Calculating Protein Concentration from Kilo Units (KU)

Calculating Protein Concentration from Kilo Units (KU)

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I am looking to purchase Pyruvate Kinase from the Sigma Website, they state the volume in Kilo Units (KU) i.e. 1, 5 or 25 KU. It also states there are 350-600 units / mg protein.

Does this mean one unit is one protein? so 1KU is 1000 units of protein? What is the relationship between the KU and mg? and how can I use this relationship to calculate my concentration in um or mg.


In this paper (look at the methods section) they calculated the concentration of 25,000 units of calmodulin in 0.5 ml to be approximately 75um which is 40,000 units/mg. How did they calculate this?

From the page linked from your link:

Unit Definition

One unit will convert 1.0 μmole of phospho(enol)pyruvate to pyruvate per min at pH 7.6 at 37 °C.

So, the unit is defined by activity, and there is no way to know how many molecules or milligrams of protein are included

The figure of 350 - 600 Units per mg refers to the specific activity of the enzyme.

The Unit is International Unit or IU and is usually defined as that amount of enzyme that will catalyze the transformation of 1 micromole of substrate (or product) per min, under defined assay conditions (such as pH, temperature, substrate concentration, presence of Mg++, etc). It is thus a measure of activity.

When the enzyme is pure (no other extraeneous proteins present), the specific activity provides important information about the catalytic capacity of the enzyme.

It is usually calculated by measuring

  • the activity of the enzyme preparation under defined assay conditions
  • the protein concentration of the same enzyme preparation (using, say, the Lowry or Biuret method for protein estimation).
    Alternatively, if the E(1%, 280) is known (see below) and the enzyme is pure, measurement of the absorbance at 280 nm gives a very good estimate of protein content (and the enzyme may be recovered 'unharmed' at the end of the measurement).

Thus, taking a figure of 450 Units/mg for the specific activity of pyruvate kinase, 25 KU (25 Kilo-Units, I presume) contains 500/9 mg (~55 mg) protein.

I notice that the Sigma product sheet provides a figure for E(0.1%, 280) = 0.54.

This means that a 1 mg/ml solution of the protein will have an absorbance at 280 nm of 0.54

E(0.1%, 280) can be used as a very convenient measure of the protein content provided that the enzyme preparation supplied by Sigma is pure.

A 'rule of thumb', useful when the E(0.1%, 280) is unknown, is that a 1mg/ml protein solution has an A280 of 1.

Thus if, say, the A280 (absorbance at 280 nm) of the resuspended lyophilized powder is 1.08 and you have 5 ml of this, the protein concentration is 2mg/ml and you have 10 mg of protein in total. You may wish to assay the enzyme yourself to determine an accurate specific activity.

The EC (Enzyme Commission) Number may also be of interest. For pyruvate kinase (EC see here.

For a great ref on PK (pdf may be downloaded) see here (Ainsworth et al.)

For your second question, I do not have access to that paper from home.

However, if calmodulin has a specific activity of 40 000 Units/mg,

  • 25 000 Units is equivalent to 0.625 mg; this is in a volume of 0.5 ml. Therefore, the calmodulin concentration is 1.25mg/ml.
  • Taking the molecular weight of calmodulin to be 16 000, then 16 000 mg /ml (theoretical) would be a 1 Molar solution. Thus a 1.25 mg/ml solution is about 78 micromolar.

Yucel Yilmaz / Getty Images

Molarity is one of the most common units of concentration. It is used when the temperature of an experiment won't change. It's one of the easiest units to calculate.

Calculate Molarity: moles solute per liter of solution (not volume of solvent added since the solute takes up some space)

M = moles / liter

Example: What is the molarity of a solution of 6 grams of NaCl (

1 teaspoon of table salt) dissolved in 500 milliliters of water?

First, convert grams of NaCl to moles of NaCl.

  • Na = 23.0 g/mol
  • Cl = 35.5 g/mol
  • NaCl = 23.0 g/mol + 35.5 g/mol = 58.5 g/mol
  • Total number of moles = (1 mole / 58.5 g) * 6 g = 0.62 moles

Now determine moles per liter of solution:

Note that I assumed dissolving the 6 grams of salt did not appreciably affect the volume of the solution. When you prepare a molar solution, avoid this problem by adding solvent to your solute to reach a specific volume.


