One of the most common reasons for Turbidity QCs failing is due to DI water that is not degassed being used for blanks and standards preparation.
Any dilutions used to prepare turbidity standards, as well as blanks, must use degassed DI water. This is especially important for accurate low-end turbidity analysis, as there is often a positive bias due to bubbles introduced into the DI water solution when it is being produced/dispensed. This effect becomes more noticeable with lower NTU readings, and can cause challenges with performing an accurate calibration. To degas DI water, it must be dispensed into a very clean bottle or container, and left to sit for ~24h. You will see bubbles form on the side of the container as the water degasses. After degassing, it is ready to use for blanks and standards preparation.
When your turbidity QCs are failing, it is best to do the following:
- Ensure you are using Degassed DI water
- If you do not have this, prepare by leaving DI water to sit for 24h in a very clean bottle or container
- Repeat the QCs with a freshly-prepared standard
- If still failing, perform a new multi-point calibration, followed by x3 blanks then the same QC standards, all with fresh solutions
- If still failing the above, remove the flow cell and clean it, and also perform a new meter calibration with the set of sealed cuvette standards
- Then, reinstall the flow cell and perform a new free calibration, then a new multi-point calibration, followed by x3 blanks then the same QC standards, all with fresh solutions
Any dilutions used to prepare turbidity standards, as well as blanks, must use degassed DI water. This is especially important for accurate low-end turbidity analysis, as there is often a positive bias due to bubbles introduced into the DI water solution when it is being produced/dispensed. This effect becomes more noticeable with lower NTU readings, and can cause challenges with performing an accurate calibration. To degas DI water, it must be dispensed into a very clean bottle or container, and left to sit for ~24h. You will see bubbles form on the side of the container as the water degasses. After degassing, it is ready to use for blanks and standards preparation.
The MANTECH turbidity flow cell has specific optical properties which are different than the cuvettes which you would manually insert (for example the sealed standards for the 3-month calibration). The difference in optical properties between the flow cell cylinder and the cuvette can cause the relationship between actual NTU and expected NTU to be slightly non-linear. This is only applicable in the low end of the measuring range, typically < 1 NTU. To ensure the lowest detection limit possible, we use multi-line to accurately capture how the optical properties of the flow cell are different than the cuvettes.
MANTECH Turbidity Standards have a one year shelf life from the date they are put in stock. The Expiry Date is always shown along with the lot number on the bottle labels.
Total suspended solids (TSS) is an analysis method that requires filter, wet weighing, drying in an oven for a few hours, then dry weighing. This is typically not performed by treatment plants and even for labs it is time consuming.
Turbidity is a surrogate measure for TSS that allows rapid automated analysis of batches of samples. A log-linear model shows strong positive correlation between TSS and turbidity (R2=0.9374) with a regression equation of [ln (TSS)=0.979 ln (Turb.) +0.574]. This model can be applied directly to turbidity analysis results to determine the TSS. MANTECH offers the MT30 analyzer for quick and easy “hands off” TSS analysis, only requiring 40mL of sample volume in batches up to hundreds of samples.
An example scatterplot showing a Turbidity:TSS correlation is provided below:
True or Filtered Color is determined by filtering samples through a 0.45 micron filter before analyzing the sample in a spectrophotometer. When running large amounts of samples on automated systems, this filtering can become time consuming and heavy on resource usage. An alternative method (Bennett and Drikas 1993) for determining true color without filtering has been established, through the use of a turbidity meter to quantify the contribution from solids present in the sample. MANTECH can easily combine automated Turbidity and Color analysis on one system, determined from one sample, to provide True Color results without the need to filter.
The determination is as follows:
C – Color result (Cu)
A – sample absorbance (Abs)
l – cell path length (cm)
E – scattering coefficient estimated at 0.00264 NTU-1 cm-1
t – turbidity (NTU)
ϵ – color absorptivity coefficient determined through calibration (Cu-1 cm-1)
Turbidity is defined as the amount of suspended particles in a solution, measured in nephelometric turbidity units (NTU). It is used as a general indicator of the quality of water, along with colour and odour. The US EPA has a maximum contaminant level (MCL) of 5 NTU for drinking and wastewaters. Read MANTECH’s turbidity method abstract here.
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.”
Any dilutions used to prepare turbidity standards, as well as blanks, must use degassed DI water. This is especially important for accurate low-end turbidity analysis, as there is often a positive bias due to bubbles introduced into the DI water solution when it is being produced/dispensed. This effect becomes more noticeable with lower NTU readings, and can cause challenges with performing an accurate calibration. To degas DI water, it must be dispensed into a very clean bottle or container, and left to sit for ~24h. You will see bubbles form on the side of the container as the water degasses. After degassing, it is ready to use for blanks and standards preparation.
Standard Method 2130B (Nephelometric Method) specifies that a laboratory or process nephelometer should have a detector system with a spectral peak response of 400 to 600 nm. MANTECH’s T10 Turbidity meter and automated turbidity applications conform to this requirement.
The timing for analysis of different parameters depends on a few different factors, like the concentration of the sample and the equipment used.
Another factor is the total available sample volume in the vessel on the AutoMax Autosampler bed. With some combinations of parameters, larger sample volume allows for simultaneous measurements, resulting in faster total analysis time than sequential measurement. A larger sample volume may require a larger sample cup, which decreases capacity on the same model Autosampler. In some, the cases the same set of parameters can be analyzed in 2-5 minutes faster when using the 125ml cups vs 50ml tubes.
It is important to understand your customers’ requirements in terms of capacity and throughput speed, total batch capacity required and/or daily sample loads and if overnight, unattended analyses will be applicable.
*** Note that all times of analysis are halved if Dual-Analysis option is included with system***
Individual Parameters
Combined Parameters
MT-10 & MT-30 Models
MT-100 Model
* Alkalinity titrations may take between 1-3 minutes depending on sample concentration. Times estimated assuming 50ppm alkalinity concentration.
EC = Electrical Conductivity
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.
The timing for analysis of different parameters depends on several different factors, like the concentration of the sample and the equipment used.
Another factor is the total available sample volume in the vessel on the AutoMax Autosampler bed. With some combinations of parameters, larger sample volume allows for simultaneous measurements, resulting in faster total analysis time than sequential measurement. A larger sample volume may require a larger sample cup, which decreases capacity on the same model Autosampler. For example, an AM73 can accommodate 73x50ml tubes, or 30x125ml cups. In some, the cases the same set of parameters can be analyzed in 2-5 minutes faster when using the 125ml cups vs 50ml tubes.
It is important to understand your requirements in terms of capacity and throughput speed, total batch capacity required and/or daily sample loads and if overnight, unattended analyses will be applicable.
Individual Parameters
Combined Parameters
MT-10 & MT-30 Models
* If alkalinity is combined with turbidity and/or colour an MT-100 System must be quoted
MT-100 Model
