Visual Colorimetry Research Articles

Development of Visual Colorimetry for Formaldehyde in Water Based on Membrane Filtration and Its Application to Tap Water

A simple, rapid and low-cost method for the visual determination of formaldehyde in water based on the retention of two ion-associates on a membrane filter is proposed. Formaldehyde in water was reacted with 3-methyl-2-benzothiazolionone hydorazone (MBTH) to form an azine. The remaining MBTH was oxidized by ferric ion to form a light-yellow cation. The cation was reacted with the azine to form a deep-blue cation. Both blue and yellow cations were reacted with tetraphenylborate anion to form blue and yellow hydrophobic ion-associates, respectively. The ion-associates were retained on a membrane filter by filtration. The color of the filter was changed from yellow, green to blue, depending on the concentration of formaldehyde. The concentration was easily determined by comparing the color with those obtained from a series of standard solutions of formaldehyde. The formaldehyde from 0 to 0.07 ppm in water was determined with error less than ±0.01 ppm. Thirty minutes was enough for the entire analytical procedure. This method was successfully applied to tap-water samples spiked with formaldehyde. It will be useful for rapid judgment of a water sample to pass the quality standard for drinking water in Japan.

A new method of histamine colorimetry using 2,3-naphthalenedicarboxaldehyde on a silica–gel column cartridge

In our work, we found, by chance, that 2,3-naphthalenedicarboxaldehyde (NDA) acts as a color development reagent to histamine (HA) in the absence of a reductant, e.g., cyanide anion, even in a weakly acidic environment. The NDA-induced color development reaction to HA shows the maximum absorption of 552 nm at pH 6 after a minimal interval of 10 min. By using this chemical property, a simple and convenient new method of visual colorimetry of HA on a short silica–gel column cartridge (called an “HA cartridge” in this study, which consisted of 50 mg of silica–gel packed into a 1.0 ml disposable syringe) was developed. The new visual method involves extraction of a 5 g sample with 5% trichloroacetic acid solution (TCA, 35 ml), followed by neutralizing with 1 M sodium hydroxide. After loading the TCA extract (500 μl) into the HA cartridge, the cartridge was then washed with a 0.1 M phosphate buffer, pH 6 (200 μl) and water (200 μl × 3 times). When a solution of 1 mM NDA in acetonitrile (200 μl) was passed through the HA cartridge, the color inside the cartridge was observed to changed at 3 min after the NDA loading from white to indigo-blue, for concentrations of HA ranging from 25 to 1000 mg kg −1. This sequence requires only 5 min to perform.

Chemically selective membrane optode for Cr(VI) determination in aqueous samples

A methodology for simultaneous preconcentration and determination of Cr(VI) from aqueous samples was developed using a membrane optode formed by physical inclusion of a Cr(VI) selective chromophore 1,5-diphenylcarbazide (DPC) into a plasticized cellulose triacetate matrix. The inclusion of an anion exchanger (Aliquat-336) was found to be effective for immobilization of both DPC and Cr(VI)–DPC complex in the optode matrix itself. The proportionality in intensity of the magenta color on the optodes loaded with varying amounts of Cr(VI) suggests its potential applications for screening of Cr(VI) in aqueous samples by visual colorimetry. On loading high amounts of Cr(VI) in the membrane optode, its color changes from magenta to yellow, which indicates the possibility of using it as a threshold detector for Cr(VI). The membrane optode was optimized in terms of obtaining maximum preconcentration efficiency for Cr(VI) and subsequent stable optical response proportional to the amount of Cr(VI) in the membrane optode sample. The membrane optodes were tested for Cr(VI) determination in tap water and seawater samples. Using this optode, Cr(VI) even at levels of 13.6 ppb could be quantitatively detected. The optodes developed in the present work were found to be stable, cost effective, easy to prepare and efficient for direct preconcentration and determination of Cr(VI) in a variety of aqueous samples using spectrophotometry. However, this membrane optode is for one time use only as the reaction of Cr(VI) with DPC is irreversible.

