It has been developed a small-scale, simple, and rapid diffusing liquid-liquid microextraction ( DLLME ) process in combination with fiber optic-linear array sensing spectrophotometry ( FO-LADS ) with charge-coupled device ( CCD ) sensor profiting from a micro-cell. The official mention methods ( ASTM D2330 – 02, ISO 7875-1 ) which require boring processs were replaced with modified method, as a consequence, it has achieved a major decrease in sample size, riddance of the usage of expensive glasswork, and a lessening in the measure of trichloromethane used every bit good as much more addition in sensitiveness. Our presented method requires merely one twentieth of sample ( 5.0 milliliter ) , less than one three-hundredth of microextraction dissolver ( chloroform = 138 AµL ) , and much reduced in analytical clip compared with official analytical methods ( less than one minute ) . The standardization curve was additive in the scope of 0.06 A- 10-1 – 0.8 A- 10-1 milligram La?’1 of Na dodecyl sulphate ( SDS ) with a correlativity coefficient ( R ) of better than 0.99 and the LOD was 0.02 A- 10-1 milligram La?’1. The repeatability of the proposed method ( n=7 ) were found to be 4.5 and 3.6 % for the concentration of 0.03 and 0.07 milligram La?’1, severally. The enrichment factor was found to be 75 for SDS.
Keywords: Diffusing liquid-liquid microextraction A· Water analysis A· Methylene blue active substance A· Anionic wetting agent A· Fiber optic-linear array sensing spectrophotometry
A turning public concern over protecting our environment obligate chemists, including analytical chemists, to alter their activities in such a manner that they will be conducted in an environmentally friendly mode. Sampling, and particularly sample readying, often involves coevals of big sums of pollutants. This is why sample readying techniques that use a little sum of organic dissolver, or none at all, have been developed [ 1-4 ] .
Anionic wetting agents ( AS ) are widely used in family cleaners, industrial detergents and decorative preparations. The wetting agents expelled to natural H2O reservoirs as municipal and industrial wastes are good known to hold inauspicious effects on aquatic beings ; hence the monitoring of wetting agents in environmental samples is of great importance [ 5, 6 ] .
For the measuring of entire surfactant concentration, titration methods have been extensively explored [ 7, 8 ] . Several ion-selective electrodes sensitive to anionic wetting agents have been reported so far [ 9-11 ] .
Anionic wetting agents are normally determined by spectrophotometric methods utilizing methylene blue ( MB ) , this standard methods being used to find AS in the surface and tap-water samples ( ASTM D2330 – 02, ISO 7875-1 ) [ 12, 13 ] . The method is based on the formation of blue-coloured trichloromethane extractible ion-pair between the AS and the cationic MB. This requires three consecutive extractions of AS-MB content in 100 milliliter of sample with 15, 10, and 10 milliliter of trichloromethane. The ion-pair is determined by spectrophotometry, mensurating the optical density at 650 nanometer. However, these official methods are non merely long and boring but besides require great measures of sample and trichloromethane which has harmful consequence on chemists and environment. Besides, this method needs batch of research lab glasswork, do these operations highly expensive and uncomfortable for the operator. So it seems necessary to seek for new offers as options for the aforesaid method in order to increase the laboratory productiveness, operator safety, comfort, and to cut down drastically the reagents ingestion and waste production.
Koga et Al. proposed a decrease of the size of sample employed for AS finding in H2O, being modified this method to utilize 50 milliliter of H2O and 5 milliliter trichloromethane, holding obtained a six times addition of the research lab productiveness [ 14 ] . An other simplified methods that cut down the measures of reagent by utilizing a certain sort of adsorbent have been proposed [ 15 ] . However, this method besides involves boring processs. Besides other research workers studied primary biodegradation of AS in aerophilic showing trials based on the formation of ion-pair of AS and MB [ 16 ] .
