Nitex filters

The filters used in the pump units generally consisted of one 305-mm diameter, 53-jLtm Nitex filter and two 280-mm diameter, l-jnm Gelman microquartz (MQ) filters (identical to Whatman type QM/A filters). The Nitex filters have been used for all LVFS and MULVFS samples the MQ filters were chosen over Mead 935 BJ glass-fiber (GF) filters previously used in LVFS studies because they had much lower blank levels for many elements (e.g., Na, Ga, Mg, K, and Fe Figure 5). 

The 53-jLtm Nitex filters followed a similar but not identical processing scheme where 100-filter batches were placed in a large tank and leached with 0.1 N HCl in deionized water followed by deionized water. After additional rinsing in deionized water they were dried and weighed to the same precision as the MQ filters and stored with the MQ filter pairs in the polyethylene bags. 

Set up filters to separate ground flies from egg chambers and to collect purified e chambers at the desired stage. Attach the Nitex filters of the appropriate mesh size to the top of a modified 50-ml Falcon tube by screwing on the cap or by using a rubber band at the bottom of a modified 100-ml beaker. 

Remove the 350- im Nitex filter and rinse the flies into the blender container with another 150 ml of Ix Robb s Medium containing 1% BSA. Blend again as in step 5. 

Nylon-mesh basket. The basket can be conveniently made from a 50-ml blue-top centrifuge tube cut in half. Cut a hole in the lid with a heated no. 15 cork-borer, and then fit the lid back onto the threaded end of the tube over a layer of Nitex filter cloth (Figure 19.4A). This basket is also required for collecting the embryos after microinjection. 

H202 Decay Studies. Unfiltered lake waters were stored in washed 2-L polyethylene bottles in the dark, and the H202 concentrations were measured at specified intervals. Lake waters were filtered through 0.2-, 1.0-, 5.0-, and 12.0-p.m microfilters (Nuclepore). Zooplankton were removed with 30- xm woven nylon (Nitex) screens. Generally 1 L of filtrate was used. 

Figure 2. (Top) Detail of the MULVFS pump unit and filter-holder assembly. The filter holder consists of three stages. The upper two plates are baffles necessary to prevent particles from being redistributed on the filters during recovery. The next plate supports the 53-gm mesh Nitex prefilter, and the bottom plate supports the pair of 1-pm micro quartz-fiber filters and seals to the pump intake. (Bottom) Pressure vs. flow rate curves for the MULVFS and LVFS pump units. Horizontal bars indicate operating ranges of the two systems during filtration.

Figure 5. The quantities of Na, Mg, Ca, K, and Fe leached during precleaning and during analysis are shown for MQ and Mead 931-BJ glass-fiber filters (used previously with the LVFS). These quantities demonstrate that the MQ filters are far cleaner by comparison. The MQ blank levels are low enough to measure accurately the trace elements Ba, Mn, Cd, and Co. Nitex blank levels have been described previously and are very low for most elements. (5).

Prior to a station at sea (Figure 6), the MQ filter sandwich and the accompanying 53-pm Nitex prefilter were loaded into the filter holders and then covered with polyethylene bags to minimize contamination. The bags remained in place while the holders were bolted onto the pumps on deck and were removed just moments prior to submersion of the pumps. Upon... 

All collected particulate material was processed withing 3 h of the recovery of the last pump the Nitex and MQ-filter sandwich (containing >53 and <53-pm particle-size fractions, respectively) were treated separately in a laminar-flow bench. Processing progressed in order of depth to minimize the degradation of the samples material collected from the nearsurface waters is most likely to degrade fastest. 

The processing scheme for the 53-jLtm Nitex samples was similar to that described previously (10) where each filter was transferred to the PVC stand, rinsed with deionized water under suction to reduce sea salt, folded once onto itself to prevent loss of large particles, and then dried at 60 °C for >24 h. Where samples larger than 53 pm have been required for lipid analysis, precombusted, 53-pm stainless steel mesh of identical specifications to the 53-jLtm Nitex was used. In this case a subsample was dried for the regular chemical analysis the remaining sample was specially preserved. 

The MQ-filter sandwich was similarly transferred to the filter-rinsing stand, the top 149-jLtm Nitex support was folded back, and three sharpened acrylic tubes were pressed into the filter pair. The MQ-filter area not enclosed by the acrylic tubes was rinsed with several aliquots of deionized water (totaling 200-300 mL) with suction alternately applied from below to reduce sea salt by an order of magnitude this process was required for accurate dry-weight and major-ion determinations. The acrylic tubes were subsequently removed, and the fresh, unrinsed subsamples were preserved for lipid analysis. The remaining filter material was dried at 60 °C for >24 h. Both the MQ and 53-jitm Nitex samples were stored and transported flat in individual polyethylene bags to prevent loss of material. 

A filter basket can be prepared from a 50-ml screw-cap tube. Cut off the end of the 50-ml screw-cap tube and cut a large hole in the cap. Place a piece of 130-mesh Nitex screen between the cap and the tube, and screw in place to cover the hole. 

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