Chemically selective membrane optode for Cr(VI) determination in aqueous samples

A methodology for simultaneous preconcentration and determination of Cr(VI) from aqueous samples was developed using a membrane optode formed by physical inclusion of a Cr(VI) selective chromophore 1,5-diphenylcarbazide (DPC) into a plasticized cellulose triacetate matrix. The inclusion of an anion exchanger (Aliquat-336) was found to be effective for immobilization of both DPC and Cr(VI)–DPC complex in the optode matrix itself. The proportionality in intensity of the magenta color on the optodes loaded with varying amounts of Cr(VI) suggests its potential applications for screening of Cr(VI) in aqueous samples by visual colorimetry. On loading high amounts of Cr(VI) in the membrane optode, its color changes from magenta to yellow, which indicates the possibility of using it as a threshold detector for Cr(VI). The membrane optode was optimized in terms of obtaining maximum preconcentration efficiency for Cr(VI) and subsequent stable optical response proportional to the amount of Cr(VI) in the membrane optode sample. The membrane optodes were tested for Cr(VI) determination in tap water and seawater samples. Using this optode, Cr(VI) even at levels of 13.6 ppb could be quantitatively detected. The optodes developed in the present work were found to be stable, cost effective, easy to prepare and efficient for direct preconcentration and determination of Cr(VI) in a variety of aqueous samples using spectrophotometry. However, this membrane optode is for one time use only as the reaction of Cr(VI) with DPC is irreversible.

Visual colorimetry of iron(II)-1,10-phenanthroline after preconcentration onto polyurethane foam.

A simple solid-phase colorimetry using polyurethane foam (PUF) for the determination of iron(II) has been proposed. The 1,10-phenanthroline (phen) method is selective and sensitive, and is widely used for the determination of Fe(II) in aqueous solution. It is worthwhile to develop this method, which is suitable for visual colorimetry. An iron(II)-phen complex and its ion-associates, such as Br−, SCN− and ClO4−, were not extracted onto PUF at all. In the presence of sodium dodecyl sulfate (SDS), we found iron(II)-phen complex was adsorbed onto PUF and the iron concentration was visually measured from the resulting color onto PUF. The recommended procedure is as follows. Five ml of a 1 M acetate buffer solution (pH 4.7), 1 ml of 10 w/v% ascorbic acid, 3 ml of 0.1 w/v% phen, and 4 ml of 5×10−3 M SDS were added to a 200 ml sample solution containing less than 200 ppb of Fe(II). A chip of PUF (2×2×2 cm) was put into the solution and stirred with a magnetic stirrer for 20 minutes. The chip taken up from the solution was rinsed with distilled water and squeezed to remove any water. The color intensity of the PUF was then visually compared by a standard series method.

Lonophore-based lithium ion film optode realizing multiple color variations utilizing digital color analysis.

Digital color analysis (DCA), utilizing colors themselves or digital information of colors, can not only be applied to various quantitative analysis using chromaticity coordinates but can also be used to develop suitable sensors for visual colorimetry based on the characteristics of human visual perception by virtual simulations based on digital color information. To achieve a clear visual color variation for lithium ion determination, we designed and prepared a color-changeable film sensor (film optode) by the use of two kinds of lipophilic dyes, KD-C4 and KD-M11, whose colors and pKa values are different. This film sensor is a plasticized PVC membrane containing the mixture of two kinds of dyes with the lithium ionophore TTD14C4 and the lipophilic anionic additive tetrakis-[3,5-bis(trisfluoromethyl)phenyl]borate sodium salt dihydrate. The simulation of the color variation using the mixed dyes was evaluated by plotting the values on a uniform chromaticity scale diagram in a*b* coordinates, after converting the tristimulus values of each dye into its L*a*b* values. When the lithium ion concentration was actually determined by the PVC film optode containing the mixed dyes whose molecular ratio of KD-C4/KD-Ml 1 was 3:1, the hues of red --> orange --> yellow --> green --> blue could be realized in the range of 10(-6)-1 M. This observed color variation was similar to the result of the virtual simulation based on DCA.

