tailieunhanh - Environmental Sampling and Analysis for Metals - Chapter 15

Không màu, các mẫu trong suốt (chủ yếu uống nước) có chứa một độ đục của ít hơn 1 NTU (đơn vị nephelometric độ đục), và một pha Được phân tích mẫu có thể được trực tiếp thông qua quang phổ hấp thụ nguyên tử hoặc quang phổ plasma cùng quy nạp cho tổng số các kim loại không tiêu hóa. Tiếp tục xác minh đối với vàng trong trao đổi ma trận xác định hiện tại, các mẫu tiêu hóa và không tiêu hóa so với Đảm bảo kết quả so sánh. . | 15 Sample Preparation for Metals Analysis GENERAL DISCUSSION Samples containing particulate or organic material generally require pretreatment before analysis. Sample Pretreatment for Total Metals Colorless transparent samples primarily drinking water containing a turbidity of less than 1 NTU nephelometric turbidity unit and single-phase samples can be analyzed directly via atomic absorption spectroscopy or inductively coupled plasma spectroscopy for total metals without digestion. For further verification or to determine changes in existing matrices compare digested and undigested samples to ensure comparable results. Digest all other samples before determination of total metals. Take care not to introduce metals into samples during preliminary treatment. During pretreatment avoid contact with rubber metal base paints cigarette smoke paper tissues and all metal products including those made of stainless steel galvanized metal and brass. Conventional fume hoods can contribute significantly to sample contamination particularly during acid digestion in open containers. Plastic pipet tips are often contaminated with copper iron zinc and cadmium. Before use soak pipets in 2N HCl or HNO3 for several days and rinse with deionized DI water. Check reagentgrade acids used for preservation extraction and digestion for purity. If excessive metal concentrations are found purify the acids by distillation or use ultra-pure acids. Carry blanks through all digestion and filtration steps and apply necessary corrections to the results. Sample Pretreatment for Dissolved Metals To analyze for dissolved metals filter the sample as in Section acidify the filtrate and analyze directly. Sample Pretreatment for Suspended Metals To determine suspended metals filter the sample digest the filter and the material on it and analyze. Preliminary Filtration of Samples If dissolved or suspended metals are to be determined filter the sample at the time of .