JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY DECEMBER 199 1 VOL. 6 675 INTER-LABORATORY NOTE Sulphur Contamination From Synthetic Materials in the Argon Gas Supply in Inductively Coupled Plasma Atomic Emission Spectrometry A. P. M. de Win CFT Chemical Analysis SAC? Nederlandse Philips Bedruven 6. V. Postbus 218 5600 MD Eindhoven The Netherlands In trace analysis the blank values contribute additional 'background' and consequently adversely affect the detec- tion limits. In order to attain adequate suppression of blank signals it is important to know the origin of the contamina- tion. Some workers1v2 have already reported the presence of a blank sulphur signal in their instruments. Different reasons for the cause of the blank signal were suggested but satisfactory proof was not given.A similar situation has been encountered in the inductively coupled plasma atomic emission spectrometry equipment (JY 38 plus) used in this laboratory. The magnitude of the persistent blank signal represents a very large value (0.9 f 0.1 mg 1-l of S). In a systematic approach using subboiled distilled water the blank appeared to originate for the main part from the nylon gas tubing. The nylon resin is plasticized with a sulphur-containing additive probably an organic sulphon- amide. The total sulphur content of the tubing material was 1.7&0.2%. All of the nylon gas tubes were changed to Teflon tubes of the same dimensions. Despite rigorous cleaning of the vital parts in the argon gas line (flow meters argon humidifier nebulizer spray chamber torch) and flushing with argon overnight the blank sulphur signals remained at a low but easily detect- able level of about 0.1 mg 1-' of s.Only after removal of the argon humidifier did the blank drop to the detection limit level. Again some synthetic parts of the humidifier contain- ing 0.7% s were shown to be the cause of the contamina- tion. The signal-to-background ratio of 1 mg 1-l of S at a wavelength of 180.73 nm was 6.0. With a relative standard deviation for the background at this wavelength of 296 the detection limit (30) was 10 pg 1-l of S. The investigations have shown that all of the synthetic materials in the argon gas line which contain appreciable amounts of sulphur can be the potential source of a contamination error. References 1 2 Morita M. Uehiro T. and Fuwa K. Anal. Chirn. Actu 1984 166,283. Attar K. Appl. Spectrosc. 1988 42 1493. Paper 1/04919D Received September 23 I991 Accepted September 30 1991