วันจันทร์ที่ 17 เมษายน พ.ศ. 2560

pH electrodes Reviews.

pH Electrode
  pH Measurement

       The most common pH measurement system utilizes glass pH electrodes. The system consists of a pH sensor(whose voltage varies proportionately) to the hydrogen ion activity of the solution), a reference electrode(which provide a stable and constant reference voltage), a conductive measurement solution and a special meter to display and measure the pH.

       The pH sensor incorporates a thin membrane of hydrogen sensitive glass blow on the end of an inert glass tube. This tube is filled with a buffered electrolyte, and a Ag/AgCl wire. This is called a pH half cell. A complinentary system produces a constant voltage; it also contain a Ag/AgCl wire and an electrolyte(often a KCl) solution saturated with AgCl). A small “filter”. Often a porous ceramic piece, connect this tube to the external sample. This system is called a reference half cell.

        The meter measures the voltage difference between the pH half cell and the reference half cell in DC millivolts. The reading is read by the meter and displayed in either mV or pH units.

        The remarkable glass pH measurement system is capable of measuring over fourteen decades of hydrogen ion concentration. The system has a proven track record for reliability and predictability. Several companies have marketed ion selective field effect transistors(ISFET technology) as a response to the need for glass free measurements(such as the use of glass in food processing). An ISFET is a chemically coated transistor that responds to hydrogen ions as well as oxidation and reduction voltages. These electrodes also require a reference electrode. ISFETS are reported to suffer from drift and instability buy may still have a niche market. The glass pH sensor is still the far better choice for the majority of applications.

Electrode Body

             Until the seventies, it was a common practice to offer two half cells separately, a glass pH sensor and separate reference electrode. Today it is more common to use a single combined electrode that has both of the components. Reference electrodes still enjoy use in other electrochemical techniques and are often preferred with ion selective electrodes(ISE) half cells.

             Combination pH electrodes are often made entirely of glass. The bodies of these electrodes are lead free glass, which is not pH sensitive. All glass electrodes are ideal for routine laboratory work because they respond quickly to temperature changes, are easily cleaned and are compatible with organic solvents. However, in the hands of some, glass can be very breakable.

            The electrode body can be made less fragile by incorporating an outer body made from a thermoplastic the uses of PEI resin, PVDF and PP as examples of materials utilized for outer body construction.

             Some industrial sensors utilize additional materials such as PVC and titanium, the space age metal. A titanium body increase immunity to electrostatic and magnetic fields and features strong corrosion resistance(even in sea water).

Matching Pin

            A matching pin is a differential measurement technique used to eliminate ground loops and common mode perturbations for the measurement system. In a system without a matching pin, electrical currents in the sample can effect the reference half cell voltage that is connected via the liquid junction with the sample. In this case, the reference electrode picks up the electromagnetic field and the measurement of the pH is altered. The matching pin isolates these current/magnetic fields from the reference electrode. Many factory manufactures a number of models with the matching pin design for safe precise pH measurements.

Measurement Preparation Procedure

        A coated measurement sensor or reference may yield slow responding and erroneous results. To ensure the best pH measurements possible, preventative maintenance and storage practices are strongly advised. A clean, conditioned pH electrode will provide the best measurements possible.

        When using a new electrode, remove the protective bulb cap and inspect the electrode. As water may have evaporated during shipping or storage, salt crystals may be found in the cap or on the pH bulb. Rinse off with water. During transport, air bubbles may have formed inside the glass bulb. Shake down the electrode as you would an old style mercury thermometer.




         Condition the sensing tip, soak the pH bulb and junction in pH storage solution for at least one hour or longer. If possible, and overnight soak is best. This will hydrate a dehydrated glass sensor, thoroughly wetting a dried reference junction(wick, ceramic etc.)

