Portable Sick House Syndrome Gas Monitoring System Based on

It was possible to monitor the HCHO gas in the room of a new apartment and school ... The establishment of the standard of 0.08 ppm HCHO in air by the...
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Environ. Sci. Technol. 2003, 37, 5695-5700

Portable Sick House Syndrome Gas Monitoring System Based on Novel Colorimetric Reagents for the Highly Selective and Sensitive Detection of Formaldehyde Y O S H I O S U Z U K I , †,‡ N O B U O N A K A N O , § A N D K O J I S U Z U K I * ,†,‡,| Collaboration of Regional Entities for the Advancement of Technological Excellence (CREATE), Kanagawa Academy of Science and Technology, 3-2-1 Sakato, Takatsu-ku, Kawasaki, Kanagawa 213-0012, Japan, Cooperation for Innovative Technology and Advanced Research in Evolutional Area (CITY AREA), Kanagawa Academy of Science and Technology, 3-2-1 Sakato, Takatsu-ku, Kawasaki, Kanagawa 213-0012, Japan, Department of Applied Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan, and Riken Keiki Company, Limited, 2-7-6, Azusawa, Itabashi-ku, Tokyo 174-8477, Japan

Formaldehyde (HCHO) emitted from the furniture and the walls in the rooms injures the eyes, nose, and respiratory organs and causes allergies, which is called sick house syndrome. We designed and synthesized novel colorimetric HCHO-sensing molecules (KD-XA01 and KD-XA02) which possess an enaminone structure and developed a handheld instrument to monitor indoor HCHO gas with the use of KD-XA01. These sensing molecules produced speedy color changes from colorless to yellow under mild conditions, which was caused by the fact that the enaminone structure in the reagent reacts with HCHO to give a lutidine derivative. This reaction took place not only in the solution phase but also in the solid phase (surface of the cellulose paper). To take advantage of this phenomena, a handy and rapid monitoring system has been developed for detecting indoor HCHO gas using a highly sensitive and selective detection tablet constructed from the porous cellulose paper that contains silica gel as an adsorbent, KDXA01, and phosphoric acid under optimum conditions. This instrument detected the surface color change of the tablet from white to yellow, which was monitored as a function of the intensity of the reflected light illuminated by an LED (475 nm). The response was proportional to the HCHO concentration at a constant sampling time and flow rate; 0.05 ppm HCHO, which is under the standard value set by the World Health Organization, was able to be detected in 5 min. The detection limit was 0.005 ppm. This monitoring system was not interfered by carbonyl compounds such as acetaldehyde and acetone, alcohols, hydrocarbons, and typical gases such as carbon * Corresponding author phone: +81-45-566-1568; fax: +81-45564-5095; e-mail [email protected]. † CREATE, Kanagawa Academy of Science and Technology. ‡ CITY AREA, Kanagawa Academy of Science and Technology. § Riken Keiki Co., Ltd. | Keio University. 10.1021/es0305050 CCC: $25.00 Published on Web 11/12/2003

 2003 American Chemical Society

monoxide, carbon dioxide, nitrogen dioxide, etc., which contributes to the measurement of correct HCHO concentrations. It was possible to monitor the HCHO gas in the room of a new apartment and school using this instrument; the response values were in good agreement with those obtained by the standard DNPH method. This highly sensitive, selective, and handy HCHO gas monitor is widely applicable and convenient for users who are not specialists in this field.

