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

Analytica Chimica Acta 558 (2006) 326–331

A new method of histamine colorimetry using 2,3-naphthalenedicarboxaldehyde on a silica–gel column cartridge Shigeyuki Oguri ∗ , Aki Mizusawa, Maiko Kamada, Minako Kohori Laboratory of Food Hygiene, Department of Home Economics, Aichi-Gakusen University, 28 Kamikawanari, Hegoshi-cho, Okazaki City 444-8520, Japan Received 28 June 2005; received in revised form 29 September 2005; accepted 3 November 2005 Available online 19 December 2005

Abstract 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 ␮l) into the HA cartridge, the cartridge was then washed with a 0.1 M phosphate buffer, pH 6 (200 ␮l) and water (200 ␮l × 3 times). When a solution of 1 mM NDA in acetonitrile (200 ␮l) 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. © 2005 Elsevier B.V. All rights reserved. Keywords: Allergy-like food poisoning; Colorimetry; Histamine; Histamine poisoning; 2,3-Naphthalenedicarboxaldehyde

1. Introduction It is a known fact that many people suffer from allergic reactions to various chemicals, house dust, pollen, animal hair, foods of certain types, etc. Some components in food can cause either food allergy or food intolerance, including allergy-like food poisoning (or histamine (HA) poisoning). Because both cases often display the same symptom due to the body’s reaction to HA, there are people who do not know the true etiology of their own symptoms. To make it possible for people to determine the cause of their symptoms and to prevent further cases of poisoning, and because most cases of allergy-like food poisoning are caused by ingested HA, a simple and reliable method for assaying for the presence of HA in food is essential. A fluorometric method officially approved by the Association of Official Analytical Chemists (AOAC) (977.13) [1] has

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0003-2670/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2005.11.021

been used routinely for 25 years as the basis for taking regulatory action on fish containing HA. The method involves an extraction with 75% methanol, removal of interfering compounds by an ion-exchange column, derivatization with o-phthaldialdehyde (OPA) [2,3], and measurement of fluorescence. Unfortunately, this official method is difficult to perform and requires considerable time and energy, hence its adoption can be viewed as being somewhat problematical. To overcome these difficulties, a wide variety of procedures for the determination of HA have been published, such as detection by means of an oxygen-based sensor electrode [4], or by an enzyme-based method [5,6], by an enzyme-linked immunosorbant assay (ELISA) method [7], by chemical colorimetry [8] and by chromatographic methods [9]. By using these techniques, recently, several commercially available test kits designed to determine HA in canned and raw fish have become available. Although they are advertised as rapid, easy to use, and capable of providing accurate results at low cost, they all have similar merits and demerits [10]. For the past decade, we have worked hard to develop simple and effective methods for determining the presence of HA or other biogenic

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amines by employing OPA [11–16]. Regretfully, our methods are still not optimally “user-friendly,” and are not, as yet, commercially available. However, during our experiments regarding 2,3-naphthalenedicarboxaldehyde (NDA), which has a chemical structure similar to that of OPA, we found by chance that NDA acts as a color development reagent to HA in the absence of a reductant, even in a weakly acidic environment. 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) was developed. 2. Experimental 2.1. Reagents and solutions NDA was obtained form Aldrich Chemical Company (WI, USA). HA and other reagents were purchased from Wako Pure Chemical Company (Osaka, Japan), and, being of the highest or liquid chromatography (LC) grade commercially available, were used without further purification. All aqueous solutions were prepared using water purified with a Milli-Q purification system (Millipore, Milford, MA, USA). HA or other amines, including amino acids, were prepared by dissolving with water or with buffered solutions to make a 0.05, 0.1, 0.5 and 1.0 mM solutions; NDA solutions were prepared by dissolving with acetonitrile to make 1.0 and 10 mM solutions. The 0.1 M buffer solutions, having pH 2 and 4, pH 6, 7 and 8, and pH 9, were prepared by dissolving sodium acetate, sodium dihydrogenphosphate and sodium tetraborate decahydrate with water, respectively. Then, each solution was adjusted to the desired pH with 1 M sodium hydroxide. The 0.1 M phosphate buffer solution (pH 5) was used for a capillary electrophoresis (CE) run buffer solution. The HA, NDA, and other amine solutions were stored in a refrigerator before usage.