By early 2006, Assadi and his research group innovated an attractive, high public presentation and powerful liquid-phase microextraction ( LPME ) method which named their techniques “ Diffusing liquid-liquid microextraction ” ( DLLME ) [ 17-19 ] . Beyond the trait of simpleness of operation and celerity, ingestion of microextraction dissolver at the micro-level volume and compatibility with analytical instruments are other profitable characteristics of DLLME as a sample pretreatment method [ 20-25 ]
For extremely sensitive, accurate, rapid, and cheap measuring with ingestion of extraction dissolver at micro-level volume, we propose a simplification of the spectrophotometric MB method that can be utile for finding anionic wetting agents in aqueous samples. A consecutive DLLME in combination with fiber optic-linear array sensing spectrophotometry ( FO-LADS ) with charge-coupled device ( CCD ) sensor profiting from a micro-cell was used for this intent.
2.1 Reagent and criterions
The reagents used in the experiments were of analytical class: MB ( used as a cationic dye ) , sodium dodecyl sulphate ( SDS, employed as a representative anionic wetting agent ) , acetone as disperser dissolvers, trichloromethane as microextraction dissolver, NaOH, HNO3 ( 65 % ) , HCl ( 37 % ) , acetic acid, and Na ethanoate for doing buffer solution ) and obtained from Merck ( Darmstadt, Germany ) . Absolute ethyl alcohol ( & gt ; 99.6 % ) purchased from Bidestan company ( Qazvin, Iran ) .
The needed measure of SDS was dissolved in pure H2O to do standard solution of 1000 mg L-1. The stock solutions of MB ( 3 A- 10-3 mol L-1 ) were prepared by fade outing appropriate sums in dual distilled H2O. All the plastic and glasswork were cleaned by soaking for 24 H in 10 % v/v HNO3. After cleansing, all containers were exhaustively rinsed three times with dual distilled H2O and twice with acetone prior to utilize. No any detergent was used to clean glasswork because it is hard to take from surfaces and causes high consequences.
2.2. Apparatus and Instrumentation apparatus
The fiber optic-linear array sensing spectrophotometer was perched from Avantes ( Eerbeek, Netherlands ) . The light beam from the UV-Vis beginning ( Deuterium-Halogen ) was focused to the sample micro-cell ( Starna Scientific, Essex, England, Cat. NO. 16.40F-Q-10/Z15 ) . The spectrograph accepts the light beam transmitted through the optical fibre and disperses it via a fixed grate across the 2048 component CCD-linear array sensor. The instrumental parametric quantities are listed in Table 1. A Universal EBA 20 extractor equipped with an angle rotor ( Angle rotor for 8 A- 15 milliliter tubings, 6000 revolutions per minute, Cat. No. 2002 ) were obtained from Hettich ( Kirchlengern, Germany ) . An adjustable pipette ( 10-100 AµL ) was prepared from Brand ( Wertheim, Germany ) . All 0.1, 1.0 and 2.5 milliliter panpipes were prepared from Hamilton ( Reno, NV, USA ) .
To clean out the micro-cell, avoid any memory consequence and better the repeatability of process, it was washed three times by about 2 milliliters of propanone between each analysis and dried with a watercourse of cold air by usage of a hair drier.
2.3. Mention process
Hundred milliliter of sample was placed into a 250 milliliter dividing funnel and 10 milliliter of a 1 A- 10a?’3 mol L-1 MB solution and 15 milliliters trichloromethane were added. After agitating the mixture smartly for 1 min, the two stages were let to divide and chloroform bed taken for analysis. Each sample was extracted to boot two times utilizing 10 ml part of trichloromethane and optical density measurings were made at 650 nanometers in forepart of an external standardization prepared from SDS. Solutions in the scope between 0.1 and 0.5 milligrams La?’1 were extracted in the same manner than samples.