Water Conductivity and pH Measurement

          pH measurement is the measurement of hydrogen ions, Ultrapure water is the perfect solvent, and readily dissolved many things. The pH glass surface can actually become dehydrated if stored or used in deionized or distilled water as ions are leached from the sensing surface. pH electrodes require ions in a solution, preferably with a  conductivity of or exceeding 200 microsiemen/cm to function properly. In the case of low conductivity samples or when working below 200 microsiemens/cm. we suggest the use of specific electrodes, such as HI10538

How Temperature effects pH measurements 

          Samples change pH as a function of temperature due to changes in ion dissociation and increased ion activity with increases in temperature. An example of this is pH buffers whose well characterized values are published on the buffer bottles. With very pure water, a change in ~1.3 pH is observed between 0 and 100 degree celcius. This example shows that even a neutral solution can have a large temperature coefficient. All samples have a temperature coefficient that is variable for actual samples. Changes in pH due to the sample temperature coefficient are not compensated for.

           This is an exception to this because buffers are well characterized, on intelligent pH meters, during calibration, the buffers are compensated for. They will display a 25 degree celcius value during calibration but will change after the calibration to read their actual pH at the temperature of measurement.

pH Compensation

           It well-made pH electrode together with modern pH instrumentation can compensate for changes in temperature related pH measurements due to thermodynamic changes demonstrated by the Nernst Equation. The electrode itself is made with an isothermal point close to pH 7 and a slope that closely follows the Nernst Equation. When temperature compensation is made with a pH meter. The slope(or gain) of the meter is changed to compensate for the Nernst slope change exhibited by the electrodes. 

Alkaline Error

            Alkaline error exists in high pH solutions when the hydrogen ions in the gel layer are partially or completely substituted with alkali ions, and the resulting pH is lower than it actually should be. The difference between the theoretical and experimental pH is called the alkaline error. Sodium ions are typically the ions that are responsible but potassium and lithium ions can also contribute to this error, In earlier glass compositions, the alkaline error was seen to start at pH9. Newer glass formulations and ones especially formulated to minimize this error now exhibit an error starting at pH12 or 13 pH.

Half Cell/Reference Electrodes

     All potentiometric measurements are taken with two electrodes, one is a sensor with a potential that varies as a function of the concentration of the species to be measured and the second is a reference electrode which keeps its potential constant. The mV reading is the difference of the two values.

Reference Half Cell Junction

      The reference half cell must be constructed so as to allow contact between the fill solution inside the half cell and the sample being measured. The fill solution must meet some requirments:

* The reference fill solution should not interfere with the measurement.

* The reference fill solution should not react with the solution measured(no precipitates or complexes).

* The reference solution should be miscible with the solution measured.

* The solution measured must not react chemically with the reference half cell.

* The mobility of the ions in the fill solution should be matched(equitransferent)

* Should be non-toxic

     The junction(the part in contact between the two liquids) is typically made with inert materials that will not increase a junction potential or be chemically attacked by the measured solutions. The materials most commonly used are :

      Porous Ceramic. Normally used in electrodes with glass bodies, because ceramic with the correct expansion coefficient is is easily welded to glass. Ceramic is available with different porosities and diameters. Also sometimes called a diaphragm.
      Porous PTFE(PolyTetraFluoro-Ethylene): is a hydrophobic material that is available with different porosities. Because of its chemical advantages, PTFE is widely used in industrial applications.
       Fiber wick : This type junction is often used on plastic bodied electrodes with gelled electrolytes. The advantage of this type junction is it is renewable; as the cloth like material is pulled out from its position, the junction is renewed with an uncontaminated fresh surface.     
       Cone Style : This junction is also renewable. As the sleeve or collar is moved fresh fill solution cleans out the junction with fresh electrolyte. This has a higher flow rate than a ceramic type and is often specified for ISE measurements.
       Open junction : This type junction is found in reference half-cell is filled with a special gel which comes into direct contact with the solution to be measure. An advantage of an open junction is low conta resistance and it is virtually impossible to clog.