Introduction Formaldehyde (HCHO) is often used in the workplace and comes from the adhesive used in the manufacture of resins, plastics, coatings, and fabrics (1). HCHO is a highly lachrymatory, odorous, and physiologically active substance and is classified as a typical toxic gas species in atmospheric and environmental chemistry. The World Health Organization has set a standard of 0.08 ppm averaged over 30 min, while the American Conference of Government Industrial Hygienists (ACGIH) has set a ceiling exposure value of 0.3 ppm. Low-level HCHO injures the eyes, nose, and respiratory organs and causes allergies, which is called sick house syndrome (2, 3). The establishment of the standard of 0.08 ppm HCHO in air by the World Health Organization has emphasized the need for a sensitive, reliable, and specific method for the detection of HCHO in environmental air. The following several methods are used to detect the HCHO concentration: (i) standard method of analysis (4), (ii) detector tube method (5), (iii) passive sampling and active sampling method (6), (iv) chemical luminescence (7), (v) electrochemical method (8). However, these methods have some disadvantages during the HCHO measurement: (i) expensive analytical instruments are needed, (ii) it takes a long time to obtain the results, (iii) the analytical reagent is toxic, and (iv) foreign substances (other carbonyl compounds, alcohol, ammonia) interfere with the correct HCHO measurement. Therefore, a highly sensitive, highly selective, easy, and widespread routine method is desired, especially to monitor for sick house syndrome gas. Absorption spectrometry is a traditional method, is used for the measurement of various chemical substances, makes it possible to carry out visual colorimetry, and allows easy measurements. There are several methods for the detection of HCHO based on absorption spectrometry such as DNPH (2,4-dinitrophenylhydrazine) (4), AHMT (4-amino-3-hydrazino-5-mercapto-1,2,4-triazole) (9), or the mixture of hydroxylamine with a pH indicator such as methyl orange or methyl yellow (10, 11). However, these methods have the following problems: multistep reactions, extreme reaction conditions (high temperature, long reaction time), low sensitivity, wet chemical procedures, inadequate for a continuous measurement, and interference by other carbonyl compounds, alcohol, and ammonia. Therefore, a novel colorimetric reagent is desired by the users. We considered several requirements when designing a novel colorimetric reagent: (i) speedy and mild reaction of a reagent with HCHO (one-step reaction, short reaction time, and reaction at room temperature), (ii) reduced interference from foreign substances, (iii) higher molar extinction coefficient, (iv) a color change from a colorless solution or white powder to the colored product, which may prevent background problems and guarantee a highly sensitive and selective detection of HCHO, (v) dry chemical procedure, which contributes to handling the instrument easily. VOL. 37, NO. 24, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 1. Chemical structures of colorimetric reagents (KD-XA01 and KD-XA02) and their transformation into lutidine derivatives after reaction with HCHO. For designing and synthesizing a reagent for the detection of HCHO based on the above requirements, we obtained two excellent colorimetric reagents, KD-XA01 and KD-XA02, as shown in Figure 1. These reagents possess an enaminone moiety as the part reactive toward HCHO. It is known that the enaminone moiety condenses with HCHO to produce a lutidine derivative under mild conditions (12-14). These reagents have an enaminone group connected to an aromatic ring, which gives the products high molar extinction coefficients and absorption bands in the long wavelength region. In addition, KD-XA01 and KD-XA02 produce colorless solutions, which prevent a background from the absorption band of the reagent and create a clear color change upon reaction with HCHO. As an application of these reagents, we describe a study to develop a monitoring tablet for the determination of HCHO gas in the range from 0 to 1.0 ppm with the use of a handheld instrument. A porous cellulose paper containing silica gel as an absorbent was impregnated with the processing solution containing KD-XA01, phosphoric acid, and methanol. The reflectance intensity from illumination by LED was detected. The experimental results clearly showed that the tablet containing KD-XA01 has excellent HCHO sensitivity and selectivity and can be used as an automatic monitor for the determination of indoor HCHO gas.

