Highly sensitive determination of mercury by improved liquid cathode glow discharge with the addition of chemical modifiers.

The sample introduction system of early miniaturized liquid cathode glow discharge (LCGD) was improved, and then LCGD was used as an excitation source of atomic emission spectrometry (AES) for the detection of mercury in water samples. The effects of chemical modifiers, such as ionic surfactants and low molecular weight organic substances, on emission intensities of Hg were investigated. The results showed that the addition of 4% methanol and 0.15% hexadecyltrimethylammonium bromide (CTAB) can enhance the net intensity of Hg about 15.5-fold and 7.7-fold, and the sensitivity (S) of Hg about 15.2-fold and 5.6-fold, respectively. Adding chemical modifiers markedly reduce the interferences from Fe, Co, Cl, Br, and I ions. The limit of detection (LOD) is reduced from 0.35 mg L for no chemical modifier to 0.03 mg L for 4% methanol and 0.05 mg L for 0.15% CTAB. The relative standard deviation (RSD) of Hg with adding 4% methanol, 0.15% CTAB and no chemical modifier is 2.38%, 1.17% and 3.00%, respectively, and the power consumption is below 75 W. All results indicated that the determination of Hg using improved LCGD with the addition of chemical modifiers has high sensitivity, low LOD, well precision and low power consumption. Water samples containing high mercury (10-20 mg L) and low mercury (0.2-5 mg L) can be determined by improved LCGD-AES with no chemical modifier and 4% methanol, respectively. Adding 4% methanol significantly reduces the matrix effects from real water samples. The measurement results of spiked samples using LCGD-AES are largely consistent with the spiked value. In addition, the recoveries of Hg are ranged from 95.7% to 114.8%, suggesting that the measurement results of Hg by LCGD-AES are accurate and reliable. Overall, the improved LCGD-AES with adding chemical modifiers is a promising technique for on-site and real-time monitoring of Hg in water samples because of its portability, lower cost and speed.