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CE run buffer used throughout these studies was 6 kV and 0.1 M phosphate buffer, pH 5, respectively. For the liquid chromatography (LC) assay, the system consisted of an intelligent PU-980 pump (Jasco, Tokyo, Japan) used for isocratic-mode elution. Samples were loaded with a Rheodyne syringe loading valve (Reodyne, CA, USA) with an injection loop containing 20 ␮l of sample. The analytical column was Wakosil-H5C18 (150 cm effective length × 4.6 mm I.D.; Wako). The column was maintained at 40 ◦ C in a CO-965 column oven (Jasco). Column effluents were monitored at 220 nm with a UV-970 UV/Vis detector (Jasco). All mobile phases were degassed through a DG-980-51 on-line degasser (Jasco). The flow-rate of the eluent was 1.0 ml min−1 . All chromatographic data were also printed with the same intelligent data processor as that for CE analysis. 2.3. Colorimetry for batchwise operation Two millilitres of a buffer solution containing 0.1 mM HA or other samples was mixed with 20 ␮l of a 10 mM NDA solution. After keeping it at room temperature, the absorbance was read at 552 nm. Note: the solution should be filtered with a disposable syringe filter unit (Modele Dismic-13 cp, Adovantec Toyou, Tokyo, Japan), if necessary. 2.4. CE examination Twenty microlitres of 10 mM NDA solution was added to 2 ml of 0.1 mM HA in a 0.1 M phosphate buffer (pH 5.0) solution. Then, the mixture was examined with the CE system at the following intervals, just shortly after starting the reaction, 15 and 30 min. The CE run buffer used here was matched to the color development reaction solvent, 0.1 M phosphate buffer, pH 5.0.

2.2. Apparatus

2.5. Sample extraction

Absorbance and fluorescence were measured with a Hitachi Model U-2000 spectrometer and a Hitachi Model F-3010 spectrophotometer (Ibaragi, Japan), respectively, in a 3 ml volume quartz cell. Food samples were homogenized with a Nissei Model AM-3 universal homogenizer (Nihon Seiki Seisakusho Company, Tokyo, Japan). For centrifugation of food samples, a Hitachi Model Himac-CR 20 refrigerated centrifuge (Ibaragi, Japan) was employed. For CE examination of the color reaction mixture, the CE system consisted of a Jasco Model CE-800 (Jasco, Tokyo, Japan) equipped with an UV/Vis detector model CE-971-UV (Jasco). All data were printed out by an intelligent data processor a model 807-IT (Jasco). A capillary tube of fused silica (25 cm effective length × 75 ␮m I.D.) was used throughout the work. The window (0.5 cm) for detection was made by removing the polyamide coating at a position located 15 cm from the cathodic end. Sample solutions were introduced into the capillary tube from the anodic side by hydrostatic injection by raising the tube 5 cm higher than the level of the cathodic electrode for 10 s. The electropherograms were recorded by monitoring the absorbance at 210 nm. The applied voltage and

The extraction of HA from food samples was carried out as follows: A 5 g amount of sample was homogenized with 40 ml of 5% trichloroacetic acid (TCA), then diluted to 50 ml as the final volume with the same solvent as was used during homogenization. Subsequently, the extract was transferred to a centrifuge tube and centrifuged (11,200 × g) at 4 ◦ C for 10 min. The supernatant was stored in a 50 ml-plastic bottle with a stopper in a refrigerator until just before use. For LC examination, the sample was extracted with methanol instead of TCA. After centrifuging the extract the same way as above, 1.0 ml of the supernatant was evaporated to dryness in vacuo. Subsequently, the resulting residue was reconstituted with 10 ml of water prior to examination by LC. 2.6. Assay by LC The LC method employed was one that was slightly modified from the ion-pared LC with UV detection method reported by Yagi [17]. The mobile phase was prepared by dissolving 1octanesulfonic acid (432 mg) with a mixture of water (830 ml),