Indicator papers in test methods of visual colorimetry

Compounds for the impregnation of indicator papers were proposed for the determination of ammonia, aniline, phenol, active chlorine, chromium(VI), nickel, nitrites, and pH of natural waters, soils, and atmospheric precipitation by test methods. The determination is performed by the intensity or tint of the test liquid after the introduction of prepared indicator papers. Test procedures were developed for the determination of the above components in air and natural and waste waters. The relative standard deviation is no higher than 50%.

Ion-pair adsorption film colorimetry of iron (III) in water samples and human serum

The anionic chelate of iron(III)-2,2′-dihydroxyazobenzene (H2L), [FeL2]−, formed 1∶ 1 ion-pair with crystal violet cation (CV+), CV+ [FeL2]−, and was adsorbed on a surface of transparent polyvinyl chloride (PVC) film plasticized with di-n-octyl phthalate. Enrichment of the blue violet species of the ion-pair onto the transparent PVC film has enabled a highly sensitive and simple method for the determination of iron(III). The detection limits are 1 × 10–8 mol dm−3 (0.6 ppb) by spectrophotometry at 592 nm, and 4 × 10–8 mol dm−3 (2 ppb) by visual colorimetry. The method has been successfully applied to the determination of iron in water samples and human serum. No preparatory procedures for the separation of serum protein and other coexisting substances are required, since ion-pair adsorption process provides a new method to prevent interference of serum matrix.

Rapid visual colorimetry of peritoneal lavage fluid

That visual colorimetry can be used to rapidly and precisely estimate the erythrocyte count of 1:5 dilutions of simulated peritoneal lavage fluid. Fifty-four normal adult human subjects. The automated or chamber RBC count is often used on fluid obtained by peritoneal lavage in patients with abdominal trauma to help determine the need for surgery. Unfortunately, this method sometimes results in excessive delay. We designed and built a simple colorimeter that facilitated rapid direct visual comparison of unknown samples with known color standards. A radiograph view box was used as a light source. Standards were prepared in 16-mm glass tubes to simulate peritoneal lavage fluid with RBC counts ranging from 0 to 140,000 in 10,000 cell/microL increments; 1:5 dilutions with water were used throughout to reduce opacity. Thimerosal was added to unknowns and standards to stabilize color; all samples were kept refrigerated at 4 C when not in use. In a double-blind in-vitro study, each subject matched 20 randomly distributed unknowns ranging from 12,000 to 131,000 erythrocytes/microL to the nearest standard. The mean absolute error for all 1,080 determinations was 3,560 RBC/microL (95% CI = 4,290-4,830; SD = 4,560; t = 39.6; df = 1,079; P less than .001). This method correctly predicted the RBC count to within 9,000 cells/microL 95% of the time. Visual comparison of 1:5 dilutions of simulated peritoneal lavage fluid with known color standards can be used to rapidly and precisely estimate the erythrocyte count.

Ion-pair adsorption film colorimetry ? A new simple method for ppb level of aluminum ion in water sample

A new, highly sensitive and simple colorimetric method for trace aluminum(III) with 2,2′-dihydroxyazobenzene, H2L, is described, based on the ion-pair adsorption of the anionic Al chelate, [A1L2−, with crystal violet cation, CV+, on the surface of Polyvinylchloride film plasticized with dioctylphthalate. The blue violet species, CV+[A1L2]−, is enriched onto the transparent film, leading to a remarkable enhancement of the sensitivity, and the detection limits are 3 ng/ml by spectrophotometry and 5 ng/ml by visual colorimetry, respectively. Using spectrophotometer, a linear calibration curve is obtained over the concentration range of 0 to 50 ng/ml of Al. Further, the color system, consisting of red ([A1L2]−), yellow (H2L), and blue violet (CV+), gave clear color changes suitable for visual determination of aluminum with an applicable range of 0 to above 3000 ng/ml. The four different color zones are khaki for 0–5 ng/ml, reddish-brown for 5–200 ng/ml, blue violet for 200 ng/ml-3μg/ml, and colorless for more than 3μg/ml. The proposed method has been successfully applied for the determination of aluminum in tap waters.