Glomerular filtration rate (GFR) is the volume of fluid filtered from the renal (kidney) glomerular capillaries into the Bowman's capsule per unit time. [4] Central to the physiologic maintenance of GFR is the differential basal tone of the afferent and efferent arterioles (see diagram). In other words, the filtration rate is dependent on the difference between the higher blood pressure created by vasoconstriction of the input or afferent arteriole versus the lower blood pressure created by lesser vasoconstriction of the output or efferent arteriole.

GFR is equal to the renal clearance ratio when any solute is freely filtered and is neither reabsorbed nor secreted by the kidneys. The rate therefore measured is the quantity of the substance in the urine that originated from a calculable volume of blood. Relating this principle to the below equation – for the substance used, the product of urine concentration and urine flow equals the mass of substance excreted during the time that urine has been collected. This mass equals the mass filtered at the glomerulus as nothing is added or removed in the nephron. Dividing this mass by the plasma concentration gives the volume of plasma which the mass must have originally come from, and thus the volume of plasma fluid that has entered Bowman's capsule within the aforementioned period of time. The GFR is typically recorded in units of volume per time, e.g., milliliters per minute (mL/min). Compare to filtration fraction.

There are several different techniques used to calculate or estimate the glomerular filtration rate (GFR or eGFR). The above formula only applies for GFR calculation when it is equal to the Clearance Rate.

Creatinine Edit

In clinical practice, however, creatinine clearance or estimates of creatinine clearance based on the serum creatinine level are used to measure GFR. Creatinine is produced naturally by the body (creatinine is a breakdown product of creatine phosphate, which is found in muscle). It is freely filtered by the glomerulus, but also actively secreted by the peritubular capillaries in very small amounts such that creatinine clearance overestimates actual GFR by 10% to 20%. This margin of error is acceptable, considering the ease with which creatinine clearance is measured. Unlike precise GFR measurements involving constant infusions of inulin, creatinine is already at a steady-state concentration in the blood, and so measuring creatinine clearance is much less cumbersome. However, creatinine estimates of GFR have their limitations. All of the estimating equations depend on a prediction of the 24-hour creatinine excretion rate, which is a function of muscle mass which is quite variable. One of the equations, the Cockcroft and Gault equation (see below) does not correct for race. With a higher muscle mass, serum creatinine will be higher for any given rate of clearance.

Inulin Edit

The GFR can be determined by injecting inulin or the inulin-analog sinistrin into the blood stream. Since both inulin and sinistrin are neither reabsorbed nor secreted by the kidney after glomerular filtration, their rate of excretion is directly proportional to the rate of filtration of water and solutes across the glomerular filter. Incomplete urine collection is an important source of error in inulin clearance measurement. [5] Using inulin to measure kidney function is the "gold standard" for comparison with other means of estimating glomerular filtration rate. [6]

Radioactive tracers Edit

GFR can be accurately measured using radioactive substances, in particular chromium-51 and technetium-99m. These come close to the ideal properties of inulin (undergoing only glomerular filtration) but can be measured more practically with only a few urine or blood samples. [7] Measurement of renal or plasma clearance of 51 Cr-EDTA is widely used in Europe but not available in the United States, where 99m Tc-DTPA may be used instead. [8] Renal and plasma clearance 51 Cr-EDTA has been shown to be accurate in comparison with the gold standard, inulin. [9] [10] [11] Use of 51 Cr‑EDTA is considered a reference standard measure in UK guidance. [12]

Cystatin C Edit

Problems with creatinine (varying muscle mass, recent meat ingestion (much less dependent on the diet than urea), etc.) have led to evaluation of alternative agents for estimation of GFR. One of these is cystatin C, a ubiquitous protein secreted by most cells in the body (it is an inhibitor of cysteine protease).

Cystatin C is freely filtered at the glomerulus. After filtration, Cystatin C is reabsorbed and catabolized by the tubular epithelial cells, with only small amounts excreted in the urine. Cystatin C levels are therefore measured not in the urine, but in the bloodstream.