Experimental Section Reagents. All chemicals used were of analytical reagent grade purchased from TCI (Tokyo, Japan), Wako (Osaka, Japan), and Nacalaitesque (Kyoto, Japan). Synthesis of colorimetric reagents is as follows: KD-XA01 (4-Amino-4-phenylbut-3-en-2-one). To a solution of 1-phenyl-1,3-butanedione (3.24 g, 0.02 mol) in dry benzene (60.0 mL), ammonium acetate (3.08 g, 0.04 mol) and acetic acid (1.0 mL) were added. The mixture was then refluxed for 12 h under a N2 atmosphere. The reaction mixture was washed with water and dried over Na2SO4. The solvent was evaporated in vacuo, and the residue was purified by column chromatography (SiO2, CHCl3:AcOEt ) 4:1 v/v) to yield a white solid. Yield 78%. 1H NMR (300 MHz, CDCl3, r.t., TMS, δ/ppm) 2.0 (s, 3H), 5.7 (s, 1H), 7.5 (m, 5H), 10.1 (br s, 1H). ESI-TOFMS(+): 162 [M + H]+, 184 [M + Na]+ KD-XA02 (3-Amino-1,3-diphenylprop-2-en-1-one). To a solution of 1,3-diphenyl-1,3-propanedione (4.50 g, 0.02 mol) in dry benzene (60.0 mL), ammonium acetate (3.08 g, 0.04 mol) and acetic acid (1.0 mL) were added. The mixture was then refluxed for 12 h under a N2 atmosphere. The reaction mixture was washed with water and dried over Na2SO4. The solvent was evaporated in vacuo, and the residue was purified by column chromatography (SiO2, CHCl3:AcOEt ) 4:1 v/v) to yield a light yellow solid. 5696

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FIGURE 2. Schematic representation of the detection tablet. Yield 40%. 1H NMR (300 MHz, CDCl3, r.t., TMS, δ/ppm) 5.7 (s, 1H), 7.3-7.6 (m, 10H), 10.1 (br s, 1H). ESI-TOFMS(+): 224 [M + H]+, 246 [M + Na]+ The 1H NMR spectra were recorded on a JEOL JSM-GSX270 or a JEOL JNM-LA 300 instrument. The 1H chemical shifts are reported in ppm relative to tetramethylsilane as the internal reference. The mass spectra were run on an Applied Biosystems Mariner ESI-TOFMS instrument. The absorption spectra were recorded at 25 °C on a Hitachi U-2000 UV/ visible spectrophotometer and a Hitachi U-3000 UV/visible spectrophotometer. Absorption Spectrometry of KD-XA01 or KD-XA02 Before and After Reaction with HCHO. The probes and HCHO were dissolved in a solution of acetonitrile:phosphate buffer (pH 5.0) ) 2:1 v/v at a concentration of 20.0 µM of reagent and HCHO from 0.0 to 10.0 µM. Both solutions were mixed at a ratio of 1:1 and then stirred for 10 min. The absorption spectra of the reaction mixture was then observed. Preparation of the Filter Paper Containing KD-XA01 and Detection Tablet Used for the HCHO Gas Measurement. KD-XA01 was dissolved in MeOH:phosphate buffer ) 9:1 v/v at a concentration from 0 to 1.0 wt %. The cellulose filter paper was impregnated with this solution and dried under a nitrogen stream for 1 h and then in vacuo for 1 h. This filter paper was placed in the sampling bag (250 × 300 mm, 3 L, made of polyester film) and then exposed to HCHO gas. Figure 2 shows the detection tablet. KD-XA01 was dissolved at a concentration from 0 to 1.0 wt % in MeOH: phosphate buffer ) 9:1 v/v. The cellulose paper, containing silica gel as an adsorbent, was impregnated by immersion with this processing solution for 1 min and then dried in an oven for 1 min at 55 °C. This sensing paper was fixed in a plastic case and stored in an aluminum bag in vacuo. Sample HCHO Gas. The standard HCHO gas mixture was continuously generated by purging the diffusion tube containing paraformaldehyde (analytical reagent grade; TCI) with a constant flow of purified air. The gas concentration