Determination of microamounts of zirconium(IV) and titanium(IV) with preliminary TLC separation

By the application of thin-layer chromatography on silica gel H and the solvent system consisting of 6 M HCl:acetylacetone: 9 M H 2SO 4 (60:2:1, v/v/v), zirconium and titanium have been quantitatively separated from each other, as well as from numerous other interfering ions. The efficiency of the chromatographic separation was evaluated by semiquantitative determination of zirconium and titanium by visual colorimetry of spots in situ, as well as by spectrophotometric determination of zirconium with rutin after its elution from silica gel H thin-layer.

Visual Colorimetry and Comparison Grading

Visual Colorimetry and Comparison Grading

A simple method for the determination of alkylbenzenesulfonate by visual colorimetry

アルキルベンゼンスルホン酸塩(ABS)はクリスタルバイオレット(CV)が存在するとき,その溶液中に浸せきされたエーテル型のポリウレタンホームに選択的に吸着され,ポリウレタンホームがABS濃度に比例して紫色に染色されるので,その色の濃さを標準列法によって肉眼で見れば簡単にABS濃度を判別することができた.2.5×10-5MのCVを含む,pH2の水溶液100ml中に2×2×2cm(見かけ比重:0.024g/cm3)のポリウレタンチップ1個を5分間浸せきした場合,視覚によるABSの検出限界は0.5ppmであった.同じ試料溶液を,同量のポリウレタンホームを詰めたカラム中を通した場合(流速:20～30ml/min),検出限界を0.1ppmに高めることができた.一方,ポリウレタンホームの着色はメタノールに容易に溶解するので,得られた着色溶液の吸光度(最大吸収波長588nm)を分光光度計を用いて測定すれば,さらに感度,精度ともによくなる.CVの代わりにメチレンブルーを用いることができるが,感度の点で劣る.

Evaluation of a visual color comparator method for determination of atmospheric nitrogen dioxide

In preliminary, widespread field surveys of atmospheric pollution concentrations, equipment for sampling and analysis that does not rely upon a source of a.c. electric power is advantageous. Low-volume battery-powered air pumps suitable for aspirating air samples through gas bubblers or filtration units and visual color comparators employing uniformly tinted glass filters mounted in a revolvable disk are commercially available. A method for measuring the concentration of oxidants in air by the phenolphthalein method using a visual color comparator has been developed (Haagen-Smith and Brunelle, 1958; Tintometer Ltd.). Because nitrogen dioxide is a common air pollutant and a satisfactory colorimetric method of analysis is available (Saltzman, 1954; US Department of Health, Education and Welfare, Public Health Service, 1965), it was thought desirable to apply this procedure to visual colorimetry using the visual color comparator. To our specifications the manufacturer of this apparatus prepared a color disk containing nine colored glass filters having appropriate spectral characteristics. This apparatus was evaluated in a comparison study of data obtained by use of the visual color comparator and data obtained spectrophotometrically. A ten-member untrained observer panel was used to obtain measurements by means of the visual color comparator.

Spectral Distribution of Typical Daylight as a Function of Correlated Color Temperature

Spectral distributions of 622 samples of daylight (skylight, and sunlight plus skylight) have been subjected to characteristic vector analysis, as composite data and in three subgroups (99 distributions measured by Budde; 249, by Condit; and 274, by Henderson and Hodgkiss). The chromaticity coordinates (x,y) computed from these distributions have been compared with direct visual determinations of chromaticity coordinates of daylight by Nayatani and Wyszecki, and by Chamberlin, Lawrence, and Belbin. It was found that the chromaticities indicated by the spectral distributions and by direct visual colorimetry cluster about the curve: y = 2.870x−3.000x2−0.275. This curve of typical daylight chromaticities falls slightly on the green side of the Planckian locus. From the mean and the first two characteristic vectors of the composite data, spectral distribution curves have been reconstituted by choice of scalar multiples of the vectors such that the chromaticity points fall on the curve of typical daylight chromaticities at places corresponding to correlated color temperatures of 4800°, 5500°, 6500°, 7500°, and 10 000°K. The representative character of these reconstituted spectral-distribution curves has been established by comparison with the measured curves from each subgroup yielding the closest approximation to the same chromaticities. The agreement so found suggests that this family of curves is more representative of the various phases of daylight between correlated color temperatures 4800° and 10 000°K than any previously derived distributions.