Equations have been developed linking estimated GFR to serum cystatin C levels. Most recently, some proposed equations have combined (sex, age and race) adjusted cystatin C and creatinine. The most accurate is (sex, age and race) adjusted cystatin C, followed by (sex, age and race) adjusted creatinine and then cystatine C alone in slightly different with adjusted creatinine. [13]

More precisely, GFR is the fluid flow rate between the glomerular capillaries and the Bowman's capsule:

  • d ⁡ Q d ⁡ t Q over operatorname t>> is the GFR.
  • K f > is called the filtration constant and is defined as the product of the hydraulic conductivity and the surface area of the glomerular capillaries.
  • P G > is the hydrostatic pressure within the glomerular capillaries.
  • P B > is the hydrostatic pressure within the Bowman's capsule.
  • Π G > is the colloid osmotic pressure within the glomerular capillaries.
  • and Π B > is the colloid osmotic pressure within the Bowman's capsule.

Kf Edit

Because this constant is a measurement of hydraulic conductivity multiplied by the capillary surface area, it is almost impossible to measure physically. However, it can be determined experimentally. Methods of determining the GFR are listed in the above and below sections and it is clear from our equation that K f > can be found by dividing the experimental GFR by the net filtration pressure: [14]

PG Edit

The hydrostatic pressure within the glomerular capillaries is determined by the pressure difference between the fluid entering immediately from the afferent arteriole and leaving through the efferent arteriole. The pressure difference is approximated by the product of the total resistance of the respective arteriole and the flux of blood through it: [15]

PB Edit

The pressure in the Bowman's capsule and proximal tubule can be determined by the difference between the pressure in the Bowman's capsule and the descending tubule: [15]

∏G Edit

Blood plasma has a good many proteins in it and they exert an inward directed force called the osmotic pressure on the water in hypotonic solutions across a membrane, i.e., in the Bowman's capsule. Because plasma proteins are virtually incapable of escaping the glomerular capillaries, this oncotic pressure is defined, simply, by the ideal gas law: [14] [15]

  • R is the universal gas constant
  • T is the temperature.
  • And, c is concentration in mol/L of plasma proteins (remember the solutes can freely diffuse through the glomerular capsule).

∏B Edit

This value is almost always taken to be equal to zero because in a healthy nephron, there should be no proteins in the Bowman's Capsule. [14]

Filtration fraction Edit

The filtration fraction is the amount of plasma that is actually filtered through the kidney. This can be defined using the equation:

Renal clearance Edit

  • Cx is the clearance of X (normally in units of mL/min).
  • Ux is the urine concentration of X.
  • Px is the plasma concentration of X.
  • V is the urine flow rate.

In clinical practice, however, creatinine clearance or estimates of creatinine clearance based on the serum creatinine level are used to measure GFR. Creatinine is produced naturally by the body (creatinine is a breakdown product of creatine phosphate, which is found in muscle). It is freely filtered by the glomerulus, but also actively secreted by the peritubular capillaries in very small amounts such that creatinine clearance overestimates actual GFR by 10% to 20%. This margin of error is acceptable, considering the ease with which creatinine clearance is measured. Unlike precise GFR measurements involving constant infusions of inulin, creatinine is already at a steady-state concentration in the blood, and so measuring creatinine clearance is much less cumbersome. However, creatinine estimates of GFR have their limitations. All of the estimating equations depend on a prediction of the 24-hour creatinine excretion rate, which is a function of muscle mass which is quite variable. One of the equations, the Cockcroft and Gault equation (see below) does not correct for race. With a higher muscle mass, serum creatinine will be higher for any given rate of clearance. [ citation needed ]

A common mistake made when just looking at serum creatinine is the failure to account for muscle mass. Hence, an older woman with a serum creatinine of 1.4 mg/dL may actually have a moderately severe chronic kidney disease, whereas a young muscular male can have a normal level of renal function at this serum creatinine level. Creatinine-based equations should be used with caution in cachectic patients and patients with cirrhosis. They often have very low muscle mass and a much lower creatinine excretion rate than predicted by the equations below, such that a cirrhotic patient with a serum creatinine of 0.9 mg/dL may have a moderately severe degree of chronic kidney disease.