FIGURE 3. Schematic representation of the HCHO monitoring instrument (A) and the optical location of the LED and photodiode to detect the reflected light from the tablet (B). was calculated from the flow rate and the mass loss of the paraformaldehyde. The diffusion tube in the gas generating system (PD-1B; Gastec) was kept at 30 ( 0.1 °C in a thermostatically controlled water bath. The large change in the concentration of the generated gas could be easily controlled by selecting the dimension of the diffusion tubes (18 mmφ, 35 mm). Humidified standard HCHO mixtures were prepared by passing dry air through a Gore-Tex (porous Teflon; 4 mm i.d., 6 mm o.d., and 50 mm in length) tube immersed in water (25 ( 2 °C) and then pumping air into the diffusion tube holder. The relative humidity of the standard gas mixture was determined by a humidity sensor (Visala, Helsinki, Finland; HM132). Apparatus for Monitoring of HCHO Gas. The experimental apparatus (15) is shown in Figure 3A. This apparatus was constructed using the detection tablet, detection component, gas flow component, and data analysis component. The sampling gas was aspirated onto the detection tablet via the sampling chamber at a constant flow rate using a suction pump (flow rate was 250 mL/min). The suction unit was sealed from the light, and the LED (CB5006X; Stanley Electric Co., Ltd.; Japan) and a PIN photodiode (S1133; Hamamatsu Photonics Co., Ltd.; Japan) were placed in order to detect the color change on the surface of the tablet as shown in Figure 3B. KD-XA01 on the detection tablet reacted with HCHO to give a homogeneous color change from white to yellow. The degree of the color change was recorded by measuring the relative reflectance at 475 nm. The output voltage of the photodiode is proportional to the intensity of the reflected light, and the degree of the color change (concentration of HCHO) is calculated according to the following equation: A ) -log(V1/V0), where A is the refractive response and V0 and V1 are outputs of a blank (atmospheric air) and sample gas, respectively.

Results and Discussion Response of KD-XA01 and KD-XA02 to HCHO in the Solution Phase and Solid Phase. To examine the photophysical properties of KD-XA01, KD-XA02, and their products, the absorption spectra were obtained in acetonitrile:phosphate buffer (pH 2.5) ) 1:1 v/v solution. Figure 4A indicates the typical absorption spectra of KD-XA01 before and after reaction with HCHO. KD-XA01 itself showed an absorption maximum at 350 nm, while the product of KD-XA01 with HCHO showed an absorption maximum at 425 nm. The color of the solution changed from a colorless solution (KD-XA01 itself) to a yellow solution (the product of KD-XA01 with HCHO) as shown in Figure 4C. Similar results were obtained for the absorption spectra of KD-XA02 itself and the product of KD-XA02 with HCHO (absorption maximum of KD-XA02 325 nm, of the product 420 nm); however, the reaction rate of KD-XA02 with HCHO was much slower than that of KDXA01, and a gas monitoring system using KD-XA02 was not carried out. These spectral changes were caused by transformation from the enaminone to the lutidine derivative, in which two KD-XA series molecules condense with HCHO as shown in Figure 1. These reagents rapidly and quantitatively react with HCHO and have a low inherent background signal due to the change in the absorption band from the UV region in KD-XA01 and KD-XA02 to the visible region for their reactions with HCHO. The absorbance at 420 nm was plotted as a function of the HCHO concentration, and this result is shown in Figure 5. This calibration curve provided a good straight line to obtain precise HCHO concentrations. To investigate the reaction of KD-XA01 with HCHO gas in the solid phase, filter paper (2 cm × 4 cm) was inserted into the solution of KD-XA01 in MeOH:phosphate buffer (pH 2.5) ) 9:1 v/v and then dried under reduced pressure. The VOL. 37, NO. 24, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 4. (A) Absorption spectra of 20.0 µM of KD-XA01 before and after reaction with 10.0 µM of HCHO at room temperature in MeCN:phosphate buffer (pH 2.5) ) 2:1 v/v. (B) Reflectance spectra of tablet containing KD-XA01 exposed to HCHO and air (reference, BaSO4 disk); (dotted line) 0.2 ppm HCHO in air; (solid line). (C) Photographs of KD-XA01 solutions before and after reaction with HCHO. (D) Photographs of filter paper containing KD-XA01 before and after reaction with HCHO.

