Pei She Loh and Volker Patzel, Department of Microbiology & Immunology, National University of Singapore, Singapore
– Photopette® Aqua enables fast and accurate measurements of Ammonia, Nitrate, Nitrite and Phosphate
– Water samples can be directly measured on-site to prevent changes in critical analyte concentrations during transport
This application note gives the reader a quick start to use Photopette® Aqua for on-site measurements of multiple water quality parameters.
In collaboration with Merck Millipore the Photopette Aqua system was developed by Tip Biosystems for water testing. It consists of the Photopette® Aqua device and Spectroquant® test kits. Photopette® Aqua is a novel handheld device with inbuilt calibrations for multiple water quality parameters such as ammonia, nitrate, nitrite and phosphate.
Water – its availability and quality impact the lives of every living species on the planet. Water is used for drinking, cooking, washing, manufacturing, irrigation and literally for almost every activity performed by humans. Without it, human live will end. There are two fundamental aspects of water, its availability & sustainable supply, and its safety & quality. Both aspects must be fulfilled to make water usable for various purposes.
This application note is directed to water quality measurements using the novel handheld device Photopette Aqua shown in Figure 1.
– Photopette® Aqua with 525 nm, 550 nm, 680 nm
All reagents are from Merck Millipore and can be purchased from the webpage at reference :
– Ammonium Test (114752)
– Nitrate Test (114773)
– Nitrite Test (114776)
Phosphate Test (100798)
To use Photopette Aqua and this application note, the user does not need to purchase the analyte standards. The calibrations are already inbuild into the Photopette Aqua software app. For completion we are listing the standards used for the calibrations provided in this note. All calibration were purchased from Merck Millipore:
– Ammonium 1.25027.0100
– Nitrate 1.32242.0100
– Nitrite 1.25041.0100
– Phosphate 1.19898.0500
Highlighted in this section are the steps to perform laboratory or in the field onside measurements of water parameters. Please refer to the “Photopette User Manual” for operating and safety precautions  and follow the video-tutorials on the Tip Biosystems webpage to get familiar with the measurement process.
Assays: For all measurements Spectroquant® test kits from Merck-Millipore are used as listed under the Materials section. Apart from the analytes: ammonium, nitrate, nitrite and phosphate which are pre-programmed into the Photopette App. The device is compatible with the following Spectroquant tests: Arsenic Test (1.01747), Cadmium Test (1.01745), Cyanuric Acid Test (1.19253), Lead Test (1.09717), Monochloramine Test (1.01632), Sulfate Test (1.02537), Aluminum Test (1.14825), Bromine Test (1.00605), Chromate Test (1.14758), Gold Test (1.14821) and Ozone Test (1.00607).
Measurements were performed as provided by the instructions of the Spectroquant kits. The test volume can be reduced to 1 mL to perform more measurements per kit. In addition to the samples a Blank was prepared for every analyte. For the Blank, deionized water was used instead of the water sample. After the sample incubation, absorbance measurements were performed with the Photopette Aqua device. Measurements are performed in parallel with a benchtop Shimadzu UV-1800 spectrophotometer for comparison.
Measurement: Turn on the Photopette® Aqua device and connect to the Photopette® iOS/Android app. Go to ‘Measurement Type‘ and select one of the 4 analytes from the list. Select dataset and set additional settings (if needed) before selecting ‘Start Measurement’. Place a CuveTipTM onto the device probe and dip into the Blank Sample to perform an Autozero measurement. Ensure there is no air bubble trapped in the CuveTipTM cavity. Presence of air bubbles can disrupt the optical path and can result in erratic values. Perform the sample measurements directly after Autozero.
Standard dilutions from ion standards purchased from Merck-Millipore were prepared and assays performed in accordance with kit instructions. Absorbance measurements were performed and the AU plotted as a function of the analyte concentration. The standard curves are presented in Figures 2 to 5 together with the standard curve plotted from data obtained with a benchtop spectrophotometer.
The slope of the curve (=sensitivity) and y-axis intersection were determined and used for the pre-programming of the calibrations into the Photopette App.
Photopette Aqua demonstrated a slightly higher sensitivity (slope of the curve) and a larger linear dynamic range compared to the benchtop instrument. The R2 value for Photopette was 0.99 and for the reference instrument only 0.973.