2.4 Recommended analytical process
Into a series of screw cap glass trial tubing with conelike underside 5.0 milliliter of the standard SDS solutions at the concentration in the studied scope were pipetted out. Then 25 AµL of 3 A- 10-3 mol L-1 MB standard solution was added. Afterwards, 2.00 milliliter ethyl alcohol ( disperser dissolver ) incorporating 138 AµL trichloromethane ( microextraction dissolver ) was injected quickly into the sample solution utilizing a 2.50-mL syringe. This injection led to a cloudy solution, caused by the all right droplets of trichloromethane into the aqueous sample. The stage separation was accelerated by centrifugating at 5500 revolutions per minute for 3 min. After this measure the spread all right droplets of trichloromethane were settled at the underside of the aqueous solution in conelike trial tubing. Subsequent to this process, for evacuating the upper aqueous solution a long needle connected to 10-mL injection syringe was immersed down in to prove tubing and pulled the speculator up till minute 200-300 AµL of aqueous stage remains at the top of organic bed. The volume of the settled organic stage was determined utilizing a 100-i?L microsyringe at 25 °C which was 65A±2 AµL. Sixty micro-liter of this settled stage was removed by micropipette and introduced into micro-cell. The ordinary optical density of AS-MB ion-pair in trichloromethane was measured at the wavelength of 650.0 nanometers by agencies of FO-LADS.
3. Result and treatment
In order to obtain a high sensitiveness, the parametric quantities impacting the DLLME such as the type of the microextraction and the disperser dissolvers every bit good as their volume, concentration of MB, pH, and the microextraction clip were optimized.
The enrichment factor ( EF ) was defined as the ratio of the analyte concentration in the settled stage to the initial analyte concentration in the aqueous sample. The analyte concentration in the settled stage was calculated from the standardization graph obtained by the conventional liquid-liquid extraction ( LLE ) /FO-LADS ( extraction conditions: 2.0 milliliters standard H2O sample in the concentration scope of 4.5 A- 10-4 – 1.5 A- 10-3 mol L-1 of MB and 1.5 – 5.0 mg L-1 SDS which extracted with 2.0 milliliters trichloromethane ) .
3.1. Chemical reaction of SDS and MB
The equilibrium between SDS, MB and the distribution of SDS-MB ion-pair in H2O and trichloromethane has been qualitatively reported in the literature [ 14 ] . The AS dissolved in H2O are somewhat soluble in trichloromethane. On the other manus, MB dissolves good in both, trichloromethane and H2O, supplying a bluish colour solution in all the instances. When pure H2O is assorted with a chloroform solution of MB, the bluish colour is quickly transferred to the aqueous stage.
3.2. Consequence of ion-pair formation status parametric quantities
The overall ion-pair formation status of SDS and MB is concentration of each, pH every bit good as clip needed. Our efforts were chiefly centered on optimising these parametric quantities under our microextraction conditions ( DLLME ) .
In this survey the clip required for ion-pair formation were tested between 0 sec -10 min. The consequences, deducing from the ion-pair formation utilizing different reaction times, exhibited that the reaction clip has no any consequence on ion-pair formation efficiency and longer clip period did non better the reaction. In order to find the optimum pH for the ion-pair formation, several sample pH values were varied from 2.5 – 7.5 to prove the ion-pair formation of AS and MB in 5.0 mL H2O samples incorporating 0.04 mg L-1 SDS and extra sum of MB. The highest microextraction efficiency was achieved in the pH of studied scope and we found that in the alkalic solution MB it self would pull out into trichloromethane in absence of any MBAS. In optimisation processs no any buffer solution were used because after adding reagents the pH of solution become somewhat acidity in coveted scope.
The influence of the MB concentration on the ion-pair formation/microextraction efficiency was performed in the scope of 0 – 2.1 A- 10-5 mol L-1 while the concentration of SDS was 0.04 mg L-1. During the fluctuation of this concentration the other experimental variables remained changeless. The consequences demonstrated that by increasing the MB concentration up to 1.5 A- 10-5 mol L-1 the microextraction efficiency increased and, so, no fluctuation were observed ( as depicted in Fig. 1 ) . Sing the fact that proposed method is additive up to 0.08 milligrams L-1, hence, the sum of 5 A- 10-5 mol L-1 MB was selected as consider adequate surplus sums.