FIGURE 5. Plot of the absorbance at 420 nm as a function of HCHO concentration. sampling bag was saturated with HCHO gas, and the filter paper containing KD-XA01 was placed in this bag. After 10 min of exposure, the surface color of the filter paper changed from white to yellow, as shown in Figure 4D. This result indicates that KD-XA01 reacted with HCHO gas on the filter paper and produced the lutidine derivative. This phenomenon is consistent with the reaction of KD-XA01 with HCHO in the liquid phase. This phenomenon suggests that it is possible to apply a monitoring system based on photoelectric photometry using a test paper and to create a convenient HCHO monitoring system. Optimum Condition for Reaction between KD-XA01 and HCHO Gas in the Detection Tablet. To examine the compatibility of the paper in the tablet and the reaction between KD-XA01 and HCHO, two types of cellulose papers [one was with white granules of SiO2 whose size is between 2 and 7 µm (Whatman; SG-81) as an adsorbent and the other was without SiO2 (Whatman; 1Chr)] were immersed in the 5698

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processing solution (KD-XA01 and phosphate buffer solution were dissolved in MeOH). When using the 1Chr, color change in the tablet was not observed in detecting 0.1 ppm HCHO at a sampling time of 30 min. On the other hand, the tablet constructed from SG-81 showed a response to HCHO. From this result, the paper containing silica gel impregnated with KD-XA01 and phosphate buffer in MeOH was able to provide a highly sensitive HCHO monitoring system. For the next examination to obtain optimum conditions, the response was investigated by changing the concentration of KD-XA01 and phosphate buffer in the processing solution. The processing solution [phosphate buffer (pH 2.5):MeOH ) 2:8 v/v] containing various concentration of KD-XA01 from 0 to 2.0 wt % was prepared, and the response of the tablet for 0.1 ppm of the HCHO gas with 15 min exposure was measured. As a result, the response linearly increased as a function of the concentration of KD-XA01 and was saturated at 1.0 wt % of [KD-XA01]. With over 2.0 wt %, KD-XA01 was precipitated and it was impossible to carry out the measurement. The processing solution used was prepared with 1.0 wt % KD-XA01. To examine the dependence of the concentration of phosphate buffer in the processing solution, the tablets made by immersion in processing solution ([KD-XA01] ) 1.0 wt %, phosphate buffer (pH 2.5):MeOH ) 1:9 f 3:7v/v), were prepared and exposured to 0.1 ppm HCHO gas for 15 min. As a result, the response for HCHO slightly increased with the increase in the volume of the phosphate buffer. With over a 30 vol % phosphate buffer, KD-XA01 was precipitated and it was impossible to carry out the measurement. Also, the processing solution without phosphate buffer did not give a response to HCHO. From this result, the volume of phosphate buffer in the processing solution was 20 vol %. To examine the pH dependence of phosphate buffer (20 vol %) in the processing solution, the response was measured under

TABLE 1. Response Upon Exposure to Various Gases gas

conc.

response (ppm)

gas

conc.

response (ppm)

toulene xylene ethylbenzene stylene di-n-butylphthalate acetaldehyde propionaldehyde ethanol ethyl acetate carbon monoxide nitrogen monoxide nitrogen dioxide sulfur dioxide

1% 1% 8800 ppm 1000 ppm 80 ppm 100 ppm 100 ppm 1% 1000 ppm 100 ppm 100 ppm 10 ppm 15 ppm

0 0 0 0 0 0 0 0 0 0 0 0 0

carbon dioxide hydrogen acetic acid hydrogen sulfide hydrogen fluoride hydrogen chloride chlorine acetone 1-butanol methyl ethyl ketone benzene formaldehyde formaldehyde + NH3

1% 1% 20 ppm 30 ppm 6 ppm 1 ppm 3 ppm 1% 7000 ppm 1000 ppm 1% 0.1ppm 0.1 ppm(HCHO) + 10 ppm(NH3)