Other types of juntions include :


        Capillary junction : Can be made with smooth or frosted glass. The advantage of a capillary junction is a fast flow rate and a very open channel. Typically used with thickened electrolytes.           
           

วันอาทิตย์ที่ 16 เมษายน พ.ศ. 2560

๊U-550 Sonic Belt Tension Meter, Digital Gates Unitta Asia

 U-550 Sonic Belt Tension Meter, Digital Gates Unitta Asia 
























ORP(Oxidation Reduction Potental) Theory and Applications.


ORP(Oxidation Reduction Potential)

         Similar to the manner in which acidic or alkaline solutions are quantified by pH measurements, solutions can also be graded as oxidizing or reducing based on measurements of ORP(sometimes called "redox").

       When an oxidizing and / or reducing agent is dissolved into an aqueous sample, they may react with materials present and produce a voltage, or electromotive force(EMF), that is related to the ratio of oxidized to reduce species in the sample. An electron exchange can develop between this solution and an inert metal sensor immersed in the solution, and the voltage can be measured(When compared to a reference electrode) with a pH/mV meter. This type of measurement is known as redox or ORP. The units of measurement are in mV. At a glance, an ORP electrode may look very similar to a pH electrode. Like a combination pH electrode, both the sensor and the reference are housed in a common body.

        The scale of measurement may be positive(indicating oxidizing potential) or negative(indicating reducing). It should be noted that when zero mV is observed, it is really an oxidizing situation because the reference voltage(~200 mV for an Ag/AgCl with KCl electrolyte) is included in the observed mV value in some cases the user may wish to offset the reading to remove the reference contribution. The mV is then said to be approaching the absolute mV scale that references a SHE(standard hydrogen electrode). This type of calibration is called relative mV calibration.

        An ORP sensor must be chemically inert ; it cannot be oxidized or reduced itself. It must also have the proper surface characteristics to promote rapid electron exchange, a property known as high exchange current density. Two noble metals have proven to work well for this purpose pure platinum and pure gold are both used in the construction of ORP sensors.

        The platinum sensor is often preferred because it is mechanically simpler and safer to produce, Platinum can be welded to glass and has the same thermal coefficient. Sensors made of gold cannot be welded to the glass and are often placed in plastic supports applied to the glass or plastic tube by means of tiny elastomeric bungs. The gold or platinum sensor signal is carried through the electrode body, and together with the reference signal is conducted to the measurement meter via a coaxial cable with BNC connector.

         An ORP system does not have a high impedance source(like a pH bulb), but is a potentiometric device that produces a voltage. It also uses similar cables, connectors and calibration solutions. For this reason, a high impedance electronic meter(pH) with many user friendly features are a benefit for this measurement also.

         Because of the close relationship between pH and ORP, there is a scale that takes into account the ratio(mV) ORP/pH, the rh scale. The rH range varies from zero to fourty-two, where the extreme values represent the reducing effect of an atmosphere of pure hydrogen(rH=0) and to the oxidizing effect of an atmosphere of pure oxygen(rH=42), respectively.

The formula for obtaining value is as follows. 

   rH = mV/0.0992(273.15 + T)/(-2 pH)

         In this equation, where T is the temperature(degree celcius) of the sample, mV is the ORP(mV) reading, and pH is the pH value of the sample. 

        The rH scale is not used in the instruments available on the market. A direct mV reading from the electrode is preferred, within the +/- 2000 mV range, without compensation/correlation with the pH/temperature value.

ORP Applications

       ORP measurements are based on the potential difference measured between the platinum or gold electrode and a reference electrode. The identical reference system utilized for the pH electrode(Ag/AgCl) is also used for redox measurements. Redox electrodes are used to monitor many chemical processes particularly those involving reversible reactions. Common applications include the following.

