Laboratory Supplies & Lab Equipment - Centrifuges, Lab Apparatus, Lab Glass, ph Meters, Labware, Medical Supplies & More

Some disinfectants are known as sterilants or sporocides which means that they destroy all microbial life including endospores.  An exmple is ethylene trioxide.  This gas is used to sterilize objects such as petri dishes and medical devices.  These objects are heat sensitive and must be sterilized with something other than heat and steam.  Sanitzers are chemical agents that reduce microbial life to tolerable levels but do not destroy all microbes.  These agents are used in the food industry to treat cooking equipment like dishes and utensils.  If a particular agent only inhibits the growth of bacterial cells but does not kill them, we say that the agent is bacteriostatic.  If agents such as this are removed the bacterial growth would resume.  Agents that kill bacterial cells are termed bacteriocidal.  Agents can also be specific to the type of microorganism.  There are bacteriocides, fungicides, and viricides designed to kill bacteria, fungi, and viruses.

Karl Fischer Titration is a specific and accurate method for water determination.  The reaction is:

B·I₂ + B·SO₂ + B + H₂O → 2BH⁺I⁻ + BSO₃

BSO₃ + ROH → BH⁺ROSO₃⁻

Where B is a base such as Imidazole and ROH is an alcohol such as anhydrous Methanol.  When all the H₂O has reacted, there is no more free I⁻ as it reacts to form I₂ .  Without I⁻ to carry current there is a steep voltage drop which indicates the endpoint.  The voltage drop is measured by a second pair of anode and cathode – the method is bipotentiometric.

In a coulometric titration the anode solution consists of the alcohol,  the base (B), SO₂  I₂ and the analyte (sample containing water).  The cathode is in a smaller compartment containing the anode solution but no analyte.  The anode compartment and cathode compartment are separated by an ion-permeable membrane.  The Pt anode generates I₂ when current is applied.  This I₂ reacts with the H₂O to produce the I⁻ ion.  When no more water is present the voltage drops abruptly – this is the endpoint.  The amount of current required to reach the endpoint determines the amount of water in the sample.

Volumetric titration involves adding I₂ to the solution using a buret.  The volume of I₂ required to complex all of the H₂O is directly related to the amount of water in the sample.

Some of he advantages 0f Karl Fischer titration are:   The method is accurate, it is specific for water, it works over a wide range of moisture, it can measure moisture in solids liquids or gases, and it can be automated.  Mettler Toledo and Lab Synergy are two  companies who manufacture automated Karl Fischer titrators.

Robin

We use antiseptics everyday.  An antiseptic is a chemical agent used to kill or control the growth of microorganisms.  Hospitals use sodium hypochlorite which is identical to household bleach to control microorganisms.  Medical professionals use alcohol to sterilize the skin before an injection and betadine (an organic form of iodine) on the skin before surgery.  The betadine prevents Staphylococcus aureus from causing a post surgical infection.  Cities add chlorine to the water supply to prevent the spread of pathogens such as Salmonella typhi from getting into the drinking water.  Chemical agents are also added to food to slow down spoilage by microorganisms.  This increases the shelf life of the packaged food.  Clostridium botulinum causes a deadly form of food poisoning and is controlled by adding chemicals to canned food.  Antiseptics are not to be confused with disinfectants which are used to control microbial activity on inanimate objects.

Well, here’s a handy item that no laboratory should be without.  An Electric Bunsen Burner by Barnstead.       The heat range is 800-1000°C.    A major benefit is the safety of electric as well as being the cleanest method out of all options.

The burner is ideal for heating test tubes, crucibles, small flasks, and beakers.  It’s conical shaped heating element  directs radiant heat upward, at the same time, air circulation from the vented housing keeps the base cool enough to be handled during operation. 

The heating element is an easily, replaceable component.   Note:  The single place percentage on/off controller (pictured to the right), is sold as an accessory and is required to properly operate the electric burner.

In a situation when a burner is only needed on an intermittent basis, a Bunsen Pilot Burner may be a consideration.  The burner works on both natural and mixed gases.  Manufacturer from steel with rustproof  zinc plating.  It has a sleeve-type regulator and stopcock for reliable gas control along with a pilot light tube that has a  screw adjustment for flame control. 

For additional assistance, please call our knowledgeable staff here at LabPlanet.  StephenG

In quantitative analysis titration is used to determine the concentration of an unknown sample.  A typical titration involves an erlenmeyer flask with the unknown sample – the analyte – and a buret filled with a reactant of a known concentration – the titrant – which will react with the unknown sample.   A magnetic stirrer can be stirring the unknown sample and an indicator reagent such as phenolphthalein may be added.  The volume of the titrant solution required to react completely with the unknown analyte will determine the concentration of the analyte.  The equivalence point is the point at which the number of moles of titrant used equals the number of moles of analyte present.  The endpoint will be indicated by a color change in the indicator.  A pH meter can be used for acid base reactions; a sudden change in pH will be the endpoint of the titration.  A sudden change in the working electrode potential will indicate the endpoint of a redox titration.

Robin