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acetonitrile (120 ml) and 0.2 M phosphate buffer (pH 3.0; 50 ml). HA was eluted at 18.3 min when 10 ␮l of 0.01% HA standard solution (this was equivalent to a 100 mg kg−1 HA-food sample) was examined by LC. 2.7. Fabrication of HA cartridge A short silica–gel column cartridge (or HA cartridge) was fabricated as follows: (1) First, a small amount of cotton was stuffed inside the bottom of a 5 ml disposable syringe (Terumo, Osaka, Japan) to retain packing materials. (2) Fifty milligrams of silica–gel (Silica–gel 60, Merck) was put on top of the cotton inside the bottom of the syringe. (3) The silica–gel was “sandwiched” by inserting another small amount of cotton into the silica–gel in the syringe. (4) Finally, the material inside of the syringe was compacted by tamping with a thin rod. 2.8. Assay with HA cartridge One millilitres of TCA extract was mixed with a 250 ␮l of 1 M sodium hydroxide. Then, the whole mixture was passed through the HA cartridge; subsequently, the cartridge was washed with a 200 ␮l of 0.1 M phosphate buffer (pH 6), followed by a 1000 ␮l of water. Finally, 200 ␮l of a 1.0 mM NDA solution was passed through the HA cartridge slowly, and the color inside the HA cartridge was observed after 3 min. 3. Results and discussion As mentioned above, NDA [18,19] generally reacts with primary amino compounds in an alkali environment in the presence of cyanide anion to yield a fluorescence derivative as shown in Fig. 1. Although OPA can react with HA in the absence of 2ME [2,18,20–22], it was believed that the reaction of NDA and HA did not occur when the cyanide ion or other reductant was absent from the reaction mixture; similarly, it was believed that the reaction did not occur in a non-alkaline environment even when cyanide anion was present, because NDA was chemically less active than OPA with regard to nucleophilic atoms present in the HA molecule, such as nitrogen. However, when a NDA solution was added to a HA solution in week acid buffer, we found, by chance, that the mixture changed color from colorless to indigo-blue. We realized that this meant that NDA could be utilized as a color-development reagent for visually detecting

Fig. 1. Schematic showing the chemical reaction of 2,3-naphthalenedicarboxaldehyde (NDA) and a primary amino compound in two cases, i.e., with cyanide anions present and with cyanide anions absent, and with two conditions of pH 10 or pH of less than 10.

Fig. 2. Picture showing the color developments of a 1 mM HA solution in 0.1 M buffer having different pHs of 2, 4, 5, 6, 7, 8 and 9, after 30 min at room temperature.

the presence of HA. Therefore, the following experiments were carried out. 3.1. Effect of pH on color development The specific NDA-induced color development reaction to HA is shown in Fig. 2 under the different conditions of pH after starting the reaction at room temperature. Under the condition of pH greater than 6, both color development and precipitation were observed in each solution. In addition, both pH 5 and 6-solutions showed color development shortly after adding the NDA solution. Color tone changed only slightly as a variable with reaction time, and some precipitation appeared only after an elapse of several minutes or several tens of minutes after starting the reaction; notably, the solutions were still colored and it was easy to recognize the difference between the color of HA solution and HA free solution even 6 h after the start of the reaction. As color development appeared to depend both on elapsed time and the pH of the solution, the effect of reaction time on color development was evaluated first, using buffers having different pHs of 3, 5, 6, 7, 8 and 9, respectively. Fig. 3 shows the effect on NDA-induced absorbance with HA at different elapsed times of

Fig. 3. Absorbance levels with change of time at different pHs of: (
) 3.0; () 5.0; () 6.0; () 7.0; () 8.0; (䊉) 9.0. The absorbance of each reaction solution (2 ml of 0.1 mM HA in buffer and 100 ␮l of 10 mM NDA solution) was measured at 552 nm.

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0.5, 1.0, 2.5, 5.0, 10, 20 and 30 min after starting the reaction. Each trace was given by measuring the absorbance at 552 nm (the reason why a wavelength of 552 nm was chosen will be explained in Section 3.2). During these experiments, some precipitation appeared in the cases of pH 5 (at 40 min after starting the reaction), pH 6 (after 15 min) and pH 7 (after 5 min); each solution was, therefore, measured after filtering or centrifuging to remove the precipitates. Thus, it was observed that the shortest time to reach the maximum absorption of 552 nm occurred at pH 6 after a minimal interval of 10 min. When the pH was either less than pH 2 or more than pH 7, very little coloring reaction was observed. In case of a solution having pH 5 or 6, it occurred shortly after starting the reaction. In addition, with regards to the reaction of NDA and HA under the condition of pH 5 or 6 at room temperature, no fluorescence was observed, neither at 1 min nor at 10 min after starting the reaction. Next, to study the effect of reaction time on color development, pH 5 was employed in order to prevent the undesirable occurrence of precipitation during the experiments. Absorption spectrums were measured at the following separate intervals, 0 (before adding NDA solution), 5, 10, 20 and 30 min, as shown Fig. 4(A)–(E), respectively. At 5 min after starting the reaction (Fig. 4(B)), the peak appeared at 552 nm, which suggested that some product formation occurred in this reaction. The increase of absorbance at 552 nm occurred rapidly until 5 min after the start of the reaction, but increased very slowly at later times. Thus, the wavelength of 552 nm was chosen as the indicator

Fig. 4. UV/Vis spectra of the reaction mixture of HA and NDA at different time lapses: (A) 0 min; (B) 5 min; (C) 10 min; (D) 20 min; (E) 30 min. Each spectrum was obtained by measuring the reaction solution (2 ml of 0.1 mM HA in a 0.1 M buffer at pH 5.0 and 20 ␮l of a 10 mM NDA solution).