3.3. Influence of the microextraction dissolver sort and volume
The choices of an appropriate microextraction dissolver have a high importance function to acquire a high sensitiveness DLLME, so sort and volume of it were studied and optimized. Microextraction dissolver should hold particular features in DLLME ; it should hold really low solubility in H2O, extraction capableness of interested compounds, and much denseness than H2O. Chloroform and C tetrachloride are available as the most celebrated microextraction dissolvers in DLLME. During our primary surveies we found that C tetrachloride is non capable to pull out the ion-pair of SDS-MB at all. Furthermore, the recommended dissolver in the standard methods is trichloromethane ; hence, it was our extinguished pick.
To look into the consequence of microextraction dissolver volume, experiments were performed by utilizing 2.00 mL ethyl alcohol incorporating different volumes of trichloromethane ( 138, 143, 148, 153, 158 and 163 i?L ) . By increasing the volume of trichloromethane from 138 to 163 AµL, the volume of the settled stage additions about from 65 to 90 AµL. Harmonizing to consequences ( Fig. 2 ) , optical density lessenings with increasing the volume of trichloromethane ; it is clear that by increasing the volume of trichloromethane the volume of the settled stage additions. Subsequently, at low volume of the microextraction dissolver high optical density or enrichment factor was obtained.
3.4. Influence of the disperser dissolver sort and volume
In DLLME, choosing an appropriate disperser dissolver is of import, since disperser dissolver should be mixable with both microextraction dissolver and aqueous sample. For the interest of geting the most suited disperser dissolver, two sorts of instead safe disperser dissolvers: propanone and ethyl alcohol were studied. A series of sample solutions were studied by utilizing 2.00 milliliter of each disperser dissolver incorporating 138 AµL of trichloromethane and the enrichment factors were investigated. The consequences showed that ethyl alcohol showed much better efficiency than propanone ( enrichment factor of 75 and 17, severally ) . Less toxicity and the higher microextraction efficiency of ethyl alcohols make it a better pick.
After taking ethanol as disperser dissolver, it is necessary to optimise the volume of it. The influence of the disperser dissolver ( ethanol ) volume on the microextraction efficiency was tested over the scope of 0.50 – 2.00 milliliter, but the fluctuation of the ethyl alcohol volume ( disperser dissolver ) caused alterations in the settled stage volume. Hence, it was impossible to see independently the influence of the ethyl alcohol volume on the microextraction efficiency in DLLME. To avoid this job and in order to achieve a changeless volume of the setteled stage, the ethyl alcohol and trichloromethane volumes were changed at the same time. The experimental conditions were fixed and included the usage of different ethanol volumes: 0.50, 1.00, 1.50, and 2.00 milliliter, incorporating 97, 102, 121, and 138 I?L of trichloromethane, severally. Under these conditions, the settled stage volume remained changeless ( 65 A± 2 I?L ) . Fig. 3 shows the curves for optical density of SDS-MB ion-pair versus the volume of ethyl alcohol. The optical density increased, when the ethanol volume increased from 0.50 to 2.00 milliliter of ethyl alcohol as disperser dissolver. Harmonizing to the consequences, a 2.00 milliliter ethyl alcohol was chosen as the optimal disperser dissolver volume.
3.5. Influence of the microextraction clip
Microextraction clip ( interval clip between the injection of a mixture of disperser dissolver and microextraction dissolver, before get downing to centrifugate ) is of import factor that may be effects microextraction efficiency of analytes from aqueous stage to organic stage. The fluctuation for microextraction efficiency of SDS-MB as a map of microextraction clip was studied in the scope of 5 unsweet – 10 min. The ensuing informations, exposing that the microextraction clip has no important consequence on the microextraction efficiency for the mark compound. It was revealed that after the formation of the cloudy solution, the contact country between the microextraction dissolver and the aqueous stage was well big, defining why the extraction equilibrium could be established really fast. In this method the most time-consuming process was centrifugation of the sample solution in the microextraction process, which was about 3 min. Sing the fact this period of clip ( 3 min ) is for eight trial tubing ( microextraction vass ) , the clip required for managing one trial tubing is less than 25 seconds.
