“Although the majority of scientific workers utilize photography for illustrative purposes, a survey of the literature shows that only a limited number fully appreciate its usefulness as a means for recording data.”
So wrote GE Matthew and JI Crabtree in a 1927 article of Journal of Chemical Education. Photography has come on since then, when they cautioned readers on the properties and limitations of photographic emulsion for quantitative purposes. Now it is much simpler, and there are many applications of photography using a mobile phone camera and a suitable app. I’ve summarised five of these below.
1. Colorimetric Analysis
This is a paper I have written about before. It essentially allows a Beer-Lambert plot to be performed from a mobile phone picture of a series of solutions of different concentrations of a coloured dye. The practical is extended to Lucozade. The original paper suggests the use of PC imaging software, but good results can be obtained with a mobile phone RGB colour determination app such as RGB Camera. Some more detail on that process is in the earlier blog post.
2. Colorimetry for chemical kinetics
This recently published paper extends the idea outlined above and uses colorimetry for kinetic analysis. The experiment is the hydrolysis of crystal violet with hydroxide ions. A similar set up to that described above, except the camera is set to acquire images every 10 s automatically. The authors describe the analysis protocol well, and suggest a mechanism for reducing data analysis time. The app mentioned here (for Android) is Camera FV-5 Lite. The supplementary information has detailed student instructions for image analysis. A very clever idea.
3. A variation on flame photometry for testing for sodium in sea water and coconut water
This is a really excellent idea where the flame test is monitored by recording a video on the mobile phone. Stock saline solutions from between 20 to 160 mg/dm3 were prepared and used to build a calibration curve. The flame colour was recorded on video. To do this, the phone was fixed approximately 40 cm from the flame, with a white background 40 cm in the opposite direction. Distilled water was sprayed into the flame to record the blank, followed by the calibration solutions and the analytes (sea water and coconut water). The videos were replayed to find the point at which the light was most intense. Again, the authors go into quite complex PC imaging analysis; a simpler option would be to pause the video at the point of greatest intensity and take a phone screenshot for analysis. RGB data can be obtained, subtracting the baseline (distilled water). I want to do this one!!
4. Determining amino-acid content in tea leaf extract – using microfluidic analysis
Students prepare a microfluidic device using a wax pen on fliter paper. A 2% ninhydrin solution is prepared (full details in paper) and this is used as the sensor on the filter paper. Tea is boiled and extracted and small drops added to the microfluid wells. After a picture is taken, the RGB data allow for analysis of the glutamic acid present. Again the authors suggest desktop software, but there is no reason why an app can’t be used. The set-up involves ninhydrin and tin (II) chloride, so is probably best for university students.
The microfluidic device is interesting though for students at all levels. Essentially any pattern can be drawn on filter paper with a wax pen. The paper is heated to 135 °C for 30 seconds, and the wax melts through the paper, creating hydrophobic walls. The main author also has a just published RSC Advances paper where the microfluidic devices are prepared using an inkjet printer, and used as a glucose assay, so this is right on the cutting edge.
5. More microfluidics: analysis of Cu2+ and Fe2+ using colorimetry
Another paper on microfluidics, but this one more applicable for the school classroom. Microfluidic arrays are prepared by cutting designs into Parafilm sheets and enclosing them between paper, and then aluminium foil, before passing through a laminator. Analysis as before is by RGB determination of the spots formed, again the paper’s SI gives a good overview of the analysis protocol for students.