For the colorimetric dye, we selected several pH indicator as bromophenolblue (BPB), boromocresol green (BCG), m-cresol purple (MCP), chlorophenol red (CPR), hydroquinone, benzoquinone and CaCl₂ were purchased from Sigma-Aldrich Co. Ltd. (St. Louis, MO, USA). Sodium alginate (SA) was purchased from Yakuri Pure Chem. Co. (Kyoto, Japan) (Figure 1 and Figure 2) [3].

All reagents were used without any other purification. 8 kinds of toxic gase s(HCl, Cl₂, CH₃NH₂, NO₂, HF, NH₃, (CH₃) ₃N, SO₂) were obtained from MG Tech. Co. (Hwasung, Korea).

The pH indicating and water soluble dyes p indicatingdyes were mixed with hydrophilic binder(Sodium Alginate, SA) to 0.1 wt% of dye in 1 w% of SA aqueous solution with or without benzoquinone (0.5 wt%), then this solution was coated on the nonwoven fabric sheet and cured with calcium chloride solution (10 wt%) (Figure 3). After curing, coating layer on nonwoven sheet showed improvement of water repellency.

The coated nonwoven fabric sheet was dried under room temperature and exposed to the vaporized toxic gas for the confirmation of time dependent color change in these coating layers using following MFC apparatus (Model 247C, MG Tech Co., Hwasung, Korea) (Figure 4). The color changing behaviors were recorded by digital camera. These behaviors of manufactured colorimetric sensors were also confirmed by portable spectrophotometer (CM-2600d, Konica-Minolta, Tokyo, Japan) through the pre-Determined time schedule using CIELAB color space system.

Figure 5 showed the time-dependent color change behaviors of dye coated colorimetric sensor (film type) after

toxic gases exposure through mass flow controller equipped gas supplier (8 kinds of toxic gases). In very short time (within 10 seconds) after gas exposure, all of the film type colorimetric sensors were changed their own color as blue to yellow or its reverse.

The color changing behaviors of the film type colorimetric sensors (BPB dye coated) with (+/−) benzoquinone were shown in Figure 6. From the data of Figure 6(a), color changes owing to gas exposure (HCl, 10 ppm) was observed after 30 seconds from initial state.

But, for the (+) benzoquinone, color changes owing to same condition was observed after 10 seconds from initial state (Figure 6(b). By the addition of benzoquinone which accelerates the electron transfer between dye and toxic gas on the basis of oxidation-reduction reaction, [4]-[6] the fast color changing was observed.

This means that electron transfer reagents which were worked in biochemical reactions of the living cell func-

tion are also available in oxidation-reduction reaction of dyes in our system for colorimetric gas detection tool in working place.

In most of working places treating toxic gases, working condition was exposed to very humid and high temperature. So water soluble dye component contained in coating layer of film type colorimetric sensor can be extracted out from the coating layer when exposed to the wet environment. And it will be also existed with high possibility that the coating layer can be dissolved under the same condition. Therefore, the water resistivity of coating layer containing water soluble dyes is essential characteristics of this colorimetric sensor. Figure 7 showed such behavior of prepared colorimetric sensor which made of sodium alginate solution containing BPB dye on non-woven sheet.

From the results of non-crosslinked film in Figure 7, most parts of coating layer consisting sodium alginate and dye was disappeared after washing. In case of crosslinked film with calcium chloride, the opposite was observed. This means that crosslinking effect of sodium alginate with CaCl₂ was effective for the enhancement of water resistance of prepared film type colorimetric sensor. Considering of the pre-mentioned results, colorimetric sensors containing various dyes manufactured through in situ coating and crosslinking process using sodium alginate solution are very useful tool for the detection of toxic gases in working place with naked eye.

The International Commission on Illumination (CIE) first recommended the CIELAB color scale as a standard approximately, uniform color scale in 1976 [7], whereby colors are plotted in a cubic color space, as shown in Figure 8. The 4 dyes contained in the colorimetric film sensor is initially blue (or yellow) in color, and is converted to yellow(or blue) upon gas-contacting. The key parameters in color change are in a*, b* and L*, and ?Δ(a, b and L)* is defined: −Δa(or b, L)* = a(or b, L)*_dark − a(or b, L)*_{sample, t} where the ‘dark’ sample was the initial state of film sensor, but before subsequent gas contacting and “sample,t” refers to the film some time, t, after gas contact [8] [9]. The total color changing results (ΔE*) were expressed as following equation and summarized in Table 1 and Figure 9.