FAAS Determination of Trace Amounts of Cadmium in Water Samples-On-line Preconcentration of Cadmium with FI-Knotted Reactor

In the FAAS determination of trace amounts of cadmium in water sample,on-line preconcentration of Cd2+ ion with flow injection knotted reactor was adopted,in which 1-pyrrolidine carbodithioic acid (ammonium salt,abbreviated as APDC) was used as ligand for Cd2+,and the mode of duplicate introduction of the APDC solution into the reactor was introduced. The APDC solution was pre-coated on the inner wall of the knotted reactor (KR),i.e.,the 1st introduction of APDC solution;and the 2nd introduction of APDC solution was carried out simultaneously with the introduction of sample solution. Flow-rate of sample solution in the FI-preconcentration was taken as 6.0 mL·min-1,and the time for preconcentration was taken as 60 s. Concentration factor of Cd2+ by this method attained to a value of 21,which is higher than the values 9 and 16 attained by either the mode of pre-coating on the inner wall of KR or the mode of introduction simultaneously with the sample solution separately. Detection limit (S/N=3) of the method found was 0.32 μg·L-1,and the sampling frequency of 36 samples per hour was achieved. Precision was tested at the concentration level of 20 μg·L-1 of Cd2+,value of RSD (n=11) obtained was 2.7%. In analyzing several water samples by this method,in which (w) 0.01% triethanolamine solution was added as masking agent,values of recovery found were in the range of 92.0%-99.0%.