astkCARE™: anionic surfactant detection
astkCARE app and reading kit FAQ
How to use the astkCARE™ reading kit and smartphone app
CRC CARE has developed a smartphone app and portable reading kit that allows quick, accurate analysis of highly toxic surfactants, including PFAS, in the lab or field.
1. Test, targets and limit
Can we use this testing kit for soil analysis?
Yes. However, you should keep in mind that this kit is developed for water tests, including surface water and ground water. Therefore, the protocol should be modified for soil analysis. You are welcome to contact CRC CARE for more details.
Do we need to follow a different protocol for surface water and ground water analysis?
No. However, ground water may exhibit a background concentration, usually < 40 ppb, which depends on the ingredients in the ground water.
Is the test quantitative?
No. It is a semi-quantitative test. The variation usually is <10% for water sample testing in our lab trial but might be up to 50% at the low concentration range for field test, such as < 50 ppb. You might conduct quantitative analysis using UV-vis spectrometer at 595 nm after this pre-screening test, or HPLC (recommended).
What is the meaning of the output of ppb?
It means the total amount of anionic surfactants in your water sample, parts per billion. Furthermore, the calibration has been established on the aqueous concentration of PFOA so that all of the surfactants have been converted and corrected as PFOA.
Is the test specific, any interference?
No, not specific and Yes, with interference. In principle, it is designed for an anionic surfactant test in water. If it can be combined with the dye to form an aqua-immiscible ion-pair, it will impact the extraction and interfere with the test. For a specific test, you might contact CRC CARE for a special protocol or HPLC-MS is recommended.
How about inorganic ion, such as Cl–, does it interfere with the test?
Yes. If the concentration is high, the interference might occur. For example, the concentration of chloride (Cl–) might be >100 ppm whilst that of PFOA might be < 100 ppb. That is, there is >1000 times difference on their concentrations so that the chloride might shield the extraction of PFOA.
Are there any approaches possible to remove interference?
Yes. Sample-preparation will remove almost all interferences, such as the dual-extraction designed by us. You can follow the protocol developed by us and demonstrated on the help module, “Sample Preparation” video. Otherwise, solid-phase-extraction (SPE) is recommended as an alternative, which demands ~3 hours more to proceed. Please contact CRCCARE for more information if required.
What measures should I take during the dual-extraction?
Dual-extraction is designed to get an accurate analysis result. You must be very careful to transfer ONLY the top layer from the first plastic vial to the second one for the second extraction. Please have a look at the help video of “Sample Preparation” and the user guide
How about the detection limit?
10 ppb is the lower limit for a water sample. 10-500 ppb can be detected directly. A higher concentration can be diluted into this range. Low concentration sample(s) can be pre-concentrated, such as by SPE.
How about the detection limit if pre-concentration is employed such as SPE?
0.5-1 ppb can reached in this case, for water sample(s).
Do I need to calibrate my app every time?
No. you can directly test if you have calibrated it before. However, we recommend you conduct a calibration regularly, such as weekly or monthly. As a newly-installed app in your smartphone, you must calibrate it before testing. When your sample is changed (such as from site to site) and your battery is changed in the reading kit, we also recommend you to calibrate your app.
Which calibration option should I use, one-point or three-point?
For normal test, one-point calibration is enough and the reagents (A&B) are provided, although the reading variation might be big. For a more accurate measurement (to remove variation originating from the sample background and the reading kit illumination), three-point calibration is recommended if the standard solutions are available.
How do I calibrate my app?
We provide reagents A&B for calibration so that you can follow the app’s procedure to calibrate the app (one-point calibration). Note you should NOT shake the mixture for >10 seconds otherwise an emulsion will appear. You can intentionally and heavily stamp your sample(s) to accelerate the appearance of two-layer structure.
Can I conduct the app test on the second day after sample preparation?
Yes, but we recommend you analyse it within 30 min (the period when the calibration curve is established). Because of the kinetics of extraction, you might think about using a similar period (time gap) from the sample-preparation to the testing. For example, if you conduct calibration around 30 min after the sample preparation, analysis of your sample at around 30 min after preparation will provide a better reading. Similarly, if you conduct the app test on the second day after the sample preparation, you should re-calibrate your app on the second day using a blank sample you prepared in parallel with your sample(s) to be analysed before the day.
