria that absorb the organic material in a wastewater treatment system are facultative in nature. This means they are adaptable to survive and multiply in either anaerobic or aerobic conditions. The nature of individual bacteria is dependent upon the environment in which they live. Usually, facultative bacteria will be anaerobic unless there is some type of mechanical or biochemical process used to add oxygen to the wastewater. When bacteria are in the process of being transferred from one environment to the other, the metamorphosis from anaerobic to aerobic state (and vice versa) takes place within a couple of hours.

Anaerobic Bacteria 

Anaerobic bacteria live and reproduce in the absence of free oxygen. They utilize compounds such as sulfates and nitrates for energy and their metabolism is substantially reduced. In order to remove a given amount of organic material in an anaerobic treatment system, the organic material must be exposed to a significantly higher quantity of bacteria and/or detained for a much longer period of time. A typical use for anaerobic bacteria would be in a septic tank. The slower metabolism of the anaerobic bacteria dictates that the wastewater be held several days in order to achieve even a nominal 50% reduction in organic material. That is why septic tanks are always followed by some type of effluent treatment and disposal process. The advantage of using the anaerobic process is that electromechanical equipment is not required. Anaerobic bacteria release hydrogen sulfide as well as methane gas, both of which can create hazardous conditions. Even as the anaerobic action begins in the collection lines of a sewer system, deadly hydrogen sulfide or explosive methane gas can accumulate and be life threatening.

Aerobic Bacteria 

Aerobic bacteria live and multiply in the presence of free oxygen. Facultative bacteria always achieve an aerobic state when oxygen is present. While the name “aerobic” implies breathing air, dissolved oxygen is the primary source of energy for aerobic bacteria. The metabolism of aerobes is much higher than for anaerobes. This increase means that 90% fewer organisms are needed compared to the anaerobic process, or that treatment is accomplished in 90% less time. This provides a number of advantages including a higher percentage of organic removal. The by-products of aerobic bacteria are carbon dioxide and water. Aerobic bacteria live in colonial structures called floc and are kept in suspension by the mechanical action used to introduce oxygen into the wastewater. This mechanical action exposes the floc to the organic material while treatment takes place. Following digestion, a gravity clarifier separates and settles out the floc. Because of the mechanical nature of the aerobic digestion process, maintenance and operator oversight are required.

Activated Sludge

Aerobic floc in a healthy state are referred to as activated sludge. While aerobic floc has a metabolic rate approximately ten times higher than anaerobic sludge, it can be increased even further by exposing the bacteria to an abundance of oxygen. Compared to a septic tank, which takes several days to reduce the organic material, an activated sludge tank can reduce the same amount of organic material in approximately 4-6 hours. This allows a much higher degree of overall process efficiency. In most cases treatment efficiencies and removal levels are so much improved that additional downstream treatment components are dramatically reduced or totally eliminated.

Filamentous Organisms

The majority of filamentous organisms are bacteria, although some of them are classified as algae, fungi or other life forms. There are a number of types of filamentous bacteria which proliferate in the activated sludge process. Filamentous organisms perform several different roles in the process, some of which are beneficial and some of which are detrimental. When filamentous organisms are in low concentrations in the process, they serve to strengthen the floc particles. This effect reduces the amount of shearing in the mechanical action of the aeration tank and allows the floc particles to increase in size. Larger floc particles are more readily settled in a clarifier. Larger floc particles settling in the clarifier also tend to accumulate smaller particulates (surface adsorption) as they settle, producing an even higher quality effluent. Conversely, if the filamentous organisms reach too high a concentration, they can extend dramatically from the floc particles and tie one floc particle to another (interfloc bridging) or even form a filamentous mat of extra large size. Due to the increased surface area without a corresponding increase in mass, the activated sludge will not settle well. This results in less solids separation and may cause a washout of solid material from the system. In addition, air bubbles can become trapped in the mat and cause it to float, resulting in a floating scum mat. Due to the high surface area of the filamentous bacteria, once they reach an excess concentration, they can absorb a higher percentage of the organic material and inhibit the growth of more desirable organisms.

