Checking the interface communication and software settings is a good place to start when troubleshooting a conductivity meter which has lost communication.

NaOH is highly hygroscopic, meaning that it absorbs water from the air. Therefore, over time the titrant will become more dilute as it absorbs water. NaOH can be standardized by titrating into a sample of potassium hydrogen phthalate (KHP) of known concentration. For example, titrate 0.05 N KHP with 0.1 N NaOH to an endpoint, and using the volume of NaOH added, the precise concentration of NaOH can be calculated. For more information on standardizing NaOH titrant, please refer to Standard Methods 2310. To limit the amount of water being absorbed, a glass drying tube with a cotton ball inserted should be used to prevent moisture going into the tube.

1:2 ratio (1 sample: 2 DI) is the acceptable dilution factor. This means that a sample volume as small as 2 ml can be diluted in 4 ml of Deionized water (DI) for a total of 6ml, when measured in a 50ml tube using the TitraPro3 pH electrode. Note that since the sample is diluted, the pH should not be reported as the sample initial pH value. Only undiluted samples should be measured and reported for initial pH. Dilutions factors that are greater, for example 1 part sample to 3 parts DI, were found to produce incorrect, lower alkalinity results. It was also noted that on higher dilutions, the pH dropped below 7, indicating a change over to the acidic side.

Changes to slope at higher pHs

Alkaline Error or Sodium Error occurs when pH is very high (e.g. pH 12) because Na+ concentration is high (from NaOH used to raise pH) and H+ is very low.
Electrodes respond slightly to Na+ and give a false low reading. This is related to the concept of selectivity coefficients where the electrode responds to many ions but is most selective for H+. This problem occurs because Na+ is 10 orders of magnitude higher than H+ in the solution.

High pH electrodes use a 0-14 pH glass. This electrode will read pH 14 (1 M NaOH) to be around pH 13.7 with a 0.3 pH sodium error.

A standard pH electrode uses a 0-12 pH glass. The electrode will read pH 14 (1 M NaOH) to be around pH 12.4 with a 1.6 pH sodium error.

Alkaline error
The alkaline effect is the phenomenon where H+ ions in the gel layer of the pH-sensitive membrane are partly or completely replaced by alkali ions. This leads to a pH measurement which is too low in comparison with the number of H+ ions in the sample. Under extreme conditions where the H+ ion activity can be neglected the glass membrane only responds to sodium ions. Even though the effect is called the alkaline error, it is only sodium or lithium ions which cause considerable disturbances. The effect increases with increasing temperature and pH value (pH > 9), and can be minimized by using a special pH membrane glass.

Sodium Ion Error
Although the pH glass measuring electrode responds very selectively to H+ ions, there is a small interference caused by similar ions such as lithium, sodium, and potassium. The amount of this interference decreases with increasing ion size. Since lithium ions are normally not in solutions, and potassium ions cause very little interference, Na+ ions present the most significant interference.
Sodium ion error, also referred to as alkaline error, is the result of alkali ions, particularly Na+ ions, penetrating the glass electrode silicon‐oxygen molecular structure and creating a potential difference between the outer and inner surfaces of the electrode. H+ ions are replaced with Na+ ions, decreasing the H+ ion activity, thereby artificially suppressing the true pH value. This is the reason pH is sometimes referred to as a measure of the H+ ion activity and not H+ ion concentration.

Na+ ion interference occurs when the H+ ion concentration is very low and the Na+ ion concentration is very high. Temperature also directly affects this error. As the temperature of the process increases, so does the Na+ ion error.
Depending on the exact glass formulation, Na+ ion interference may take effect at a higher or lower pH. There is no glass formulation currently available that has zero Na+ ion error. Since some error will always exist, it is important that the error be consistent and repeatable. With many glass formulations, this is not possible since the electrode becomes sensitized to the environment it was exposed to prior to experiencing high pH levels. For example, the exact point at which the Na+ ion error of an electrode occurs may be 11.50 pH, after immersion in tap water, but 12.50 pH after immersion in an alkaline solution.

Controlled molecular etching of special glass formulations can keep Na+ error consistent and repeatable.

This is accomplished by stripping away one molecular layer at a time. This special characteristic provides a consistent amount of lithium ions available for exchange with the hydrogen ions to produce a similar millivolt potential for a similar condition.

If your titration standards are not reading the correct concentrations, for example, the alkalinity standard reading is low, first make sure the titrant has been standardized. Secondly, the precision of the results can indicate if this is a mechanical or chemical problem. If the results are precise, it is likely a chemical issue. Check your standards and titrant standardization. It is also possible that the sample volume may be incorrect.