Industrial wastewater Treatment

      The redox systems used in water treatment are the reduction of chromates and oxidation of cyanides. Waste hexavalent chromium is reduced to trivalent chromium by the addition of sodium bisulfite or sulphur dioxide. In the case of cyanide, chlorine or sodium hypochlorite is used to oxidize the cyanide, followed by the hydrolysis of cyanate to ammonia and carbon dioxide.

Water Sanitation

       ORP measurements are being increasingly used as an effective measure of the sanitizing activity in pool, spa and potable water. The kill time of E.coli bacteria in water depends on the ORP value. ORP is a reliable indicator of bacteriological water quality. Water having an ORP value equal to or higher than six hundred and fifty mV are well within accepted sanitization levels for pool and spa waters.

ORP and Sample Preparation Solutions

      ORP standard solutions allows users to test the precision of ORP electrodes. For example, by immersing the electrode in ORP solution, reading should fall within the 200 to 275 mV range(@20 degree celcius/ 68 degree farenhite)

วันเสาร์ที่ 15 เมษายน พ.ศ. 2560

The Importance of Soil Testing

Soil is not merely a support system for plants, but a complex world from which the roots obtain water and other required elements. In addition, soil is inhabited by small animals, insects, microorganisms(e.g.fungi and bacteria) which all influence the plant life in one way or another. Soil evolution is a change in its characteristics based upon climate, presence of animals and plants as well as man's action. A natural soil in which evolution is slow, is very different from a cultivated one. 
   
           Soil evolution is a change in its characteristics based upon climate, presence of animals and plants as well as man's action. A natural soil, in which evolution is slow, is very different from a cultivated one. Soil is composed of solids(minerals and organic matters), liquids(water and dissolved substances), gases(mostly oxygen and carbon dioxide) and living organisms contains. All these elements provide its physical and chemical properties.

          Managing the soil properly is necessary in order to preserve its fertility, obtain better yield and respect the environment. Testing the soil however, is a must in oder to manage it properly. The physical structure of the soil depends on the dimension of the particles of its composition in addition, the particles also differ based on their shape and volumic mass(mass per unit of volume).

Particles classification according to "international Society of Soil Science"(ISSS)

        Soil is divided into many classes of texture, according to the percentage of the basic particles(clay, sand and slit). If, for example, we have a soil with thirty-seven percent clay, thirty-eight percent sand and twenty-five percent silt, the soil is classified as "clay loam". Among different types of soil, the loam soil is considered as being suitable for crop growth. However, other types of soil, with a rational management, can also provide positive results.

        The soil texture is the cause of important aspects such as porosity, tenacity, adhesivity and plasticity. Porosity is important for the exchange of gases and liquids. Microporosity(porous less than two to ten micrometre) permits water to be retained while macro-pososity(porous more than 10 micrometre) contributes to a fast circulation of air and water. Plants therefore are in need of a correct relationship between micro and macro porosity.

        Clay soils have a greater micro-porosity than sandy soils and hence hold more water and remain wet for a longer period. Because of the greater tenacity and adhesivity of clay soils, they are called heavy, while sandy soils are referred to as light.

        Organic matter, caused by animal and vegetable residues, is another important constituent of the solid part of the soil. Organic matter has a positive effect on the soil fertility by adding nutrients, stabilizing the pH reaction and permitting a good retainment of water. Organic matter is also important for the activity of microorganisms and in general, contributes towards prevention of soil erosion. The collioidal portion, composed of micro-particles(one to one hundred micrometre), is important for holding nutrients. Since most of these particles have a negative charge, the colloidal portion has a particularly large capacity to retain cations(ammonium ion, potassium ion, sodium ion, calcium ion, magnesium ion, etc.). The CEC(Cation Exchange Capacity) is higher in soils rich with clay and organic matter than in sandy soils.