Protozoans and Metazoans

In a wastewater treatment system, the next higher life form above bacteria is protozoans. These single-celled animals perform three significant roles in the activated sludge process. These include floc formation, cropping of bacteria and the removal of suspended material. Protozoans are also indicators of biomass health and effluent quality. Because protozoans are much larger in size than individual bacteria, identification and characterization is readily performed. Metazoans are very similar to protozoans except that they are usually multi-celled animals. Macroinvertebrates such as nematodes and rotifers are typically found only in a well developed biomass. The presence of protozoans and metazoans and the relative abundance of certain species can be a predictor of operational changes within a treatment plant. In this way, an operator is able to make adjustments and minimize negative operational effects simply by observing changes in the protozoan and metazoan population.

Dispersed Growth

Dispersed growth is material suspended within the activated sludge process that has not been adsorbed into the floc particles. This material consists of very small quantities of colloidal (too small to settle out) bacteria as well as organic and inorganic particulate material. While a small amount of dispersed growth in between the floc particles is normal, excessive amounts can be carried through a secondary clarifier. When discharged from the treatment plant, dispersed growth results in higher effluent solids.

Taxonomy

Taxonomy is the science of categorizing life forms according to their characteristics. Eighteen different categories are used to define life forms from the broadest down to the most specific. They are: Kingdom, Phylum, Subphylum, Superclass, Class, Subclass, Cohort, Superorder, Order, Suborder, Superfamily, Family, Subfamily, Tribe, Genus, Subgenus, Species and Subspecies. Identifying the genus is usually specific enough to determine the role of the organisms found in a wastewater treatment system.

Process Indicators

Following taxonomic identification, enumeration and evaluation of the characteristics of the various organisms and structures present in a wastewater sample, the information can be used to draw conclusions regarding the treatment process. Numerous industry references, such as WASTEWATER BIOLOGY: THE MICROLIFE by the Water Environment Federation, can be used to provide a comprehensive indication of the conditions within a treatment process. As an example, within most activated sludge processes, the shape of the floc particles can indicate certain environmental or operational conditions. A spherical floc particle indicates immature floc, as would be found during start-up or a process recovery. A mature floc particle of irregular shape indicates the presence of a beneficial quantity of filamentous organisms and good quality effluent. An excess of dispersed growth could indicate a very young sludge, the presence of toxic material, excess mechanical aeration or an extended period of time at low dissolved oxygen levels. Certain protozoans, such as amoebae and flagellates dominate during a system start-up. Free swimming ciliates are indicative of a sludge of intermediate health and an effluent of acceptable or satisfactory quality. A predominance of crawling ciliates, stalked ciliates and metazoans is an indicator of sludge with excellent health and an effluent of high quality.

Factors affecting Chlorine Demand in waste water treatment plants

Ammonia increase will change the free chlorine/chlorine demand be converting to chloramine - but not nitrate. Nitrate does not recombine to ammonia unless there is a catalyst to break the nitrate and add free hydrogen. Since that is usually an oxidative process - this would break the chlorine down in addition - so unless you've added AOT technology or utilizing hydrogen peroxide or permanganate - doubt that the cause. Probably a increase due to some other chemical or metal that you have not received in abundance before. Since the list of such could be very long and costly to identify, check with the city or county agency that handles permitting, even the building inspector's office could lead you to a likely source if industry is able to discharge direct to the city sewer system without permit. Many small brass and valve mfg (such as those that make dental components and such) are allowed to dump their cleaners direct to city sewer systems without permit. OSHA might know of any new industrial start-ups also.

Chlorination Chemistry

When chlorine is added to water, a variety of chemical processes take place.  The chlorine reacts with compounds in the water and with the water itself.  Some of the results of these reactions (known as the chlorine residual) are able to kill microorganisms in the water.  In the following sections, we will show the chemical reactions which occur when chlorine is added to water.  

Chlorine Demand

When chlorine enters water, it immediately begins to react with compounds found in the water.  The chlorine will react with organic compounds and form trihalomethanes.  It will also react with reducing agents such as hydrogen sulfide, ferrous ions, manganous ions, and nitrite ions. 

Let's consider one example, in which chlorine reacts with hydrogen sulfide in water.  Two different reactions can occur:

Hydrogen Sulfide + Chlorine + Oxygen Ion → Elemental Sulfur + Water + Chloride Ions
H₂S + Cl₂ + O^2- → S + H₂O + 2Cl^-

Hydrogen Sulfide + Chlorine + Water → Sulfuric Acid + Hydrochloric Acid
H₂S + 4Cl₂ + 4 H₂O → H₂SO₄ + 8 HCl

I have written each reaction using both the chemical formula and the English name of each compound.  In the first reaction, hydrogen sulfide reacts with chlorine and oxygen to create elemental sulfur, water, and chloride ions.  The elemental sulfur precipitates out of the water and can cause odor problems.  In the second reaction, hydrogen sulfide reactions with chlorine and water to create sulfuric acid and hydrochloric acid.  