0 0 0 0 0 0 0 0 0 0 0 0.1 0.1

FIGURE 6. Relationship between the response and HCHO concentration at various sampling times (5, 10, 15 min). various pH conditions. As a result, a two times higher response of the pH 2.5 phosphate buffer than that of the pH 6 one was observed. On the basis of these points, 20 vol % phosphate buffer solution (pH 2.5) was used in the processing solution. A previous study (10) indicated that an effective humectant is necessary for a good response to HCHO, in particular, glycerin provides moisture on the surface of the paper. The processing solution containing 10 vol % glycerin was prepared, and the response to HCHO was measured. However, a response was not observed. A similar result was obtained using other humectants such as 1,2-propanediol, 1,3-propanediol, and propylene glycol. On the other hand, the detection tablet without a humectant gave a response to HCHO. This was caused by the fact that the humectants inhibit the reaction between KD-XA01 and HCHO. In this study, humectants were not added to the processing solution. Reflectance Spectra of the Tablet. To examine the photophysical properties of the tablet containing KD-XA01, the visible reflectance spectra of the tablet were recorded before and after exposure to 0.2 ppm HCHO gas for a sampling time of 30 min at a flow rate of 250 mL min-1. The data are shown in Figure 4B. KD-XA01 itself showed an absorption maximum at 350 nm, while the product of KD-XA01 with HCHO showed new absorption maximum at 425 nm. This result was consistent with that shown in Figure 4A. Calibration Graph. A typical calibration graph of the response to HCHO under optimum experimental conditions is shown in Figure 6. The response value of the gas monitor was evaluated as a function of the HCHO gas concentration from 0 to 1.0 ppm at specific monitoring times (5, 10, 15 min). The output value was proportional to the HCHO gas concentration from 0 to 0.6 ppm and was saturated over 0.6 ppm. The response to the fixed concentration of HCHO gas increased as a function of the sampling time in the region of 0-1.0 ppm. For the sampling time of 5 min, it was possible to detect 0.05 ppm of HCHO gas, which is under the standard value set by the World Health Organization. The detection limit was 0.005 ppm (the sampling time was 15 min, signal to noise ratio was 5.0).

The tablets are used only once and discarded because the reaction between KD-XA01 and HCHO was irreversible. To examine the reproducibility from tablet to tablet, the reproducibility tests (n ) 10) were carried out. As a result, the relative standard deviation of the response was 2.0% for 0.1 ppm HCHO gas. Dependence of Humidity and Temperature on the Response and Lifetime of the Tablet. To investigate the dependence of the humidity of the sample gas on the response to HCHO, the humidity in the gas was controlled in the range of 30-70% RH at 25 ˚C and the response to HCHO was then monitored. As a result, the response to HCHO was not affected by humidity in the range from 30% to 70% RH. Above this region of the humidity, the response depended on the humidity for monitoring the very low concentrations of the HCHO gas from 0 to 0.01 ppm, whereas above 0.01 ppm HCHO gas, the response was not affected by the humidity. To investigate the effect of gas temperature on the response, the temperature of the sample gas was varied within the range from 5 to 35 °C and the response was monitored. The response was affected by temperature; however, it was possible to detect the correct HCHO concentration due to the temperature correction by the thermistor in the handheld instrument. The lifetime of the tablet containing KD-XA01 is important for monitoring the HCHO gas in the air. The tablets were stored in an aluminum bag in vacuo at room temperature. After storage for about 6 months, the response to the HCHO gas was about 90% of the original value. This result indicates that KD-XA01 is a very stable compound and that this tablet produces a reliable quantitative response to HCHO after a long period of nonexposure to the gas. Selectivity of HCHO against Foreign Gases and Comparison with Other Monitoring Methods. The responses of this tablet to various gases (NH3, acetaldehyde, propionaldehyde, hydrocarbon compounds, and typical gases in the air) are shown in Table 1. The responses for these gases at high concentrations were 0. To investigate the response for HCHO in the presence of another gas, the mixture gas containing 0.1 ppm of HCHO and 10 ppm of NH3 was exposed to the tablet for 30 min. As a result, the instrument indicated 0.1 ppm, which showed that KD-XA01 did not react with NH3 and correct HCHO monitoring was successful under the excess amount of NH3 as shown in Table 1. Similar results were obtained in the presence of other gases. The comparison of this method with the detection tube and TAB(HA), which is constructed from hydroxylamine sulfate, and a pH indicator are shown in Table 2. The detection tube and TAB(HA) were affected by foreign gases such as ammonia, nitrogen dioxide, hydrogen chloride, and carbonyl compounds. From this result, KD-XA01 has a high selectivity for HCHO versus other carbonyl compounds, hydrocarbon VOL. 37, NO. 24, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 2. Comparison of Results from This Study with Other Monitoring Methods detection tube

