resonance light scattering ( rls ) is 
 an elastic scattering and occurs when an incident beam in energy is close to an 
 absorption band . first established the rls technique to study 
 the biological macromolecules by means of an ordinary fluorescence spectrometer 
 . due to its high sensitivity , selectivity , and convenience , rls studies 
 have attracted great interest among researchers . in recent years , rls technique 
 has been used to determine pharmaceutical [ 25 ] , ion 
 , bacteria , and various biological macromolecules , such as nucleic acids [ 810 ] , proteins [ 1115 ] , and peptide 
 . over the years , numerous analytical methods for cl   in a variety of samples have been developed , such as ion chromatography 
 [ 17 , 18 ] , near - infrared spectrometry , 
 spectroscopy , ion - selective electrode method , turbidimetric 
 method , and so on . among these methods , the turbidimetric method was 
 popular and regarded relatively reliable for the quantification of cl . although it often 
 provided very accurate results , it suffered from the long experimental time , lower 
 sensitivity , and complexity . partly , because of the lower sensitivity , few 
 of the above methods were applied to determine cl in biological 
 systems . the classical ion - selective electrode method is currently used in food 
 analysis of cl in drinks . nevertheless , these 
 methods similarly suffered from the drawbacks of low sensitivity and 
 inapplicability to low chloride - containing samples . the objectives of this report are to establish a rapid , sensitive , and selective rls analytical method 
 to determine of cl and to develop an alternative standard method for determination of cl   in marketing 
 drink . the obtained results were compared with that of the ion - selective 
 electrode method . rls spectra were recorded on a jasco fp-6500 spectrofluorophotometer equipped with a thermostated cell 
 compartment using quartz cuvettes ( 1.0 cm ) ( japan ) . the width of excitation and 
 emission slits was set at 3.0 nm . a bayer rapidchem 744 electrolyte 
 analyzer ( uk ) was used in the ion - selective electrode detection . the ph measurements were carried out on a 
 phs-3c exact digital ph meter equipped with phonix ag - agcl reference electrode 
 ( cole - parmer instrument co. , ill , usa ) , which was calibrated with standard 
 ph buffer solutions . a stock solution containing 355.00 ng ml of cl was prepared by 
 dissolving 0.5850 g of nacl ( > 99.99% , sigma co. , mo , usa ) in doubly distilled water and diluting to 
 1000 ml . the working solutions were obtained by diluting the stock solution 
 prior to use . a working solution of silver nitrate ( 169.87 g ml ) all other reagents and solvents were 
 of analytical reagent grade and used as purchased . hac and nh3h2o ( 0.01 mol l ) 
 were used to control the acidity , while 0.10 mol l nano3 was 
 used to adjust the ionic strength of the aqueous solutions . an appropriate aliquot of cl working solution was added to 1.0 ml of silver nitrate working 
 solution and diluted to 10.0 ml with water . after 
 standing for five minutes , the solution was synchronous scanned on the spectroflourometer through the 
 wavelength range of 250750 nm . the 
 obtained rls spectra were recorded , and the intensity was 
 measured at 571 nm . the enhanced rls signal of agcl system was represented as i = i  i0 
 ( i and i0 are the rls intensity of the system in the presence and absence of cl , resp . ) . the mineral water , pure 
 water , and green tea commonly found in the supermarket were used as samples . the famous brands such as nongfu spring , laoshan , nestl , robust , watsons , and 
 masterkong were taken into account . these samples were diluted with 
 double - distilled water and sterilized by filtration ( 0.2 m ) before testing . chloride ion in each sample was determined by the above - mentioned procedures by 
 adding a 1.0 ml aliquot of the prepared sample instead of the chloride ion working solution . the rls spectra of cl   and agno3 in water were shown in figure 1(a ) and ( b ) , respectively . it can be seen that 
 the rls intensity of agno3 solution is quite weak in the whole 
 scanning wavelength region . in contrast , upon addition of trace amount of cl to agno3 solution , a remarkably enhanced rls with a maximum peak at 571 nm was observed 
 under the same conditions ( 1.0 ml of silver nitrate ) . the 
 addition of increasing cl   to the solution 
 leads to the gradual enhancement in rls intensity , exhibiting a 
 concentration - dependent relationship . the production of rls and its intensity are correlative with the formation of the aggregate and its 
 particle dimension in solution . bearing on this point , we 
 inferred that the cl ion may displace 
 no3 ion in agno3 ( aq ) , forming a new agcl ( s ) compound that 
 could be expected to be an aggregate . the size of agcl ( s ) 
 particles may be much less than the incident wavelength , and thus the enhanced 