Each of these reactions uses up the chlorine in the water, producing chloride ions or hydrochloric acid which have no disinfecting properties.  The total amount of chlorine which is used up in reactions with compounds in the water is known as the chlorine demand.  A sufficient quantity of chlorine must be added to the water so that, after the chlorine demand is met, there is still some chlorine left to kill microorganisms in the water. 

Reactions of Chlorine Gas with Water

At the same time that chlorine is being used up by compounds in the water, some of the chlorine reacts with the water itself.  The reaction depends on what type of chlorine is added to the water as well as on the the pH of the water itself.

Chlorine may be added as to water in the form of chlorine gas, hypochlorite, or chlorine dioxide.  All types of chlorine will kill bacteria and some viruses, but only chlorine dioxide will effectively kill Cryptosporidium, Giardia, protozoans, and some viruses.  We will first consider chlorine gas, which is the most pure form of chlorine, consisting of two chlorine atoms bound together. 

Chlorine gas is compressed into a liquid and stored in metal cylinders.  The gas is difficult to handle since it is toxic, heavy, corrosive, and an irritant.  At high concentrations, chlorine gas can even be fatal.

When chlorine gas enters the water, the following reaction occurs:

Chlorine + Water → Hypochlorous Acid + Hydrochloric Acid
Cl₂ + H₂O → HOCl + HCl

The chlorine reacts with water and breaks down into hypochlorous acid and hydrochloric acid.  Hypochlorous acid may further break down, depending on pH:

Hypochlorous Acid ↔ Hydrogen Ion + Hypochlorite Ion
HOCl ↔ H⁺ + OCl^-

Note the double-sided arrows which mean that the reaction is reversible.  Hypochlorous acid may break down into a hydrogen ion and a hypochlorite ion, or a hydrogen ion and a hypochlorite ion may join together to form hypochlorous acid. 

The concentration of hypochlorous acid and hypochlorite ions in chlorinated water will depend on the water's pH.  A higher pH facilitates the formation of more hypochlorite ions and results in less hypochlorous acid in the water.  This is an important reaction to understand because hypochlorous acid is the most effective form offree chlorine residual, meaning that it is chlorine available to kill microorganisms in the water.  Hypochlorite ions are much less efficient disinfectants.  So disinfection is more efficient at a low pH (with large quantities of hypochlorous acid in the water) than at a high pH (with large quantities of hypochlorite ions in the water.)   

Hypochlorites
Instead of using chlorine gas, some plants apply chlorine to water as a hypochlorite, also known as a bleach.  Hypochlorites are less pure than chlorine gas, which means that they are also less dangerous.  However, they have the major disadvantage that they decompose in strength over time while in storage.  Temperature, light, and physical energy can all break down hypochlorites before they are able to react with pathogens in water. 

There are three types of hypochlorites - sodium hypochlorite, calcium hypochlorite, and commercial bleach:

Sodium hypochlorite (NaOCl) comes in a liquid form which contains up to 12% chlorine.  Calcium hypochlorite (Ca(OCl)²), also known as HTH, is a solid which is mixed with water to form a hypochlorite solution.  Calcium hypochlorite is 65-70% concentrated.   

Commercial bleach is the bleach which you buy in a grocery store.  The concentration of commercial bleach varies depending on the brand - Chlorox bleach is 5% chlorine while some other brands are 3.5% concentrated.

Hypochlorites and bleaches work in the same general manner as chlorine gas.  They react with water and form the disinfectant hypochlorous acid.  The reactions of sodium hypochlorite and calcium hypochlorite with water are shown below:

Calcium hypochlorite  + Water → Hypochlorous Acid + Calcium Hydroxide
Ca(OCl)₂ + 2 H₂O → 2 HOCl + Ca(OH)₂

Sodium hypochlorite + Water → Hypochlorous Acid + Sodium Hydroxide
NaOCl + H₂O → HOCl + NaOH

In general, disinfection using chlorine gas and hypochlorites occurs in the same manner.  The differences lie in how the chlorine is fed into the water and on handling and storage of the chlorine compounds.  In addition, the amount of each type of chlorine added to water will vary since each compound has a different concentration of chlorine.  