Why does the shaking time be 10 seconds for blank sample whilst 60 seconds for analysing sample?
Blank sample means no reaction with the dye so that a longer / vigorously shaking (>10 second) will lead to appearance of emulsion, rather than a two-layer structure. For sample analysing, however, the reaction between anionic surfactant and dye takes time, the extraction also needs time. Together, we recommend 60 second for that.
Why do we need a set of reagents, A, B, C, D?
Basically, what we need is reagents C&D for dual-extraction. Reagents A&B are for calibration. You can also use reagents C&D for calibration, as mentioned in the help module, “Sample Preparation” video.
Why is the number of reagents C&D much higher than that of Reagents A&B?
In principle, you can conduct a calibration (using reagents A&B) once for hundreds of tests (using reagents C&D). You can also use reagents C&D for calibration when reagents A&B are not available.
Is the reagent toxic?
Yes. Acetone and ethyl acetate are present so all testing liquid must be recycled for proper disposal.
Do the reagents expire?
Maybe. If you store them in a cool location (not refrigerated) and minimise exposure to light, one year should not be any problem.
Does the Milli Q / DI water water expire?
Maybe. If you take measures to protect it, half a year should be OK. You can source more from any analytical lab or CRC CARE.
How can I break the ampoule tip to pour out the reagent?
Usually you can break it easily using your hand after you mark/scratch the bottle neck with a triangle file or rasp or glass cutter (please have a look on the help video). As an alternative method (and to protect your hand), you might use your pen/mobile to beat it, akin to a nurse for an injection.
Does the glass need to be recycled?
Yes. Glass must be disposed of properly after recycling.
Is a reading kit necessary for the test?
No. However, your results might yield significant variations when you directly read the colour with the provided colour chart as a reference, using your eyes. You must consider that the background light will vary, such as on a sunny, cloudy or rainy day, outdoor or indoor use, etc., which may influence your analysis results. Furthermore, your eye may vary in its assessment as you get tired and is also not as sensitive as a smartphone camera for the colour reading.
Is an app necessary for the test?
No. This is answered in question above.
Why is the GPS not working?
Ensure you have activated the GPS on your smartphone. Another reason may be that the GPS is not available at the testing position. Similarly, on-line help might be not available due to the off-line.
Why can’t I install the app on my smartphone?
Some restrictions on your smartphone security may be preventing installation and may need to be removed / reset.
Do I need to change the battery in the reading kit?
The circuit is designed to keep the illumination constant. However, you might need to change the battery regularly. The app includes a reminder message to change the battery when the voltage drops.
Can I conduct analysis in field?
Yes. The reading kit is designed for field testing. You can bring the reading kit with you and find a flat/horizontal position to put your reading kit for the test.
What position in the sample should the reading be taken from, for the reading kit test?
The top layer of the prepared sample should be horizontally aligned with your smartphone camera. From the app, the top layer should be at the central part of your smartphone screen at the “record new sample” or “calibration” modules.
Do different smartphones yield different results?
Maybe. However the calibration is recommended prior to your test and this should remove the variation arising from the smartphone.
Can I use my own vial for test, rather than your provided vial?
Yes. However, you must consider several requirements. First of all, the vial or container must be chemically clean. Secondly, a plastic vial is better than glass, particularly for a low concentration test (<100 ppb). Thirdly, it should resist the organic solvents, such as acetone and ethyl acetate. Fourthly, the vial should be colourless and transparent. Fifth, the vial should have the same size (particular the diameter) with ours.
Can I reuse the provided plastic vials?
Yes. However, the precondition is that you know how to clean it. If so, you can clean and reuse it.
Can I reuse the syringe / dropper?
Yes but it depends. You should be careful to avoid contamination, particularly for the Milli Q water. You should also wash your syringe whether you have used it to take sample(s) or Milli Q water.
How can I get help?
From the app, you can find help videos and a link to contact us.
Any other suggestions?
- For accurate readings, clean the plastic vial surface with the cotton provided and handle the vial on the lid to avoid touching the colour-reading area.
- Similarly, when you open the ampoule, after marking/scratching the neck, clean any possible dust using the cotton again prior to opening it / pouring reagent.
- Be careful of sharp glass edges when opening the reagent bottles.