Estimated GFR (eGFR) is now recommended by clinical practice guidelines and regulatory agencies for routine evaluation of GFR whereas measured GFR (mGFR) is recommended as a confirmatory test when more accurate assessment is required. [3]

Creatinine clearance CCr Edit

One method of determining GFR from creatinine is to collect urine (usually for 24 h) to determine the amount of creatinine that was removed from the blood over a given time interval. If one removes 1440 mg in 24 h, this is equivalent to removing 1 mg/min. If the blood concentration is 0.01 mg/mL (1 mg/dL), then one can say that 100 mL/min of blood is being "cleared" of creatinine, since, to get 1 mg of creatinine, 100 mL of blood containing 0.01 mg/mL would need to have been cleared.

Creatinine clearance (CCr) is calculated from the creatinine concentration in the collected urine sample (UCr), urine flow rate (Vdt), and the plasma concentration (PCr). Since the product of urine concentration and urine flow rate yields creatinine excretion rate, which is the rate of removal from the blood, creatinine clearance is calculated as removal rate per min (UCr×Vdt) divided by the plasma creatinine concentration. This is commonly represented mathematically as

Example: A person has a plasma creatinine concentration of 0.01 mg/mL and in 1 hour produces 60 mL of urine with a creatinine concentration of 1.25 mg/mL.

The common procedure involves undertaking a 24-hour urine collection, from empty-bladder one morning to the contents of the bladder the following morning, with a comparative blood test then taken. The urinary flow rate is still calculated per minute, hence:

To allow comparison of results between people of different sizes, the CCr is often corrected for the body surface area (BSA) and expressed compared to the average sized man as mL/min/1.73 m 2 . While most adults have a BSA that approaches 1.7 m 2 (1.6 m 2 to 1.9 m 2 ), extremely obese or slim patients should have their CCr corrected for their actual BSA.

Twenty-four-hour urine collection to assess creatinine clearance is no longer widely performed, due to difficulty in assuring complete specimen collection. To assess the adequacy of a complete collection, one always calculates the amount of creatinine excreted over a 24-hour period. This amount varies with muscle mass and is higher in young people/old, and in men/women. An unexpectedly low or high 24-hour creatinine excretion rate voids the test. Nevertheless, in cases where estimates of creatinine clearance from serum creatinine are unreliable, creatinine clearance remains a useful test. These cases include "estimation of GFR in individuals with variation in dietary intake (vegetarian diet, creatine supplements) or muscle mass (amputation, malnutrition, muscle wasting), since these factors are not specifically taken into account in prediction equations." [16]

A number of formulae have been devised to estimate GFR or Ccr values on the basis of serum creatinine levels. Where not otherwise stated serum creatinine is assumed to be stated in mg/dL, not μmol/L—divide by 88.4 to convert from μmol/Lto mg/dL.

Cockcroft-Gault formula Edit

A commonly used surrogate marker for estimate of creatinine clearance is the Cockcroft-Gault (CG) formula, which in turn estimates GFR in ml/min: [17] It is named after the scientists, the asthmologist Donald William Cockcroft [de] (b. 1946) and the nephrologist Matthew Henry Gault (1925–2003), who first published the formula in 1976, and it employs serum creatinine measurements and a patient's weight to predict the creatinine clearance. [18] [19] The formula, as originally published, is:

e C C r = ( 140 − A g e ) × Mass (in kilograms) × [ 0.85 if Female ] 72 × [ Serum Creatinine (in mg/dL) ] = imes < ext> imes [< ext<0.85 if Female>>]> imes [< ext>]>>> This formula expects weight to be measured in kilograms and creatinine to be measured in mg/dL, as is standard in the USA. The resulting value is multiplied by a constant of 0.85 if the patient is female. This formula is useful because the calculations are simple and can often be performed without the aid of a calculator.

When serum creatinine is measured in μmol/L:

One interesting feature of the Cockcroft and Gault equation is that it shows how dependent the estimation of CCr is based on age. The age term is (140 – age). This means that a 20-year-old person (140 – 20 = 120) will have twice the creatinine clearance as an 80-year-old (140 – 80 = 60) for the same level of serum creatinine. The C-G equation assumes that a woman will have a 15% lower creatinine clearance than a man at the same level of serum creatinine.