TAB(HA)

this method

4 4 4 × ×

× O × × ×

O O O O O

ammonia nitrogen dioxide hydrogen chloride acetone acetaldehyde

a (O) Without interference, (4) removal of low concentration gas after the pretreatment, (×) with interference.

TABLE 3. HCHO Emitted from Furniture Detected by the Tablet and DNPH Method detecting place

this method (ppm)

DNPH (ppm)

closet living room furniture

0.030 0.020 0.040

0.030 0.025 0.050

TABLE 4. HCHO Emitted in the Three Different Schools Detected by the Tablet and DNPH

school A

school B

school C

this method (ppm)

DNPH (ppm)

temp. (°C)

humidity (%RH)

0.025 0.025 0.050 0.025 0.000 0.010 0.025 0.010 0.015 0.015 0.010 0.010

0.025 0.030 0.045 0.025 0.000 0.010 0.020 0.010 0.020 0.020 0.010 0.010

22.9 22.6 22.5 22.7 17.7 17.9 18.5 18.3 18.4 18.4 18.3 17.5

41 40 25 38 31 38 50 33 50 50 33 27

compounds, and typical gases in the environment, and it is possible to monitor the correct HCHO gas concentration. Detection of HCHO in the Rooms of a New Apartment and in Three Schools. The concentration of HCHO in the rooms of a new apartment and in three different schools was measured using this monitoring method. The results were compared with those of the DNPH method, which is the standard method for the detection of HCHO. These results are shown in Tables 3 and 4. The concentration of HCHO using this method was in good agreement with that of the DNPH method. From this result, this monitoring system was successful in the detection of indoor HCHO. This method is considered applicable for the highly sensitive and selective monitoring of HCHO as a sick house syndrome gas in the home, workplace, and other environments. The present study demonstrated the highly selective and highly sensitive detection of HCHO by two novel analytical reagents, KD-XA01 and KD-XA02. These reagents reacted

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with only HCHO in solution or in the solid phase under mild conditions. Other gases such as acetaldehyde, toluene, and benzene did not interfere with the monitoring of HCHO; therefore, this guaranteed the correct detection of the HCHO concentration. As an application of these reagents, the highly selective and highly sensitive detection of HCHO gas was performed using a portable HCHO monitoring instrument composed by a detection tablet which is impregnated with a processing solution containing KD-XA01 under the optimum preparation conditions. The successful demonstration of the detection of HCHO gas in the range from 0.005 to 0.6 ppm in a short time was performed using a gas detector containing a detection tablet (0.05 ppm HCHO was able to be detected within 5 min as a minimum time). This HCHO monitoring system detected HCHO selectively and sensitively without any interferences by foreign gases and guarantees that the HCHO gas in the environment was able to be monitored and was in good agreement with the DNPH method. Recently, sick house syndrome has become a major problem and several easy detection systems for monitoring HCHO have been developed. This monitoring system is small in size, specific, allows unattended operation, and has a low operating cost; therefore, it is recommended for monitoring HCHO in the laboratory, home, workshop, and other fields and is widely applicable as a convenient method.

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Received for review June 10, 2003. Revised manuscript received September 11, 2003. Accepted September 16, 2003. ES0305050