         Soil pH can be acid, neutral, or alkaline. Each plant has a range of pH in which it thrives and most plants prefer conditions near the neutral mark(pH 5.5 - 7.5). There are however plants that prefer acid or alkaline environments. The solubility of the nutrients, that is the ability of the plants to absorb them, depends largely on their pH value. The soil microbiological activity is also pH dependent. Most bacteria, specially those putting nutrients at the plants disposition, prefer moderately acid of slightly alkaline conditions. The pH level hence influences the fertility of the soil.

         Fruit and Vegetable : Testing the nitrogen and phosphorus level in your soil is important, especially before seeding and replanting. While root vegetables need phosphorus, leafy plants require more Nitrogen. Potassium however, helps increase the quality of the crop. With the Hanna Quick Soiltest, growers able to keep these three important elements under control.

        Flowers and Shrubs : The right quantity of potassium is the key factor in ensuring beautiful and fragrant flowers. The other elements play an important role too in achieving quick and harmonious growth.

         Lawns : A lush lawn is the result of care and attention. In addition to tilling and irrigation, the pH and nitrogen levels need regular checks.

         Fruit and Decorative Trees : Trees are the most appealing feature of our gardens.Nitrogen and phosphorus help in speeding up the growth of young plants, encouraging abundance of foliage and strengthening the trunk and the roots. Potassium, on the other hand keeps, the plants in tip top condition by protecting them from disease.

        Bonsai and Houseplants : Every time a houseplant, but in particular a bonsai is potted, the choice of soil mixture is of prime importance. Having prepared the mixture, The Hanna Quick Soiltest will in a matter of minutes test the level of pH and other elements ensuring a livelier plant.

       The chemical composition of soil includes pH and chemical elements. Soil analysis is necessary for better management of fertilization and to know the residues of fertilization and to know the residues of fertilizers in relation to the crop, tillage and the most suitable plant choice for soil composition. An analysis can highlight shortages and help the understanding of the causes of an abnormal growth. By using the Hanna soiltest, it is possible to measure pH and the most important elements for plant growth, that is, nitrogen(N), phosphorus(P) and potassium(K).

      Testing the soil during each crop cycle and comparing the results with plant growth can be a useful experiment for subsequent cultivations.

       In agricultural applications, monitoring the quality of the soil is extremely important for the health and growth of crops. The pH level is an excellent guide as to which plants may thrive in a particular terrain, as well as indicating which conditioners and fertilizers to use, Hanna combination test kits allow you to test not only for pH, but for nitrogen, phosphorous and potassium which are all important for the quality of soil as well


Hanna Instruments HI3896 Professional Agriculture Test Kit for 25 Tests



Soil Savvy - Soil Test Kit


วันศุกร์ที่ 14 เมษายน พ.ศ. 2560

Acidity Olive oil tester

Acidity Olive oil tester 

        Acidity, defined as percent oleic acid, is a parameter that indicates olive oil freshness. A high acidity value indicates the oil quality has diminished and is at risk of becoming rancid. Acidity is used to discriminate an extra virgin olive oil from all other olive oils. According to the CEE 2568/91 regulation, olive oil is considered extra virgin when its acidity level is below one percent. A low acidity value also indicates a natural extraction process occurred soon after olive harvesting.

        Acidity(expressed as percent oleic acid) is the most fundamental measurement of olive oil. It is the primary indicator of olive oil purity and freshness. The quanlity of olive oil is directly related to the degree of breakdown of the fatty acids in the oil. As  the bound fatty acids break down, free fatty acids are formed which increase the acidity of the percent oil. Acidity, expressed as oleic acid, is a measure of the free fatty acid present in the oil, which is directly related to its purity.

        The quanlity of olive oil can be adversely affected during maturation or by environm ental conditions. Mishanding, processing and bruishing during harvesting can also contribute to a breakdown of fatty acids and an increase in free acidity. Improper and / or long term storage can cause olive oil to breakdown and become rancid. Regular acidity testing is the best way to ensure and maintain quality and freshness.