Modification of Diet in Renal Disease (MDRD) formula Edit

Another formula for calculating the GFR is the one developed by the Modification of Diet in Renal Disease Study Group. [20] Most laboratories in Australia, [21] and the United Kingdom now calculate and report the estimated GFR along with creatinine measurements and this forms the basis of diagnosis of chronic kidney disease. [22] [23] The adoption of the automatic reporting of MDRD-eGFR has been widely criticised. [24] [25] [26]

The most commonly used formula is the "4-variable MDRD", which estimates GFR using four variables: serum creatinine, age, ethnicity, and gender. [27] The original MDRD used six variables with the additional variables being the blood urea nitrogen and albumin levels. [20] The equations have been validated in patients with chronic kidney disease however, both versions underestimate the GFR in healthy patients with GFRs over 60 mL/min. [28] [29] The equations have not been validated in acute renal failure.

A more elaborate version of the MDRD equation also includes serum albumin and blood urea nitrogen (BUN) levels:

These MDRD equations are to be used only if the laboratory has NOT calibrated its serum creatinine measurements to isotope dilution mass spectrometry (IDMS). When IDMS-calibrated serum creatinine is used (which is about 6% lower), the above equations should be multiplied by 175/186 or by 0.94086. [30]

Since these formulae do not adjust for body size, results are given in units of mL/min per 1.73 m 2 , 1.73 m 2 being the estimated body surface area of an adult with a mass of 63 kg and a height of 1.7m.

CKD-EPI formula Edit

The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) formula was published in May 2009. It was developed in an effort to create a formula more accurate than the MDRD formula, especially when actual GFR is greater than 60 mL/min per 1.73 m 2 . This is the formula currently recommended by NICE in the UK. [23]

Researchers pooled data from multiple studies to develop and validate this new equation. They used 10 studies that included 8254 participants, randomly using 2/3 of the data sets for development and the other 1/3 for internal validation. Sixteen additional studies, which included 3896 participants, were used for external validation.

The CKD-EPI equation performed better than the MDRD (Modification of Diet in Renal Disease Study) equation, especially at higher GFR, with less bias and greater accuracy. When looking at NHANES (National Health and Nutrition Examination Survey) data, the median estimated GFR was 94.5 mL/min per 1.73 m 2 vs. 85.0 mL/min per 1.73 m 2 , and the prevalence of chronic kidney disease was 11.5% versus 13.1%. Despite its overall superiority to the MDRD equation, the CKD-EPI equations performed poorly in certain populations, including black women, the elderly and the obese, and was less popular among clinicians than the MDRD estimate. [31]

where SCr is serum creatinine (mg/dL), k is 0.7 for females and 0.9 for males, a is −0.329 for females and −0.411 for males, min indicates the minimum of SCr/k or 1, and max indicates the maximum of SCr/k or 1.

As separate equations for different populations: For creatinine (IDMS calibrated) in mg/dL:

This formula was developed by Levey et al. [32]

The formula CKD-EPI may provide improved cardiovascular risk prediction over the MDRD Study formula in a middle-age population. [33]

Mayo Quadratic formula Edit

Another estimation tool to calculate GFR is the Mayo Quadratic formula. This formula was developed by Rule et al., [28] in an attempt to better estimate GFR in patients with preserved kidney function. It is well recognized that the MDRD formula tends to underestimate GFR in patients with preserved kidney function. Studies in 2008 found that the Mayo Clinic Quadratic Equation compared moderately well with radionuclide GFR, but had inferior bias and accuracy than the MDRD equation in a clinical setting. [34] [35]

If Serum Creatinine < 0.8 mg/dL, use 0.8 mg/dL for Serum Creatinine.

Schwartz formula Edit

In children, the Schwartz formula is used. [36] [37] This employs the serum creatinine (mg/dL), the child's height (cm) and a constant to estimate the glomerular filtration rate:

The method of selection of the constant k has been questioned as being dependent upon the gold-standard of renal function used (i.e. inulin clearance, creatinine clearance, etc.) and also may be dependent upon the urinary flow rate at the time of measurement. [39]

In 2009 the formula was updated to use standardized serum creatinine (recommend k=0.413) and additional formulas that allow improved precision were derived if serum cystatin C is measured in addition to serum creatinine. [40]