Photopette Aqua demonstrated a higher sensitivity of 0.021 AU/mg compared to the benchtop instrument with 0.179 AU/mg. For both instruments the linearity and R2 value are excellent.
Photopette Aqua demonstrated a higher sensitivity of 1.979 compared to the benchtop spectrophotometer of only 1.596. Photopette Aqua also demonstrated a higher R2 value and much better linearity.
Photopette Aqua demonstrated a higher sensitivity of 0.85 AU/mg compared to the benchtop spectrophotometer of only 0.0071 AU/mg. Photopette AQUA also demonstrated a higher R2 value and better linearity.
The dynamic range of the different analytes was tabulated in Table 1 below.
Limit of Detection
The Limit of Detection (LOD) for the 4 analytes was determined by factoring in the standard-deviation for blank measurements and the experimental data using the equation given below :
LOD = 3 x SDblank / SlopeStandard Curve.
The Standard Deviation (SD) for blank measurements (50 repeats) was found to be 0.006 AU.
The limit of detection for ammonium measurement is:
LOD = 3 x 0.006 AU / 0.793 L AU/mg = 0.023 mg/L
The limit of detection for nitrate measurement is:
LOD = 3 x 0.005 AU / 0.0198 L AU/mg
= 0.9 mg/L
The limit of detection for nitrite measurement is:
LOD = 3 x 0.006 AU / 1.99 L AU/mg = 0.009 mg/L
The limit of detection for phosphate measurement is:
LOD = 3 x 0.006 AU / 0.0087 L AU/mg = 2.1 mg/L
Upper measurement-limit and Linear Range
Measurements with the Photopette Aqua device resulted in very good linear relationship with high sensitivity for all analytes with very high R2 value of 0.99.
|Nitrate||1 – 110 mg/l NO3–||Nitrate Test (114773)|
|Nitrite||0.01 – 1.5 mg/L NO2–||Nitrite Test (114776)|
|Ammonium||0.01 – 0.8 mg/L NH4+||Ammonium Test (114752)|
|Phosphate||3 – 300 mg/L PO43-||Phosphate Test (100798)|
|0.01 – 9.00 mg/l Cl2||Chlorine Test (100598)|
Table 1: Merck-Millipore Spectroquant® test kits used for factory calibration of the Photopette Aqua and measurement range as ion concentration in mg/L (The reagent name has an embedded link to the webpage of the reagents manufacturer).
The Photopette® Aqua performed very well in comparison to a benchtop spectrophotometer and in many cases exceeded the performance of the benchtop device.
This high performance and large dynamic range are attributed to Tip Biosystems proprietary algorithms to determine absorbance values from several measurements within a short time period together with its environmental light correction.
The Photopette® Aqua features make it ideal for water testing in the lab, but also in the field, waterproof, dustproof, very durable, long-lasting battery, and unlimited data logging. Intuitive and easy to use software allow anyone with minimum training to use it. It comes with five inbuiltcalibrations for Merck-Millipore Spectroquant® water test kits and can measure a total of 18 analytes from the Spectroquant® family.
The Photopette® App allows data storage and instant data transfer to cloud storage, e-mail and various apps on your mobile device. Photopette® data can be analyzed by existing software such as Microsoft Excel®. Photopette® is an attractive addition to the modern laboratory that improves productivity and enables non-trained personal to perform quality measurements.
The details of the technical specifications can be found on the Tip Biosystems webpage at this link:
Merck-Milipore link for prchases of the reagents https://www.merckmillipore.com
“Photopette User Manual V1.0.3,” Tip Biosystems Pte Ltd, Singapore, 2016.
Using 3 x SD will result in a confidence of 99.86%.
Photopette and CuveTip are registered trademarks of Tip Biosystems Pte Ltd, Singapore. Excel® is a registered trademark of the Microsoft Corp. Spectroquant® is a registered trademark of Merck Millipore.
Conflict of Interest Statement
Volker Patzel is shareholder of Tip Biosystems. This shareholding did not affect the results, interpretations and conclusions.
The views and opinions expressed herein are those of the authors and do not represent the views and opinions of the National University of Singapore or any of its subsidiaries or affiliates.