Apparent Dissociation Constant of Phenol Red as Determined by Spectrophotometry and by Visual Colorimetry

Abstract The apparent pK' of phenol red was determined in buffered NaCl solutions of known composition at 25° and 37°, by both spectrophotometric and visual colorimetric measurement of the concentration ratios of the alkaline to acid form of the indicator. A small but statistically significant difference was obtained by the two procedures. The pK' values obtained in 0.15M NaCl spectrophotometrically (7.67 at 25° and 7.57 at 37°) were approximately 0.03 unit lower than those obtained colorimetrically. Measurements made as a function of NaCl concentration at 25° were in accord with the Debye-Hückel theory. Small variation was observed between solutions buffered with phosphate or tris at the higher NaCl concentrations. The results indicate that in addition to ionic strength and temperature, variations in method of measurement and in the source of the preparation are important factors in the determination and use of pK' values for phenol red. Attention is called to the pertinence of these results to the measurement of blood pH by colorimetric and spectrophotometric methods.

Propagation of errors in spectrophotometric colorimetry.

An important part of the basis of instrumental colorimetry, namely, the uncertainty of spectrophotometric data, has been neglected in the investigations of color and color specification. The uncertainty of measurement of spectral data results from recurrent and random fluctuations such as slit-width and stray-energy effects and photometric-scale and wavelength-scale effects. By means of the theory of propagation of errors in a computed result the variances in each of the CIE chromaticity coordinates are determined. As the chromaticity coordinates are correlated, the covariance between x and y is also determined. Uncertainty ellipses are formed by assuming that the variates have normal distributions about their mean values with the determined covariance matrix. These ellipses have been computed for a representative series of colors for the special case of constant spectral uncertainty. These ellipses are compared with the perceptibility ellipses of MacAdam. As in visual colorimetry, an instrumental measurement of chromaticity coordinates does not establish a single point on the chromaticity diagram, but rather indicates that the true chromaticity point probably lies within an elliptical area surrounding this point.

The spectrophotometry of light sources

The calibration and use of simple, non-automatic equipment for spectrophotometry of light sources is described, with particular attention to precautions required for accuracy. The computation of chromaticity from the spectral energy distribution curves is illustrated, with results for a variety of lamps. These results show better agreement with visual colorimetry than in other recently published work. The change of chromaticity of fluorescent lamps with varied loading is analysed by the same methods, and the application to the study of phosphors briefly mentioned.

Photometric Methods in Water Analysis

measurement of the intensity of light, and it includes visual colorimetry, filter photometry, spectrophotometry, flame photometry, turbidimetry, fluorimetry, and other specialized branches. The first three techniques are used extensively in water analysis because of their speed, convenience, and sensitivity. Nevertheless, the application of these methods is not as simple as is sometimes pictured. A discussion of the principles involved and of some of the available techniques may aid the analyst in avoiding pitfalls and in obtaining the maximum accuracy that is possible with the equipment at hand. In recent years, a considerable number of books and papers has been published on the pratical and theoretical aspects of photometric methods of analysis, reflecting an increasing use of, and interest in, such methods throughout the field of chemistry. Annual reviews have been appearing in Analytical Chemistry since 1949 (1-4). In addition to the other references

PHOTOMETRY AND COLORIMETRY OF RAILROAD FUSEES

In connection with the preparation of a standard specification, it became necessary to investigate the luminous intensity and color of a large number of railroad fusees. The rapid and wide fluctuations in intensity made it necessary to use special methods of colorimetry. The intensity was recorded by a highspeed electronic potentiometer and a barrier-layer photocell with correcting filter. To the pen carriage of the potentiometer was attached a special diaphragm which, with a lens and slit, acted as a 'light valve' to keep the flux into the colorimeter at a constant level over a range of about four to one. The very rapid flickering was, of course, not entirely eliminated. Visual colorimetry was used, the comparison field being produced in the lower half of a divided integrating sphere, the upper half of which received light from the fusee under test. The field, 2° in diameter, could be observed with both eyes. The accuracy of the colorimetry was made adequate by a careful choice of filters, advantage being taken of a fortunate circumstance regarding the color of the fusees. The results of testing more than 200 fusees are summarized.