IDMS standardization effort Edit

One problem with any creatinine-based equation for GFR is that the methods used to assay creatinine in the blood differ widely in their susceptibility to non-specific chromogens, which cause the creatinine value to be overestimated. In particular, the MDRD equation was derived using serum creatinine measurements that had this problem. The NKDEP program in the United States has attempted to solve this problem by trying to get all laboratories to calibrate their measures of creatinine to a "gold standard", which in this case is isotope dilution mass spectrometry (IDMS). In late 2009 not all labs in the U.S. had changed over to the new system. There are two forms of the MDRD equation that are available, depending on whether or not creatinine was measured by an IDMS-calibrated assay. The CKD-EPI equation is designed to be used with IDMS-calibrated serum creatinine values only. [ citation needed ]

The normal range of GFR, adjusted for body surface area, is 100–130 average 125 mL/min/1.73m 2 in men and 90–120 ml/min/1.73m 2 in women younger than the age of 40. In children, GFR measured by inulin clearance is 110 mL/min/1.73 m 2 until 2 years of age in both sexes, and then it progressively decreases. After age 40, GFR decreases progressively with age, by 0.4–1.2 mL/min per year. [ citation needed ]

A decreased renal function can be caused by many types of kidney disease. Upon presentation of decreased renal function, it is recommended to perform a history and physical examination, as well as performing a renal ultrasound and a urinalysis. [ citation needed ] The most relevant items in the history are medications, edema, nocturia, gross hematuria, family history of kidney disease, diabetes and polyuria. The most important items in a physical examination are signs of vasculitis, lupus erythematosus, diabetes, endocarditis and hypertension. [ citation needed ]

A urinalysis is helpful even when not showing any pathology, as this finding suggests an extrarenal etiology. Proteinuria and/or urinary sediment usually indicates the presence of glomerular disease. Hematuria may be caused by glomerular disease or by a disease along the urinary tract. [ citation needed ]

The most relevant assessments in a renal ultrasound are renal sizes, echogenicity and any signs of hydronephrosis. Renal enlargement usually indicates diabetic nephropathy, focal segmental glomerular sclerosis or myeloma. Renal atrophy suggests longstanding chronic renal disease. [ citation needed ]

Chronic kidney disease stages Edit

Risk factors for kidney disease include diabetes, high blood pressure, family history, older age, ethnic group and smoking. For most patients, a GFR over 60 mL/min/1.73m 2 is adequate. But significant decline of the GFR from a previous test result can be an early indicator of kidney disease requiring medical intervention. The sooner kidney dysfunction is diagnosed and treated the greater odds of preserving remaining nephrons, and preventing the need for dialysis. [ citation needed ]

CKD stage GFR level (mL/min/1.73 m 2 )
Stage 1 ≥ 90
Stage 2 60–89
Stage 3 30–59
Stage 4 15–29
Stage 5 < 15

The severity of chronic kidney disease (CKD) is described by six stages the most severe three are defined by the MDRD-eGFR value, and first three also depend on whether there is other evidence of kidney disease (e.g., proteinuria):

0) Normal kidney function – GFR above 90 mL/min/1.73 m 2 and no proteinuria 1) CKD1 – GFR above 90 mL/min/1.73 m 2 with evidence of kidney damage 2) CKD2 (mild) – GFR of 60 to 89 mL/min/1.73 m 2 with evidence of kidney damage 3) CKD3 (moderate) – GFR of 30 to 59 mL/min/1.73 m 2 4) CKD4 (severe) – GFR of 15 to 29 mL/min/1.73 m 2 5) CKD5 kidney failure – GFR less than 15 mL/min/1.73 m 2 Some people add CKD5D for those stage 5 patients requiring dialysis many patients in CKD5 are not yet on dialysis.

Note: others add a "T" to patients who have had a transplant regardless of stage.

Not all clinicians agree with the above classification, suggesting that it may mislabel patients with mildly reduced kidney function, especially the elderly, as having a disease. [41] [42] A conference was held in 2009 regarding these controversies by Kidney Disease: Improving Global Outcomes (KDIGO) on CKD: Definition, Classification and Prognosis, gathering data on CKD prognosis to refine the definition and staging of CKD. [43]

Each percentage type can be calculated by making small changes to the same method. For example, to find the % w/v of a solution the calculation is:

(Mass of Solute (g) / Volume of Solution (ml)) x 100

Therefore, to figure out the % w/v of a 100ml solution that is made up of 65g nitric acid, we would divide 65g by 100ml and then multiply the answer by 100. This tells us that there is a nitric acid solution of 65% w/v.