Most MANTECH electrodes are connected to the Interface module via a BNC cable with a detachable S7 connection. This S7 connection is located at the electrode cable junction, allowing for easy detachment from the cable, and removal of the electrode while leaving the cable in place. This applies to all electrodes except the Ammonia Electrode and all Conductivity electrodes. See below for pictures of a pH electrode with the S7 connection attached, and detached.

The reason you may have negative conductivity values at the low end is that there is a PC-Titrate software calibration being applied on the raw conductivity values from the meter. They are not wrong and it means the value is zero (0). You see this often with DI water measurements. If you turned off the software calibration then you would get the exact same values as displayed on the conductivity meter.

Mantech Burettes have a static IP address assigned to them. These addresses can be changed if there are communication issues between the Burette and the software.
If an IP address needs to be changed, then you can manually change it using the following steps:
1. Open the Network and Sharing Centre on your computer through the advanced network settings, or through searching on the Control Panel.
2. Open Command Prompt on your computer by searching it in your Windows Search Engine.
3. Extract this folder to your computer.
4. Plug in the burette. In the Network and Sharing Centre, find the active network for the burette (ethernet connection) and open the properties by selecting the blue “Ethernet”. Open the properties.
5.Internet Protocol Version 6 should be unselected, and Internet Version 4 should be selected. Click OK and open the Details for the ethernet status. The Value for IPv4 Address should be 192.168.1.1. If not, change the IP address in the Internet Protocol Version 4 properties.
6. In Command Prompt, type in ping and the IP address found on the back of the burette and then the enter key. For example, “ping 192.168.1.50” without the quotations and the enter key. The burette should reply.

7. Open the Burette IP Change folder now on your computer and open the application that is in the bin subfolder.
8. Type in the IP address and “Connect”. Click OK. Then type in the new IP address and select “Set IP”.
9. In Command Prompt again, ping the new IP address to ensure it works.

Specific notes:
If the IP address is not known, then in command prompt, type in “arp -a” without the quotes and the IP address for the burette will be given as the first line under the IPv4 Address Value. This can be done after Step 5.

If using PC-titrate, ensure that the version used is 889 or later. Previous versions do not support the ethernet Burettes without an upgrade. Contact support@mantech-inc.com for the ethernet burette software upgrade.
If using Mantech Pro, you can find the IP address of the burette (if it is not the one already in the address line) in hardware configuration using the “Configure Adapter”. The software will find the IP address that works for that burette and can be used to test the ping as well for burette response.

Calibrations can be linear, logarithmic, single-line, and multi-line fit.

The calibration method used depends on the method required.
pH and Color calibrations are linear, single-line fit calibrations.

Conductivity and Turbidity calibrations are multi-line, linear type calibrations.

ISE (Fluoride, Chloride, Ammonia, etc.) use a logarithmic multi-line calibration type.

For water soluble contaminants, rinse probe in deionized (DI) water. If ineffective, soak probe in warm DI water with household detergent for 15 – 30 minutes.
For oil-based contaminants, rinse probe in ethanol or acetone for short (5-minute) periods.
After cleaning, rinse probe in DI water to remove residual cleaning reagents. Perform a meter calibration before proceeding with sample analysis.

MANTECH recommends the use of turbidity standards made with suspensions of microspheres of styrene-divinylbenzene copolymer for all turbidity applications. Standard Methods dictate that “Secondary standards made with suspensions of microspheres of styrene-divinylbenzene copolymer typically are as stable as concentrated formazin and are much more stable than diluted formazin.

For optimal performance the flow cell should be cleaned from once a year to once a month, depending on the type of samples being analysed. Manually pump 50 ml of 0.1 N Hydrochloric Acid into the color module and leave the cell to soak overnight. In the morning, pump 100 ml of deionized water through the module to rinse the cell. This process can be automated to occur after every rack of samples run.

MANTECH recommends storing pH and other electrodes immersed in a 1:10 dilution of pH 4 buffer in Tap Water. Conductivity electrodes can be stored in air for system configurations that do not place it on the same holder as another electrode.

For MANTECH’s ion-selective electrodes, MANTECH recommends each ion should be stored in a dilute solution of the ion that it measures. For example, store your chloride electrode in a solution of 1.0 x 10-2 M chloride solution.

To safely store or ship your MANTECH pH electrode, first fill the electrode with fill solution and fill the storage boot ¾ full with fill solution. Then, insert the probe into the boot and screw tight. Place the fill solution plug in its hole and parafilm over the plug, as well as around the body. Then, parafilm over the cable connection spot, making sure not to overlap with the parafilm around the plug.