         Normally, testing acidity is a complicated process requiring the use of various chemicals in a laboratory environment. Studies have shown that the quality of olive oil has a direct impact on its health benefits. Extra Virgin Olive Oil contains higher levels of antioxidants, particularly phenols and vitamin E (because it is less processed). Antioxidants can help prevent oxidation damage to body tissue caused by free radicals, Studies have also shown that the oxidation of LDL (or bad) Cholesterol is associated with the hardening of arteries that can lead to heart disease. With some test kit, it is possible to easily and accurately test the quality of olive oil at various stages of processing and storage to monitor and maintain the highest quality.

           In accordance with the European Community(EC) reg. CEE2568/91 quality classification of olive oil based on acidity(expressed as percent oleic acid) is as follows :

           Extra Virgin Olive Oil : Acidity</= 1% "Perfect flavor and odor", with a maximum acidity, expresses as oleic acid of 1 g/100 g.
           Virgin Olive Oil : Acidity 1 - 2 % "Perfect flavor and odor", with a maximum acidity, expresses as oleic acid, of 2g/100 g.
            Ordinary Virgin Olive Oil : Acidity 2 - 3 .3%(tolerance of 10 %) "Good flavor and odor", with a maximum acidity, expressed as oleic acid, of 3.3g/100 g.
             Virgin Lampante Olive Oil : +3.3 %. Not fit for human consumption "Off flavor and odor", with a maximum acidity, expresses as oleic acid, > 3.3g/100 g.


           Today our water supplies are becoming more contaminated with corrosive chemicals from industrial dumping or acid rain. Therefore, acidity measurements are an essential monitoring device to define and control pollution in sewers, lakes and rivers. Acidity of water is equally important to monitor in soils and fish farming to maximize the growing environment.


             The acidity of a water sample is its capacity to neutralize hydroxide ions. Acidity may be caused by mineral acids such as sulfuric acid or hydrochloric acid or by dissolved carbon dioxide. Most commonly in drinking water. Carbon dioxide is the principal cause of acidity in drinking water, but also it can be caused by mineral and organic acids. Acidity increase the corrosive behavior of water. Drinking water with high acidity level is likely to be corrosive to copper water pipes and to the solder which joins those pipes. 

             High levels of copper and lead indrinking water often occur when acidic water stands in pipes for extended periods of time(such as over night). In addition to creating a possible health hazard due to dissolved metal ions, acidity in water can cause copper plumbing to develop pin hole leaks after a few years.


             With the use of diluted sodium hydroxide as the titrant and bromphenol blue or phenolphthalein indicators, the contribution of strong or organic acids can be determined. The measurement of the strong acid contribution to the sample acidity is known as methyl orange acidity. This is carried out by titrating with sodium hydroxide until the solution turns from yellow to green/blue(pH endpoint about 4.5). The total acidity caused by both mineral and organic acids is determined by titrating to an endpoint pH of 8.3, using phenolphthalein as an indicator. This is known as phenolphthalein inacidity.


             The total exchangeable acidity(TEA) is a measure of the amout of acidic cations(hydrogen, aluminum, iron and manganese) present is soil. It is expressed in milliequivalent per one hundred grams(meq/100 g) of soil. The more acidic it is a soil, the lower the soil pH value will be Soils in humid regions normally accumulate increasing amounts of exchangeable acidity as they get older. Soil acidity may develop toxicity that can damage or kill plants. The extraction method is the potassium chloride method. The acidic cations are firstly leached from the soil and then titrated with a standard alkali. The reaction endpoint is visually indicated by a color change(from colorless to pink) of the indicator reagent.

SATO Analog Thermo - Hygrometer Model 7562-00 Reviews.

SATO Analog Thermo - Hygrometer 

Model 7562-00










Hygro with Thermometer Available at 

amazon.com

SATO Thermo-Hygrometer Model 7542-00 Reviews.

SATO Thermo-Hygrometer Model 7542-00