[Total proteins of the cerebrospinal fluid obtained by punction of the cisterna magna: normal values. Variations related to sex]

Sub-microlitre dialysis system to enable trace level peptide detection from volume-limited biological samples using MALDI-TOF-MS

The detection of peptides with mass spectrometry from volume-limited biological samples is a challenging task due to low sample volume, a broad range of peptide concentrations down to trace levels, endogenous high proteins and salt levels. Previously, a microspotting method was presented for trace-level peptide detection with MALDI-MS from sub-microlitre samples with biological salt levels. However, in the presence of proteins, peptide signals are significantly reduced. This paper presents a novel dialysis device for removal of proteins from sub-microlitre samples using a semipermeable hollow fiber membrane to enhance peptide detection. A dialysis device was constructed to perform sub-microlitre dialysis to remove proteins from complex samples. Angiotensin I was used as a model peptide in the presence of 350 mg L(-1) BSA prepared in physiological saline to mimic biological samples. In the absence of BSA, clear angiotensin I peaks were seen at 250 pM, yet in the presence of the BSA, 10 nM angiotensin I was barely detected. After dialysis, peak detection was improved to a 500 pM level. Protein removal and peptide recovery (approximately 66%) were determined using CE-LIF. Clinical vitreous samples as low as 200 nL were successfully dialyzed in 30 min and a 3-fold increase in peptide peaks were detected with greatly improved signals. This method is simple and can be a useful technique for trace level peptide detection from volume-limited biological samples.

[Cerebrospinal fluid proteins: I. Comparative study of concentration methods]

Four protein concentration methods, applicable to cerebrospinal fluid, were compared in order to choose a procedure that not causing protein denaturation, is accurate, precise and easy to perform in routine laboratories. The studied methods were: dialysis against arabic-gum solution, centrifuge-ultrafiltration, absorption of low molecular weight substances by dry polyacrylamide gel and pressure ultrafiltration. Blood serum was diluted, then concentrated by these procedures and analyzed by cellulose acetate electrophoresis; the undiluted serum served as control. It was observed that two methods: pressure ultrafiltration and absorption of low molecular weight substances by polyacrylamide hydrogel, are not suitable for concentrating diluted fluids because they frequently cause protein denaturation. It was concluded that dialysis against arabic-gum is the most suitable, of the methods studied, for application in routine laboratories taking in account that this procedure is precise, relatively accurate, simple and of low cost.