Evaluation of X-ray fluorescence spectroscopy as a method for the rapid and direct determination of sodium in cheese.

Cheese manufacturers indirectly determine Na in cheese by analysis of Cl using the Volhard method, assuming that all Cl came from NaCl. This method overestimates the actual Na content in cheeses when Na replacers (e.g., KCl) are used. A direct and rapid method for Na detection is needed. X-ray fluorescence spectroscopy (XRF), a mineral analysis technique used in the mining industry, was investigated as an alternative method of Na detection in cheese. An XRF method for the detection of Na in cheese was developed and compared with inductively coupled plasma optical emission spectroscopy (ICP-OES; the reference method for Na in cheese) and Cl analyzer. Sodium quantification was performed by multi-point calibration with cheese standards spiked with NaCl ranging from 0 to 4% Na (wt/wt). The Na concentration of each of the cheese standards (discs: 30mm×7mm) was quantified by the 3 methods. A single laboratory method validation was performed; linearity, precision, limit of detection, and limit of quantification were determined. An additional calibration graph was created using cheese standards made from natural or process cheeses manufactured with different ratios of Na:K. Both Na and K calibration curves were linear for the cheese standards. Sodium was quantified in a variety of commercial cheese samples. The Na data obtained by XRF were in agreement with those from ICP-OES and Cl analyzer for most commercial natural cheeses. The XRF method did not accurately determine Na concentration for several process cheese samples, compared with ICP-OES, likely due to the use of unknown types of Na-based emulsifying salts (ES). When a calibration curve was created for process cheese with the specific types of ES used for this cheese, Na content was successfully predicted in the samples. For natural cheeses, the limit of detection and limit of quantification for Na that can be determined with an acceptable level of repeatability, precision, and trueness was 82 and 246mg/100g of cheese, respectively. Calibration graphs should be created with standards that reflect the concentration range, ratio, and salt type present in the cheeses. This XRF method can be successfully used for the rapid and direct measurement of Na content in a wide variety of natural cheeses. Commercial process cheese manufacturers use proprietary blends of ES. We did find that the XRF technique worked for process cheese when the calibration graphs were created with the specific types of ES actually used.

Extra protein loss not caused by surgical bleeding in patients with ovarian cancer.

BACKGROUND: [corrected] Clinical experience in patients with ovarian cancer has shown special difficulties in maintaining cardiovascular stability during surgery. METHODS: To evaluate the causes for this observation, 15 patients with benign ovarian tumours (group I) and 13 patients with ovarian cancer (group II) were investigated perioperatively. Plasma volume (indocyanine green-dilution technique), haematocrit, plasma protein concentration, mean arterial pressure, heart rate, and central venous pressure were measured immediately before and after cytoreductive surgery. RESULTS: Normal values of blood-, plasma-, and red cell volume were determined preoperatively in both groups, and in relation to body surface area there were no intergroup differences of these parameters. In group I, the significant decrease in red cell volume of 313 ml postoperatively was compensated for by an increase in plasma volume of 371 ml (median values). In contrast to group I, the decrease in red cell volume of 328 ml in group II was not related to a significant increase in plasma volume, so that blood volume postoperatively was 483 ml lower than preoperatively, although the same standardized infusion regimen as in group I was applied. Patients of group II had a significantly higher loss of intravascular protein (49 g vs 13 g in group I), which left the intravascular space by another way than by surgical bleeding. This extra protein loss is termed Intraoperative Protein Shift (IPS). CONCLUSION: IPS could be an important quantity in perioperative fluid balance. We assume that different surgical procedures predispose to occurrence of differing amounts of IPS.

Isovolemic hemodilution alters the ratio of whole-body to large-vessel hematocrit (F-cell ratio). A prospective, randomized study comparing the volume effects of hydroxyethyl starch 200,000/0.62 and albumin.

OBJECTIVE: To evaluate potential changes in the ratio of whole-body/large-vessel hematocrit (f-cell ratio) during isovolemic hemodilution and to compare the volume effects of 2 different plasma exchange solutions (hydroxyethyl starch 200,000/0.62 6% and human albumin 5%). DESIGN: Prospective, randomized, controlled trial. SETTING: Operating theater in a university hospital. PATIENTS: 24 gynecological patients scheduled for elective surgery. INTERVENTIONS: Isovolemic hemodilution was performed using 2 different plasma exchange solutions. Plasma volume was determined using dye dilution technique before and after hemodilution. The volume of withdrawn blood was measured from the change in weight of the blood bags taking into account the specific gravity of blood. RESULTS: The volume of administered plasma exchange solutions exceeded the amount of withdrawn blood by 80 +/- 47 ml (p < 0.001). Plasma volume was 3,067 +/- 327 ml before and 3,517 +/- 458 ml after hemodilution. Using red cell volumes calculated from measured plasma volumes and peripheral hematocrit, a deficit of 249 +/- 133 ml (p < 0.0001) in red cells after hemodilution appeared with the measured withdrawn red cell volumes taken into account. This finding can be explained by a change in the f-cell ratio during isovolemic hemodilution. The volume effect of the exchange solutions was 1.05 for hydroxyethyl starch and 0.95 for albumin. CONCLUSIONS: The results demonstrate that a change in the f-cell ratio occurs during isovolemic hemodilution. The estimation of red cell volume or plasma volume changes by using either the hematocrit or plasma or red cell volume determinations together with the hematocrit may lead to erroneous results.

Determination of plasma volume with indocyanine green in man.

We investigated the feasibility of using indocyanine green (ICG) for plasma volume (PV) determination in man. Duplicate PV measurements were carried out in 23 healthy subjects to test repeatability. ICG (0.25 mg/kg) was injected intravenously into one arm and venous blood was withdrawn from the opposite arm. Optical density of plasma samples from minute 3 to 9 was measured in a densitometer. ICG concentration at injection time was determined by monoexponential extrapolation. The mean (SD) difference (MD) was -23 ml (183) or -0.6% (5.7%). Linear regression revealed PV2 = 0.92.PV1 + 226 (r = 0.92). The PV values corresponded well with data from other studies. In 26 surgical patients PV was determined using two methods: 1) the same as in healthy subjects and 2) using a modification of this method in whole blood (PVB). For PVB measurement blood was drawn through a cuvette-densitometer from an arterial line. Calculations were the same as in PV determination except for the use of hematocrit to achieve plasma concentrations of ICG from whole blood. In patients MD were -53 ml (144) or -1.3% (4.3) for PV and -19 ml (161) or -0.3% (5.1) for PVB. Comparing PVB and PV revealed MD = -113 ml (149) or -3.3% (4.2). The whole blood method is easier to perform and reduces blood waste to almost zero. In conclusion, ICG is a suitable tracer for PV determination.