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of the present coloring reaction in this study. The absorbance peak at 262 nm, corresponding to the naphthalene ring of NDA, decreased slowly with the reaction time and the broadband absorbance appeared at around 245 nm (Fig. 4(D) and (E)) at 20 min after the start of the reaction. During this interval, the change in color was observable with the naked eye. To study the reaction further, the reaction mixture was examined with CE. Because the color reaction depended on pH, the CE run buffer used here was matched to the color development reaction buffer, 0.1 M phosphate buffer having pH 5, to avoid the effect of pH on the reaction products during their CE migration. Just shortly after starting the reaction, the two peaks at migration times of 3.7 and 11.5 min were identified, which corresponded to HA and NDA, respectively, as shown in Fig. 5(A). At 15 and 30 min after starting the reaction, more than six peaks corresponding to reaction products (or by-products) were observed between the both HA and NDA peaks on both electropherograms (Fig. 5(A) and (B)). These results suggest that complex products are yielded in this reaction. Regretfully, the chemical structures corresponding to those six peaks have not yet been identified. Regarding this chemical reaction mechanism, we suspect that it is a type of reaction similar to that, which occurs with OPA in the absence of a reductant [20–23].

Fig. 5. Electropherograms of the reaction mixture (2 ml of 0.1 mM HA in a 0.1 M buffer at pH 5.0 and 20 ␮l of a 10 mM NDA solution) at different times: (A) just after starting the reaction; (B) 15 min after starting the reaction; (C) 30 min after starting the reaction, all cases at room temperature. Peaks indicated in (1) and (2) on each electropherogram correspond to HA and NDA, respectively. The arrows indicate the time at which CE analysis was started. (Refer to the CE conditions described in Section 2.)

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3.2. Effect of HA concentration on the color development To make sure that this coloring reaction developed in proportion with increasing amounts of HA, the effect of HA concentration on color development was evaluated by plotting the absorbance (552 nm) at concentrations of 0.05–1.00 mM HA in pH 6 after a 10 min-reaction with NDA. The absorbance increased linearly with increasing concentrations of HA. This implied that colorization took place between HA and NDA. In addition, the linearity and reproducibility (at 0.5 mM) were calculated as r = 0.997 and 1.38% center of value (n = 5), respectively. 3.3. Detection of HA with HA cartridge By causing this coloring reaction to take place in an HA cartridge, HA was detected in food. The HA cartridge can also serve as device for removing components other than HA in food extracts that might react with NDA to develop coloration before developing the NDA–HA reaction on the HA cartridge. To determine the best way for detecting HA in food samples with the HA cartridge, a number of experiments were carried out, such as what amount of the 1 M sodium hydroxide should be added to a sample TCA extract, what amount of sample extract should be injected into the HA cartridge, which kinds of buffer solution should be employed for washing the cartridge, and so on. Regarding the packing material for the HA cartridge, the performance of various materials was also examined to determine optimum performance. After doing various combinations of washing solvents and packing materials, such as ion-exchange resin and octadecyl silane (ODS) particles for LC, it was concluded that the following 4-step protocol resulted in the best performance to date: (1) addition of 1 M sodium hydroxide to an sample extract, (2) passing the extract through the HA cartridge, (3) washing the HA cartridge, and (4) loading a NDA solution. This sequence requires only 5 min to perform. There are many kinds of pseudo-allergens containing HA, such as fruit, vegetables, wines, and certain kinds of animal meat and fish meat. Scombridae or Tuna is by far the riskiest food regarding contamination with HA. Thus, raw tuna-meat was chosen as the test sample for this experiment; control samples spiked with HA to make concentrations of 0, 25, 50, 100, 500 and 1000 mg kg−1 were separately prepared for this study. Before preparing the spiked samples, sample which contained no HA (less than 1.0 mg kg−1 ) was checked with the LC method. After treating the sample extracts the above-mentioned procedures, the color change inside each HA cartridge was observed after 3 min, as shown in Fig. 6. Accordingly, the visual detection limits were observed at 25 mg kg−1 HA. Furthermore, these observations were possible even after an elapse of several hours, although the tone of the observed color changed slightly with reaction time. It should be noted, however, that it was not possible to detect HA directly with these samples using batchwise colorimetry, due to colorization of the HA-free sample extract (0 mg kg−1 HA).