 light - scattering signal occurs under the given conditions . in this way , the resonance 
 light scattering formula could be applicable to the agcl 
 system . the newly - formed agcl ( s ) particles may be 
 ascribed to the higher electrostatic attraction between ag and cl   than that of the 
 coexistent no3 ion . moreover , the rls is relevant to the 
 size of the formed aggregated species . hence , the ph value and ionic strength may exert certain influence on the attraction 
 strength and the dimension of suspension particles , and thus the rls production 
 and its intensity . the rls intensity of agcl and 
 agno3 solution did not change with the variation of ph in range of 
 2.011.0 . the unexpected observation is that both of the rls intensity of agcl and agno3 system hardly changed with the 
 concentration changes of added nano3 ( figures are not presented ) . the formation process of 
 aggregation particles generally includes three steps : nucleation , crystal 
 growth , and aggregation . the size of the particles is one important factor 
 affecting the rls production and its intensity . to improve the reproducibility 
 of rls intensity of a suspension system however , the agcl 
 system is very stable in 40 minutes and the average deviation of rls signal was 
 found to be lower than 3.80% ( figure is not 
 presented ) . moreover , the addition order of the reagents has little 
 effect on the rls spectra . to gain an insight into the rls selectivity of 
 the agcl for detection of cl   in drinks , the 
 interference of some commonly coexistent ions , such as na , zn , 
 ca , fe , mg , al , co3 , 
 so3 , so4 , po4 , 
 k , and i , was investigated under the same conditions . the results demonstrated 
 that the co3 and po4 in excess of 1000 folds in 
 concentration relative to cl influenced the rls of agcl ( s ) particles . this may be due to the formation of extended aggregate around agcl particle cores by the relatively higher 
 negatively - charged ions of co3 and po4 . i in the same concentration relative to cl   strongly affected 
 the rls signal . however , chloride is a prominent negatively charged ion of the 
 drinks . all concentration of other anions is lower than chloride ion . when the 
 concentration of each ion was the same as or somewhat lower than that of cl , no interference 
 was observed ( results were not presented herein ) . sodium ion ( nano3 ) 
 hardly exerts interference as well as when its concentration reaches to ca . therefore , the 
 tolerance levels of the interference of these coexisting ions in the samples 
 were very high and the assays can be performed without removing them . the detection and quantification limits were calculated as sb + 3s and sb + 10s , 
 respectively , where sb is the average rls signal of ten blank solutions ( 16.99 g ml of silver nitrate ) and s is the 
 standard deviation . when the rls intensity at 571 nm was selected , the 
 detection and quantification limit were calculated to be 0.71 ng ml and 1.42 ng ml , respectively , 
 indicating high sensitivity of this method for the determination of cl . the sensitivity of the rls method is 
 prominently higher than that of turbidimetry 
 ( results are not presented ) . according to the above standard procedure , the calibration curve was obtained by plotting 
 the concentration of cl against the 
 intensity of rls spectrum at 571 nm under the optimum conditions ( figure 2 ) . the linear regression equation using the least square method was i = 26.97 + 27.25ccl ( ng ml)(r = 0.9989 ) in the range of 1.428.52 ng ml of cl . the proposed 
 method was applied to determine the concentration of cl in drinks and 
 the results were shown in table 2 . to further examine the accuracy of the proposed rls method , the recovery experiments were carried out 
 by adding known amounts of cl to drinks 
 diluted samples ( table 3 ) . the 
 recovery results were obtained in the range of 94.08105.63% , 
 which indicated that the proposed rls method is practical to assay the cl in drinks . the proposed method was applied to determine the concentration of chloride ion in 
 drinks and the results were shown in table 2 . to verify the veracity and 
 practicality , the samples were analyzed simultaneously by the currently used 
 ise method ( table 2 ) . it can be seen that the results determined by the rls 
 method were almost in agreement with those by the ise method . the average rsd 
 of the rls method is 1.01%2.43% , which is some lower than that of ise method ( 1.23%3.46% ) , which 
 proved that the rls assay in drinks was practical . these two methods , rls 
 and ise , can give the similar results of chloride ion in drinks ( table 2 ) . 
 however , the operations of rls and ise methods were significantly different . as we know , ise 
 method is an electrochemistry analytical method , in which the variation of 
 temperature , fluctuation of voltage , and treatment of electrode may bring on 
 significant influence on the determination though it features high selectivity .