When working out the % v/v of a solution, the same method is used except it is the volume of the solute (ml) that is divided by the volume of the solution (ml). For example, a 1000ml solution that contains 450ml methanol has a methanol concentration of 45% v/v (450 / 1000 x 100).

Again, the method for calculating % w/w uses the same steps instead it is weight divided by weight.

It is important to understand exactly what you’re purchasing. That’s why, at ReAgent, we have a skilled and dedicated team who you can speak with about any product enquiry you may have. Get in touch today to see how we can help.

How can I calculate the percent concentration of a solution?

The percentage concentration of any solution is most commonly expressed as mass percent:

Mass % of any component of the solution =
(Mass of the component in the solution / Total mass of the solution) x 100

Volume % of a component =
(Volume of the component/Total volume of the solution) x 100

i.e. Mass by Volume percentage =
(Mass of solute in grams/Volume of solution in mL) x 100

Here's a point to be kept in mind :
Whenever we say mass or volume of the solution, you need to add the respective masses and volumes of ALL the components of the solution. Do NOT commit the error of taking the mass or volume of only the solute or solvent in the denominators of the above expressions.

The concentration of a solution is most of the time expressed as the number of moles of solute present in 1 Liter of the solution (also called molarity )

(There are also other ways to express concentration. Please follow this link. )

(a) If 25 moles of NaCl are present in 100 L of a solution wherein H2O is the solvent, then the concentration of the solution is #25/100=0.25 "mol·L"^-1# .

(b) What is the molarity of a solution prepared by dissolving 15.0 g of sodium hydroxide in enough water to make a total of 225 mL of solution?

Moles of NaOH = 15.0 g NaOH × #(1"mol NaOH")/(40.00"g NaOH")# = 0.375 mol NaOH

How to Calculate the Concentration of a Solution

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In chemistry, a solution’s concentration is how much of a dissolvable substance, known as a solute, is mixed with another substance, called the solvent. The standard formula is C = m/V, where C is the concentration, m is the mass of the solute dissolved, and V is the total volume of the solution. If you have a small concentration, find the answer in parts per million (ppm) to make it easier to follow. In a lab setting, you may be asked to find the molarity, or molar concentration, of the solution instead.

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It has been shown experimentally that if the amount of the enzyme is kept constant and the substrate concentration is then gradually increased, the reaction velocity will increase until it reaches a maximum. After this point, increases in substrate concentration will not increase the velocity (delta A/delta T). This is represented graphically in Figure 8.

It is theorized that when this maximum velocity had been reached, all of the available enzyme has been converted to ES, the enzyme substrate complex. This point on the graph is designated Vmax. Using this maximum velocity and equation (7), Michaelis developed a set of mathematical expressions to calculate enzyme activity in terms of reaction speed from measurable laboratory data.

The Michaelis constant Km is defined as the substrate concentration at 1/2 the maximum velocity. This is shown in Figure 8. Using this constant and the fact that Km can also be defined as:

K +1 , K -1 and K +2 being the rate constants from equation (7). Michaelis developed the following

Michaelis constants have been determined for many of the commonly used enzymes. The size of Km tells us several things about a particular enzyme.

  • A small Km indicates that the enzyme requires only a small amount of substrate to become saturated. Hence, the maximum velocity is reached at relatively low substrate concentrations.
  • A large Km indicates the need for high substrate concentrations to achieve maximum reaction velocity.
  • The substrate with the lowest Km upon which the enzyme acts as a catalyst is frequently assumed to be enzyme's natural substrate, though this is not true for all enzymes.

How to Calculate Molecular Weight

This article was co-authored by Bess Ruff, MA. Bess Ruff is a Geography PhD student at Florida State University. She received her MA in Environmental Science and Management from the University of California, Santa Barbara in 2016. She has conducted survey work for marine spatial planning projects in the Caribbean and provided research support as a graduate fellow for the Sustainable Fisheries Group.

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The molecular mass, often called the molecular weight (MW), is the weight of all atoms in a given molecular formula. Molecular weight is measured in Atomic Mass Units, usually expressed as u or amu. [1] X Research source In order to calculate the molecular weight of a formula, you'll need to add up the atomic masses of each element present.

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