**4.2.1.1 Hemodialysis procedure**

Three groups of hemodialysis patients with mature functioning arteriovenous fistula participated in this study. Their mean age was 48 ± 12 yr, and they had been receiving dialysis treatments for 35 ± 14 months with an average frequency of 3 times per wk. For each patient, Hct was determined at the beginning of the hemodialysis session.

Standard midweek hemodialysis sessions were analyzed, and bicarbonate dialysate was used. The dialysate contained 140 mmol/L sodium, 2 mmol/L potassium, 108 mmol/L chloride, 1.50 mmol/L calcium, 0.5 mmol/L magnesium and 32 mmol/L bicarbonate. The blood flow was 200 ml/min and the dialysate flow was 500 ml/min. Three kinds of dialyzers (PES, polysulfone (PSF), and polyamide (PA)) were used for the three groups of patients, respectively.

### **4.2.1.2 Calculation of solute clearance**

The levels of urea, creatinine, phosphate, total proteins, albumin (ALB), alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) were determined using an Auto Biochemistry Analyzer 7170A (Hitachi Co., Ltd., Tokyo, Japan).

The removal of 2-microglobulin was established by the changes in plasma level during the treatment at different time intervals (30, 60, 120, 180 and 240mins). Plasma 2-microglobulin levels were determined using a commercially produced ELISA assay (Cambridge Life Sciences, Cambridge, UK).

Electrolyte levels were determined before and after hemodialysis. The levels of K+, Na+ and Cl- were determined using electrolyte analyzer (NOVA CRT-4, US), and Ca2+ was determined using an Auto Biochemistry Analyzer 7170A (Hitachi Co., Ltd., Tokyo, Japan).