Fig. 6. Picture showing the color development tests of fresh tuna-meat spiked with HA at concentrations of 0, 25, 50, 100, 500, and 1000 mg kg−1 , just 3 min after an 1 mM NDA solution was passed through an HA cartridge.

3.4. Cross-reactivity tests Cross-reactivity tests for the present coloring reaction were separately performed by using both batchwise (in solution) and HA cartridge methods. For these studies, 18 kinds of amino acids, viz., alanine (Ala), arginine (Arg), aspartic acid (Asp), glutamic acid (Glu), glycine (Gly), histidine (His), hydroxyproline (Opr), isoleucine (Ile), leucine (Leu), lysine (Lys), methionine (Met), phenylalanine (Phe), proline (Pro), serine (Ser), taurine (Tau), threonine (Thr), triptophan (Trp), valine (Val),) and six kinds of bioamines, viz., cadaverine (Cad), putrescine (Put), serotonin (5HT), spermidine (Spr), tyramine (Tyr), and histamine (HA) were employed. For the batch test, each amine solution was prepared with 0.1 M phosphate buffer, pH 6, and the test was done by measuring absorption 5 min after starting the reaction to avoid occurrence of the undesirable some precipitation during the measurements. HA, His and 5HT showed absorbance of 1.55, 0.35 and 1.12, respectively. Trp was colored yellow, but the absorbance at 552 nm showed 0.03. All other amines showed absorbance of less than 0.03. Regarding the HA cartridge tests, each sample of tuna-meat spiked with one of the amino acids or biogenic amines (0, 25, 50, 100, 500 and 1000 mg kg−1 ) was separately tested by the same method as mentioned in Section 3.3, but none of the amines, except HA, showed a change of color inside of an HA cartridge, even when the concentration was at the highest level (1000 mg kg−1 ). This suggested that, for the batch test, the four compounds, except for HA showing a color change, could be removed by washing the HA cartridge with a buffer solution (pH 6) and water before inciting the NDA–HA reaction on the HA cartridge. 3.5. Testing of real samples To demonstrate real-sample applicability, samples of fresh tuna-meat were first aged for 8 and 24 h at room temperature and then examined by means of the previously reported procedure [17] with a slight modification. The assay results showed HA levels of 28 and 625 mg kg−1 in the 8 and 24 h-aged samples, respectively. Then, both of the above two samples were separately tested with the present method using HA-cartridge. The resulting color tones of both cartridges are shown in Fig. 7. To estimate the concentration of HA present, the color tone was compared with those of the standards shown in Fig. 6. The color tone of the cartridges of the 8 and 24 h-aged samples were

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preserve the HA kit in good condition than with the other methods, because the HA kit includes stable materials, not unstable biological ones, such as enzymes or a HA specific antibodies; (4) the HA kit is HA-selective. Our final goal of HA analysis in food is to produce an inexpensive, handy, portable-type kit that can be used to confirm the presence or absence of HA in food by anyone at anytime and anywhere, without any special techniques. Although the present method has less detection sensitivity in comparison with the official AOAC method, the HA cartridge has sufficient sensitivity to help prevent allergy-like food poisoning induced by HA contamination. References Fig. 7. Two samples of tuna-meat, aged for 8 h (A) and 24 h (B) at room temperature, were tested. The LC assay results showed that HA contents in (A) and (B) were 28 and 625 mg kg−1 , respectively.

somewhere between that of 25 and 50 mg kg−1 -spiked standard sample and 500 and 1000 mg kg−1 -spiked standard sample, respectively. These results correspond closely with the results of the LC assays. Although the present method cannot be used as an alternative of the official method due to the poor detection sensitivity and poor quantitative determination, we believe that the method using HA cartridge, or so called “HA-detection kit,” presented here can be considered as a candidate for a first-screening or pre-testing for the presence of HA in food. Based on our limited clinical information, allergy-like food poisoning caused by HA requires that the food in question be contaminated by more than 500 or 1000 mg kg−1 of HA. Taking this into account, the present sensitivity (25 mg kg−1 ) and selectivity were sufficient to “rule out” pseudo-allergen containing HA as a possible cause of allergy-like food poisoning. 4. Conclusions By using the new visual color development reaction of HA with NDA, we developed a simple detection method for the presence of HA in a food sample. The present method using the HA cartridge has the following merits: (1) the present HA kit has a detection sensitivity 25 mg kg−1 , which might be enough to prevent the occurrence of HA poisoning, by preventing the sale, serving and ingesting of HA contaminated food which has been “pre-screened” for the presence of HA; (2) the time needed to measure HA in a TCA extract of food is only 5 min, which is as short or shorter than any other method; (3) It is much easier to

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