"Bial’s Test, A Simple Method for Formaldehyde Detection"

Current high-fidelity formaldehyde detection in waterbased
samples requires chemical derivatization followed by ion
chromatography or liquid chromatography [1-3]. These methods
are labor intensive and require expensive instrumentation. Here,
we propose an additional method for detecting and quantifying
aqueous formaldehyde that is based on Bial’s test and simple
photometric equipment. Our approach also allows for a convenient
qualitative color test that is applicable to samples with high
formaldehyde concentrations. The foundation of our method was
developed by Bial in the form of a colorimetric test for identifying
pentose sugars in the urine of patients with pentosuria [4]. Bial’s
solution consist of orcinol, hydrochloric acid, and iron (III) chloride
[4]. The concentrations of the components vary from study to study
and some authors have substituted hydrochloric acid with ethanol
[5] When heated with pentose sugars, Bial’s solution reacts to form
furfurals and changes color from a light pale yellow to blue or green
[6].


Introduction
Current high-fidelity formaldehyde detection in waterbased samples requires chemical derivatization followed by ion chromatography or liquid chromatography [1][2][3]. These methods are labor intensive and require expensive instrumentation. Here, we propose an additional method for detecting and quantifying aqueous formaldehyde that is based on Bial's test and simple photometric equipment. Our approach also allows for a convenient qualitative color test that is applicable to samples with high formaldehyde concentrations. The foundation of our method was developed by Bial in the form of a colorimetric test for identifying pentose sugars in the urine of patients with pentosuria [4]. Bial's solution consist of orcinol, hydrochloric acid, and iron (III) chloride [4]. The concentrations of the components vary from study to study and some authors have substituted hydrochloric acid with ethanol [5] When heated with pentose sugars, Bial's solution reacts to form furfurals and changes color from a light pale yellow to blue or green [6].
When heated with hexose sugars, Bial's solution reacts to form hydroxymethylfurfurals and turns from a light-yellow color to a gray or brown color [6]. A quantitative version of Bial's test using spectrophotometry has been developed for simultaneous determination of both hexoses and pentoses [7]. Moreover, Sumner noted that the addition of a few drops of formaldehyde into Bial's solution turned color from a pale yellow to dark yellow [5], however, no quantitative method for detecting formaldehyde in this fashion has been reported. Simple methods exist for detecting formaldehyde in solution using different phenols or chromotropic acid, photometrically or colorimetrically [8][9][10][11]. These methods do not yield an observable precipitate at higher concentrations; moreover, many of them are less sensitive; additionally, the older colorimetric methods are primarily qualitative [8][9][10][11]. Our method is the first to utilize orcinol to detect formaldehyde in a quantitative fashion. For higher concentrations, our test serves as a colorimetric method, the color change and noticeable precipitant formed during heating allow for quick simple detection by non-specialists. For milli molar and sub milli molar concentration uv/visible spectroscopy can be used to generate a simple calibration curve quickly and with precision.

Methods and Materials
We prepared Bial's solution using 0.4 g of orcinol (Spectrum), 0.5 mL of 0.37 M FeCl 3 (Fisher Scientific), and 200 mL of 0.5 M HCl (Fisher Scientific). Due to orcinol sometimes degrading in storage we validated the purity of the orcinol using proton NMR and found it to be uncontaminated. We aliquoted ACS certified, reagent grade formaldehyde (Macron, 12 M) and serially dilute to produce a set of samples with concentrations ranging from 3.6 mM to 0.6 μM.
We mixed 1 mL of these samples with 1 mL of Bial's solution in

Results and Discussion
When heated the solution turns various shades of yellow based on the concentration of formaldehyde (Figure 1a). Representative absorption spectra are shown in Figure 2a and    Accordingly, it should be possible to deconvolute the different contributions using chemometric methods. We also note that the addition of NaOH to our processed formaldehyde solutions causes an extremely bright photoluminescence that could allow the development of analytical methods with even lower LODs using emission fluorescence spectroscopy.

Conclusion
We have described and validated a simple analytical method for the detection of formaldehyde. Firstly, a qualitative test based on a visible precipitate that allows for the quick determination of formaldehyde levels exceeding about 1 mM. Secondly, a quantitative method for concentrations in the range of 0.03 mM (0.9 ppm) to 1 mM requiring only absorption measurements of visible, violet light. This method maybe used quickly and simply compared to most to detect formaldehyde contamination in medical, industrial, or food sources. It can also be used to verify formaldehyde concentrations quickly and affordably for formaldehyde-based chemistries that use high concentrations of formaldehyde such as the formose reaction.

Conflict of Interest
The authors declare no competing financial interest.