3.6. Analytic features of the method
To measure the practical pertinence of the proposed DLLME/FO-LADS technique for finding of MBAS in H2O samples, several analytical public presentation features such as enrichment factor, one-dimensionality, bound of sensing ( LOD ) and repeatability were investigated under optimized conditions. The standardization curve was additive in the scope of 0.06 A- 10-1 – 0.8 A- 10-1 milligram La?’1 of SDS with a correlativity coefficient ( R ) of better than 0.99.
The LOD, defined as CL =3 SB/m ( where CL, SB and m are the bound of sensing, standard divergence of the space and incline of the standardization graph, severally ) , was 0.02 A- 10-1 milligram La?’1. The repeatability of the proposed method expressed as comparative criterion divergences ( RSDs, n=7 ) were found to be 4.5 and 3.6 % for the concentration of 0.03 and 0.07 milligram La?’1, severally. The enrichment factor was found to be 75 for SDS.
3.7. Consequence of diverse ions and application to practical samples
Any organic or inorganic compound that will organize a trichloromethane extractable ion-pair with MB will interfere by bring forthing high consequences. These positive intervention include organic sulfonates, carboxylates, phosphates, and phenols, every bit good as inorganic cyanates, chlorides, nitrates, and thiocyanates. On the other manus, any compound efficaciously viing with MB to organize an AS ion-pair will give negative consequences. These negative interventions cause by some aminoalkanes and have analytical significance in the instance of quaternate ammonium compounds. For pretreatment of MBAS in all Waterss and waste Waterss that contain meddlesome substances the undermentioned process is recommended by ASTM mention method. The selected sample is hydrolysed by boiling under partial reflux with hydrochloric acid. The residuary merchandises are neutralized to a controlled pH value, and reacted with 1-methylheptylamine. The resulting ion-pairs are extracted into a trichloromethane stage and evaporated to dryness on a steam bath. The amine constituent of the ion-pair is removed by boiling in an aqueous alkaline media and the stray MBAS are so determined under the described mention process. Besides other research workers examined the consequence of assorted diverse ions on the finding of AS by similar method [ 14, 6 ] .
In order to set up the cogency and pertinence of proposed method, it was applied to the finding of AS in several existent H2O samples ( mineral, pat, and good H2O samples ) by proposed method. For this intent, 5.0 milliliter of each sample was preconcentrated utilizing DLLME technique as described before ( pH was adjusted with acetic acid/sodium ethanoate buffer if necessary ) . In order to measure matrix consequence, the standard add-on method was applied for the finding of AS ( at spiking degrees of 0.02 and 0.05 mg L-1 ) in spiked existent samples which the comparative recoveries of analytes are mentioned in Table 2. The obtained consequences were compared with those obtained from spiked distilled H2O. In all instances, the spike recoveries confirm the dependability of the proposed method. The obtained comparative recoveries indicates that matrix does non act upon the microextraction efficiency in the mentioned samples ( no serious interventions ) , hence, there was non any duty to take interventions. As it can be seen in table 3, the public presentation of proposed method shows distinguishable advantages over other methods with mention to try volume, extraction dissolver volume, RSDs, LODs and additive dynamic scope
This survey demonstrated that DLLME process with really pleasant and robust features for check of AS seems to offer possible campaigners for mention method, which utilizes really little sum of microextraction dissolver every bit good as its low cost. Furthermore, freshly DLLME process in combination with FO-LADS equipped with charge-coupled device ( CCD ) sensor profiting from a micro-cell demonstrated that LPME ( DLLME ) could be combine with spectrophotometer system despite of micro-level sample volume without any dilution and diminishing the sensitiveness. Analysis of several existent samples for AS content illustrated the truth, dependability, simpleness, dependability and bargain rate of method. It appears to be a time-saving technique, chiefly for research labs executing analysis of a big figure of samples with a rapid coverage clip. Besides we suggest the pertinence of this method for supervising the biodegradation of AS.
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