Chloramines

Some plants use chloramines rather than hypochlorous acid to disinfect the water.  To produce chloramines, first chlorine gas or hypochlorite is added to the water to produce hypochlorous acid.  Then ammonia is added to the water to react with the hypochlorous acid and produce a chloramine.  

Three types of chloramines can be formed in water - monochloramine, dichloramine, and trichloramine.  Monochloramine is formed from the reaction of hypochlorous acid with ammonia:

Ammonia + Hypochlorous Acid → Monochloramine + Water
NH₃ + HOCl → NH₂Cl + H₂O

Monochloramine may then react with more hypochlorous acid to form a dichloramine:

Monochloramine + Hypochlorous Acid → Dichloramine + Water

NH₂Cl + HOCl → NHCl₂ + H₂O

Finally, the dichloramine may react with hypochlorous acid to form a trichloramine:

Dichloramine + Hypochlorous Acid → Trichloramine + Water
NHCl₂ + HOCl → NCl₃ + H₂O

The number of these reactions which will take place in any given situation depends on the pH of the water.  In most cases, both monochloramines and dichloramines are formed.  Monochloramines and dichloramines can both be used as a disinfecting agent, called a combined chlorine residual because the chlorine is combined with nitrogen.  This is in contrast to the free chlorine residual of hypochlorous acid which is used in other types of chlorination. 

Chloramines are weaker than chlorine, but are more stable, so they are often used as the disinfectant in the distribution lines of water treatment systems.  Despite their stability, chloramines can be broken down by bacteria, heat, and light.  Chloramines are effective at killing bacteria and will also kill some protozoans, but they are very ineffective at killing viruses.

Breakpoint Chlorination

The graph below shows what happens when chlorine (either chlorine gas or a hypochlorite) is added to water.  First (between points 1 and 2), the water reacts with reducing compounds in the water, such as hydrogen sulfide.  These compounds use up the chlorine, producing no chlorine residual.  

Next, between points 2 and 3, the chlorine reacts with organics and ammonia naturally found in the water.  Some combined chlorine residual is formed - chloramines.  Note that if chloramines were to be used as the disinfecting agent, more ammonia would be added to the water to react with the chlorine.  The process would be stopped at point 3.  Using chloramine as the disinfecting agent results in little trihalomethane production but causes taste and odor problems since chloramines typically give a "swimming pool" odor to water.

In contrast, if hypochlorous acid is to be used as the chlorine residual, then chlorine will be added past point 3.  Between points 3 and 4, the chlorine will break down most of the chloramines in the water, actually lowering the chlorine residual.

Finally, the water reaches the breakpoint, shown at point 4.  The breakpoint is the point at which the chlorine demand has been totally satisfied - the chlorine has reacted with all reducing agents, organics, and ammonia in the water.  When more chlorine is added past the breakpoint, the chlorine reacts with water and forms hypochlorous acid in direct proportion to the amount of chlorine added.  This process, known as breakpoint chlorination, is the most common form of chlorination, in which enough chlorine is added to the water to bring it past the breakpoint and to create some free chlorine residual.   

Chlorine Dioxide
There is one other form of chlorine which can be used for disinfection - chlorine dioxide.  We have not discussed chlorine dioxide previously because it disinfects using neither hypochlorous acid nor chloramines and is not part of the breakpoint chlorination process.

Chlorine dioxide, ClO₂, is a very effective form of chlorination since it will kill protozoans,  Cryptosporidium, Giardia, and viruses that other systems may not kill.  In addition, chlorine dioxide oxidizes all metals and organic matter, converting the organic matter to carbon dioxide and water.  Chlorine dioxide can be used to remove sulfide compounds and phenolic tastes and odors.  When chlorine dioxide is used, trihalomethanes are not formed and the chlorination process is unaffected by ammonia.  Finally, chlorine dioxide is effective at a higher pH than other forms of chlorination.

So why isn't chlorine dioxide used in all systems?  Chlorine dioxide must be generated on site, which is a very costly process requiring a great deal of technical expertise.  Unlike chlorine gas, chlorine dioxide is highly combustible and care must be taken when handling the chlorine dioxide.